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1
Ficarra, Christina Helene. "ANALYSIS OF ADHESIVE BONDED FIBER-REINFORCED COMPOSITE JOINTS." NCSU, 2001. http://www.lib.ncsu.edu/theses/available/etd-20010626-155040.
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The work presented in this thesis involved the analysis of adhesive bonded joints for composite bridge decks and was divided into three phases. The first phase involved a parametric study on a single lap joint using ANSYS finite element analysis software. The purpose of the parametric study was to alter the geometry and material properties of the joint and study their effects on the stress distribution in both the adherends and adhesive. The four different cases studied included adding a taper to the adherends, different edge shapes on the adhesive layer, a material stiffness imbalance and a geometric stiffness imbalance. It was found that for the taper case and the edge shape case, the stress field in the joint was affected slightly. The material and geometric stiffness imbalance cases had the most drastic affect on the stress field of both the adhesive and adherend. Phase two of this study involved physical tests on single lap joints pulled in uniaxial tension. Tests were performed on three different types of laminates in order to study the interfacial effects these laminates had on the adhesive bond. It was found that by changing the surface of the composite, the mode of failure changed significantly.Phase three of this research involved a study on surface preparation. Three different surface preparations were conducted on the adherends of a butt-strap joint. The first included an acetone wipe. The second involved sanding the adherends. The third surface preparation involved adding APRIME-2, a secondary bonding agent, to the adherends before adding the strap. By simply sanding the adherends, the load to failure was increased by 350% compared to an acetone wipe. The ATPRIME-2 improved the load to failure by an additional 60% as well as improved the failure mode to a fiber tear. It was concluded that surface preparation has a major impact on the behavior of adhesively bonded joints.
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Shāhid, Muḥammad. "Adhesion characterisation of bonded steel/composite cleavage joints." Thesis, University of Glasgow, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.402470.
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Osiyemi, Stephen Olusegun. "The fatigue performance of adhesively bonded fibre-composite joints." Thesis, Imperial College London, 1992. http://hdl.handle.net/10044/1/7971.
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Brett, Michael Alexander de Oliveira. "Prediction of the performance of adhesively-bonded composite joints." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9545.
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The use of adhesively-bonded joints instead of the traditional types of joining can give reduced weight and increased stiffness in a structure. However, most industries have concerns about the use of adhesive joints in anything other than secondary structures, due to uncertainties over the long-term service life. This thesis discusses the prediction of the lifetime of adhesively-bonded composite structures. A fracture mechanics approach was used to characterise the fracture behaviour of an epoxy film adhesive, Cytec FM-300M, mainly using composite substrates prepared using wet peel ply, removing the need for any additional surface treatment. Aluminium alloy substrates were also used for some tests. Tapered double cantilever beam and double cantilever beam specimens were used to determine the mode I critical strain energy release rate, GIC, and end loaded split specimens were tested to obtain the mode II critical strain energy release rate, GIIC. Lastly, fixed ratio mixed mode specimens were used to obtain the relationship between GIC and GIIC when a joint undergoes mixed mode failure. For validation purposes, single lap joint and double scarf joint specimens were also tested. These data were then applied in finite element models using Abaqus. Two different modelling techniques were used, the virtual crack closure technique and cohesive zone modelling, CZM. Simulations of the tests performed were executed, in the process obtaining the CZM fitting parameters. Good agreement with the experimental data was verified for each of the models tested. Fatigue tests were also performed in order to obtain the mode I and mode II threshold values of the fracture energy below which crack growth did not occur, by executing double cantilever beam and end loaded split tests, respectively. For validation purposes, single lap joint fatigue tests were also performed to determine the threshold maximum load the joint could withstand without failure. Finally, using the CZM fitting parameters obtained in the quasi-static tests and the experimentally obtained threshold values of the fracture energy, modelling of single lap and double scarf joints was performed in order to predict the maximum load value for which no failure would occur when subject to cyclic loading. These predictions showed excellent agreement with the experimental results, showing that this simpler model can obtain good results.
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Pillai, Govind Ramakrishna Lankarani Hamid M. "Response of adhesively bonded composite joints to low velocity impact." Diss., A link to full text of this thesis in SOAR, 2006. http://soar.wichita.edu/dspace/handle/10057/676.
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Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering."December 2006." Title from PDF title page (viewed on Nov. 4, 2007). Thesis adviser: Hamid M. Lankarani. Includes bibliographic references (leaves 64-67).
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Mosher, Bryan C. "Failure Prediction of Adhesively Bonded Hardboard Doorskin Joints." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/42867.
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Wood and wood based composites such as hardboard have become very common materials for use in non-structural applications, which include pre-finished paneling, siding, exterior trim, furniture, and door skins. This thesis describes the results of a study of the failure of hardboard door skins. Forces applied during manufacture load the door skins in bending, and in some cases cause a split at the edge of the hardboard. A finite element model as well as a closed form solution based on mechanics of materials were developed to analyze the stresses and deformations of the door skin/stile assembly so that stresses could be predicted for various stile widths and loading conditions. The wood members that make up the frame along the perimeter of the doors, or stiles, were modeled as orthotropic and their properties were selected from available literature. The hardboard was modeled as transversely isotropic, and its properties were determined experimentally. The closed form solution developed can be used to determine the critical geometry for different combinations of hardboard thickness and adhesive joint stiffness. It predicts that as the stile width decreases, the point of maximum deflection, and greatest stresses, moves toward the outside edge of the panel. The ability to predict the critical stile width, or the stile width below which the maximum deflection and stress occurs at the outside edge of the panel, allows one to design the joint to be able to withstand specific loadings and prevent unwanted delamination of the hardboard during manufacture.Master of Science
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Pohlit, David Joseph. "Dynamic Mixed-Mode Fracture of Bonded Composite Joints for Automotive Crashworthiness." Thesis, Virginia Tech, 2007. http://hdl.handle.net/10919/33837.
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An experimental evaluation of the mixed-mode fracture behavior of bonded composite joints is presented. Commonly used experimental techniques for characterizing the mode I, mixed-mode I/II, mode II, and mode III fracture behavior have been employed for the purpose of developing a fracture envelope to be utilized in the automotive design process. These techniques make use of such test geometries as the double cantilever beam (DCB), asymmetric double cantilever beam (ADCB), single-leg bend (SLB), end-loaded split (ELS), and split cantilever beam (SCB) specimens. Symmetric versions of the DCB, SLB, and ELS specimens produced mode mixities of 0°, 41°, and 90° respectively, while the testing of ADCB specimens allowed for mode mixities of 18°, 31°.
Pronounced stick-slip behavior was observed for all specimen test geometries under both quasi-static and dynamic loading conditions. Due to the nature of the adhesive studied, a limited number of data points were obtained under mode I loading conditions. A significant increase in the number of measurable crack initiation events was observed for mixed-mode I/II loading conditions, where stick slip behavior was less pronounced. Additionally, a comparison of the measured fracture energies obtained under mixed-mode I/II loading conditions reveals that the addition of a small mode II component results in a decrease in the mode I fracture energy by roughly 50%, as the crack was driven to the interface between the adhesive layer and composite adherends. Furthermore, the propensity of debonds to propagate into the woven composite laminate adherends under mode II loading conditions limited the number of crack initiation points that could be obtained to one or two usable data points per specimen. A limited number of experimental tests using the SCB specimen for mode III fracture characterization, combined with a numerical analysis via finite element analysis, revealed a significant mode II contribution toward the specimen edges. Similarly, FE analyses on full bond width and half bond width SCB specimens was conducted, and results indicate that by inducing a bond width reduction of 50%, the mode II contribution is greatly decreased across the entire width of the specified crack front.
To provide a means for comparison to results obtained using the standard DCB specimen, an alternative driven wedge test specimen geometry was analyzed, as this geometry provided a significant increase in the number of measurable data points under mode I loading conditions. A three-dimensional finite element analysis was conducted to establish ratios of simple beam theory results to those obtained via FEA, GSBT/GFEA, were of particular interest, as these ratios were used to establish correction factors corresponding to specific crack lengths to be used in correcting results obtained from an experimental study utilizing a driven wedge technique. Corrected results show good agreement with results obtained from traditional mode I double cantilever beam tests.
Finally, bulk adhesive experiments were conducted on compact tension specimens to establish a correlation between adhesively bonded composite joint and bulk adhesive fracture behavior under mode I loading conditions. Measured fracture energy values were shown to gradually drop across a range of applied loading rates, similar to the rate-dependent behavior observed with both the DCB and driven wedge specimens. Application of the time-temperature superposition principle was explored to determine whether or not such techniques were suitable for predicting the fracture behavior of the adhesive studied herein. Good correlation was established between the fracture energy values measured and the value of tan d obtained from dynamic mechanical analysis tests conducted at corresponding reduced test rates.Master of Science
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Wang, Xiao. "Stress-Function Variational Methods for Stress Analysis of Composite Laminates and Adhesively Bonded Composite Joints." Thesis, North Dakota State University, 2015. https://hdl.handle.net/10365/27639.
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Adhesively bonded composite joints (ABCJs) have been broadly used to connect multimaterials
and show their structural and economic advantages compared to traditional bonding
methods. However, robust methods are still desired for efficient and accurate lay-wise stress
analysis of ABCJs involving multiple boundaries and layers.
The purpose of this work was to extend the stress-function variational method for free-edge
stress analysis of composite laminates with a finite length. At each interface of the laminate, two
unknown Lehknitskii?s stress potential functions were introduced to interpolate the stresses
across the layer. A set of 4th-order governing ODEs of the functions was obtained via evoking the
complementary virtual work, solved by eigenvalue-function method under proper traction
conditions. Corresponding MATLAB? program was developed and validated by the FEM
(ANSYS?). This method can also examine the stress-suppression effect after composite
laminates interleafing. Consequently, the above method was furthered for determining the laywise
stress distribution in ABCJs.
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Tiu, W. P. "Fatigue strength prediction of adhesively bonded unidirectional carbon fibre reinforced composite joints." Thesis, City University London, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378857.
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Jolly, Prateek. "Lamb wave based active damage identification in adhesively bonded composite lap joints." Thesis, Mississippi State University, 2016. http://pqdtopen.proquest.com/#viewpdf?dispub=10100288.
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Bonding composite structures using adhesives offers several advantages over mechanical fastening such as better flow stress, weight saving, improved fatigue resistance and the ability to join dissimilar structures. The hesitation to adopt adhesively bonded composite joints stems from the lack of knowledge regarding damage initiation and propagation mechanisms within the joint. A means of overcoming this hesitation is to continuously monitor damage in the joint. This study proposes a methodology to conduct structural health monitoring (SHM) of an adhesively bonded composite lap joint using acoustic, guided Lamb waves by detecting, locating and predicting the size of damage. Finite element modeling of a joint in both 2D and 3D is used to test the feasibility of the proposed damage triangulation technique. Experimental validation of the methodology is conducted by detecting the presence, location and size of inflicted damage with the use of tuned guided Lamb waves.
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Radice, Joshua J. "The analysis and design of adhesively bonded composite structures." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 1.10Mb , 279 p, 2005. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3181889.
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Flor, Felipe Rendeiro. "Damage monitoring in composite structures via vibration based method: metal-composite bonded joints and sandwich structures." Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-04042016-161659/.
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The present document covers the studies over Structural Health Monitoring systems via vibration based methods. The topic is organized in two parallel studies. The first one analyzes the integrity of metal-composite single lap bonded joints. The second one approaches similar analyses for sandwich structures. The monitoring was made by investigating the dynamic response both computationally and experimentally to verify the reliability of applying vibration based SHM procedures, specifically with the objective of identifying the presence of debonding damage. The dynamic responses were obtained via accelerometers and piezoelectric sensors placed on top of the investigated structures (on the outward surface). The purpose for the accelerometers is to provide reference data for the analyses involving the piezoelectric sensors. Different metrics of damage identification were investigated, all working over a determined frequency range. They quantify the damage by analyzing either the magnitudes or phase angles of the dynamic responses among the undamaged and damage structures. This present work proposed modifications to some methodologies of damage quantification found in the literature and compared the results. The new metrics offered more reliable values for the damage quantification on several of the analyses. It was verified that the metrics are valid for the scenarios observed in the present study. The experimental analyses showed also the influence on the dynamic response due to the position of small elastomeric elements. In regards to the finite element analyses, the computational models showed similar results to the experimental data, the more accurate ones being the models for the bonded joints. For the computational models, improvements can be applied into the piezoelectric sensor (e.g. by using new finite element formulations), as well as the region of debonding (e.g. by using contact algorithms). It is important to highlight that the elastic properties of the skins for the sandwich structure were obtained by the literature, so the model can be improved in the future by applying properties obtained experimentally.Esta dissertação aborda os estudos realizados no campo de Sistemas de Monitoramento da Integridade Estrutural por meio de métodos baseados em vibrações. O tópico abordado é organizado em dois estudos paralelos. O primeiro é relativo ao monitoramento da integridade de juntas coladas metal-compósito. O segundo versa sobre análises semelhantes em estruturas sanduíche. O monitoramento foi executado através das análises das assinaturas dinâmicas das estruturas, tanto computacionalmente quanto experimentalmente, visando avaliar a capacidade de metodologias vibracionais de SHM em detectar dano de descolamento. As respostas dinâmicas foram obtidas por meio de acelerômetros e sensores piezelétricos dispostos sobre a superfície das estruturas avaliadas. Os acelerômetros fornecem dados de referência para as análises realizadas com base nas respostas do sensor piezelétrico. Diferentes métricas de identificação de dano são abordadas, sendo que todas estão baseadas em análise no domínio da frequência, utilizando parâmetros de magnitude ou ângulo de fase das estruturas danificadas e intactas. O presente trabalho propôs alterações em algumas das metodologias encontradas na literatura e comparou os resultados das métricas originais com as modificadas. As métricas modificadas apresentaram resultados mais consistentes em vários cenários de análise. Constatou-se também que as métricas abordadas mostram-se válidas para os casos observados no presente estudo. As análises experimentais também evidenciaram a influência na assinatura dinâmica da estrutura sanduíche causada pelo posicionamento de pequenos elementos elastoméricos. Com relação às análises via elementos finitos, os modelos computacionais apresentaram resultados similares aos obtidos experimentalmente, sendo os da junta colada os mais precisos. Tais modelos computacionais podem ser melhorados no futuro por meio de uma modelagem mais detalhada dos elementos piezelétricos (por exemplo: por meio de novas formulações), como também da região de descolamento (por exemplo: por meio da implementação de algoritmos de contato). Deve-se ressaltar também que as propriedades elásticas das lâminas externas da estrutura sanduíche foram obtidas da literatura, assim sendo, o modelo poderá ser melhorado em estudos futuros por meio do emprego de propriedades obtidas experimentalmente.
13
Lubke, Kathleen A. "Investigation of cold temperature and environmental effects of adhesively bonded joints." Thesis, Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/20016.
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Owens, James F. P. "Studies on stiffness and fracture behaviour in adhesively bonded composite-to-metal shear joints." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape17/PQDD_0013/MQ35515.pdf.
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Capell, Tobias F. "Applications of embedded chirped fibre Bragg grating sensors for damage and defect detection in composites and composite bonded joints." Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.580337.
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This thesis reports investigations into the application of a type of optical sensor to detect and monitor damage in composites structures. The chirped fibre Bragg grating (CFBG) is a type of optical component that is sensitive to both strain and temperature and is commonly found in the telecommunications industry as a filter. Its small diameter and low cost makes it a potentially inexpensive sensor ideal for embedding in composite materials. This work consisted of extending the use of CFBG sensors into three areas: monitoring of disbonding in composite-metal bonded joints; detection of manufacturing defects in composite-composite bonded joints; monitoring of delamination lengths for a specimen subjected to mode II loading. All of these areas were investigated using a combination of experimental testing and theoretical predictions (using finite element analysis and optical prediction software). The first area investigated used a bonded joint composed of one metal adherend (aluminium) and one composite adherend with an embedded CFBG, bonded together at elevated temperature. Thermal strains were generated in the bonded joint on cooling the joint from the adhesive cure temperature to room temperature. The joint was then subject to tension-tension fatigue loading, which caused the joint to progressively disbond. The relaxation of the thermal strain in the composite adherend due to the advancing disbond front caused perturbations in the reflected spectra from the embedded CFBG sensor which allowed the development of the disbond to be tracked to within about 2 mm. In the second area, CFBG sensors were embedded within one of the composite adherends in a composite-composite bonded joint with an included manufacturing defect in the bondline. The first defect used was PTFE and the reflected spectrum from the CFBG sensor showed a clear perturbation at the defect location (the joint was externally loaded). Subsequent tests used more realistic defects (i.e. "air gaps" introduced into the bond) as the defect, and perturbations were observed in the CFBG spectra for both glass fibre reinforced plastic (GFRP-GFRP) joints and carbon fibre reinforced plastic (CFRP-CFRP) bonded joints. The effect of defect size and position was also investigated. The results for detecting the air defects were not as clear as for the PTFE artificial defect; however defects of 5 mm or longer could be detected at any position within the joints. The third area investigated in this work used embedded CFBGs to monitor delamination lengths in specimens subjected to mode II loading. A CFRP End-notch flexure specimen (ENF) was modelled using finite element analysis and predictions were made of the reflected CFBG spectra to establish the effect of sensor position on the reflected spectra. ENF specimens were then manufactured with sensors embedded in the positions which would produce the clearest perturbations (based on the computer modelling). Delaminations were grown in the ENF specimens and the effects on the reflected spectra were compared with the predictions, with excellent agreement between the extension of the delaminations as monitored directly and by the CFBG sensors, but only when low-reflectivity sensors (i.e. 40% reflectivity) were used. Indeed, a very important and supplementary part of the delamination study showed that sensor sensitivity to non-uniform strain fields (i.e. the type of strain distribution generated by damage in composite materials) is increased with decreasing CFBG reflectivity
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Musaramthota, Vishal. "Prediction of Fracture Toughness and Durability of Adhesively Bonded Composite Joints with Undesirable Bonding Conditions." FIU Digital Commons, 2015. http://digitalcommons.fiu.edu/etd/2513.
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Advanced composite materials have enabled the conventional aircraft structures to reduce weight, improve fuel efficiency and offer superior mechanical properties. In the past, materials such as aluminum, steel or titanium have been used to manufacture aircraft structures for support of heavy loads. Within the last decade or so, demand for advanced composite materials have been emerging that offer significant advantages over the traditional metallic materials. Of particular interest in the recent years, there has been an upsurge in scientific significance in the usage of adhesively bonded composite joints (ABCJ’s). ABCJ’s negate the introduction of stress risers that are associated with riveting or other classical techniques. In today’s aircraft transportation market, there is a push to increase structural efficiency by promoting adhesive bonding to primary joining of aircraft structures. This research is focused on the issues associated with the durability and related failures in bonded composite joints that continue to be a critical hindrance to the universal acceptance of ABCJ’s. Of particular interest are the short term strength, contamination and long term durability of ABCJ’s.
One of the factors that influence bond performance is contamination and in this study the influence of contamination on composite-adhesive bond quality was investigated through the development of a repeatable and scalable surface contamination procedure. Results showed an increase in the contaminant coverage area decreases the overall bond strength significantly. A direct correlation between the contaminant coverage area and the fracture toughness of the bonded joint was established. Another factor that influences bond performance during an aircraft’s service life is its long term strength upon exposure to harsh environmental conditions or when subjected to severe mechanical loading. A test procedure was successfully developed in order to evaluate durability of ABCJ’s comprising severe environmental conditioning, fatiguing in ambient air and a combination of both. The bonds produced were durable enough to sustain the tests cases mentioned above when conditioned for 8 weeks and did not experience any loss in strength. Specimens that were aged for 80 weeks showed a degradation of 10% in their fracture toughness when compared to their baseline datasets. The effect of various exposure times needs to be further evaluated to establish the relationship of durability that is associated with the fracture toughness of ABCJ’s.
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Chadegani, Alireza. "Strain energy release rate analysis of adhesive-bonded composite joints with a prescribed interlaminar crack." Thesis, Wichita State University, 2008. http://hdl.handle.net/10057/2023.
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Composite materials together with adhesive-bonding have been increasingly used in the aviation industry. Delamination is among the critical failure modes in fiber-reinforced laminated composite structures including adhesive-bonded assemblies. This thesis presents an analytical approach by taking into account the first-ply failure in adhesive-bonded composite joints subjected to axial tension. The ASTM D3165 standard test specimen geometry is followed for model development derivations. The field equations, in terms of displacements within the joint, are formulated by using the first-order, shear-deformable, laminated plate theory together with kinematics relations and force equilibrium conditions. The stress distributions for the adherends and adhesive are determined after the appropriate boundary and loading conditions are applied and the equations for the field displacements are solved. The equivalent forces at the tip of the
prescribed interlaminar crack are obtained based on interlaminar stress distributions. The strain energy release rate of the crack is then determined by using the virtual crack closure technique (VCCT). The system of second-order differential field equations is solved to provide the adherend and adhesive stresses using the symbolic computation tool, Maple 9.52. Finite element analyses using the J-integral as well as the VCCT are performed to verify the developed analytical model. Finite element analyses are conducted using the commercial finite element analysis software ABAQUS 6.5-1. Results determined using the analytical method are shown to correlate well with the results from the finite element analyses.Thesis [M.S] - Wichita State University, College of Engineering, Dept. of Aerospace Engineering
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Chadegani, Alireza Yang Charles. "Strain energy release rate analysis of adhesive-bonded composite joints with a prescribed interlaminar crack." A link to full text of this thesis in SOAR, 2008. http://hdl.handle.net/10057/2023.
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Makhecha, Dhaval Pravin. "Dynamic Fracture of Adhesively Bonded Composite Structures Using Cohesive Zone Models." Diss., Virginia Tech, 2005. http://hdl.handle.net/10919/29631.
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Using experimental data obtained from standard fracture test configurations, theoretical and numerical tools are developed to mathematically describe non-self-similar progression of cracks without specifying an initial crack. A cohesive-decohesive zone model, similar to the cohesive zone model known in the fracture mechanics literature as the Dugdale-Barenblatt model, is adopted to represent the degradation of the material ahead of the crack tip. This model unifies strength-based crack initiation and fracture-mechanics-based crack progression.
The cohesive-decohesive zone model is implemented with an interfacial surface material that consists of an upper and a lower surface that are connected by a continuous distribution of normal and tangential nonlinear elastic springs that act to resist either Mode I opening, Mode II sliding, Mode III sliding, or a mixed mode. The initiation of fracture is determined by the interfacial strength and the progression of the crack is determined by the critical energy release rate. The adhesive is idealized with an interfacial surface material to predict interfacial fracture. The interfacial surface material is positioned within the bulk material to predict discrete cohesive cracks. The interfacial surface material is implemented through an interface element, which is incorporated in ABAQUS using the user defined element (UEL) option.
A procedure is established to formulate a rate dependent model based on experiments carried out on compact tension test specimens. The rate dependent model is incorporated into the interface element approach to capture the unstable crack growth observed in experiments under quasi-static loading conditions. The compact tension test gives the variation of the fracture toughness with the rate of loading, this information is processed and a relationship between the fracture toughness and the rate of the opening displacement is established.
The cohesive-decohesive zone model is implemented through a material model to be used in an explicit code (LS-DYNA). Dynamic simulations of the standard test configurations for Mode I (Double Cantilever Beam) and Mode II (End Load Split) are carried out using the explicit code. Verification of these coupon tests leads to the crash analysis of realistic structures like the square composite tube. Analyses of bonded and unbonded square tubes are presented. These tubes shows a very uncharacteristic failure mode: the composite material disintegrates on impact, and this has been captured in the analysis.
Disadvantages of the interface element approach are well documented in the literature. An alternative method, known as the Extended Finite Element Method (XFEM), is implemented here through an eight-noded quadrilateral plane strain element. The method, based on the partition-of-unity, is used to study simple test configuration like the three-point bend problem and a double cantilever beam. Functionally graded materials are also simulated and the results are compared to the experimental results available in the literature.Ph. D.
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Palaniappan, Jayanthi. "The use of a CFBG sensor for detecting damage in composite laminates and adhesively bonded joints." Thesis, University of Surrey, 2008. http://epubs.surrey.ac.uk/940/.
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Reliable in-situ damage detection techniques which can detennine the existence and location of damage in composite materials and structures are critical for the effective use of these materials. In this work, embedded chirped fibre Bragg grating (CFBG) sensors have been shown to be successful for both detection and location of matrix cracks in composite laminates and disbond detection in bonded composite joints. In all the cases, the CFBG reflection spectra were predicted using commercial software and agreed well with the experimental results. In the matrix cracking work, single matrix cracks in cross-ply GFRP (glass' fibre reinforced plastic) laminates were detected and located using a CFBG sensor embedded within the 0° plies, near the 0/90 interface. The CFBG sensor showed an approximately sinusoidal variation of the intensity of the reflected spectrum at the position of the crack, enabling both crack development and crack position to be identified. It was shown that the precise position of the cracks does not correspond with the bottom of a dip in the reflected spectrum, as has previously been thought. Disbond initiation and progression from either end of a composite bonded joint was monitored by embedding the CFBG sensor in one of the GFRP adherends, with the low wavelength end ofthe sensor positioned at the cut end ofthe adherend. A shift in the low wavelength end of the spectrum to lower wavelengths indicated disbond initiation and movement of a perturbation in the reflected spectrum towards higher wavelengths indicated disbond propagation. In a related fashion, disbond initiation and propagation was detected from the high-wavelength end ofthe spectrum (adjacent to the other cut end of the adherend). With the aid of a parametric study based on a closed-form solution for the strain field in the bonded joint (available in the literature), it has been shown that the sensitivity ofthe CFBG sensor in detecting the disbond depends mainly on the position of the sensor within the adherend and the strain distribution in the adherend. Finally, artificial manufacturing defects were introduced into GFRP-GFRP bonded joints using Teflon inserts and it has been demonstrated that the location of the defects is possible using the CFBG technique.
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Khan, Minhaj A. "Development of rules for the design of adhesively bonded fibre-reinforced plastic composite joints in aerospace applications." Thesis, University of Surrey, 2018. http://epubs.surrey.ac.uk/848672/.
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This thesis describes progression towards developing an enhanced design methodology for laminated composite bonded joints in aerospace applications. The premise of a universal failure criterion is impractical given the number of adhesive-adherend configurations available. However, for a finite number of joint configurations, design rules can be developed based on experimental test data and detailed finite element modelling. By using these techniques rather than the traditional, overly conservative knock-down factors, more of the performance of composite bonded joints can be accessed. While complex damage modelling techniques are available, the additional material data and analysis time required renders them not suitable for the vast majority of time-sensitive industrial applications. Initially, the work presented in this thesis experimentally studied the effect of the substrate material, substrate layup, adhesive material and adhesive thickness on several laminated composite bonded joint configurations. The corresponding failure surfaces were extensively analysed and failure modes identified. Following this, detailed FE models were developed to identify the trends associated with altering joint parameters. Finally, the stresses and strains within the adhesive and substrate were analysed at each joint’s respective failure loads to identify critical parameters, which would later be used to develop a Critical Parameter Method for evaluating joint performance. Once these parameters were consolidated, they were validated against a unique set of joints. The critical parameter approach was able to predict joint strength with an average error of 26% compared experimental strength. Traditional FE criterions presented an average error of 61% compared to experimental strength. After further consolidation, joint strength prediction reduced to within 3% of experimental strength using the Critical Parameter Method, representing a substantial improvement in predictive capabilities.
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Abdel, Monsef Said Ahmed Ibrahim. "A comprehensive methodology to analyse bonded joints subjected to different environmental conditions." Doctoral thesis, Universitat de Girona, 2020. http://hdl.handle.net/10803/669651.
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Cohesive zone models are widely used for modelling delamination and bonded joints under different loading conditions. In the current thesis, an objective inverse method has been developed to extract the cohesive law from experimental load-displacement data for both mode I and mode II. In addition, the influence of the mode II test configuration on the cohesive law of bonded joints is discussed. Besides, the influence of environmental conditions on the fracture behaviour of two types of adhesively bonded joints is experimentally studied for Mode I and Mode II tests. The dependence of the cohesive laws on the testing temperature and ageing is also analysed. Finally, a phenomenological expression that describes the effect of temperature and ageing on the cohesive law shape is formulated. Using this expression, a constitutive cohesive zone model is enhanced to simulate the influence of the environmental conditions on the mechanical response.Els models de zona cohesiva s’utilitzen per simular delaminació i el comportament mecànic de les unions adhesives. S'ha desenvolupat un mètode invers per extreure la llei cohesiva a partir de dades experimentals de desplaçament i càrrega en la manera I i la manera II de càrrega. A més, es discuteix la influència de la configuració de l’assaig en mode II sobre la llei cohesiva. La influència de les condicions ambientals en el comportament de fractura de dos tipus d’unions adhesives s’estudia experimentalment per a assajos de mode I i mode II. També s’analitza la dependència de les lleis cohesives de la temperatura i l’envelliment. Finalment, es formula una expressió fenomenològica que descriu l’efecte de la temperatura i l’envelliment en la llei cohesiva. Mitjançant aquesta expressió, s’actualitza la formulació d’un model de zona cohesiva constitutiva per simular la influència de les condicions ambientals en la resposta mecànica.
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Simon, Pavel. "Progresivní styčníky FRP kompozitů konstrukcí dopravní infrastruktury." Doctoral thesis, Vysoké učení technické v Brně. Fakulta stavební, 2018. http://www.nusl.cz/ntk/nusl-390279.
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This thesis deals with junction points of construction used in transport infrastructure, which are made of FRP composite material. Main focus is on bonded joints. The material and geometrical criteria od FRP material and there influence to junctions are analyzed. In sequential steps the development of the design of joints applicable to reference constructions - pedestrian walkways is documented. There are also presented practical experiences from the tests of joints of overlapped and single-sided joints, as well as experience from the design, production and testing of two types of pedestrian bridges on a real scale. Furthermore, extensive comparison of joints, in particular T-joints with closed profiles for selected types of fasteners, is provided. From a simple connection, screws and rivets or plain bonding to combined joints. These are assessed both in terms of bearing capacity and their deformation behavior. These tests are performed for two material combinations, FRP-FRP and FRP-steel.
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Roy, Samit. "A finite element analysis of adhesively bonded composite joints including geometric nonlinearity, nonlinear viscoelasticity, moisture diffusion and delayed failure." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/88624.
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A two-dimensional finite-element computational procedure is developed for the accurate analysis of the strains and stresses in adhesively bonded joints. The large displacements and rotations experienced by the adherends and the adhesive are taken into account by invoking the updated Lagrangian description of motion. The adhesive layer is modeled using Schapery's nonlinear single integral constitutive law for uniaxial and multiaxial states of stress. Effect of temperature and stress level on the viscoelastic response is taken into account by a nonlinear shift factor definition. Penetrant sorption is accounted for by a nonlinear Fickean diffusion model in which the diffusion coefficient is dependent on the penetrant concentration and the dilatational strain. A delayed failure criterion based on the Reiner-Weisenberg failure theory has also been implemented in the finite element code. The applicability of the proposed models is demonstrated by several numerical examples.Doctor of Philosophy
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Crammond, G. "Development of optical techniques for the experimental analysis of local stress and strain distributions in adhesively bonded composite joints." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/355981/.
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This research seeks to evaluate the local stress and strain distributions formed in adhesively bonded composite joints under quasi static and high strain rate loading. A literature review of current analytical, numerical and experimental studies of adhesively bonded joints is presented and identifies the lack of knowledge in the behaviour of composite bonded joints in the through-thickness direction. Detailed analysis of the stress and strain in the joint, and their impact on the development of damage prior to and during failure have been obtained using Digital Image Correlation (DIC). An experimental methodology is established to perform DIC at the mesoscopic scale using high magnification optics, enabling accurate, high spatial resolution analysis of the strains around the geometric discontinuity between adherends. It is demonstrated that the small through-thickness strains are critical in the development of damage in the joint around the discontinuity between adherends. Errors in the DIC technique are assessed using a robust morphological methodology to evaluate the quality of different speckle patterns based upon the properties of the speckles in the pattern. The strain data is manipulated to evaluate the principal stresses in the joint, which govern failure in the brittle epoxy matrix of the composite, providing a concise evaluation of the transfer of load between the adherends and damage initiation within the joint. The DIC results and methodology are validated against independent infra-red measurements using Thermoelastic Stress Analysis (TSA). Limitations in the TSA analysis approach are identified around joint discontinuity due to the varying principal stress direction. A new TSA analysis methodology is presented to overcome this. The results of the experimental analysis are used to validate a representative 2D finite element model modelling approach for adhesively bonded joints, showing good agreement to the experimental data. Finally the full-field DIC methodology is applied to analyse the response of a single lap joint during high strain rate loading, providing unprecedented full-field measurement of the strain fields up to failure.
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Wong, King Jye. "Moisture absorption characteristics and effects on mechanical behaviour of carbon/epoxy composite : application to bonded patch repairs of composite structures." Phd thesis, Université de Bourgogne, 2013. http://tel.archives-ouvertes.fr/tel-00949293.
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Le travail présenté dans ce mémoire avait pour objectif d'étudier le processus de la pénétration d'eau dans les composites en carbone/époxyde dans un premier temps, et dans un deuxième temps, d'étudier l'effet de la prise en eau par ces matériaux sur les performances mécaniques des composites et leur joints collés. L'intégration de ces phénomènes physiques dans la modélisation numérique est d'une grande importance dans la prédiction de la durabilité d'une structure en composite subissant un vieillissement hygrothermique. Par conséquent, ce travail consiste non seulement en des observations expérimentales, mais aussi en des simulations numériques. Des corrélations entre les résultats obtenus permettent d'une part de mieux comprendre ce qui se passe dans un système composite avec l'assemblage collé soumis à des charges mécaniques, de l'initiation d'endommagement jusqu'à la rupture finale ; d'autre part, de valider un modèle numérique robuste dans le but de la conception et de l'optimisation. Les originalités de ce travail se situent à différents niveaux en proposant : 1. un nouveau modèle de diffusion à deux-phases permettant de mieux décrire l'effet de l'épaisseur des stratifiés sur la pénétration de l'eau; 2. un nouveau modèle RPM " Residual Property Model " afin de prévoir la dégradation des propriétés mécaniques due à la prise en eau ; 3. une nouvelle loi de traction-séparation linéaire-exponentiel pour décrire la courbe-R observée dans les essais DCB en mode I pur sur les composites stratifiés afin de les intégrer plus facilement dans les modèles numériques
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Pérez, Galmés Magdalena. "Analysis and development of experimental characterization methodologies of mode II fracture toughness on CFRP bonded joints." Doctoral thesis, Universitat de Girona, 2018. http://hdl.handle.net/10803/664508.
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Adhesives have been shown to be an excellent solution for joining fibre reinforced polymer (FRP) components thanks to their capacity to redistribute loads, reduces stress concentrations and contribute to overall weight saving in the structure. The most relevant mechanical property in adhesive bonded joints design is the shear (mode II) fracture toughness of the adhesive.
The application of the existing mode II delamination standards to adhesive joints entails some major limitations that result in severe under/over estimations of the adhesive properties and, in many cases, can even prevent results from being obtained from tests.
The main objective of the present thesis is to develop robust tools for the determination of shear (mode II) facture toughness in adhesive joints. This includes studying data reduction methods as well as the test geometriesEls adhesius han demostrat ser una magnífica solució per unir components de polímers reforçats amb fibres (FRP) gràcies a la seva capacitat per redistribuir càrregues, reduir les concentracions de tensions i contribuir a l’estalvi general de pes en l’estructura. La propietat mecànica més rellevant en el disseny d’unions adhesives és la tenacitat a la fractura a tallant (mode II) de l’adhesiu. L’aplicació dels actuals assajos estandaritzats a les unions adhesives pot derivar en estimacions errònies, per sota o per sobre, de les propietats adhesives i, en molts casos, evitar que l’assaig es pugui realitzar satisfactòriament. L’objectiu principal d’aquesta tesi és el desenvolupament d’eines robustes per a la determinació de la tenacitat a la fractura a tallant (mode II) d’unions adhesives. S’estudia l’aplicabilitat dels mètodes d’assaig de deslaminació en mode II existents a les unions adhesives estructurals. Això inclou l’estudi dels mètodes de reducció de dades i de les geometries d’assaig
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Nicoli, Edoardo. "Characterization of Mixed-Mode Fracture Testing of Adhesively Bonded Wood Specimens." Diss., Virginia Tech, 2010. http://hdl.handle.net/10919/28372.
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The primary focus of this thesis was to investigate the critical strain energy release rates (G) for mixed-mode (I/II) fracture of wood adhesive joints. The aims of the study were: (1) quantifying the fracture properties of two material systems, (2) analyzing the aspects that influence the fracture properties of bonded wood, (3) refining test procedures that particularly address layered orthotropic systems in which the layers are not parallel to the laminate faces, of which wood is often a particular case, and (4) developing testing methods that enhance the usefulness of performing mixed-mode tests with a dual-actuator load frame. The material systems evaluated experimentally involved yellow-poplar (Liriodendron tulipifera), a hardwood of the Magnoliaceae family, as adherends and two different adhesives: a moisture-cure polyurethane (PU) and a phenol/resorcinol/-formaldehyde (PRF) resin. The geometry tested in the study was the double cantilever beam that, in a dual-actuator load frame, can be used for testing different levels of mode-mixity. The mixed-mode loading condition is obtained by applying different displacement rates with the two independently controlled actuators of the testing machine.
Characteristic aspects such as the large variability of the adhesive layer thickness and the intrinsic nature of many wood species, where latewood layers are alternated with earlywood layers, often combine to confound the measures of the critical values of strain energy release rate, Gc. Adhesive layer thickness variations were observed to be substantial also in specimens prepared with power-planed wood boards and affect the value of Gc of the specimens. The grain orientation of latewood and earlywood, materials that often have different densities and elastic moduli, limits the accuracy of traditional standard methods for the evaluation of Gc. The traditional methods, described in the standards ASTM D3433-99 and BS 7991:2001, were originally developed for uniform and isotropic materials but are widely used by researchers also for bonded wood, where they tend to confound stiffness variations with Gc variations. Experimental analysis and analytical computations were developed for quantifying the spread of Gc data that is expected to be caused by variability of the adhesive layer thickness and by the variability of the bending stiffness along wooden beams.Ph. D.
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Carraro, Paolo Andrea. "Multiaxial fatigue behaviour of composite materials: characterisation and modelling." Doctoral thesis, Università degli studi di Padova, 2014. http://hdl.handle.net/11577/3423782.
Full textAbstract:
Thanks to their lightness and versatility combined with excellent mechanical properties, composite materials underwent an increasing relevance in the last twenty years in many industrial fields, also for structural applications.
This class of materials offer a wide range of advantages but it is still characterized by a quite high cost with respect to more traditional structural materials. One of the reasons is the lack of reliable design procedures, as well as of extensive experimental investigations in the literature providing clear and general information.
This is particularly evident with reference to the behaviour of composite laminates and bonded joints under multiaxial fatigue loading, which often characterise in-service conditions.
With the aim to acquire information on the multiaxial fatigue behaviour of unidirectional composites, a specimen configuration was first defined, suitable to characterise the matrix-dominated multiaxial fatigue behaviour of a composite lamina, which is of great importance for the damage evolution in laminates (chapter 2). Tubular specimens subjected to combined tension/torsion loading were identified as the best compromise between reliability of results, easiness of testing and possibility to obtain multiaxial stress states of interest.
In the third chapter the results of an extensive experimental investigation on tubular specimens is presented. Tubes were fatigue tested with several values of the biaxiality (shear to transverse) ratio and load ratio (ratio between the minimum and the maximum fatigue loads). A strong influence of both parameters was found on the off-axis crack initiation and propagation phenomena, as well as on the damage mechanisms at the micro-scale.
Uniaxial fatigue tests were then carried out on multidirectional flat laminates, designed to achieve local multiaxial stress states similar to those applied to the tubes by means of tension/torsion external loads. This activity, presented in the fourth chapter, revealed the equivalence between external (obtained by applying external loads in different directions) and internal (due to material anisotropy) multiaxial stress states. This represents a fundamental step for the extension of experimental results and predictive models to general loading conditions.
The experimental activity on tubes provided information on the damage mechanisms at the micro-scale, responsible for fatigue failure of a unidirectional lamina. On the basis of these mechanisms a criterion for predicting crack initiation in a unidirectional lamina under multiaxial fatigue was developed by means of a multiscale approach (chapter 5). This criterion resulted in sound agreement with the new data on tubes, with data on flat unidirectional laminates from the literature and with crack initiation data on the off-axis layers of the laminates reported in chapter 4.
A basic topic related to the analysis of multidirectional laminates is the stiffness degradation due to off-axis cracks in their plies. Dealing with such a topic, an analytical model was developed for predicting the stiffness of a laminate as a function of the crack density in its layers accounting for the interaction between cracks in different layers (chapter 6). In addition the model is capable of calculating the stress re-distribution due to the presence of cracks. This is fundamental for the development of a new procedure for predicting the fatigue crack density evolution in multidirectional laminates, presented in chapter 7.
To this aim the experimental observations, the analytical models and criteria previously presented, combined with a statistical approach, have been used to predict the initiation and propagation of multiple cracks in a laminate. As a consequence, when this procedure is combined with the model presented in chapter 6, both the stiffness degradation and the stress re-distribution, useful for the estimation of the total fatigue life, can be predicted.
When composite laminates are used as adherends in bonded joints the bonding surface represents a critical position for the onset of fatigue cracks. As a consequence an experimental investigation on the propagation of a bondline crack in composite bonded joints subjected to mixed mode I + II (opening + sliding) fatigue loading was carried out and presented in chapter 8. A criterion to predict the crack propagation rate under mixed mode loading was also developed, based on the damage mechanisms observed during the experimental campaign.
Eventually, in Appendix A an analytical model for predicting the initiation of a fibre-matrix debond crack under biaxial static loads is presented. The model provides useful information on the influence of the main geometrical and interface parameters of the fibre-matrix interface strength.Grazie alla loro leggerezza e versatilità combinate ad eccellenti proprietà meccaniche, i materiali compositi hanno acquisito un'importanza sempre maggiore negli ultimi vent'anni in molti settori industriali, anche per applicazioni strutturali. A fronte dei numerosi vantaggi offerti da questa classe di materiali vi è un costo che rimane ancora piuttosto elevato rispetto ai più tradizionali materiali da costruzione. Una delle ragioni è la mancanza di procedure di progettazione affidabili e riconosciute, nonché l'assenza, in letteratura, di estese caratterizzazioni sperimentali da cui acquisire informazioni di carattere generale. Ciò è particolarmente evidente in riferimento al comportamento a fatica multiassiale di lamine, laminati e giunzioni incollate in composito. Al fine di sopperire alla mancanza di informazioni sul comportamento a fatica multiassiale di lamine unidirezionali, nonché all'assenza di una procedura adeguata di test, è stata inizialmente definita una configurazione di provini adatta a caratterizzare la risposta matrix-dominated (particolarmente significativa per il danneggiamento a fatica di laminati) di materiali compositi unidirezionali (capitolo 2). Provini tubolari soggetti a carichi ciclici di trazione e torsione combinati sono stati identificati come il miglior compromesso tra affidabilità dei risultati, semplicità di testing e possibilità di ottenere condizioni multiassiali di interesse. Nel terzo capitolo sono riportati i risultati di un'estesa campagna sperimentale su tali provini tubolari in presenza di diversi rapporti di biassialità (tensione di taglio su tensione trasversale) e rapporti di ciclo (rapporto tra il minimo e il massimo carico di fatica). É stata riscontrata una notevole influenza di tali parametri sull'innesco e propagazione di cricche off-axis, nonché sui meccanismi di danneggiamento su scala microscopica. Sono poi stati testati a fatica uni-assiale dei laminai piani multi-direzionali progettati per avere condizioni di multiassialità locali simili a quelle ottenute sui provini tubolari tramite carichi esterni in diverse direzioni. L'attività, presentata al quarto capitolo, ha permesso di verificare l'equivalenza tra condizioni multiassiali ti tipo esterno (carichi in più direzioni) e interno (dovute all'anisotropia di lamine e laminati in composito). Ciò rappresenta uno step fondamentale per l'estensione di risultati sperimentali e modelli previsionali a condizioni di carico generiche. L'attività sperimentale sviluppata sui tubi ha fornito informazioni sui meccanismi di danneggiamento a livello microscopico che sono responsabili del cedimento a fatica della lamina unidirezionale. Sulla base di tali meccanismi è stato proposto un criterio per l'innesco di cricche a fatica multiassiale in lamine in composito basato su un approccio multiscala (capitolo 5). Il criterio è risultato in ottimo accordo con i nuovi dati sperimentali sui campioni tubolari, con dati disponibili in letteratura riguardanti lamine unidirezionali piane e con i dati ad innesco sugli strati off-axis dei laminati testati al capitolo 4. Parlando quindi di laminati multi-direzionali, un aspetto fondamentale è la diminuzione di rigidezza di questi ultimi dovuto all'innesco e propagazione di cricche multiple negli strati off-axis. A tal proposito è stato proposto un modello analitico in grado di legare la densità di cricche in ciascuno strato di un laminato alla diminuzione di rigidezza globale considerando anche l'interazione tra cricche presenti su strati diversi (capitolo 6). Tale modello fornisce anche le distribuzioni di tensione dovute alla presenza delle cricche stesse. Questo è un aspetto di fondamentale importanza per lo sviluppo di una procedura per prevedere l'evoluzione della densità di cricche in laminati multi-direzionali sollecitati a fatica, presentata al capitolo 7. A tale scopo le osservazioni sperimentali, i modelli analitici e i criteri sviluppati in precedenza, combinati ad un approccio di tipo statistico, vengono utilizzati per prevedere l'innesco e propagazione di cricche multiple in un laminato. Di conseguenza, combinata con il modello precedentemente illustrato, la procedura consente di prevedere sia la diminuzione di rigidezza di laminati sia la ridistribuzione delle tensioni per effetto del danneggiamento rappresentando quindi uno strumento utile anche alla stima della vita a fatica totale di un laminato. Quando i laminati in composito sono utilizzati come aderendi in giunzioni incollate, l'interfaccia di incollaggio rappresenta una zona particolarmente critica per l'innesco di cricche a fatica. Di conseguenza è stata analizzata sperimentalmente la propagazione di cricche in giunzioni incollate soggette a carichi ciclici di modo misto I + II (apertura + scorrimento). Ancora una volta i meccanismi osservati su scala microscopica sono stati utilizzati per la formulazione di un criterio damage-based per la previsione della velocità di propagazione di cricche in giunzioni incollate sollecitate in modo misto (capitolo 8). In fine, in Appendice A è presentato un modello analitico sviluppato per la previsione dell'innesco di una cricca di debonding tra fibra e matrice in condizioni di carico statico biassiale. Il modello è utile per trarre informazioni sull'influenza dei principali parametri geometrici e interfacciali sulla resistenza dell'interfaccia fibra-matrice.
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Elder, David James, and d. elder@crc-acs com au. "Optimisation of parametric equations for shock transmission through surface ships from underwater explosions." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2006. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20080212.105012.
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Currently shock effects on surface ships can be determined by full scale shock trials, Finite Element Analysis or semi empirical methods that reduce the analytical problem to a limited number of degrees of freedom and include hull configurations, construction methods and materials in an empirical way to determine any debilitating effects that an explosion may have on the ship. This research has been undertaken to better understand the effect of hull shape on surface ships' shock response to external underwater explosions (UNDEX). The study is within the semi empirical method category of computations. A set of simple closed-form equations has been developed that accurately predicts the magnitude of dynamic excitation of different 2- D rigid-hull shapes subject to far-field UNDEX events. This research was primarily focused on the affects of 2-D rigid hull shapes and their contribution to global ship motions. A section of the thesis,
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Budhe, Sandip Rudha. "Effect of pre-bond moisture on the static and fatigue behaviour of bonded joints between CFRP laminates for structural repairs." Doctoral thesis, Universitat de Girona, 2014. http://hdl.handle.net/10803/283567.
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In recent years, the use of composite materials in the aeronautic, automotive, marine construction, etc. has increased significantly. Hence, there is an increasing need for repair technologies on primary structural components, as replacing a damaged component by a new one is not cost effective in many cases. The composite structures experience damage in service that comes from accidental impacts, mechanical stresses, environmental factors (moisture and temperature), etc. Thus, maintenance and repair is the concern of the end users as well as of the manufacturers. Suitable material systems and controlled curing conditions are essential to fabricate reliable repairs. In this work, the effect of pre-bond moisture is analyzed for co-bonded adhesive joints subjected to static and fatigue loads. Specimens with three levels of pre-bond moisture (0%, 0.33% and 1.25%) and two different adhesive films (F1, F2) have been used in the analysisDurant els últims anys, la utilització de materials compòsits en la indústria aeronàutica, automoció, construcció marina, etc. ha tingut un gran creixement. Es per aquesta raó, que cada vegada té més importància el desenvolupament de mètodes per a la seva reparació, i especialment la definició mètodes de reparació en components que realitzen una funció estructural, doncs la substitució del component no és econòmicament viable en molts dels casos. És un fet conegut, que les estructures de material compòsit en condicions de servei pateixen danys provocats per impactes accidentals, tensions mecàniques, efectes ambientals (humitat i temperatura), etc. Per tant, el manteniment i la reparació d’aquestes estructures són considerats processos de vital importància per a l’usuari final i també per als fabricants. Una bona tria dels materials, així com un bon control dels processos de curat, tenen un gran efecte en l’obtenció de reparacions fiables. En aquest treball s’ha analitzat l’efecte la l’absorció de la humitat en el substrat abans del procés de curat en unions co-encolades sotmeses a càrregues estàtiques i de fatiga. L’anàlisi s’ha dut a terme amb provetes amb 3 nivells d’absorció d’humitat (0%, 0.33% y 1.25%) i dos tipus d’adhesius laminats (F1 i F2)
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Houhou, Noureddine. "Durabilité des interfaces collées béton/renforts composites : développement d'une méthodologie d'étude basée sur un dispositif de fluage innovant conçu pour être couplé à un vieillissement hygrothermique." Phd thesis, Université Paris-Est, 2012. http://tel.archives-ouvertes.fr/tel-00765147.
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Le programme de recherche développé dans le cadre de cette thèse a pour principal objectif de concevoir, réaliser et valider une méthodologie d'étude des effets du vieillissement des interfaces collées, basée sur l'utilisation d'un dispositif de fluage innovant pouvant être couplé à un vieillissement hygrothermique. Celui-ci reprend la configuration classique de joint à double recouvrement mais permet de solliciter sous charge constante l'assemblage collé béton/composite. Il présente de plus certaines spécificités (zones de joint non sollicitées, compatibilité avec une machine d'essai à simple recouvrement existante,...) qui permettent de recueillir un grand nombre de résultat expérimentaux complémentaires. En premier lieux, nos travaux présentent une synthèse bibliographique retraçant le contexte du renforcement par composites collés et précisant les principaux mécanismes physico-chimiques susceptibles d'affecter la durabilité des adhésifs. Le manuscrit décrit ensuite les travaux expérimentaux menés pour étudier le comportement mécanique et physico-chimique des deux adhésifs sélectionnés pour la réalisation des joints collés béton/composites. Finalement, une approche prédictive basée sur i) des tests de fluage thermo-stimulés, ii) sur l'application du Principe de Superposition Temps-Température et iii) sur l'utilisation du modèle rhéologique de Burger, a permis de proposer un modèle de fluage non linéaire pour chacun des deux systèmes de colle. La seconde partie des travaux expérimentaux concerne la conception et la validation d'un dispositif innovant destiné à la caractérisation du comportement en fluage des interfaces collées béton/composite. Un élément important du cahier des charges de ce dispositif était d'en limiter l'encombrement, de sorte qu'il soit possible de tester plusieurs corps d'épreuve dans une chambre climatique au volume réduit, en vue d'étudier les effets synergiques du fluage et du vieillissement environnemental sur la durabilité des joints collés. Dans ce contexte, un prototype capable de solliciter en fluage trois corps d'épreuves à double recouvrement réalisés avec le procédé de renforcement Sika®Carbodur®S et connectés sur un unique circuit hydraulique, a été conçu et réalisé. Les résultats issus du prototype ont permis de le valider, en vérifiant notamment le maintient dans le temps de la charge appliquée, et le comportement symétrique des corps d'épreuve à double recouvrement. Le comportement mécanique des interfaces collées s'est révélé répétable, symétrique et conforme aux diverses modélisations réalisées, soit en calculant la réponse instantanée de l'interface au moyen d'un logiciel aux Eléments Finis (E.F.) ou à partir du modèle analytique de Volkersen, soit en calculant la réponse différée de l'interface en intégrant le modèle de fluage non linéaire de l'adhésif identifié précédemment dans le calcul aux E.F.. La dernière partie des travaux présentés dans le manuscrit concerne la réalisation d'un banc complet de fluage impliquant 14 corps d'épreuves à double recouvrement. Ces corps d'épreuve sont réalisés pour moitié avec le système de renforcement Sika®Carbodur®S et pour l'autre moitié avec le système Compodex. Le banc de fluage est installé dans la salle de vieillissement hygrothermique du Département Laboratoire d'Autun (40°C ; 95% H.R.). Tous les corps d'épreuves sont sollicités en fluage par un système de chargement alimenté par un circuit hydraulique similaire à celui utilisé pour le prototype, mais complété par une centrale hydraulique régulant la pression à partir de la mesure d'un capteur de pression. Pour compléter ces caractérisations sur interfaces collées, des essais de vieillissement sont également menés sur des éprouvettes d'adhésifs massiques stockées dans la salle climatique, certaines d'entre elles étant simultanément soumises à des sollicitations de fluage
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Madureira, Fernando. "Fabricação e controle de espessura de juntas coladas single lap joint: caracterização mecânica dos aderentes e do adesivo." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-10122018-205044/.
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Devido a suas vantagens comparadas aos métodos tradicionais de união mecânica, a utilização de juntas coladas estruturais só tende a crescer, entretanto, devido suas propriedades e modos de falha dependerem de diversos parâmetros (tratamento superficial, geometria, material, condições de tralho, etc.) uma utilização mais ampla desta técnica ainda é restrita pela ausência de modelos de falhas confiáveis. O presente trabalho consiste na apresentação de métodos para fabricação de juntas coladas em material compósito e verificação da influência da espessura da camada adesiva na resistência de juntas simples coladas (single lap joints) submetidas à tração. São também apresentados métodos para fabricação dos aderentes, corpos de prova de adesivo puro para ensaios de caracterização e realização de ensaios mecânicos para obtenção das propriedades mecânicas tanto dos aderentes quanto do adesivo. As propriedades mecânicas dos aderentes e do adesivo foram obtidas através de ensaios realizados em uma máquina de tração universal com o auxílio da técnica de correlação digital de imagem, e a obtenção das energias críticas de resistência à fratura (GIc,GIIc) da camada adesiva foram calculadas através de ensaios Double Cantilever Beam (DCB) e End Notched Flexure (ENF). Foram estudados métodos para gerar falha coesiva nas juntas adesivas, sendo que o melhor método encontrado foi o de tratamento superficial dos aderentes com jateamento abrasivo seguido pela limpeza superficial com acetona. O controle preciso da espessura da camada adesiva foi alcançado através do desenvolvimento de um dispositivo de fácil construção, compostos por suportes de madeira, hastes e linhas de nylon. Nos ensaios em juntas coladas foi constatado uma relação inversamente proporcional entre a espessura da camada adesiva e a resistência máxima suportada pela junta, ou seja, quanto maior a espessura do adesivo menor sua resistência. Os métodos aqui apresentados foram os resultados de vários meses de estudo e compreensão das normas e técnicas disponíveis na literatura, o aprimoramento das técnicas foram frutos de um ciclo compostos por fabricação, testes e análise de resultados.Amongst the joining techniques, adhesively bonding joints are one of the most commonly applied nowadays. However, a lack of reliable failure criteria still exists, limiting in this way a more widespread application of adhesively bonded joints in principal load-bearing structural applications. An accurate strength prediction of the adhesively bonded joints is essential to decrease the amount of expensive testing at the design stage. This work consists to show methods for manufacturing single lap joints and to verify the adhesive thickness influence on the joint resistance. The manufacturing process of the composite adherends and adhesives for bulk tests was also covered. The mechanical properties of the adherends and bulk adhesive were performed on a universal testing machine with assistance of a digital image correlation (DIC) technique. The fracture toughness energy release rates (GIc,GIIc) of the adhesive layer were obtained respectively through Double Cantilever Beam (DCB) and End Notched Flexure (ENF) tests. Cohesive failure was achieved by grit blasting the adherents followed by cleaning with acetone. A constant adhesive thickness was guaranteed by placing nylon fishing lines between the adherents. Single lap joints tests showed that the joint resistance decrease with increasing adhesive thickness.
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White, Caleb, and caleb white@rmit edu au. "Health Monitoring of Bonded Composite Aerospace Structures." RMIT University. Aerospace, Mechanical and Manufacturing Engineering, 2009. http://adt.lib.rmit.edu.au/adt/public/adt-VIT20090602.142122.
Full textAbstract:
Airframe assemblers have long recognised that for a new aircraft to be successful it must use less fuel, have lower maintenance requirements, and be more affordable. One common tactic is the use of innovative materials, such as advanced composites. Composite materials are suited to structural connection by adhesive bonding, which minimises the need for inefficient mechanical fastening. The aim of this PhD project was to investigate the application of existing, yet immature Structural Health Monitoring (SHM) techniques to adhesively bonded composite aerospace structures. The PhD study focused on two emerging SHM technologies - frequency response and comparative vacuum monitoring (CVM). This project aimed to provide missing critical information for each technique. This included determining sensitivity to damage, repeatability of results, and operating limitations for the frequency response method. Study of the CVM technique aimed to address effectiveness of damage detection, manufacture of sensor cavities, and the influence of sensor integration on mechanical performance of bonded structures. Experimental research work is presented examining the potential of frequency response techniques for the detection of debonding in composite-to-composite external patch repairs. Natural frequencies were found to decrease over a discrete frequency range as the debond size increased; confirming that such features could be used to both detect and characterise damage. The effectiveness of the frequency response technique was then confirmed for composite patch and scarf repair specimens for free-free and fixed-fixed boundary conditions. Finally, the viability of the frequency response technique was assessed for a scarf repair of a real aircraft component, where it was found that structural damping limited the maximum useable frequency. The feasibility of CVM technique for the inspection of co-cured stiffener-skin aircraft structures was explored. The creation of sensor cavities with tapered mandrels was found to significantly alter the microstructure of the stiffener, including crimping and waviness of fibres and resin-rich zones between plies. Representative stiffened-skin structure with two sensor cavity configurations (parallel and perpendicular to the stiffener direction) was tested to failure in tension and compression. While tensile failure strength was significantly reduced for both configurations (up to 25%), no appreciable differences in compression properties were found. Two potential sensor cavity configurations were investigated for the extension of the CVM technique to pre-cured and co-bonded scarf repair schemes. The creation of radial and circumferential CVM sensor cavities was found to significantly alter the microstructure of the adhesive bond-line and the architecture of the repair material in the case of the co-bonded repair. These alterations changed the failure mode and reduced the tensile failure strength of the repair. A fibre straightening mechanism responsible for progressive failure (specific to co-bonded repairs with circumferential cavities) was identified, and subsequently supported with acoustic emission testing and numerical analysis. While fatigue performance was generally reduced by the presence of CVM cavities, the circumferential cavities appeared to retard crack progression, reducing sensitivity to the accumulation of fatigue damage. These outcomes have brought forward the implementation of SHM in bonded composite structures, which has great potential to improve the operating efficiency of next generation aircraft.
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Ribeiro, Marcelo Leite. "Programa para análise de juntas coladas: compósito/compósito e metal/compósito." Universidade de São Paulo, 2009. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-19012011-122529/.
Full textAbstract:
O presente trabalho consiste basicamente no desenvolvimento de um programa de engenharia denominado SAJ (sistema de análise de juntas) capaz de realizar uma análise detalhada do comportamento de dois dos diversos tipos de juntas coladas existentes, a junta simples colada (\"single lap joint\") e a junta dupla colada (\"double lap joint\"). Sendo que foram analisadas juntas coladas com aderentes de material compósito ou, então, compostas de aderentes de compósitos e metal. O programa de engenharia desenvolvido possibilita o cálculo das tensões, dos esforços e dos deslocamentos nessas juntas. Para validar o referido programa, os resultados obtidos do mesmo foram confrontados com os resultados obtidos para condições semelhantes utilizando \"softwares\" comerciais de elementos finitos e de cálculo de juntas. Após a validação do programa, são apresentados alguns estudos de fatores que influenciam na resistência da junta colada, verificando a influência do comprimento de \"overlap\" (sobreposição), a rigidez do adesivo e a espessura da camada adesiva. Também é apresentada uma análise de falha dos aderentes de compósito evidenciando assim, as potencialidades e limitações desta ferramenta computacional para a área de desenvolvimento de produto.This work consists on the development of software called SAJ which can analyze a bonded joint behavior in detail, not only for single lap joint, but also, for double lap joint. These joints could be made of composite/composite materials or metal/composite as adherentes. The software developed can calculate the joints stresses, loads and displacements. The results obtained are compared to the results obtained using commercial software and the same problems proposed. After the validation of SAJ, some studies were performed in order to determine how some characteristics affect the joint stresses distribution as overlap length, adhesive elastic modulus, adhesive thickness and a failure analysis of composite adherents showing the potential and limitation of this computational tool for the product development area.
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Bhamare, Vinay Vasant Lankarani Hamid M. "Transverse impact characteristics of adhesively bonded composite single lap joint." Diss., Click here for available full-text of this thesis, 2006. http://library.wichita.edu/digitallibrary/etd/2006/t080.pdf.
Full textAbstract:
Thesis (M.S.)--Wichita State University, College of Engineering."May 2006." Title from PDF title page (viewed on October 29, 2006). Thesis adviser: Hamid M. Lankarani. Includes bibliographic references (leaves 62-64).
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Melcher, Ryan James. "Characterization of polymer matrix composites and adhesively bonded joints in a cryotank environment." Thesis, Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/16035.
Full text
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Choudhry, Rizwan Saeed. "Characterisation and modelling of impact damage in bonded joints of woven fibre polymeric composites." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.498781.
Full textAbstract:
Bonded joints are key structural elements and for parts made from fibre reinforced polymeric matrix composites (FRC), these are preferred over mechanical fasteners such as rivets and bolts. Low velocity impact loading of structures is frequently encountered both in-service and during maintenance and when an object made from FRC is subjected to impact loading, the resulting damage is often quite complex in terms of both multiplicity and unpredictability of damage modes. If the structure involves bonded joints the complexity is increased further. Since the use of composite materials is continuously increasing in all type of structural components the impact threat can no longer be dealt with simplified design approaches and unrealistic in-service operating requirements. All the major commercial Aircraft manufacturers are looking at fibre polymeric composites as the material of choice for the future aircrafts, however, the poor understanding of impact Induced damage mechanisms necessitate the use Of generous safety factors for product design. This often results in offsetting the weight saving advantage promised by composite materials, which is a consequence of their higher in-plane specific modulus and strength. Hence, from both an academic and industrial point of view it is important to Increase the understanding of impact damage in bonded joints of composites.
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Sarr, Cheikh Ahmed Tidiane. "Vers une auscultation par acousto-ultrasons des renforcements par composites collés de structures du génie civil." Thesis, Ecole centrale de Nantes, 2022. http://www.theses.fr/2022ECDN0005.
Full textAbstract:
Un rapport sénatorial de Juin 2019 estime le parc d’ouvrages vieillissants de la France à plus de 25000 ponts routiers. Une des solutions préconisées pour éviter la ruine de ces structures est leur renforcement par collage de matériaux composites. Cette solution technique permet d’augmenter la durée de vie des ouvrages tout en prenant en compte de nouvelles sollicitations (augmentation drastique du trafic et risques sismiques). Cependant, elle est efficace que lorsque le joint de colle est bien exécuté et exempt de tout défaut ou endommagement. Ainsi, son utilisation est limitée par une méconnaissance de la qualité réelle des joints de colle sur site. L’objectif de cette thèse est de proposer à partir d’une technique non destructive, les acoustoultrasons, une méthodologie de détection et d’identification des principaux types de défauts rencontrés dans des assemblages collés. Les deux types de substrats les plus communément utilisés en génie civil à savoir l’acier et le béton ont été étudiés dans cette thèse. Par le biais d’une analyse monoparamétrique et d’une analyse statistique en composantes principales (ACP), l’ensemble des défauts créés dans des assemblages d’acier-composite et de béton-composite ont été détectés avec succès. L’identification de ces défauts a été obtenue grâce aux outils de l’intelligence artificielle (IA) à travers l’algorithme de classification de la forêt d’arbres décisionnels. Les facteurs pouvant influencer cette méthodologie ont été passés en revue avant qu’elle ne soit validée sur des échantillons de plus grande échelle, proches des réalisations sur site. Enfin, via une simulation par éléments finis de la propagation du signal dans un assemblage collé, nous soulignons les perspectives que peut offrir cette technique dans la constitution de bibliothèques d’apprentissage pour l’application des techniques de l’IA au diagnostic et au pronostic de l’état de joints de colleA Senate report from June 2019 estimates France’s ageing structures at more than 25,000 road bridges. One of the recommended solutions to prevent the collapse of these structures is their bonding reinforcement of composite materials. This technical solution allows us to increase their lifeservice by taking into account new acquired stresses (drastic increase in traffic and seismic risks). However, the reinforcing is effective only when the adhesively bonded joint is well executed and free of defects or damages. Thus, the use of this method is limited by a lack of knowledge of the real quality of adhesive joints on site. The objective of this thesis is to propose from a nondestructive technique, the acousto-ultrasonics, a methodology of detection and identification of all types of defects encountered in adhesively bonded assemblies.We studied the most common types of substrates used in civil engineering: steel and concrete. Through a mono-parametric analysis and a statistical principal components analysis (PCA), all the elaborated defects in compositesteel and composite-concrete assemblies were successfully detected. The identification of these defects was obtained using Machine Learning tools through the Random Forest classification algorithm. The factors that could influence this methodology were studiedbefore it was validated on specimens of a larger scale, closer to the on-site achievements. Finally, through a finite element simulation of signal propagation in a bonded assembly, we underline the perspectives that this technique can offer in building learning libraries for the application of Machin Learning techniques to the diagnosis and prognosis of the state of adhesively bonded joints
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Kaymak, Yalcin. "A Composite Frame/joint Super Element For Structures Strengthened By Externally Bonded Steel/frp Plates." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/1052547/index.pdf.
Full textAbstract:
A materially non-linear layered beam super element is developed for the analysis of RC beams and columns strengthened by externally bonded steel/FRP plates. The elasto-plastic behavior of RC member is incorporated by its internally generated or externally supplied moment-curvature diagram. The steel plate is assumed to be
elasto-plastic and the FRP laminate is assumed to behave linearly elastic up to
rupture. The thin epoxy layer between the RC member and the externally bonded lamina is simulated by a special interface element which allows for the changing failure modes from steel plate yielding/FRP plate rupture to separation of the bonded plates as a result of bond failure in the epoxy layer. An empirical failure criterion based on test results is used for the epoxy material of the interface.
The most critical aspect of such applications in real life frame structures is the anchorage conditions at the member ends and junctions. This has direct influence on the success and the effectiveness of the application. Therefore, a special corner piece anchorage element is also considered in the formulation of the joint super
element, which establishes the fixity and continuity conditions at the member ends
and the joints.
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Simon, Joshua Cameron. "Response and Failure of Adhesively Bonded Automotive Composite Structures under Impact Loads." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/34881.
Full textAbstract:
An experimental technique for conducting low speed impact of adhesively bonded automotive composite joints is presented. Based on the use of a modified drop tower, mode I, II, and mixed mode values for critical energy release rate were determined for a composite/epoxy system and used to create a fracture failure envelope. Because load measurements become erratic and unreliable at higher test rates, displacement-based relationships were used to quantify these energy release rates. Displacement data was collected with an imaging system that utilized edge detection to determine displacement profiles, end displacements, and opening displacements where applicable. Because of the resolution of the image-based approach used, determining crack length experimentally was extremely difficult. As a result, numerical methods were developed to objectively determine the crack length based on the available experimental data in mode I, II, and mixed mode I/II configurations.
This numerical method uses a nonlinear fit to determine mode I crack lengths and a theoretical model based on cubic equations for mode II and mixed-mode I/II, where the coefficients of the equations are determined by using both boundary and transition conditions that are a result of the test setup. A double cantilever beam (DCB) geometry was chosen to collect mode I data, an end-loaded split (ELS) geometry was used for mode II, and a single leg bend (SLB) geometry was used for mixed-mode I/II. These geometries were used to determine the fracture characteristics of adhesively bonded automotive composites to create fracture failure envelopes as well as provide mode I, II, and mixed-mode I/II data to be used in finite element models.
The chosen adhesive exhibited unstable, stick-slip crack growth, which resulted in very few data points being collected from each static DCB specimen as well as drastic drops in energy release rate between initiation and arrest points. Unstable growth also created issues in dynamic testing, as data points surrounding these "stick-slip" events were lost due to the insufficient sampling rate of the available imaging system.
Issues also arose with differences between thick and thin composite adherend specimens. These differences could result from additional curing in thick adherend composite specimens due to the adherends retaining heat. DSC testing was conducted on uncured adhesive using a 2, 5, and 10 minute hold at the cure temperature, and significant additional curing was observed between the two and five minute cures. Due to the difference in relative stiffness between the 12 and 36 ply composite, the local loading rate at the crack tip was lower in the 12 ply adherends, possibly allowing for a larger plastic zone and thus a higher energy release rate. As a result, tests were conducted on 36 ply composite specimens at rates of 1 mm/min and 0.1 mm/min to determine if there were loading rate effects. This testing showed that higher initiation energy relase rates were found at the lower test rate, thus reinforcing the local loading rate theory.
Due to issues with plastic deformation in aluminum adherends, mode II and mixed-mode I/II data were collected using only composite adherends. Only one data point was collected per specimen as the crack propagated directly into the composite after initiating from the precrack, thus multiple tests were conducted to collect sufficient data for constructing a failure envelope.
Once mode I, II and mixed-mode I/II fracture data was collected, a fracture failure envelope was created. This failure envelope, combined with a predetermined factor of safety, could provide some of the necessary tools for design with this adhesive/composite system.Master of Science
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Grasso, Paolo. "Numerical simulations of the effects of residual stresses in adhesively bonded composite specimen." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016. http://amslaurea.unibo.it/10268/.
Full textAbstract:
In this work the problem of performing a numerical simulation of quasi-static crack propagation within an adhesive layer of a bonded joint under Mode I loading affected by stress field changes due to thermal-chemical shrinkage induced by cure process is addressed. Secondly, a parametric study on fracture critical energy, cohesive strength and Young's modulus is performed. Finally, a particular case of adhesive layer stiffening is simulated in order to verify qualitatively the major effect.
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Chowdhury, Uraching. "Theoretical and Computational Studies of the Mechanical Strength and Fracture Toughness of Adhesively Bonded Joints and Polymer Nanoclay Composites." Thesis, North Dakota State University, 2019. https://hdl.handle.net/10365/29274.
Full textAbstract:
Increasing use of adhesively bonded joints (ABJs) and polymer nanoclay composites (PNCs) in modern vehicles and other industrial sectors has deeply shaped the design and manufacturing of advanced materials and structures for better mechanical stiffness, durability, and fracture toughness. (1) A nonlinear fracture model is formulated for accurately extracting the fracture toughness of ABJs with large plastic deformations and springback and further validated by ABJ fracture data available in the literature. (2) Cohesive zone model (CZM) is integrated into finite element method (FEM) to simulate the debonding process of ABJs at varying adhesive layer geometries and material properties. (3) CZM is further utilized for exploring the failure mechanisms of PNCs under external loading at varying PNC geometries and material properties. The present studies can be useful for effective and accurate data reduction and further improving the design and manufacturing of ABJs and PNCs with tailorable mechanical properties.North Dakota State University. Department of Mechanical Engineering
U.S. Department of Energy
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McGee, Caleb. "NUMERICAL EVALUATION OF ADHESIVE JOINTS IN COMPOSITE STRUCTURES USING FEA." OpenSIUC, 2015. https://opensiuc.lib.siu.edu/theses/1743.
Full textAbstract:
The increasing use of composite materials in many industries such as aerospace, automotive, and civil industries has increased the need for the development of effective techniques to detect defects in the bondlines of adhesive joints in composite structures. Currently, composite structures used in commercial applications such as modern aircraft use mechanical fasteners in redundancy to adhesive bonds to ensure structural integrity due to a lack of methods to reliably detect defects in the bondline of composite structure. As such, this thesis facilitates the development of nondestructive evaluation techniques for detecting bondline defects by using finite element (FE) modeling to simulate the effects of disbond defects caused by contamination of the bondline. These models were developed for single-lap joint specimens made of metal, composite, and dissimilar materials (metal bonded with composite) with contamination induced disbonds. The created FE models were used to generate whole-field strain data for single-lap joints under tensile loading. This generated strain data was then used to provide a model for evaluating and interpreting experimental strain measurements captured by digital image correlation (DIC). Finally, conclusions were drawn outlining the observed capability of strain measurement in the evaluation of bondline contamination in single-lap joints.
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Liddel, Paul Daniel. "Transforming composite design by use of structural health monitoring." Thesis, Cranfield University, 2016. http://dspace.lib.cranfield.ac.uk/handle/1826/12380.
Full textAbstract:
Commercial composite aerospace structure is required to be designed and managed under the damage tolerant principle. Airworthiness is maintained through a process of regulated inspections and if required maintenance. Currently inspections use visual and assisted visual (non-destructive inspection - NDI) techniques. Damage tolerant operation is therefore reliant on inspectability. Unlike metal structure composite and adhesively bonded structure may show few if any recognisable indicators prior to rapid failure, either visually or using NDI. Although stringent manufacturing processes are demanded to best ensure components are fit for service strategies such as reducing stresses by oversizing components or in the case of bonded features additional mechanical fasteners may be included to allow operation with this potential structural uncertainty. Structural Heath Monitoring (SHM) uses data from in-situ sensors to assess the condition of the structure. If via SHM any uncertainty associated with difficult to inspect components could be eliminated less reliance would be required of additional structure or features allowing lighter and more efficient structure to be viable with no impact on current airworthiness demands. Despite much previous research no SHM system is in use with in-service composite or bonded aerospace components. When operating a structure under Damage-tolerance operational requirements damage must be positively identified to allow repairs to be made whist ensuring appropriate airworthiness demands are maintained. Such demands must also be met by structure inspected using SHM. Unlike previous studies this research combines the process of structural design and in-situ monitoring to address the issues identified. Termed SHM enabled design this approach allows the implementation of monitoring technology and the potential for benefits including the reduced reliance on inefficient additional structure to be viably included in actual structure ... [cont.].
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Caggegi, Carmelo. "Experimental analysis of the efficiency of carbon fiber anchors applied over CFRP to firebrick bonded joints." Doctoral thesis, Università di Catania, 2013. http://hdl.handle.net/10761/1410.
Full textAbstract:
In these recent years, the strengthening of masonry building has known a massive use of CFRP sheets. Those composite materials glued on the elements to reinforce are exposed to prematurely debonding crisis due to a tension load which is much smaller than the tensile strength of the CFRP. A way to upgrade failure load of CFRP-to-support bonded joint is to reinforce the cohesion between the fibers and the support by the use of mechanicals anchors built with the same fibers of the composite and fastened in the support like nails . Research on the use of anchors for masonry supports has been limited and there are no experimental analyses related to the design and the placement of fiber anchors.
The aim of this thesis is to provide experimental data to quantify the efficiency of the carbon fiber anchors applied on a reinforced fire brick. This is a ground work to study CFRP to masonry bonded joint fastened by fiber nails . Specifically, the analysis of the displacement and the strain fields of the reinforced surface have been realized by means of Digital Image Correlation (DIC), an optical appealing method never used to study a FRP to support bonded joint fastened by FRP anchor.
The experimental analyses shown that the CFRP anchors applied onto a CFRP to support bonded joint permit to achieve two main advantages:
1) The increase of the maximal load peak
2) The attribution of a resistance post peak, and therefore, the increase of the ductility of the reinforced system.
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Caggegi, Carmelo. "Experimental analysis of the efficiency of carbon fiber anchors applied over CFRP to firebrick bonded joints." Thesis, Paris Est, 2013. http://www.theses.fr/2013PEST1025/document.
Full textAbstract:
Dans les dernières années, le renforcement des bâtiments en maçonnerie a connu une usure massive des bandes CFRP. Ces matériaux composites, attachés sur les éléments à renforcer, sont exposés à une fracture prématurée pour délaminage (...). Une façon pour accroître la résistance maximale du système renforcé par CFRP est d'améliorer la cohésion entre support et composite en utilisant des ancrages mécaniques. Ces derniers sont réalisés en utilisant les mêmes typologies de fibres de renforcement et en les insérant dans le support comme des «clous». Les recherches scientifiques sur l'usure de cette façon d'ancrage sur support en maçonnerie ont été très limitées et, dans ce contexte, il n'y a pas d'études expérimentales sur le projet et le placement des ancrages. L'objectif principal du présent travail de thèse est de quantifier l'efficacité des ancrages en fibre de carbone appliqués sur brique (...) par les bandes CFRP. Cette recherche est la première phase d'une étude plus vaste sur les systèmes de maçonnerie-CFRP renforcés par « carbon fiber anchor ». Dans l'étude, l'analyse des déplacements et des déformations de la surface renforcée a été faite en utilisant la Corrélation des Images (DIC), une avantageuse méthode optique jamais utilisée pour l'étude des systèmes «support-CFRP band- ancrages».Le présent travail de thèse démontre que les ancrages en CFRP augmentent le résistance maximale et la ductilité des renforcements par bande de composites. Donc, cette typologie d'ancrage augmente la sécurité des personnes pendant les tremblements de terre et ne permettent pas la fracture fragile de la structure renforcée. La corrélation des images a été un bon outil pour l'étude des déformations, des avantages et des inconvénients de cette méthode et ont été évalué pendant la rechercheIn these recent years, the strengthening of masonry building has known a massive use of CFRP sheets. Those composite materials glued on the elements to reinforce are exposed to prematurely debonding crisis due to a tension load which is much smaller than the tensile strength of the CFRP. A way to upgrade failure load of CFRP-to-support bonded joint is to reinforce the cohesion between the fibers and the support by the use of mechanicals anchors built with the same fibers of the composite and fastened in the support like “nails”. Research on the use of anchors for masonry supports has been limited and, in this framework, there are no experimental analyses related to the design and the placement of fiber anchors. The aim of this thesis is to provide experimental data to quantify the efficiency of the carbon fiber anchors applied on a reinforced fire brick. This is a ground work to study CFRP to masonry bonded joint fastened by fiber “nails”. Specifically, the analysis of the displacement and the strain fields of the reinforced surface have been realized by means of Digital Image Correlation (DIC), an optical appealing method never used to study a FRP to support bonded joint fastened by FRP anchor. The research demonstrates that the use of the CFRP anchor increases the resistance and the ductility of the reinforcements. The latter are important to augment the mechanical features of the structural members and, especially, to increase the safety of people during earthquakes by avoiding the brittle collapse of the strengthened elements. The digital image correlation has been a good tool for the strain field analysis; strengths and weaknesses of this method have been evaluated
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Guvendik, Ozen. ""." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605523/index.pdf.
Full textAbstract:
In this Thesis, the problems of the Free Flexural (or Bending) Vibrations of Composite, Orthotropic Plates and/or Panels with Various Bonded Joints are formulated and investigated in detail. The composite bonded plate system is composed of Plate Adherends adhesively bonded by relatively very thin adhesive layers. The general problem is considered in terms of the three Main PROBLEMS, namely Main PROBLEM I, Main PROBLEM II and Main PROBLEM III.
The theoretical formulation of the Main PROBLEMS is based on Mindlin Plate Theory which is a First Order Shear Deformation Plate Theory (FSDPT). Thus, the transverse shear deformations, the transverse and the rotary moments of inertia of the plates are included in the formulation. Very thin, elastic deformable adhesive layers are considered as continua with transverse normal and shear stresses. The
damping effects in the plates and the adhesive layers are neglected.
The entire composite bonded joint assembly is assumed to be simple supported along the two opposite edges, so that the Classical Levy’
s Solutions can be applied in this direction. The dynamic equations of the Bonded Joint System which combines together the Mindlin Plate dynamic equations with the adhesive layer equations are reduced to a system of First Order Ordinary Differential Equations in the state vector form. This special form of the Governing System of the First Order Ordinary Differential Equations are numerically integrated by means of the Modified Transfer Matrix Method which is a combination of the Classical Levy&
#8217
s Method, the Transfer Matrix Method and the Integrating Matrix Method (with Interpolation Polynomials and/or Chebyshev Polynomials). The Main PROBLEMS are investigated and presented in terms of the mode shapes and the corresponding natural frequencies for various sets of boundary conditions. The significant effects of the hard and the soft adhesive layer elastic constants on the mode shapes and on the natural frequencies are demonstrated. Some important parametric studies such as the influences of the Joint Length Ratio, the Joint Position Ratio, the Bending Stiffness Ratio, etc. on the natural frequencies are computed and plotted for the hard and soft adhesive cases for several support conditions.
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Sagnard, Maxime. "Detection of Weak Bonds in Bond ed CFRP Assemblies using Symmetrical LAser Shock Adhesion Test (S-LASAT)." Thesis, Paris, ENSAM, 2019. http://www.theses.fr/2019ENAM0022.
Full textAbstract:
L’une des grandes problématiques actuelles des secteurs aéronautique et spatial est la réduction du taux d’émission de CO2. Une des solutions est l’allègement et l’optimisation des structures. Dans cette optique, certains avions comme l’a380 ou l’a350 XWB ont été fabriqués en grande partie à l’aide de matériaux composites. Plus résistants et plus légers, ils permettent un gain de poids important comparés aux matériaux métalliques. Cependant, ces pièces composites sont encore assemblées à l’aide de rivets ou de boulons. Ces procédés non adaptés aux matériaux composites limitent le gain de poids que pourrait engendrer leur utilisation. L’emploi de colles en revanche permettrait ce palier à ce problème, permettant ainsi de réduire de manière plus efficace le poids des structures. Cependant, ce procédé peut aussi être à l’origine de la création de joints faibles. Un joint est qualifié de faible quand sa tenue mécanique est inférieure à sa tenue nominale prévue. Actuellement, l’absence de Control Non Destructif (CND) permettant d’évaluer les propriétés mécaniques de ces pièces collées est l’un des principaux verrous à l’utilisation de ce procédé d’assemblage.Le Test d’Adhérence par Choc Laser (LASAT) a déjà prouvé sa capacité à évaluer la tenue mécanique de joints de colle dans des structure en Polymère Renforcé de Fibres de Carbone (PRFC). Cependant il ne peut s’appliquer qu’à quelques géométries d’assemblage spécifiques et a aussi démontré des limites en termes de détection de joint faible. Ce travail propose une étude expérimentale et numérique d’une des optimisations du LASAT : le Test d’Adhérence par Choc Laser Symétrique (S-LASAT). Le but est d’approfondir la compréhension de la physique mise en jeu afin de mieux appréhender les prérequis nécessaires à la technologie pour détecter les joints faibles. Cette étude conclura sur une étude unique de test d’adhérence réalisée sur de vraies pièce aéronautiques colléesThe limitation of carbon dioxide emissions is one of today’s greatest challenges for the aerospace industry. Weight reduction is seen as one of the most promising lead for that matter and a first step has already been made toward this goal through the use of composite materials. Lighter and more mechanically efficient than their metallic counterparts, their use helped optimising the weight of several aircrafts such as the A350 XWB or A380. Nevertheless, if the material has changed, the assembly process did not evolve along with it. Hence, techniques such as riveting or bolting previously used for metallic structure are still used for composite parts assembly, but they are not suitable anymore for this type of material (creation of local constraints, corrosion, …). Instead, bonding composite parts using adhesives would be a better solution and could help further reducing the overall weight of the aircraft. However, with this new assembly method also come new problems, such as weak bonding. A weak bond is characterised by a loss of mechanical adherence that cannot be spotted using conventional Non-Destructive Tests (NDTs) such as ultrasound scanning. Since the industry currently lacks these NDTs to assess the mechanical integrity of bonded structures, the use of adhesives for composite assembly is limited.The LAser Shock Adhesion Test (LASAT), has already demonstrated its capacity to evaluate bonded composite assembly but also proved to be limited in terms of assembly configuration and weak bond detection capability. This work focuses on one of its optimisations, the Symmetrical LASAT (S-LASAT). Both experimental and numerical studies are realised to better understand the prerequisites of the technique as well as the level of mastery required for the technology to best detect weak bonds within Carbon Fibre Reinforce Polymer (CFRP) structures. This manuscript concludes with a one of a kind experimental campaign realised on real bonded CFRP aircraft parts
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Dobiáš, Jiří. "Studium adheze lepených balistických kompozitů v závislosti na použitých materiálech." Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2018. http://www.nusl.cz/ntk/nusl-376803.
Full textAbstract:
The aim of this work was to investigate the properties of bonded ballistic materialsBalistic composites are mainly glued to reduce weight while keeping their protective properties. On this basis, the materials used were ballistic steel, ceramics, rubber kevlar, non-gummed kevlar, Dyneema and fiberglass. For bonding used were a one-component adhesive Collano 36.104 and two-component adhesive Biresin U1305. The strength of the joint was measured in shear at tensile loads. From these results, deformation energy was further calculated.