Щоб переглянути інші типи публікацій з цієї теми, перейдіть за посиланням: Composite materials Delamination.
Дисертації з теми "Composite materials Delamination"
Оформте джерело за APA, MLA, Chicago, Harvard та іншими стилями
Ознайомтеся з топ-50 дисертацій для дослідження на тему "Composite materials Delamination".
Біля кожної праці в переліку літератури доступна кнопка «Додати до бібліографії». Скористайтеся нею – і ми автоматично оформимо бібліографічне посилання на обрану працю в потрібному вам стилі цитування: APA, MLA, «Гарвард», «Чикаго», «Ванкувер» тощо.
Також ви можете завантажити повний текст наукової публікації у форматі «.pdf» та прочитати онлайн анотацію до роботи, якщо відповідні параметри наявні в метаданих.
Переглядайте дисертації для різних дисциплін та оформлюйте правильно вашу бібліографію.
1
Whitcomb, J. D. "Instability-related delamination growth of embedded and edge delaminations." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/77755.
Повний текст джерелаАнотація:
Compressive loads can cause local buckling in composite laminates that have a near-surface delamination. This buckling causes load redistribution and secondary loads, which in turn cause interlaminer stresses and delamination growth. The goal of this research effort was to enhance the understanding of this instability-related delamination growth in laminates containing either an embedded or an edge delamination.
There were three primary tasks: 1) development of a geometrically nonlinear finite element analysis named NONLIN3D; 2) performance of a parametric analytical study to determine the effects of strain, delamination shape, and delamination size on the distribution of the strain energy release rate components along the delamination front; and 3) performance of a combined experimental and analytical study of instability-related delamination growth (IRDG). Two material systems (AS4/PEEK and IM7/8551-7) and two stacking sequences (0/90/90/0)₆ and (90/0/0/90)₆ were examined. The laminates were fabricated with Kapton inserts between the fourth and fifth plies from the top surface to give an initial delamination.
The analysis predicted a large variation of GI and GII along the delamination front. The GIII component was always small. The location of maximum GI and GII depended on the delamination shape and applied strain. In general, the strain-energy release rates were small except in a small region. Hence, delamination growth was expected to occur over only a small portion of the delamination front. Experiments corroborated this prediction. The laminate stacking sequence had a large effect on the shape of the deformed region, the direction of delamination growth, and the strain at which delamination growth occurred. These effects were predicted by the analysis. The GI component appeared to govern initial delamination growth in the IM7/8551-7 laminates. Matrix ply cracking generally accompanied delamination growth. In some cases fiber micro-buckling also occurred shortly after delamination growth occurred.Ph. D.
2
Van, Hoof J. "Modelling of impact induced delamination in composite materials." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0028/NQ52335.pdf.
Повний текст джерела
3
Van, Hoof Jack (Jacobus Franciscus Adrianus Maria) Carleton University Dissertation Engineering Mechanical and Aerospace. "Modelling of impact induced delamination in composite materials." Ottawa, 1999.
Знайти повний текст джерела
4
Malik, Basharat U. "Fatigue delamination growth under cyclic compression in unidirectional composites." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/12094.
Повний текст джерела
5
Awal, Mohammad A. 1959. "Transient response of delamination, intersecting and transverse cracks in layered composite plates." Thesis, The University of Arizona, 1989. http://hdl.handle.net/10150/276955.
Повний текст джерелаАнотація:
A numerical method is developed to determine the dynamic behavior of delamination and transverse cracks in multilayered plates. The plate is subjected to a time dependent antiplane shear stress field which is acting on the plate surfaces. The interaction of waves diffracted at the crack tip with those reflected at the plate boundaries and transmitted at the material interface makes the problem very complicated, so analytical study of this problem cannot be carried out with our present state of knowledge; hence the problem is solved numerically. The finite element equations are obtained by variational calculus applied in the frequency domain. Thus time intregration schemes are avoided, but time dependent response can still be obtained after inverting the frequency dependent response spectra numerically by Fast Fourier Transform (FFT) routine. Another advantage of the frequency domain analysis is that the resonance frequency can be easily detected from the sharp peaks of the response spectra. The numerical difficulty associated with the singular behavior of the stress field near the crack tip has been avoided by using quarter point elements. The numerical results obtained from this investigation are compared with analytical results to verify the accuracy of the method.
6
Gambone, Livio R. "The effect of R-ratio on the mode II fatigue delamination growth of unidirectional carbon/epoxy composites." Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/29968.
Повний текст джерелаАнотація:
An investigation of the effect of R-ratio on the mode II fatigue delamination of AS4/3501-6 carbon/epoxy composites has been undertaken. Experiments have been performed on end notched cantilever beam specimens over a wide range of R-ratios (-l ≤R ≤0.50). The measured delamination growth rate data have been correlated with the mode II values of strain energy release rate range ∆G[formula omitted]), maximum strain energy release rate (G[formula omitted]) and stress intensity factor range (∆K[formula omitted]). The growth rate is dependent on the R-ratio over the range tested. For a constant level of ∆G[formula omitted], the crack growth rate decreases with increasing R-ratio. A similar trend is observed when the data is plotted as a function of G[formula omitted]. The effect of plotting the growth rate as a function of ∆K[formula omitted] is to produce an R-ratio dependence opposite to that obtained by either the ∆G[formula omitted] or G[formula omitted] approach. For a constant level of ∆K[formula omitted], the crack growth rate increases with increasing R-ratio.
Master equations which completely characterize the fatigue behaviour as a function of ∆G[formula omitted] and ∆K[formula omitted] have been derived, based on the observation that the growth rate law exponent, n and constant, A are unique functions of R-ratio. Values for n are surprisingly large and increase with increasing R-ratio whereas values for A decrease with increasing R-ratio.
The effect of time-at-load has been considered in an attempt to explain the existence of the R-ratio dependence of the growth rate. The correct trend can be established for the exponent, n but not for the constant, A. Friction between the crack faces, particularly at higher R-ratios, is proposed as a possible explanation for the observed anomaly. Further evidence of a frictional mechanism operating at higher R-ratios has been discovered through a postmortem fracture surface examination.
Additional fractographic observations are presented over the entire range of R-ratios tested. In regions subjected to negative R-ratio cycling, there is no evidence of the characteristic mode II hackle features. Instead, loose rounded particles of matrix material are found. An extensive amount of hackling is observed in regions subjected to low positive R-ratio cycles. The extent of hackle damage visibly decreases in areas where higher levels of R-ratio are imposed. A correlation between the general fracture surface morphology and the fatigue data provides support for the hypothesis that energy for delamination is always available in sufficient quantity, and that growth is dependent on the stresses ahead of the crack tip being sufficiently high.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
7
Tenek, Lazarus H. "Delamination dynamics and vibrothermographic-thermoelastic evaluation of advanced composite materials." Thesis, This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-10312009-020116/.
Повний текст джерела
8
Lee, Jaehong. "Vibration, buckling and postbuckling of laminated composites with delaminations." Diss., This resource online, 1992. http://scholar.lib.vt.edu/theses/available/etd-06062008-170322/.
Повний текст джерела
9
Barlas, Fatma Aylin. "Variable complexity modeling of postbuckled stiffeners for delamination initiation." Thesis, This resource online, 1993. http://scholar.lib.vt.edu/theses/available/etd-10312009-020245/.
Повний текст джерела
10
Chang, Cherng-Chi. "Finite element analysis of laminated composite free-edge delamination specimens /." The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487584612162791.
Повний текст джерела
11
Xu, Ying. "Detection of delamination in composites with fiber optic sensor /." View abstract or full-text, 2004. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202004%20XU.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Hong Kong University of Science and Technology, 2004.Includes bibliographical references (leaves 194-209). Also available in electronic version. Access restricted to campus users.
12
Garcia, Jorge David Aveiga. "A delamination propagation model for glass fiber reinforced laminated composite materials." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-31072018-143609/.
Повний текст джерелаАнотація:
The employment of composite materials in the aerospace industry has been gradually considered due to the fundamental lightweight and strength characteristics that these type of materials offer. The science material and technological progress that has been reached, matches perfectly with the requirements for high-performance materials in aircraft and aerospace structures, thus, the development of primary structure elements applying composite materials became something very convenient. It is extremely important to pay attention to the failure modes that influence composite materials performances, since, these failures lead to a loss of stiffness and strength of the laminate. Delamination is a failure mode present in most of the damaged structures and can be ruinous, considering that, the evolution of interlaminar defects can carry the structure to a total failure followed by its collapse. Different techniques are usually adopted to accurately predict the behavior of damaged structures but, due to the complex nature of failure phenomena, there is not an established pattern. The present research project aims to develop a delamination propagation model to estimate a progressive interlaminar delamination failure in laminated composite materials and to allow the prediction of material\'s degradation due to the delamination phenomenon. Experimental tests assisted by ASTM Standards were performed to determine material\'s parameter, like the strain energy release rate, using GFRPs laminated composites. The delamination propagation model proposed was implemented as subroutines in FORTRAN language (UMAT-User Material Subroutine) with formulations based on the Fracture Mechanics. Finally, the model was compiled beside with the commercial Finite Element program ABAQUSTM.O emprego de materiais compósitos na indústria aeroespacial tem sido gradualmente utilizado devido às suas características fundamentais, como peso leve e alta rigidez, que este tipo de material oferece. Tanto a ciência do material como o desenvolvimento tecnológico que se tem logrado, possibilitaram que estes materiais cumprissem com os requisitos de desempenho para aplicações em estruturas aeronáuticas e aeroespaciais, por tanto, o desenvolvimento de elementos de estruturas primárias usando materiais compósitos, passou a ser muito conveniente. É de extrema importância prestar atenção aos modos de falha que comprometem a performance dos materiais compósitos, uma vez que, estas falhas levam a uma perda de resistência e rigidez do laminado. A delaminação é um modo de falha presente na maioria de estruturas danificadas e pode ser desastroso, considerando que, a evolução dos defeitos interlaminares podem levar a estrutura a falhar seguido pelo colapso estructural. Diferentes técnicas são geralmente adotadas para prever, de maneira correta, o comportamento de estruturas danificadas, porém, devido à natureza complexa do fenômeno de falha, não existe um padrão estabelecido. O presente trabalho de pesquisa visa desenvolver um modelo de delaminação e de propagação da delaminação para estimar a evolução da falha interlaminar em materiais compósitos laminados e permitir a predição do comportamento do material com a evolução da delaminação. Ensaios experimentais auxiliados por normas ASTM foram realizados para determinar parâmetros do material, tais como, as taxas de liberação de energia de deformação, usando materiais compósitos laminados de matriz polimérica reforçada com fibra de vidro. O modelo de propagação da delaminação proposto, foi implementado como uma sub-rotina em linguagem FORTRAN (UMAT – User Material) com formulações baseadas na Mecânica da Fratura. Finalmente, o modelo foi compilado com o software comercial de Elementos Finitos, ABAQUSTM.
13
Huang, Haiying. "Single and multiple delamination behavior in composite plates." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/12541.
Повний текст джерела
14
Stevanović, Dejan. "Delamination properties of a vinyl-ester/glass fibre composite toughened by particle-modified interlayers /." View thesis entry in Australian Digital Theses Program, 2001. http://thesis.anu.edu.au/public/adt-ANU20030421.212730/index.html.
Повний текст джерела
15
Harries, Richard. "Process modeling and interfacial delamination in peripheral array packages." Thesis, Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/16622.
Повний текст джерела
16
Dávila, Carlos G. "Delamination initiation in postbuckled dropped-ply laminates /." This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-07282008-134842/.
Повний текст джерела
17
Palmer, David W. "The effect of internal delamination on unsymmetric laminated composite plates." Diss., Georgia Institute of Technology, 1995. http://hdl.handle.net/1853/12021.
Повний текст джерела
18
La, Saponara Valeria. "Crack branching in cross-ply composites." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/11973.
Повний текст джерела
19
Barbieri, Ettore. "Meshfree methods for the analysis of composite materials." Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.558846.
Повний текст джерелаАнотація:
The proposed research is essentially concerned on numerical simulation of materials and structures commonly used in the aerospace industry. The work is primarily focused on the study of the fracture mechanics with emphasis to composite materials, which are widely employed in the aerospace and automotive industry. Since human lives are involved, it is highly important to know how such structures react in case of failure and, possibly, how to prevent them with an adequate design. It has become of primary importance to simulate the material response in composite, especially considering that even a crack, which could be invisible from the outside, can propagate throughout the structure with small external loads and lead to unrecoverable fracture of the structure. In addition, structures made in composite often present a complex behaviour, due to their unconventional elastic properties. A numerical simulation is then a starting point of an innovative and safe design. Conventional techniques (nite elements for example) are not su-cient or simply not ecient in providing a satisfactory description of these phenomena. In fact, being based on the continuum assumption, mesh-based techniques suer of a native incapacity of simulating discontinuities. Novel numerical methods, known as Meshless Methods or Meshfree Methods (MM) and, in a wider perspective, Partition of Unity Methods (PUM), promise to overcome all the disadvantages of the traditional finite element techniques. The absence of a mesh makes MM very attractive for those problems involving large deformations, moving boundaries and crack propagation. However, MM still have signicant limitations that prevent their acceptance among researchers and engineers. Because of the infancy of these methods, more efforts should be made in order to improve their performances, with particular attention to the computational time. In summary, the proposed research will look at the attractive possibilities offered by these methods for the study of failure in composite materials and the subsequent propagation of cracks.
20
Tan, Xinyuan. "Co-cured composite joint strength investigation based on behavior characterization of [0/±θ/90]s family". Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26578.
Повний текст джерелаАнотація:
Joints provide a path for transfer of load and are important components in an assembly of structures, particularly in translating joint strength improvements directly to significant cost savings. This cost savings is more evident in composite joints since manufacturing of more complex single piece components results in a reduction of both part count and labor. An improvement in joint strength for co-cured composite joints through minimized free-edge delamination was investigated for quasi-isotropic [0/±45/90]s lay-up based on the quantitative assessments of the quasi-static and fatigue strength and qualitative understanding of the fatigue damage initiation and propagation for the [0/±θ/90]s family of co-cured composite joints. A previously proposed co-cured joint concept, the Single Nested Overlap (SNO) joint, was compared against a Straight Laminate (SL) and a single lap joint. The SL represents a "perfect" joint and serves as an upper bound whereas the single lap joint represents the simplest generic joint and is the base design for the SNO joint concept. Three categorized failure types, which represented predominant failure modes in the SL, single lap and SNO joints, along with two different fatigue strength indicators were used for quasi-static and fatigue strength comparison. With fatigue run-out defined at 1 x 106 cycles, the fatigue damage initiation and propagation at high loadings was monitored with an Infrared Thermoelastic Stress Analysis (IR-TSA) technique, while a damage type comparison was used at low loadings. Quasi-static Acoustic Emission (AE) counts were observed to be Fatigue Limit (FL) predictors for [0/±θ/90]s SL and SNO joints. The validity of these FL predictors were also assessed in the damage type comparison.
21
Shen, Luming. "Multi-scale modeling and simulation of multi-physics in film delamination /." free to MU campus, to others for purchase, 2004. http://wwwlib.umi.com/cr/mo/fullcit?p3144456.
Повний текст джерела
22
Píttaro, Agustín Alejandro. "Numerical evaluation of mixed mode I and II delamination in composite materials." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16172/.
Повний текст джерела
23
Maranon, Alejandro. "Characterising delamination in composite materials : a combined genetic algorithm - finite element approach." Thesis, Loughborough University, 2004. https://dspace.lboro.ac.uk/2134/7688.
Повний текст джерелаАнотація:
A novel delamination identification technique based on a low-population genetic algorithm for the quantitative characterisation of a single delamination in composite laminated panels is developed, and validated experimentally The damage identification method is formulated as an inverse problem through which system parameters are identified. The input of the inverse problem, the central geometric moments (CGM), is calculated from the surface out-of-plane displacements measurements of a delaminated panel obtained from Digital Speckle Pattern Interferometry (DSPI). The output parameters, the planar location, size and depth of the flaw, are the solution to the inverse problem to characterise an idealised elliptical flaw. The inverse problem is then reduced to an optimisation problem where the objective function is defined as the L2 norm of the difference between the CGM obtained from a finite element (FE) model with a trial delamination and the moments computed from the DSPI measurements. The optimum crack parameters are found by minimising the objective function through the use of a low-population real-coded genetic algorithm (LARGA). DSPI measurements of ten delaminated T700/LTM-45EL carbon/epoxy laminate panels with embedded delaminations are used to validate the methodology presented in this thesis.
24
Zhao, Dongming. "Interlaminar fracture behavior of woven fabric composites and mode III delamination analysis." Diss., Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/10075.
Повний текст джерела
25
Kuriakose, Sunil. "Analysis of damage in composite laminates under bending." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/12054.
Повний текст джерела
26
Bruhschwein, Taylor John. "Identification of Delamination Defects in CFRP Materials through Lamb Wave Responses." Thesis, North Dakota State University, 2014. https://hdl.handle.net/10365/27328.
Повний текст джерелаАнотація:
Delamination is currently a largely undetectable form of damage in composite laminate materials. This thesis will develop a method to more easily detect delamination damage within composite materials. Using finite element analysis modeling and lab testing, a new method from interpreting the results obtained from existing structural health monitoring techniques is developed. Lamb waves were introduced and recorded through an actuator and sensors made of piezoelectric material. The data was then analyzed through a novel data reduction method using the Fast Fourier Transform (FFT). Using the data from FFT, the idea of covariance of energy change was developed. By comparing the covariance of energy change in beams with differing delamination size, thickness and depth, correlations were able to be developed. With these correlations, the severity and of damage was able to be detected.
27
Ferrie, Catherine H. "Effect of transverse shear on the postbuckling and growth characteristics of delaminated composites." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12355.
Повний текст джерела
28
Shalev, Doron. "Prediction model for the onset of edge-effect delamination at holes in composite laminates." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/81007.
Повний текст джерелаАнотація:
Composite laminates are prone to delamination at free edges, straight edges or at holes, due to the mismatch at interfaces where two adjacent plies have different fiber orientations and/or different material properties. The linear analysis of the mismatch at the edge results in a mathematical singularity. That phenomenon occurs in a boundary layer and has to be treated mathematically and physically as such. In the literature it is called the "Boundary Layer Effect" or simply the "Edge Effect". It is of great importance to recognize and be able to predict delamination locations at edges prone to such events. The goal of this research was to create a model capable of providing such a prediction. In an effort to generalize the model, the more complicated case of a free edge at holes in the composite laminate was chosen rather than the case of a straight free edge.
A sequel of three major efforts was completed: 1) Development of the analysis of the free-edge effect at a hole in a composite laminate, 2) Performance of an extensive experimental program to provide data for the creation of the prediction model, and 3) On the basis of the analysis, establishment of the model, and comparison with the experimental results.
The prediction model consists of two major products of the analysis, the order of the singularity and the strain energy release rate. Both are useful in locating the interface most prone to delaminate and the point along the hole circumference where it initiates.
Two material systems (AS4/3501-6 and AS4/1808) and two stacking sequences [(0/45/0/-45)s)₄] and [ (0/45/90/-45)s)₄]s , quasi-orthotropic and quasi-isotropic respectively, were quasi-statically tested under tension and compression. The specimens were X-rayed after each loading stage in order to locate the initiation of delaminations. The fact that both materials consisted of the same type of fibers, was an excellent opportunity to examine the performance of the matrix and its influence on the process of delamination. Matrix dependent behavior was successfully examined and studied through the experiments and the prediction model. Results showed good correlation and high sensitivity to the type of matrix material involved.Ph. D.
29
Dávila, Carlos G. "Delamination initiation in postbuckled dropped-ply laminates." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/38915.
Повний текст джерела
30
Shor, Ofir. "Adaptive insertion of cohesive elements for simulation of delamination in laminated composite materials." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/59338.
Повний текст джерелаАнотація:
Composite materials are increasingly being used in advanced structural ap- plications. Debonding of adjacent laminate layers, also known as delamination, is considered to be one of the most dominant damage mechanisms affecting the behavior of composite laminates. Various numerical methods for simulating delamination in composite materials do exist, but they are generally limited to small-scale structures due to their complexity and high numerical cost. In this thesis, a novel technique aimed to allow efficient simulation of delamination in large-scale laminated composite structures is presented. During the transient analysis, continuum elements within regions where delamination has the potential to initiate are adaptively split through their thickness into two shell elements sandwiching a cohesive element. By elimi- nating the a priori requirement to implant cohesive elements at all possible spatial locations, the computational efforts are reduced, thus lending the method suitable for treatment of practical size structures. The methodol- ogy, called the local cohesive zone method (LCZ), is verified here through its application to Mode-I, Mode-II and Mixed-Mode loading conditions, and is validated using a dynamic tube-crushing loading case and plate impact events. Good agreement between the numerical results and the available experimental data is obtained. The results obtained using the LCZ method are compared favourably with the numerical results obtained using the con- ventional cohesive zone method (CZM). The numerical performance of the method and its efficiency is investi- gated. The efficiency of the method was found to be superior compared to that of the conventional CZM, and was found to increase with increasing model size. The LCZ method is shown to have a lower effect on reducing the structural stiffness of the structure, compared to the conventional CZM. The results obtained from the application of the LCZ method to the various cases tested are encouraging, and prove that the local and adaptive insertion of cohesive zones into a finite element mesh can effectively capture the delamination crack propagation in laminated composite structures. It is expected that further improvements in speed and accuracy will be attained once the algorithm is embedded within commercial finite element solvers as a built-in feature.Applied Science, Faculty of
Graduate
31
Minnaar, Karel. "Experimental and numerical analyses of damage in laminate composites under low velocity impact loading." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/15812.
Повний текст джерела
32
Wolfe, David R. "Delamination buckling, postbuckling, and growth in axially loaded beam-plates." Thesis, Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/80114.
Повний текст джерелаАнотація:
The purpose of this study is to develop a simple one-dimensional model to analyze axially loaded beam-plates containing cracks which extend through the thickness of the beam-plates. Although the material analyzed is isotropic, these cracks will be referred to as delaminations. Buckling, postbuckling, and growth of delaminations in these beam-plates will be analyzed. A finite element method in which all of the terms of the stiffness matrices are obtained by exact integration is employed to determine the linear buckling load and postbuckling solution. The energy release rate is then determined using the postbuckling solution. Curves are provided to show the effect of delamination length and location on buckling loads, energy release rates, and strengths of the beam-plates. The problem of buckling and postbuckling of beams with multiple delaminations is also considered. A method of calculating the energy release rate for beams with multiple delaminations using numerical differentiation is introduced.Master of Science
33
Eswonia, Eugene Everett. "Effects of Delamination on Composite Sandwich Structures Under Static and Fatigue Loading." DigitalCommons@CalPoly, 2009. https://digitalcommons.calpoly.edu/theses/222.
Повний текст джерелаАнотація:
This thesis will present the experimental and numerical analysis of composite sandwich structures under monotonic and fatigue loading. The sandwich skins were made of fiberglass and the core used was a closed cell PVC foam. Initial delaminations were introduced into the sandwich structures during manufacturing to see the effect of delamination size on the ultimate strength and monotonic fracture. Fiberglass rods, called shear keys, added to the foam core to determine whether or not they increased the strength of the test specimens. Furthermore, shear key locations were also varied and their effects noted. The fixed rate static behavior for all of the above cases listed were determined. The fatigue life and behavior were determined for sandwich structures with no initial delamination, 0.5 inch initial delamination, and 0.5 inch initial delamination with a shear key 0 inch from the delamination depth. The fatigue specimens were tested at various percentages of the ultimate monotonic failure loads to determine the fatigue life. A static numerical analysis was performed using Abaqus/CAE 6.7.1 to observe at the monotonic behavior of the test specimens with no initial delamination and with 0.5 inch initial delamination. The sandwich structures with an initial delamination and/or a shear key in the foam core experienced over a 70% reduction in the ultimate monotonic failure load. The two delamination lengths had no significant effect on the ultimate monotonic failure load, but the presence of an initial delamination corresponded to a material response dominated by plastic behavior. The experimental testing also showed that the location of the shear key in the sandwich structure had little effect on the monotonic strength, but moving the shear keys further away from the back edge of the delamination caused a reduction in strength. The monotonic testing determined that composite sandwich structures containing shear keys had approximately a 7% reduction in the monotonic failure load of test specimens with an initial delamination. Numerical analysis results matched the ultimate failure loads within 5% for the test specimens with a 0.5 inch an initial delamination and within 15% for the test specimens with no initial delamination. The fatigue testing showed that sandwich structures containing shear keys had life reduction of approximately 33%. Preliminary experiments involved with rotating the shear keys 90° showed increased ultimate monotonic failure loads of the composite sandwich structures by as much as 30%. Future funding and research would be necessary to verify the increased structural performance of the newly oriented shear keys.
34
Muñoz, Dante Mejia. "Finite element modeling of nondestructive test methods used for detection of delamination in hot mix asphalt pavements." To access this resource online via ProQuest Dissertations and Theses @ UTEP, 2009. http://0-proquest.umi.com.lib.utep.edu/login?COPT=REJTPTU0YmImSU5UPTAmVkVSPTI=&clientId=2515.
Повний текст джерела
35
Barbero, Ever J. "On a generalized laminate theory with application to bending, vibration, and delamination buckling in composite laminates." Diss., Virginia Polytechnic Institute and State University, 1989. http://hdl.handle.net/10919/54484.
Повний текст джерелаАнотація:
In this study, a computational model for accurate analysis of composite laminates and laminates with including delaminated interfaces is developed. An accurate prediction of stress distributions, including interlaminar stresses, is obtained by using the Generalized Laminate Plate Theory of Reddy in which layer-wise linear approximation of the displacements through the thickness is used. Analytical, as well as finite-element solutions of the theory, are developed for bending and vibrations of laminated composite plates for the linear theory. Geometrical nonlinearity, including buckling and post-buckling are included and used to perform stress analysis of laminated plates. A general two-dimensional theory of laminated cylindrical shells is also developed in this study. Geometrical nonlinearity and transverse compressibility are included. Delaminations between layers of composite plates are modeled by jump discontinuity conditions at the interfaces. The theory includes multiple delaminations through the thickness. Geometric nonlinearity is included to capture layer buckling. The strain energy release rate distribution along the boundary of delaminations is computed by a novel algorithm. The computational models presented herein are accurate for global behavior and particularly appropriate for the study of local effects.Ph. D.
36
Machado, Carla Maria Moreira. "Empirical models for quantification of machining damage in composite materials." Doctoral thesis, Faculdade de Ciências e Tecnologia, 2012. http://hdl.handle.net/10362/9058.
Повний текст джерелаАнотація:
Dissertação para obtenção do Grau de Doutor em
Engenharia MecânicaThe tremendous growth which occurs at a global level of demand and use of composite materials brings with the need to develop new manufacturing tools and methodologies. One of the major uses of such materials, in particular plastics reinforced with carbon fibres, is their application in structural components for the aircraft industry with low weight and high stiffness. These components are produced in near-final form but the so-called secondary processes such as machining are often unavoidable. In this type of industry, drilling is the most frequent operation due to the need to obtain holes for riveting and fastening bolt assembly of structures. However, the problems arising from drilling, particularly the damage caused during the operation, may lead to rejection of components because it is an origin of lack of resistance. The delamination is the most important damage, as it causes a decrease of the mechanical properties of the components of an assembly and, irrefutably, a reduction of its reliability in use. It can also raise problems with regard to the tolerances of the assemblies. Moreover, the high speed machining is increasingly recognized to be a manufacturing technology that promotes productivity by reducing production times. However, the investigation whose focus is in high speed drilling is quite limited, and few studies on this subject have been found in the literature review. Thus, this thesis aims to investigate the effects of process variables in high speed drilling on the damage produced. The empirical models that relate the delamination damage, the thrust force and the torque with the process parameters were established using Response Surface Methodology. The process parameters considered as input factors were the spindle speed, the feed per tooth, the tool diameter and the workpiece thickness. A new method for fixing the workpiece was developed and tested. The results proved to be very promising since in the same cutting conditions and with this new methodology, it was observed a significant reduction of the delamination damage. Finally, it has been found that is possible to use high speed drilling, using conventional twist drills, to produce holes with good quality, minimizing the damage.
37
Lopez-Armas, Carlos Alberto. "Evaluation of constitutive laws for the computer simulation of fatigue driven delamination in composite materials." Thesis, Imperial College London, 2008. http://hdl.handle.net/10044/1/1384.
Повний текст джерелаАнотація:
A simple mathematical model (cylinder model) is proposed and used to evaluate various constitutive laws used in finite element codes to simulate fatigue-driven delamination in composite materials. The cylinder model has one degree of freedom and allows the evaluation of several parameters of the constitutive laws in an ffcient and accurate way without worrying about the complex interactions that may arise while using a nite element code. This cylinder model enabled a large number of analysis to be performed in a relatively short time and made possible parametric studies with tens of thousands of dfferent sets of parameter values of the constitutive laws. Different fatigue degradations strategies have been implemented into the cylinder model and investigated. A systematic comparison of the different strategies has been performed and it was found that the behaviour of the different strategies is similar but with some variations in the sensitivity to the spacing of the springs and to the size of the increment in the number of loading cycles. The results confirm that the more accurate results are found for smaller values of these two variables. A new fatigue degradation strategy is also proposed. It is based on the construction of a 3-D surface that represents the behaviour of the interface under fatigue loading. This surface has been incorporated into the cylinder model and its performance has been evaluated.
38
CERIONI, AGOSTINO. "Simulation of delamination in composite materials under static and fatigue loading by cohesive zone models." Doctoral thesis, Università degli Studi di Cagliari, 2009. http://hdl.handle.net/11584/266000.
Повний текст джерелаАнотація:
This thesis is a dissertation focusing on the mechanics of delamination in laminated composites. Delamination, one of the most critical forms of failure in composite materials, may occur as a result of many causes and different types of loading, such as, for example, static or cyclic loading.
This work presents an examination of the potential of cohesive interface elements for the prediction of delamination propagation under quasi-static mode I, mode II and mixed mode (I and II) loading, by a comparison between experimental tests and parametric analyses in order to evaluate the sensitivity of the elements to some parameters. The results of the comparison show that a rather good accordance may be obtained between experimental data and numerical simulations with a proper choice of the main model parameters.
Moreover, a simplified mathematical model for the study of fatigue driven delamination is described. This model is particularly useful for investigating the performance of various formulations of interface elements that are used to simulate delamination under cyclic loading, because of its simplicity and efficiency that allow evaluating a large number of sets of parameter values. The model has been studied with different static constitutive laws and damage definitions, coupled with a particular fatigue degradation strategy. In particular, the sensitivity of the model, with the different proposed constitutive laws, has been evaluated with respect to some its key parameters.
39
Swindeman, Michael James. "A Regularized Extended Finite Element Method for Modeling the Coupled Cracking and Delamination of Composite Materials." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1324605778.
Повний текст джерела
40
Lallemant, Lucas. "Numerical homogenization of a rough bi-material interface." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41111.
Повний текст джерелаАнотація:
The mechanical reliability of electronic components has become harder and harder to predict due to the use of composite materials. One of the key issues is creating an accurate model of the delamination mechanism, which consists in the separation of two different bounded materials. This phenomenon is a very challenging issue that is investigated in the Nano Interface Project (NIP), in which this thesis is involved.
The macroscopic adhesion force is governed by several parameters described at different length scales. Among these parameters, the roughness profile of the interface has a pronounced influence. The main difficulty for an accurate delamination characterization is then investigating the effects of this roughness profile and the modifications it implies for the overall cohesion.
The objective of the NIP is to develop an interface model for the numerical testing of electronic components in a finite element software. The problem is that a direct modeling of all the mechanisms described previously is really expensive in term of computation time, if possible at all. This difficulty is increased by the huge mismatch of the mechanical properties of the materials in contact. A scale transition method is therefore required, which is provided by homogenization. The idea is to consider the delamination at a wider scale. Rather than modeling the whole roughness profile, the adhesion at the interface will be described by homogenized, or macroscopic, parameters extracted from a representative model at the micro-scale, the RVE. This thesis will deal with the determination of these homogenized parameters.
41
Kolhar, Arvind Shrikant. "Analysis of delamination in drilling of circular plate composite materials with a multi-facet drill bit." Thesis, Wichita State University, 2007. http://hdl.handle.net/10057/1510.
Повний текст джерелаАнотація:
Delamination is recognized as one of the most critical defects that can result from the machining of composites. Delamination has been a major form of failure in drilled composite materials due to the composite’s lack of strength in the direction of drilling, which results in poor surface finish, reduction in bearing strength, reduction in structural integrity, and ultimately poor performance of the composite. Delamination due to drilling has been a major research interest for many years, and a considerable amount of work has been done to reduce it. This thesis work involved deriving a formula to determine what applied thrust force would cause delamination in a particular drill bit, the multi-facet drill bit. To achieve that goal, a formula was developed. The conditions and the drill bit used were altered. The thrust force at which delamination occurred was dependent on the thickness and the composition of the material being used. Experimental validation of the physical model involved calculating the thrust force that would cause delamination, using the formula, and drilling at the calculated thrust force. The thrust force was applied as a correlation of feed rate and spindle speed.Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical Engineering
42
Kolhar, Arvind Shrikant Bahr Behnam. "Analysis of delamination in drilling of circular plate composite materials with a multi-facet drill bit /." Thesis, A link to full text of this thesis in SOAR, 2007. http://hdl.handle.net/10057/1510.
Повний текст джерелаАнотація:
Thesis (M.S.)--Wichita State University, College of Engineering, Dept. of Mechanical EngineeringDelamination is recognized as one of the most critical defects that can result from the machining of composites. Delamination has been a major form of failure in drilled composite materials due to the composite⁰́₉s lack of strength in the direction of drilling, which results in poor surface finish, reduction in bearing strength, reduction in structural integrity, and ultimately poor performance of the composite. Delamination due to drilling has been a major research interest for many years, and a considerable amount of work has been done to reduce it. This thesis work involved deriving a formula to determine what applied thrust force would cause delamination in a particular drill bit, the multi-facet drill bit. To achieve that goal, a formula was developed. The conditions and the drill bit used were altered. The thrust force at which delamination occurred was dependent on the thickness and the composition of the material being used. Experimental validation of the physical model involved calculating the thrust force that would cause delamination, using the formula, and drilling at the calculated thrust force. The thrust force was applied as a correlation of feed rate and spindle speed.
43
Tran, Tony D. "An Investigation of Initially Delaminated Composite Sandwich with Delamination Arrest Mechanism under Buckling Loading." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/428.
Повний текст джерелаАнотація:
This thesis involves the development of a fiberglass-foam composite sandwich structure with the introduction of delamination arrestment keys; therefore, a study of an initially delaminated composite sandwich structure was the experimental analysis on multiple configurations in how the arrestment keys are placed.
The first part of this thesis research was to the experimental design and manufacturing of the composite sandwich plates. These plates were later cut down to the specific test dimensions and manufacturing processes for the composite sandwich plates and test specimens were created. The composite sandwich plates were manufactured using a vacuum resin infusion process. The dimensions of the composite layup are 14 inches in length with a width of 10.75 inches. The width size has margin to account for machining. The actual dimensions of the test specimen after it is prepared are 14 inches by 0.75 inches. The test anvil length is 11 inches and is used to perform tests to determine mechanical characteristics of the structures under buckling loading. These plates provide approximately 9 to 13 specimens per each case. All the test specimens have 4 plies of 18 oz fiberglass woven roving fabric from Jamestown Distributors, a LAST-A-FOAM FR-6710 foam core, and 5 to 1 ratio of West Systems 105/206 epoxy. Also, a non-porous material was integrated into the structure to create an initial delamination in some of the case studies. The integration of the delamination arrestment keys involve milling the foam core to provide the necessary grooves for key placements before the structure is vacuumed and epoxy is flowed. The arrestment keys are made of unidirectional fiberglass strand and the West Systems 105/206 epoxy using a wet layup process. In addition, fiberglass woven roving specimens were created to see the material characteristics under compression and tensile loading. The same is created to determine the material properties of the foam core, wood boundary core, and arrestment keys under compression loading.
The second part to this thesis investigation is the experimental testing of the test specimens with all different variables considered. Those variables includes determining the final solid cure duration of the fiberglass skin, the geometric lengths between pure compression and pure buckling, behaviors of different initial delamination size, effects of continuous and discontinuous arrestment keys parallel and perpendicular to the in-plane loading, and material properties. The final solid cure duration differ from what the manufacturer gave on their epoxy. This experiment testing followed ASTM D-3039 standard to see the differences in elastic modulus over duration of 15 days. The resulting data shows that the test specimen fully cures after 13 to 14 days. The test specimens in search of the geometric buckling length for this investigation did not follow ASTM C-364 standard in full, but follows a variation of the ASTM C-364 standard in order to support buckling loading condition and the limited accessibility of the test equipments. Instead, the modifications are found with a different test jig design and test specimen configuration. The test jig was created to provide a pinned condition with a 0.25 inch diameter. The test specimen is laid up with a foam and wood cores. Two wood cores are laid at each edge of the foam core to increase loading capacity and holes are drilled through the wood cores to create a pinned-pinned case for the optimum buckling condition. The results detailing the geometric buckling show that after 9 inches anvil length there is no compression; only buckling occurs with a cross-sectional dimension of 0.75 inch by 0.575 inch. The 11 inch foam length was chosen for convenience of machining. This modified setup was also used for testing the different configuration with the embedded arrestment keys. The multiple different configurations completed for these test specimens under unstable loading, the experiment results show that a continuous arrestment key embedded significantly improve the loading capacity over a perfectly sound non-delaminated specimen and maintain the majority of loading capacity even with an introduced delamination. The embedded continuous key also provided a higher horizontal displacement capability before fracture in comparison to the initially delaminated test specimens. As for the test specimens used to determine the material characteristics, ASTM D-3410 and modified ASTM C-364 standards were followed. The test specimens had a fiber volume fraction of approximately 0.60, which details the brittle failure under tensile and compression loading. The results also show that the fibrous fiberglass test specimens have a higher ultimate strength in compression or buckling then in tension.
All of the experimental testing was completed in the Aerospace Engineering Structural/Composite Lab at California Polytechnic State University at San Luis Obispo, California. Therefore, an introduction of a continuous arrestment key parallel to the in-plane loading and embedded into the composite sandwich structure provided a significant increase in loading and buckling capabilities in comparison to the control test specimens with and without an initial delamination and no embedded key. The continuous key placed parallel to the load vector increased the structural strength with an increase of 126% from a 1-inch delaminated structures and only an 11% drop from non-delaminated structures. That is, 1-inch and 2-inch delaminated structures showed a 61% drop and 81% drop from non-delaminated structures. Some configurations have reduced or arrested of the delaminated region.
44
Davis, Richard Anthony. "The Effects of a Damage Arrestment Device on the Mechanical Behavior of Sandwich Composite Beams Under Four-Point Bending." DigitalCommons@CalPoly, 2011. https://digitalcommons.calpoly.edu/theses/506.
Повний текст джерелаАнотація:
The demand for an insert on composite sandwich structures to aid in the arrestment of face-core delamination is of great need. This research studies the use of a damage arrestment device (DAD) that connects the carbon fiber face sheets to the foam core to find whether an increase in the structural integrity of the sandwich beam results. Experimental analysis was employed to test the samples and was verified by a theoretical and finite element approach.
The mechanical properties of LTM45/CF1803 pre-impregnated carbon fiber and Last-A-foam FR 6710 polyvinylchloride foam were experimentally analyzed using ASTM D3039 and ASTM D1621 standards respectively to verify the manufacturer’s data for the given material. With all the mechanical data, the effects of adding DAD keys to a delaminated composite sandwich beam were studied under a four-point bending test using ASTM standard D6272 and compared with non-delaminated beams to see if an increase in ultimate strength could be achieved. The initial delamination in the beams under consideration was one inch in length and located in between the loaded span of the beam. Two control beams were utilized for comparison: one with no defects, and another with a one inch delamination introduced at the face-core interface. The DAD keys were added in two different configurations to potentially stop the delamination propagation and increase the ultimate strength. In the first configuration DAD keys were added 0.25 inches on either side of the initial delamination in the transverse direction and provided a significant increase in strength over the delaminated control beam. The second configuration had a DAD key running along the longitudinal axis of the sandwich beam and resulted in a significant increase in ultimate strength over the delaminated control beam. After testing ten successful samples for each of the six different configurations, it was concluded that the addition of DAD keys in both configurations significantly increased the structural integrity of both the delaminated and non-delaminated control beams.
With all the experimental data acquired, finite element models were created in COSMOS. The purpose of the finite element analysis was to validate the experimental results by comparing the deflections of the beam subjected to four-point bending during the experiment to the deflections found numerically. The deflections for the various DAD key configurations found in the experimental work were in agreement with the finite element results.
45
Sans, Canovas Daniel. "Advances in fibre Bragg grating sensors for damage detection in composite laminates: application in quasi-static and fatigue delamination tests." Doctoral thesis, Universitat de Girona, 2013. http://hdl.handle.net/10803/117357.
Повний текст джерелаАнотація:
The use of composite materials in industrial applications such as aeronautical, aerospace or wind energy production has greatly increased in recent decades. Due to their inherent properties, these materials allow lighter, larger and more resistant structures. However, the use of composite materials for components or structures with highly stringent requirements, is hampered by the lack of knowledge of their reliability. In this thesis, some fundamental aspects about the use of fibre Bragg grating (FBG) sensors for internal strain measurements in composite laminates are discussed. In addition, a highly accurate method for locating the crack tip position in mixed-mode delamination growth has been presented. Finally, an experimental application of FBGs to dynamic measurements in mode I fatigue test has been performedL’ús de materials compostos en aplicacions de caràcter industrial com per exemple l’aeronàutica, aeroespacial o la de producció d’energia eòlica, ha crescut exponencialment durant les últimes dècades. Degut a les seves extraordinàries propietats, l’ús d’aquests materials permet la construcció d’estructures més lleugeres, grans i resistents, tot i que el seu ús en components d’alta responsabilitat estructural està limitat per la manca de coneixement en relació a la seva fiabilitat estructural. En aquesta tesi es discuteixen alguns aspectes significants sobre l’ús de FBGs per a mesurar camps de deformació en l’interior de laminats de material compòsit, s’ha analitzat també la capacitat de localització de la punta d’una esquerda en creixement de mode mixt i per últim s’ha desenvolupat una aplicació pràctica dels FBG en temps real en assaigs a fatiga en mode I
46
Ligato, Edoardo. "Numerical evaluation of the delamination behaviour in Mixed Mode Bending CFRP specimens." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2016.
Знайти повний текст джерелаАнотація:
The raising interest in composite materials of last decades, justifed by their amazing properties, is pushing to fill the knowledge gap which constraints their employment. Damage behavioural predictions are required to be good enough in order to satisfy the strict aeronautical regulations. The study performed in this thesis work,
which is located in the above described framework, aimed to supply informations about crack propagation under mixed-mode loading condition. In particular, critical forces and Strain Energy Release Rates have been determined to describe the behaviour in the range between pure mode I and II. Two different FEM approaches have been employed to analyze a CFRP Mixed Mode Bending specimen in several
mode-mixing configurations. The first selected methodology is the Virtual Crack Closure Technique, but the obtained outcomes resulted to be far from expected ones. The final goal was instead achieved with the relatively new Cohesive Zone Models approach, for which an increased interest can be observed in recent years.
47
Garrett, Joseph Daniel. "Experimentation of Mode I and Mode II Fracture of Uni-Directional Composites and Finite Element Analysis of Mode I Fracture Using Cohesive Contact." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1670.
Повний текст джерелаАнотація:
As the use of fiber-reinforced composites has increased over the decades, so has the need to understand the complexity of their failure mechanisms as engineers seek to improve the damage tolerance of composite laminated structures. One of the most prevalent and limiting mode of failure within composite laminates is delamination, since it not only reduces a structures stiffness and strength, but can be very difficult to detect without the use of special non-destructive equipment. Industry testing organizations have utilized several fracture tests in order to characterize the fracture toughness of composite materials under different loading conditions. For this research, ASTM D5528, ASTM D7905 & 4ENF tests were performed to evaluate the fracture resistance of uni-directional pre-preg laminates; the 4ENF was used to compare its effectiveness as to ASTM D7905.
Finite element methods such as the use of cohesive elements have been developed to simulate delamination within composite laminates. While there has been much work in evaluating the effectiveness of cohesive elements, very little exists within literature as to studying the success of cohesive surface contact for accurately modeling coupon level fracture testing. Cohesive contact interaction in Abaqus/Standard was used to simulate the mode I double cantilever beam (DCB) experiment of ASTM D5528. Cohesive contact was found to accurately and efficiently model DCB testing as the critical load- displacement values and steady state fracture agreed with experimental data. A parametric study was performed and found that cohesive contact was less sensitive in varying key model parameters than that commonly expected of cohesive elements.
48
Dupleix-Couderc, Chloé. "Sur une stratégie multi-échelle d'analyse des grands délaminages en dynamique transitoire." Thesis, Cachan, Ecole normale supérieure, 2011. http://www.theses.fr/2011DENS0013/document.
Повний текст джерелаАнотація:
Les matériaux composites sont largement utilisés dans les structures aéronautiques. Les travaux présentés ici visent à mettre en place une méthode de calcul permettant de prédire les délaminages dans ces structures stratifiées soumises à des chargements dynamiques tout en assurant des coûts de calculs compatibles dans un contexte industriel. Une méthode de décomposition de domaine en dynamique est d’abord utilisée, afin de coupler des modélisations et des pas de temps de calcul différents. Une modélisation fine est utilisée uniquement dans les zones en cours de dégradation. Une représentation macroscopique du stratifié par des éléments de coque 3D est développée et employée dans le reste de la structure. Les coûts de calcul sont ainsi réduits tout en assurant une bonne précision des résultats. Pour éviter un remaillage avec l’avancée du délaminage, une approche multi-échelle en temps et en espace est ensuite proposée. Un maillage global de coque 3D de l'ensemble de la structure est défini. Des maillages utilisant une représentation fine du matériau sont utilisés localement. Des pas de temps adaptés sont utilisés dans les deux types de maillageThe part of composite materials in aeronautic structures is increasing due to their specific properties and the mass reduction they enable. Accurate numerical simulations are thus needed in order to design these structures, particularly to verify if they could resist dynamic charges such as soft bodies impact. Nevertheless, using a refined model to represent phenomenon such as delamination leads to computing time and dofs number incompatible with an industrial context. The aim of the present work is to propose a multi-scale method in space and time to solve dynamic impact problems on laminate structures. A domain decomposition method for dynamic problems is first used to couple different kinds of models and time discretisations. A refined model for the laminate is used in the degradating areas only - elsewhere, a coarser representation using 3D-shell elements is used. This approach reduced the cost of the simulation giving accurate results. To avoid a remeshing due to delamination propagation within the structure, a multi-scale method is then proposed. A global 3D shell elements mesh for the whole structure is defined. Local meshes based on a refined representation of the laminates are used only if required. Coupling between global and local representation is done using velocity field
49
Kulkarni, Mandar Madhukar. "Prediction of Elastic Properties of a Carbon Nanotube Reinforced Fiber Polymeric Composite Material Using Cohesive Zone Modeling." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1235433423.
Повний текст джерела
50
Le, Guen-Geffroy Antoine. "Marine ageing and fatigue of carbon/epoxy composite propeller blades." Thesis, Brest, 2019. http://www.theses.fr/2019BRES0104.
Повний текст джерелаАнотація:
Les travaux présentés portent sur l’étude du vieillissement en milieu marin d’un composite carbone époxy pour applications pâles d’hélice de navires. La caractérisation de la prise en eau dans la résine pure et le composite a montré un comportement Fickien. La présence d’eau dans les porosités du composite a également été mise en évidence analytiquement. Le vieillissement accéléré de la résine a mis en évidence trois phénomènes : l’oxydation, le vieillissement physique et la plastification. L’effet mécanique de ces deux derniers a été particulièrement étudié. La présence d’eau et donc d’une résine plastifiée a eu l’effet d’accélérer le vieillissement physique. L’effet du vieillissement accéléré sur le composite a ensuite été étudié sous différentes sollicitations quasi statiques et de fatigue. Peu d’effets de l’eau ont été relevés pour les sollicitations de traction sur des orientations sens fibres. Cependant, des pertes de plus importantes des propriétés mécaniques ont été observés en traction sens transverse aussi bien en statique qu’en fatigue. Ces mêmes résultats ont été trouvés sous sollicitations de flexion grâce à l’essai de flexion quatre points. Ce dernier a été discuté du fait de l’endommagement qu’il provoque. Enfin, le composite a été étudié sous sollicitations de délaminage suivant deux modes de fissuration: ouverture et cisaillement dans le plan. La présence d’eau a eu pour effet de diminuer l’énergie de fissuration dans les deux modes. Ce même résultat a été trouvé sous chargement de fatigue. L’influence du vieillissement physique sur les propriétés mécaniques du composite a également été démontré, son effet étant négatif, il nécessite d’être pris en compteThe current document presents the long term seawater ageing effect on the fatigue properties of carbon fibre reinforced epoxy marine propeller blades. Seawater uptake in the resin and the composite was identified to correspond to a Fickian diffusion. Calculations of the mass to saturation of the composite based on that of the resin reveal the presence of water in the composite’s porosities.Accelerated ageing of the pure resin highlighted three ageing phenomena: oxidation, plasticization and physical ageing. The last two were mechanically characterized separately and coupled with one another. Above all, it was shown that the presence of seawater accelerated the physical ageing kinetics by reducing the relaxation time. The composite was studied under different quasistatic and cyclic loadings.Few effects of seawater have been found for tensile stresses on fibre oriented loadings. This was not the case for transversely loaded composite that showed a non-negligible decrease of the mechanical properties for both static and fatigue loadings. This was also the case for flexure loading which was studied under four-point flexure. This latter test method was particularly studied due to the particular induced damage. The composite was studied under two delamination loadings: crack opening and inplane shear. It was observed that seawater decreased the critical strain energy release rates for both load cases as well of the fatigue resistance of both crack modes. Finally, the effect of physical ageing on the composite was studied and found to be non-negligible, demonstrating the necessity of taking it into account for both ageing and mechanical design