Дисертації з теми "Delamination of Composites"
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1
Alessa, Hassan Ali. "Delamination in Hybrid Carbon/Glass Fiber Composites." University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1399037290.
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2
Canturri, Gispert Carla. "On delamination directionality and migration in laminated composites." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/18169.
Повний текст джерелаАнотація:
Delamination is recognised as the most critical damage process in laminated composites under compressive or bending loading conditions and managing this failure mode has been key to using composites in primary structures. However, predictive modelling of delamination growth has been limited, since even a simple, single plane defect can result in multiplane delamination growth which is often associated to other secondary processes such as intralaminar or translaminar damage. The objective of this thesis has been to experimentally investigate the fundamental phenomena associated with delamination growth which were isolated from the observations made in embedded defects: delamination preferentially grows along the direction of the fibres at a ply interface (directionality) and, if forced to grow obliquely to the fibres, a change of delamination plane typically ensues (migration). Directionality was demonstrated with a bespoke test to grow delamination in a preferential direction. The geometrical effect of the fibres on the direction of delamination growth was also studied using a macroscopic model of the delaminating interface. A numerical strategy was introduced to model directionality. Cohesive elements and the virtual crack closure technique were modified to include the effect of fibre orientation at the interface at which delamination propagated. Migration was isolated with a series of delamination tests in cross-ply laminates under variable mode mixities. Finally, the insight gained in delamination growth mechanisms was demonstrated on a set of sandwich configurations with embedded defects to understand growth in complex composite geometries. Fractographic studies were used to glean a detailed understanding of the migration process. This work has successfully characterised the detailed processes by which delaminations grow and provided knowledge to develop damage tolerant designs.
3
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/.
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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.
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5
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.
6
Daniewicz, David Joseph 1965. "Edge delamination in advanced laminated composites, theory and verification." Thesis, The University of Arizona, 1990. http://hdl.handle.net/10150/277294.
Повний текст джерелаАнотація:
A damage evolution theory capable of predicting the effects of edge delamination phenomena on composite laminate response is developed. The theory is a mechanics-based formulation which quantifies the damage development of a laminate under general loading, and incorporates it directly to the constitutive behavior of the laminate. The theoretical development introduces a laminate-specific constant φ; the methodology of φ selection is presented for [±15/±50]s, [±45/0/90]s, and [0₂/90₂]s T300 graphite/epoxy laminates. Edge effects are demonstrated by comparing the damage state of the above laminates with and without edge delamination damage. The capability of the theory in predicting the volume scaling effect is shown through consideration of the failure strengths of the [±25/90n]s laminate series.
7
Javidrad, Farhad. "The development of a finite element for delamination growth in composites." Thesis, Imperial College London, 1995. http://hdl.handle.net/10044/1/7731.
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8
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
9
Gozluklu, Burak. "Delamination Analysis By Using Cohesive Interface Elements In Laminated Composites." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12611005/index.pdf.
Повний текст джерелаАнотація:
Finite element analysis using Cohesive Zone Method (CZM) is a commonly used method to investigate delamination in laminated composites. In this study, two plane strain, zero-thickness six-node quadratic (6-NQ) and four-node linear (4-NL) interface elements are developed to implement CZM. Two main approaches for CZM formulation are categorized as Unified Mode Approach (UMA) and Separated Mode Approach (SMA), and implemented into 6-NQ interface elements to model a double cantilever beam (DCB) test of a unidirectional laminated composite. The results of the approaches are nearly identical. However, it is theoretically shown that SMA spawns non-symmetric tangent stiffness matrices, which may lower convergence and/or overall performance, for mixed-mode loading cases. Next, a UMA constitutive relationship is rederived. The artificial modifications for improving convergence rates such as lowering penalty stiffness, weakening interfacial strength and using 6-NQ instead of 4-NL interface elements are investigated by using the derived UMA and the DCB test model. The modifications in interfacial strength and penalty stiffness indicate that the convergence may be improved by lowering either parameter. However, over-softening is found to occur if lowering is performed excessively. The morphological differences between the meshes of the models using 6-NQ and 4-NL interface elements are shown. As a consequence, it is highlighted that the impact to convergence performance and overall performance might be in opposite. Additionally, benefits of selecting CZM over other methods are discussed, in particular by theoretical comparisons with the popular Virtual Crack Closure Technique. Finally, the numerical solution scheme and the Arc-Length Method are discussed.
10
Datta, Sidhyartha. "Investigation of the micromechanics of delamination in fibre reinforced composites." Thesis, Imperial College London, 2005. http://hdl.handle.net/10044/1/7867.
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11
Greenhalgh, Emile Smith. "Characterisation of mixed-mode delamination growth in carbon-fibre composites." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/7975.
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Dyson, Igor Niladri. "The fracture behaviour of carbon fibre/polyetheretherketone composites." Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309100.
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13
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.
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14
Pelegri, Assimina A. "Delamination growth behavior in cross-ply composites under compressive cyclic (fatigue) loading." Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/12004.
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La, Saponara Valeria. "Crack branching in cross-ply composites." Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/11973.
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16
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.
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17
Bhat, Narendra Venugopal. "Delamination suppression in graphite/epoxy composites via efficient use of film adhesive layers." Thesis, Massachusetts Institute of Technology, 1989. http://hdl.handle.net/1721.1/42979.
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18
El-Senussi, A. K. "Interlaminar delamination in unidirectional carbon epoxy composites induced by static and fatigue loading." Thesis, University of Bristol, 1986. http://hdl.handle.net/1983/5db427ad-9653-4c84-999d-59a5a511ef30.
Повний текст джерелаАнотація:
The research is concerned with the interlaminar delamination problem in unidirectional Carbon Fibre Reinforced Plastic (CFRP) laminates under static and fatigue loading. Analytical models backed by experimental techniques are employed to describe the delamination behaviour in 00 interfaces. The problem of a semi-infinite elastic plate loaded along its straight boundary is persued to develop an analytical and realistic Double Cantilever Beam (DCB) Model which accounts for the end deflections associated with deformation beyond a crack tip. Comparisons with the predictions of existing models and with available experimental data show good agreement. The analysis is used to formulate the strain energy release rate (SERR) and the corresponding stress intensity coefficient. This shows excellent agreement with other results from more elaborate methods. The SERR is also formulated for a tapered double cantilever beam and this agrees well with experiment. DCB type specimens were tested in load control where the SERR is measured and compared with theory for, 0* CFRP. Other specimens were tested- in fatigue and the delamination is described for various maximum loads. A Paris type formula is given for predicting crack growth in Oý CFRP. A theoretical analysis is presented for the crack propagation in a layered fibre reinforced plastic strip in compression, in the presence-of a blister. Account is taken of a resin rich layer at the delaminating edge and of an initial deflection* in the blister geometry. Typical design curves are, produced which show the influence of blister length, applied strain and resin stiffness on loads required for delamination. Blistered sandwich specimens were tested in static compression where debonding characteristics are explained. The loads required to initiate delamination are found to compare reasonably well with theory. Similar specimens were tested in constant amplitude fatigue compression loading and delamination behaviour is illustrated.
19
Fox, Bronwyn Louise, and blfox@deakin edu au. "The Manufacture, Characterization and Aging of Novel High Temperature Carbon Fibre Composites." The Australian National University. Faculty of Engineering and Information Technology, 2001. http://thesis.anu.edu.au./public/adt-ANU20011207.114246.
Повний текст джерелаАнотація:
High temperature composite materials used in aerospace applications are exposed to extremely harsh conditions and must be able to withstand moisture and extremes of temperature. For example, the surface of an aircraft flying at Mach 2.4 has been estimated to reach around 177°C as a result of aerodynamic heating. This thesis has examined the effect of isothermal aging on two high temperature composite materials, a novel CSIRO composite and a commercial composite, both based on bismaleimides. Changes in mechanical properties and resin chemistry at two different temperatures were measured in order to assess the validity of accelerated aging tests.
¶
Delamination is a major cause of failure in materials, therefore, the Mode I interlaminar fracture toughness (GIC) of both materials was measured using the double cantilever beam (DCB) test. After aging at 250°C, the CSIRO CBR 320/328 composites exhibited better retention of GIC than the CIBA GEIGY Matrimid® 5292 composites. After 6 weeks of aging at this temperature, the CBR 320/328 material retained 100% of its initial interlaminar fracture toughness, however the Matrimid® 5292 material retained only 64% of its initial GIC. This trend was reversed at the lower aging temperature, when after 30 weeks of aging at 204°C, GIC was measured at 13% of its original value for the CSIRO composites, whereas it was measured at 64% in the case of the Matrimid® composites. When the fracture surfaces of these specimens were examined using scanning electron microscopy (SEM), the commercial material was observed to show an increasing degree of porosity with aging at 204°C. It was concluded that the good property retention at the temperature, despite this observed porosity, was a result of the excellent fibre/matrix adhesion exhibited by this material.
¶
Chemical degradation of the matrix of the composites was monitored by Fourier Transform Infrared (FTIR) and Raman Spectroscopy. Chemical changes at the core of both of these materials were found to occur concurrently with the observed changes in interlaminar fracture toughness. FTIR analysis of both matrix materials revealed the predominant degradation mechanism to be oxidation, specifically the oxidation of the methylene group bridging two aromatic rings common to the structure of both resins, was substantiated by the ingrowth of a broad peak centred at 1600cm-1. In addition to this, the pyromellitic anhydride unit present only in the CBR 320/328 composites was found to be highly resistant to the effects of aging, whereas the saturated imide, common to the cured structures of both materials, was observed to degrade.
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Raman spectroscopy showed an increase in the intensity of a peak at 1646 cm-1 in the Matrimid® 5292 composites aged at 250°C towards the centre of the sample as a result of increased reaction of the allylic carbon-carbon double bond. At 204°C, the degree of reaction increased towards the surface of the material, possibly as a result of a reverse Diels-Alder reaction. The glass transition temperatures of both materials were found to decrease with aging, with the exception of the CSR 320/328 composites aged at 204°C, which initially increased due to continued crosslinking of the resin.
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It is concluded that the degradation mechanisms at the two aging temperatures are very different. The reliability of results from accelerated (elevated temperature) aging tests has been drawn into doubt.
20
Govender, Reuben Ashley. "Characterisation of Glass Fibre Polypropylene and GFPP based Fibre Metal Laminates at high strain rates." Doctoral thesis, University of Cape Town, 2011. http://hdl.handle.net/11427/25150.
Повний текст джерелаАнотація:
Fibre reinforced polymers (FRP) are finding increasing use in structures subjected to
high rate loading such as blast or impact. Proper design of such structures requires
thorough characterisation of the material behaviour over a range of loading rates from
quasi-static to impact. This thesis investigated the quasi-static and impact response
of Glass Fibre Polypropylene (GFPP) in compression, bending and delamination. The
bending and delamination response of Fibre Metal Laminates (FMLs) based on GFPP
and aluminium was also investigated at quasi-static and impact rates.
High strain rate (5x10^2 to 10^3 /s) compression tests were conducted on GFPP using
a compressive Split Hopkinson Pressure Bar (SHPB) and a Direct Impact Hopkinson
Pressure Bar (DIHPB), in the through-thickness and in-plane directions. In both loading
directions, the peak stress of GFPP increased linearly with the logarithm of strain
rate. For in-plane loading, the failure modes were dominated by localised fibre buckling
and kink bands, leading to delamination. The through thickness loading produced
macroscopic shear and spreading failure modes. However, both of these failure modes
are linked to in-ply fibre failures, due to through thickness compression causing transverse
tensile strain. Previous studies of similar materials have not explicitly stated the
link between through thickness compression and fibre failure associated with transverse
tensile strain.
A novel test rig was developed for Three Point bend testing at impact rates. The
specimen was supported at the outer points on a rigid impacter and accelerated towards
a single output Hopkinson Pressure Bar (HPB), which impacted the specimen
at its midspan. Previous impact bend test rigs based on HPBs were limited to testing
specimens with deflections to failure up to approximately 1mm, whereas the rig implemented
herein measured deflections up to approximately 10 mm. This configuration
permits the output HPB to be chosen purely on the magnitude of the expected impact
force, which resulted in superior force resolution to configurations used in other
studies. The HPB Impact Bend rig was used to test GFPP and aluminium-GFPP FML
specimens, at impact velocities ranging from 5 to 12 m/s. The flexural strength of GFPP
increased with strain rate, while the flexural response of the FML specimens was relatively
insensitive to strain rate.
v
Several candidate delamination test geometries were investigated at quasi-static
displacement rates (1 mm/min), and the Single Leg Bend (SLB) test was identified as
suitable for adaptation to higher rate testing. Single Leg Bend delamination tests of
both GFPP and FML specimens were performed using the HPB Impact Bend rig, at
impact velocities of 6 to 8 m=s. The shape of the force displacement response for the
high rate testswas markedly different from the quasi-static tests, for both the GFPP and
FML specimens. Finite element (FE) simulation of the quasi-static and impact rate SLB
tests on GFPP indicated that the difference was probably due to the interaction of flexural
vibrations and stress waves in the specimen and the impacter cross member. The
experimental results and FE analysis suggest that the delamination fracture toughness
of GFPP decreases slightly as strain rate increases. High rate delamination tests on
FML specimens resulted in unstable crack growth.
21
Lee, Hao. "Damage modelling for composite structures." Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/damage-modelling-for-composite-structures(ee416524-935c-487d-bcd5-282875e6027a).html.
Повний текст джерелаАнотація:
Modelling damage in composite materials has played an important role in designing composite structures. Although numerical models for the progressive damage in laminated composites (e.g. transverse cracking, delamination and fibre breakage) have been developed in the literature, there is still a need for further improvement. This thesis aimed at developing damage models suitable for predicting intra-laminar and inter-laminar damage behaviour in fibre-reinforced composite materials. Several approaches such as fracture mechanics and continuum damage mechanics have been adopted for constructing the damage model. Meso-macro-mechanics analysis was performed to gain an insight into the entire damage process up to the final failure of the composite laminate under various conditions. Cohesive elements were placed in the finite element model to simulate the initiation and propagation of matrix crack and delamination in cross-ply laminates. This helped to understand the direct interactions between damage modes, i.e. whether one damage mode would initiate the other damage mode. The formation of a single matrix crack and its propagation across the layer thickness was also revealed. A new cohesive zone/interface element model was developed to consider the effect of through-thickness compressive stress on mode II fracture resistance by introducing friction into the constitutive law of the conventional cohesive zone model. Application of the model to practical problem in composite laminates shows that this model can simulate delamination failure more accurately than the cohesive element in ABAQUS.Damage models based on continuum damage mechanics were proposed for predicting intra-laminar damage and interlaminar damage. Five intra-laminar failure modes, fibre tension, fibre compression, matrix tension, matrix compression and shear failure, were modelled. Damage initiation was predicted based on stress/strain failure criteria and damage evolution law was based on fracture energy dissipation. The nonlinear shear behaviour of the material was considered as well. These models have been implemented into ABAQUS via a user-defined material subroutine and validated against experimental/numerical results available in the literature. The issue related to numerical implementation, e.g. convergence in the softening regime, was also addressed. Numerical simulation of the indentation test on filament-wound pipe was finally conducted and damages generated in the pipe were predicted using the above developed damage models. The predictions show an excellent agreement with experimental observations including load/indentation responses and multiple delaminations shape and size. Attempt was made to detect damage-induced leakage path in the pipe after indentation.
22
Costa, Elisabete Fernandez Reia Da. "Liquid moulding of carbon nanoparticle filled composites." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/7276.
Повний текст джерелаАнотація:
This thesis focuses on the incorporation of carbon nanoparticles within continuous fibre reinforcements by liquid composite moulding processes, in order to provide enhanced electrical and delamination properties to the multiscale composites. The mechanisms controlling the flow and filtration of these nanoparticles during liquid composite moulding are studied, in order to develop a predictive 1-D model which allows design of the processing of these composite materials. Five different carbon nanoparticles at 0.25 wt% loading, three unmodified and one surface modified carbon nanotube systems and one carbon nanofibre system, were utilised to modify a commercial two-component epoxy resin utilised to impregnate carbon and glass reinforcements at high fibre volume fraction by resin transfer moulding. The dispersion of the nanofillers in the prepolymer was carried out by ultrasonication, high shear mixing or triple roll milling or a combination of the three. Electrical conductivity measurements of the carbon nanoparticle liquid suspensions during dispersion, alongside optical microscopy imaging and rheological analysis of these allowed the selection of the concentration of nanofiller and the appropriate dispersion technique for each nanoparticle system. The resin transfer moulding process required adaptation to incorporate the dispersion and modify degassing steps, especially when utilising unmodified carbon nanoparticles suspensions, due to their higher viscosity and tendency to be filtered. Nanoparticle filtration was identified by electrical conductivity measurements and microscopy of specimens cut at increasing distances from the inlet. Cake filtration was observed for some of the unmodified systems, whereas deep bed filtration occurred for the surface modified CNT material. Property graded composites were obtained due to filtration, where the average electrical conductivity of the carbon and glass composites produced increased by a factor of two or one order of magnitude respectively. The effect of filler on the delamination properties of the carbon fibre composites was tested under mode I. The results do not show a statistically significant improvement of delamination resistance with the presence of nanoparticles, although localised toughening mechanisms such as nanoparticle pull-out and crack bridging as well as inelastic deformation have been observed on fracture surfaces. Particle filtration and gradients in concentration resulted in non-linear flow behaviour. An 1-D analytical and a finite difference model, based on Darcy’s law accompanied by particle mass conservation and filtration kinetics were developed to describe the flow and filtration of carbon nanoparticle filled thermosets. The numerical model describes the non-linear problem by incorporating material property update laws, i.e. permeability, porosity and viscosity variations on concentration of retained and suspended particles with location and time. The finite difference model is consistent and converges to the analytical solution. The range of applicability of the analytical model is limited to lower filtration coefficients and shorter filling lengths, providing an approximate solution for through thickness infusion; whereas the numerical model presents a solution outside this range, i.e. in-plane filling processes. These models allow process design, with specified carbon nanoparticle concentration distributions achieved via modifying the nanofiller loading at the inlet as a function of time.
23
Moradi, Shapour. "Application of differential quadrature method to the analysis of delamination buckling of laminated composites." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape8/PQDD_0008/NQ39323.pdf.
Повний текст джерела
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Kiefer, Konstanze. "Simulation of high-cycle fatigue-driven delamination in composites using a cohesive zone model." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/25155.
Повний текст джерелаАнотація:
In this PhD thesis several published strategies for the simulation of high-cycle fatigue-driven delamination using cohesive elements are investigated in mode I using an efficient analytical model which eliminates the numerical errors involved in a finite element simulation. A detailed sensitivity study of all the models is performed with respect to the element size and the cycle-jump. The models are then compared and their advantages and disadvantages highlighted. For two of the models improvements are proposed and investigated using the analytical model. Necessary conditions for a successful fatigue model are then highlighted and a new model is proposed. A sensitivity study demonstrates a very good performance of this model. The new fatigue degradation strategy is implemented into a user defined element (UEL) within the commercial finite element software ABAQUS. Two simulations are then performed for pure mode I and mode II fatigue-driven delamination. The new strategy is shown to achieve good agreement with the input Paris law and is also shown to perform well in comparison with FE implementations of some of the published cohesive element strategies for fatigue-driven growth of delamination.
25
Brown, Kevin S. "Embedded Distributed Fiber Optic Strain Measurements for Delamination Detection in Composite Laminates." University of Dayton / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1543330547266239.
Повний текст джерела
26
Poutord, Antoine. "Étude du perçage à sec de l'empilage Ti6Al4V/Composite fibre de carbone." Thesis, Paris, ENSAM, 2014. http://www.theses.fr/2014ENAM0149/document.
Повний текст джерелаАнотація:
Le secteur aéronautique ayant des exigences toujours plus contraignantes, l’emploi de nouveaux matériaux pour les structures a été incontournable. C’est pourquoi le composite à fibre de carbone a fait son apparition dans les structures d’avions, épaulé par des pièces en alliage de titane, majoritairement du Ti6Al4V. Ces matériaux sont alors disposés en empilages et percés en une seule opération pour être ensuite assemblés par des rivets ou des boulons. Un certain nombre de problèmes, d’un point de vue industriel, sont soulevés par cette opération, générant des surcoûts importants. Les verrous technologiques et scientifiques liés à cette opération seront donc analysés au cours de cette étude.La connaissance des efforts locaux exercés par l’outil sur la matière usinée constitue un premier point permettant l’amélioration de la compréhension des phénomènes survenant lors de la coupe. Pour cela plusieurs procédés seront expérimentés pour déterminer avec précision les efforts subis par l’outil tout au long du perçage. Afin de compléter les informations relatives aux efforts sur l’outil, l’analyse de la température au sein du foret est nécessaire. Plusieurs dispositifs expérimentaux de mesure de la température in-situ sont développés.Ces dispositifs ont permis l’usinage instrumenté de trous à la fois dans chacun des deux matériaux composant l’empilage et dans l’empilage afin de comprendre au mieux les phénomènes survenant lors de ces opérationsThe aeronautic field has stronger and stronger requirements so the use of materials for structures has been unavoidable. That’s why carbon fiber composite is appeared in plane structures, used with elements in titanium alloy, and most part of them in Ti6Al4V. These materials are also dispatched in stacks and are drilled in a “one shot” operation, in the aim of being assembled with rivets or bolts. Through the industrial point of view, many problems are highlighted by this operation, generating several over costs. Technologic and scientific locks linked with this operation will be analyzed in this study.The knowledge of local stresses exerted by the tool on the machined matter is the first point allowing the improvement of the understanding of phenomenon that occurs during cutting. Few processes will be experimented to determine stresses submitted by the tool during drilling with accuracy. In the aim of completing the knowledge of the cutting operation, the analysis of the temperature inside the drill is needed. That’s why different experimental devices of thermal measurement are developed.These devices have allowed instrumented machining of holes in each material separately and in the stack of Ti6Al4V/CFRP in order to understanding phenomenon that occur during this operations
27
Patel, Kinjalkumar. "Functional multi-scale composites by coating of fibrous reinforcements." Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/functional-multiscale-composites-by-coating-of-fibrous-reinforcements(92842a85-98a9-44f6-9bd7-dcbd13ab57b6).html.
Повний текст джерелаАнотація:
This study reports a novel and simple technique for successfully coating multi-walled carbon nanotubes (MWCNTs) on to the surface of carbon fibre (CF) fabric for the production of multi-scale CF-epoxy composites. Initially, epoxy composites with multi-scale reinforcement were produced by resin infusion (RI) using woven CF fabric coated with a dispersion of 1 wt. % MWCNTs in an epoxy binder of low molar mass. The effects of this reinforcement on the CF-epoxy interface with MWCNTs was studied in mode I and mode II interlaminar fracture toughness (ILFT) using double-cantilever beam (DCB) and 4 point end-notch flexure (4ENF) tests, respectively. Relative to an equivalent composite reinforced with non-coated CF reinforcement, the binder/MWCNTs coating increased significantly the ILFT of the CF-epoxy composite; in mode I by 105% and in mode II by 50%. This increase in ILFT was attributed to two main effects: Firstly, the binder alone (without MWCNTs), which has a much lower glass transition temperature (Tg) than that the matrix (45 vs. 140 °C), hindered crack propagation and increased the ILFT of the epoxy matrix by 25% for mode I and 15% for mode II; Secondly, the energy absorbing mechanisms of MWCNTs during fracture particularly pull-out and crack bridging. However the Tg of the matrix epoxy of the multi-scale composites was reduced to 118 °C compared to 140 °C, for the unmodified composite, due to phase mixing with the low Tg binder. For RI processing, the CF volume fraction of the composites prepared using coated CF was ≈50% compare to at ≈55% for the composite with non-coated CF. Curing agents were added to the binder, which not only increased the Tg from ≈50 °C to ≈100 °C, but also increased the Tg of the matrix epoxy of the multi-scale composites to 154 °C. Relative to an equivalent composite reinforced with non-coated CF reinforcement, the curable-binder/MWCNTs coating increased the ILFT of the CF-epoxy composite; in mode I by 120% and in mode II by 90%. A hybrid RI-hot press (HP) process was used to prepare CF-epoxy composites from coated fabrics with CF volume fractions of ≈55%. The damping curves for the HP-composites consisted of a β-peak, due to the formation of a third mixed phase, in addition to a γ-peak (assigned to the Tg of the binder) and an α-peak (assigned to the Tg of matrix epoxy). The β-peak, and the uniformly distributed nodular particles observed on the fracture surface of the matrix, by SEM, for HP-composites, are indicative of the formation of mixed-phase particles due to reaction induced phase separation (RIPS). Relative to an equivalent RI-composite, the curable-binder/MWCNTs treatment increased the ILFT of the CF-epoxy multi-scale composite; in mode I by 134% and in mode II by 15% for HP-composites. Impact test results showed that HP-composites absorbed more energy, due to CF fracture, compared to equivalent RI composites, which showed larger delamination areas after 5 J and 10 J impact. The out-of-plane electrical conductivity and thermal conductivity of the HP-composite with CF coated with curable-binder/MWCNTs was increased by ≈38% and ≈50%, respectively, compared to the composite with non-coated CF, indicating formation of MWCNTs networks in the matrix rich areas of the multi-scale composite.
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Clarke, M. P. "The effect of low velocity impact damage on the compressive properties of carbon fibre reinforced composites." Thesis, University of Bristol, 1997. http://hdl.handle.net/1983/98ed8240-fdad-4241-87ab-ec69d9d35532.
Повний текст джерела
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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
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Maillet, Irène. "Propagation de délaminage par fatigue vibratoire dans un matériau composite." Thesis, Toulouse, ISAE, 2013. http://www.theses.fr/2013ESAE0010/document.
Повний текст джерелаАнотація:
Dans le domaine aéronautique les structures sont soumises à de la fatigue sonique due aux phénomènes aéro-acoustiques. Le dimensionnement statique actuel des avions composites couvre les cas de charge en fatigue. Mais avec le besoin de toujours plus réduire la masse de l’avion et l’augmentation des connaissances dans le comportement matériau, les marges statiques vont être réduites dans un futur proche et la propagation par fatigue deviendra un enjeu majeur. Il sera donc nécessaire d’évaluer la possibilité de propagation d’un délaminage dû à une erreur de fabrication ou un impact dans une structure composite. Dans ce contexte, une méthode a été proposée pour étudier la propagation de délaminage sous chargement vibratoire. Tout d’abord, des essais de caractérisation de la propagation de délaminage sous chargement vibratoire ont été mis en place et validés pour les deux principaux modes de rupture. Les effets induits par la fréquence élevée de sollicitation, auto-échauffement induit et vitesse de chargement élevée, ont été pris en compte dans la mise au point et le traitement de ces essais. Ensuite, des outils numériques ont été développés pour permettre la simulation d’une structure délaminée sous chargement vibratoire et l’étude de la propagation du délaminage. A l’aide des approches expérimentales et numériques mises en place et des données matériau identifiées, l’analyse a pu être conduite sur un cas réel de structure aéronautique. Un essai de fatigue vibratoire sur une structure de reprise de plis a ainsi été réalisé. L’évolution du délaminage pendant l’essai est représenté de façon satisfaisante par le modèle numériqueBecause of their lightness, stress adaptive design and strong stiffness, composite materials are more and more used in aeronautics. Aeronautical structures are submitted to vibrations during their service life due to aerodynamic turbulent flow around the structure. The current static design of composite aircraft covers fatigue loading cases. But with the need to more and more lighten the structure, and the knowledge increase in material behavior, the static reserve factors will be reduced in the near future and sonic fatigue will become a major issue. It will be necessary to evaluate the possibility of a delamination propagation in a composite structure due to a manufacturing error or to an impact. In this context, a method has been proposed to study the propagation of a delamination under vibratory loading. Firstly, tests to characterize the propagation of delamination under vibration loading have been developed and validated for the two main failure modes. The effects induced by the highfrequency loading, self-heat generation and high speed loading, were considered in the elaboration of these tests and in the data reduction. Then, numerical tools have been developed to allow the simulation of a delaminated structure under vibratory loading in order to study the delamination propagation. Using experimental and numerical approaches and the material data identified, the analysis could be conducted on a real case of aircraft structure. A vibration fatigue test on a ply-drop structure has been achieved. The evolution of delamination during the test is adequately modelized by the numerical model
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Turon, Travesa Albert. "Simulation of delamination in composites under quasi-static and fatigue loading using cohesive zone models." Doctoral thesis, Universitat de Girona, 2006. http://hdl.handle.net/10803/7764.
Повний текст джерелаАнотація:
Es desenvolupa una eina de disseny per l'anàlisi de la tolerància al dany en composites. L'eina pot predir el inici i la propagació de fisures interlaminars. També pot ser utilitzada per avaluar i planificar la necessitat de reparar o reemplaçar components durant la seva vida útil. El model desenvolupat pot ser utilitzat tan per simular càrregues estàtiques com de fatiga.El model proposat és un model de dany termodinàmicament consistent que permet simular la delaminació en composites sota càrregues variables. El model es formula dins el context de la Mecànica del Dany, fent ús dels models de zona cohesiva. Es presenta un metodologia per determinar els paràmetres del model constitutiu que permet utilitzar malles d'elements finits més bastes de les que es poden usar típicament. Finalment, el model és també capaç de simular la delaminació produïda per càrregues de fatiga.
A design tool for the analysis of delamination in laminated composites was developed. The design tool is developed using the damage-tolerance concept to predict both delamination initiation and growth. Therefore, the model developed can be used to perform either strength or damage-tolerance verification of new components, and can be used to assess the necessity to repair or replace in-service components. The model developed can be used either to simulate quasi-static or fatigue loading.
A thermodinamically consistent damage model is proposed for the simulation of delamination in composite materials under variable-mode loading. The model is formulated in the context of Damage Mechanics by means of the Cohesive Zone Model concept. Moreover, a methodology to determine the parameters of the constitutive model is proposed. The methodology presented allows the use of coarser meshes that is usually admissible. Finally, the model has been enhanced to simulate high cycle fatigue.
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Stevanovic, Dejan, and dejan@mso anu edu au. "Delamination Properties of a Vinyl-Ester/Glass Fibre Composite Toughened by Particulate-Modified Interlayers." The Australian National University. Faculty of Engineering and Information Technology, 2002. http://thesis.anu.edu.au./public/adt-ANU20030421.212730.
Повний текст джерелаАнотація:
The main aim of this work is to examine fracture toughness improvement mechanisms of a
composite material containing tough interlayers modified with large thermoplastic
particles.
¶
Various vinyl-ester (VE)/ poly(acrylonitrile-butadiene-styrene) (ABS) blends were used
for the interlayer-toughening of a VE/glass fibre composite to increase delamination
resistance of the material under mode I and mode II loading. Dry ABS powder was mixed
with the liquid resin in four different weight ratios: 3.5, 7, 11 and 15 phr (parts per
hundred parts of resin) while the layer thickness was varied from 150 to 500um.
Firstly, the tensile and mode I fracture toughness properties of the VE/ABS blends were
assessed, and, by using the Raman Spectroscopy technique, a chemical reaction was
discovered which occurred during ABS/VE mixing. This reaction consisted of butadiene
dissolution from the ABS particles into the VE. Also, butadiene saturation within the VE
was achieved at a composition of around 7% ABS particle content. Both mode I and mode II
fracture toughness of the composite were significantly improved with the application of
interlayers. Mode I fracture toughness GIc was found to be a function of
interlayer thickness and ABS particle content variations, with the latter dominating
GIc after the saturation point. Mode II fracture toughness was found to be
independent of interlayer thickness and only moderately influenced by particle content.
The toughening mechanisms that were the most influential within this interlayered
material were plastic deformation and micro-cracking of the layer materials. Evidence of
both mechanisms was found using optical and scanning electron microscopy (SEM).
¶
A numerical analysis was conducted, using the experimental results from this study, to
further explain the basic toughening mechanisms and fracture behaviour in the materials.
The aim of the analysis was to examine the influence of the particles on the plastic zone
size that develops in front of the crack tip, and the interaction between the particles
and the crack tip. For this purpose FEA elastic-plastic crack propagation models were
employed. Good agreement with the experimental data was found.
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Troulis, Emmanouil. "Effect of Z-Fiber® pinning on the mechanical properties of carbon fibre/epoxy composites." Thesis, Cranfield University, 2003. http://dspace.lib.cranfield.ac.uk/handle/1826/107.
Повний текст джерелаАнотація:
This study investigates the effects of Z-pinning on the delamination performance in opening and shear loading modes in woven fabric reinforced / epoxy composite materials, as well as the effects of friction between specimen crack faces and the Z-pin failure mechanisms involved in mode II delamination. Mode I and mode II delamination tests are carried out on Z-pinned unidirectional (UD) and woven laminates. Both UD and woven laminates exhibit enhanced delamination resistance and crack propagation stability through Z-pinning. The effects of various structural and Z-pin parameters on the mode I and mode II delamination behaviour are separately assessed. The 4ENF testing configuration is deemed as the appropriate mode II configuration for the testing of Z-pinned laminates. A new basic friction rig is used to measure the friction coefficient between crack faces in woven laminates. An additional friction effect attributed to fibre architecture is identified. A specially designed delamination specimen is used to overcome the difficulty of accurately measuring crack propagation in Z-pinned woven fabric materials and aid data reduction using the available analytical methods. The failure mechanisms involved in the mode II delamination of Z-pinned laminates have been investigated with the implementation of a new test. Z-pins fail under shear loading through a combination of resin crushing, laminate fibre breakage, pin shear, pin bending and pin pullout. The balance of the failure mechanisms is shown to be a function of the crack opening constraint, material type, stacking sequence, Z-pin angle and insertion depth to Z-pin diameter ratio. Z-pin and material parameters influencing Z-pinning quality are identified, categorised and quantified. The importance of controlling Z-pin insertion depth is underlined and updated manufacturing procedures are proposed. Partial pinning appears as an advantageous alternative. A reduction in in-plane stiffness and in-plane strength in UD and woven fabric composites is measured, whilst no significant change of in-plane shear stiffness of UD materials is observed. A reduction in the fibre volume fraction is the single most important parameter affecting the in-plane stiffness. The performance of a Z-pinned sub-structural component is investigated. Enhanced loading carrying capacity and damage tolerance is achieved through Z-pinning.
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Zubillaga, Eceiza Lierni. "Experimental and analytical study of delamination caused by free-edges and matrix cracks in laminated composites." Doctoral thesis, Universitat de Girona, 2014. http://hdl.handle.net/10803/284759.
Повний текст джерелаАнотація:
In the last decades, the use of laminated composites, such as Carbon Fiber Reinforce Polymer has increased in many industrial sectors. Different failure mechanisms different damage mechanism can appear in laminated composites. Among the different damage mechanisms, delamination or interlaminar failure is the one that reduces the load-carrying capacity of composite structures and may compromise structural integrity. Nowadays, the prediction of delamination can be done using computational tools that involve high computational costs, limiting their applicability in the initial stages of the design of new structural components. In this work, quick-analysis tools for delamination predictions are proposed. Two different sources of delamination have been studied: free-edge and matrix-crack induced delamination. A methodology to predict both types of induced delamination is proposed and it has been validated with experimental resultsEn los últimos años se ha incrementado el uso de materiales compuestos en diferentes campos de la tecnología. Este tipo de materiales presentan varios tipos de fallo, siendo uno de ellos la deslaminación o fallo interlaminar. La deslaminación puede reducir la capacidad de carga de los compuestos y puede comprometer la integridad estructural. En la actualidad, se puede predecir la deslaminación mediante herramientas numéricas, pero estas implican un alto coste computacional que imposibilita su utilización en las primeras etapas del diseño de un componente estructural. En esta tesis se aborda esta problemática, proponiendo métodos de cálculo de bajo coste computacional que permiten predecir la deslaminación en las primeras etapas del diseño estructural. Se han desarrollado métodos de análisis para dos distintos tipos de deslaminación: por efectos de borde y provocada por grietas en la matriz, y se han validado mediante una campaña experimental
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Zhang, Chao. "Random delamination of graphite/epoxy laminated composites : stress analysis, failure criteria, experimental characterization and stochastic modeling." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2001. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp05/NQ63992.pdf.
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Abisset, Emmanuelle. "Un mésomodèle d’endommagement des composites stratifiés pour le virtual testing : identification et validation." Thesis, Cachan, Ecole normale supérieure, 2012. http://www.theses.fr/2012DENS0035/document.
Повний текст джерелаАнотація:
Afin de fiabiliser la démarche de conception par simulation numérique des structures en composites stratifiés, l’industrie a besoin de modèles matériau dédiés pertinents et de code de calcul robustes. L’objectif de ce travail est de répondre à une partie de ces besoins : valider un mésomodèle d’endommagement des stratifiés, celui développé au LMT Cachan, pour le virtual testing. Une démarche de validation est proposée, basée sur le suivi de l’évolution des mécanismes de dégradation dans le matériau jusqu’à la rupture de l’éprouvette. Elle est ensuite appliquée au modèle sur des essais de tractions sur plaques trouées et d’indentation statique, avec études des effets d’échelle. Le premier cas test montre la capacité du modèle à reproduire le changement de mode de rupture, d’une rupture dominée par la rupture des fibres à celle dominée par le délaminage, mais souligne aussi une certaine faiblesse pour la représentation des zones d’endommagement localisées (splits). Une étude complémentaire, axée sur les mécanismes de fissuration transverse, de délaminage et de leur couplage, permet de corriger en partie le modèle et d’améliorer la compréhension du rôle de ces mécanismes dans la rupture des structures. Pour l’étude de l’indentation, une campagne expérimentale complète est construite et réalisée en collaboration avec le laboratoire ACCIS de Bristol. Elle met en évidence des évolutions de l’endommagement différentes selon l’épaisseur de la plaque, principalement en terme de délaminage. Les premières simulations réalisées montrent une capacité relative du modèle à reproduire l’apparition des dégradations mais aussi des limites numériques du code éléments finis utilisésIn order to provide reliable numerical simulations for the design of composite structures, both accurate, physically based material models and high performance numerical codes are necessary. The aim of this thesis is to validate one of these models: the LMT damage mesomodel for laminated composites. A new validation process, based on the evolution of the degradation mechanisms in the material up to failure, is defined. This approach is then applied on two chosen test cases: open-hole tensile tests and static indentation tests, focusing on the scaling effects. The first test case highlights the model capabilities to mirror the failure mode change with ply thickness: from a fiber breaking dominated failure to a delamination dominated one. Nevertheless, it also underlines one of the model weaknesses: the bad representation of localised damage such as splits. A study of the transverse cracking, the delamination and their interaction allow to improve the capabilities of the model and to understand in depth the role of these mechanisms in the structure failure. Concerning the static indentation, a complete experimental campaign was built and performed in collaboration with the ACCIS laboratory in Bristol. It brings out different damage evolution depending on plate thickness that can be used to validate the model. The first simulations performed show that the model does not manage to mirror all the experimental observations, and underline numerical limitations of the finite elements code used
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Thiagarajan, C. "Smart characterisation of damage in carbon fibre reinforced composites under static and fatigue loading condition by means of electrical resistivity measurements." Thesis, Cranfield University, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.309660.
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Treutenaere, Sylvain. "Modélisation du comportement des composites stratifiés à préformes textiles avec prédiction du délaminage pour des simulations d'impact." Thesis, Valenciennes, 2016. http://www.theses.fr/2016VALE0001/document.
Повний текст джерелаАнотація:
Les composites à matrice organique et renforcés par des préformes textiles (CMORT) sont en passe d’être déployés sur les véhicules de grandes séries pour réduire leur poids. Lorsqu’ils sont soumis à des impacts basse vitesse ces matériaux présentent des comportements complexes qui doivent être précisément modélisés et prédis au moyen de simulations par éléments finis. Dans ce but, un modèle matériau a été développé et implémenté dans un code éléments finis commercial. Soumis à un impact basse vitesse, un CMORT présente quatre mécanismes physiques majeurs qui altèrent la rigidité initiale du matériau : fissuration matricielle intralaminaire, rupture des fibres, délaminage et sensibilité à la vitesse de déformation. L’endommagement matriciel est modélisé grâce à un modèle constitutif reposant sur la mécanique de l’endommagement des milieux continus. Basé sur l’Onera Damage Model, il prend en compte les mécanismes de friction aux abords des fissures. La sensibilité à la vitesse de déformation est introduite au moyen d’un modèle de Maxwell généralisé. Ensuite, un critère de rupture est utilisé pour prédire l’initiation de la rupture des fibres et l’endommagement des fibres qui en découle est régularisé par l’utilisation d’un modèle de rupture progressive. Finalement, afin de prédire précisément le comportement hors-plan d’un stratifié, le calcul d’une distribution de déformation réaliste à travers l’épaisseur est réalisé au niveau du modèle matériau. Cette modélisation est capable de prendre en compte les effets du délaminage en utilisant seulement un élément coque. De plus, l’intégralité du modèle est formulé suivant la description Lagrangienne totale afin d’assurer l’objectivité et la cohérence matérielle durant la simulation. La procédure d’identification, ainsi que les tests de validation et les corrélations essais/simulations sont décrits pour chaque mécanisme physique. Enfin, le modèle est évalué au travers de la prédiction du comportement d’une structure automobile industrielleCarbon Fabric Reinforced Polymers (CFRP) will soon used in high volume automotive production in order to reduce the vehicle weight. For safety and design reasons, their complex behaviours under low-speed impacts, such as pedestrian impacts, need to be accurately modelled and predicted by finite element simulations. For this purpose, a material model dedicated to explicit finite element simulations has been developed and implemented in a commercial finite element code. Subject to low-speed impacts, the CFRP shows four different physical mechanisms which alter the initial stiffness of the material: intralaminar matrix cracks, fibre failure, delamination and strain-rate sensitivity. The intralaminar damage is modelled through constitutive equations based on the continuum damage theory. It is based on the Onera Damage Model, but with the consideration of friction mechanisms between crack lips in order to represent the hysteresis loops in case of cyclic loading. The strain-rate sensitivity is introduced by means of the rheological generalised Maxwell viscoelastic model. Regarding the fibre damage, a failure criterion based on the strain of the fibre direction is introduced. The energy release due to the fibre failure is also regularised thanks to a smeared crack approach. Finally, in order to welldescribed the out-of-plane behaviour, such as bending, of a laminated CFRP material, a recomputation of a realistic strain field through-the thickness of the laminate is introduced at level of the material model. Based on strain energy equilibrium between usual shell element theory and higher-order zigzag theory, this formulation is able to consider delamination at ply interfaces by using only one shell element through-the-thickness of a laminate. In addition, the model is placed in a total Lagrangian framework to ensure both objectivity and material coherence. The identification procedure, with the needed experimental tests, as well as validation tests and experimental/numerical correlations are given for all physical mechanisms previously described. Finally, this model is evaluated through the behaviour prediction of an industrial structure
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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.
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Blanco, Villaverde Norbert. "Variable mixed-mode delamination in composite laminates under fatigue conditions: testing & analysis." Doctoral thesis, Universitat de Girona, 2005. http://hdl.handle.net/10803/7760.
Повний текст джерелаАнотація:
La majoria de les fallades en elements estructurals són degudes a càrrega per fatiga. En conseqüència, la fatiga mecànica és un factor clau per al disseny d'elements mecànics. En el cas de materials compòsits laminats, el procés de fallada per fatiga inclou diferents mecanismes de dany que resulten en la degradació del material. Un dels mecanismes de dany més importants és la delaminació entre capes del laminat. En el cas de components aeronàutics, les plaques de composit estan exposades a impactes i les delaminacions apareixen facilment en un laminat després d'un impacte. Molts components fets de compòsit tenen formes corbes, superposició de capes i capes amb diferents orientacions que fan que la delaminació es propagui en un mode mixt que depen de la grandària de la delaminació. És a dir, les delaminacions generalment es propaguen en mode mixt variable. És per això que és important desenvolupar nous mètodes per caracteritzar el creixement subcrític en mode mixt per fatiga de les delaminacions. El principal objectiu d'aquest treball és la caracterització del creixement en mode mixt variable de les delaminacions en compòsits laminats per efecte de càrregues a fatiga. Amb aquest fi, es proposa un nou model per al creixement per fatiga de la delaminació en mode mixt. Contràriament als models ja existents, el model que es proposa es formula d'acord a la variació no-monotònica dels paràmetres de propagació amb el mode mixt observada en diferents resultats experimentals. A més, es du a terme un anàlisi de l'assaig mixed-mode end load split (MMELS), la característica més important del qual és la variació del mode mixt a mesura que la delaminació creix. Per a aquest anàlisi, es tenen em compte dos mètodes teòrics presents en la literatura. No obstant, les expressions resultants per l'assaig MMELS no són equivalents i les diferències entre els dos mètodes poden ser importants, fins a 50 vegades. Per aquest motiu, en aquest treball es porta a terme un anàlisi alternatiu més acurat del MMELS per tal d'establir una comparació. Aquest anàlisi alternatiu es basa en el mètode dels elements finits i virtual crack closure technique (VCCT). D'aquest anàlisi en resulten importants aspectes a considerar per a la bona caracterització de materials utilitzant l'assaig MMELS. Durant l'estudi s'ha dissenyat i construït un utillatge per l'assaig MMELS. Per a la caracterització experimental de la propagació per fatiga de delaminacions en mode mixt variable s'utilitzen diferents provetes de laminats carboni/epoxy essencialment unidireccionals. També es du a terme un anàlisi fractogràfic d'algunes de les superfícies de fractura per delaminació. Els resultats experimentals són comparats amb les prediccions del model proposat per la propagació per fatiga d'esquerdes interlaminars.Most of the failures in structural elements in use are a consequence of mechanical fatigue. Therefore, fatigue is a decisive factor in designing durable mechanical elements. In laminated composite materials, the fatigue process involves different damage mechanisms that result in the degradation of the material. One of the most important damage mechanisms is the delamination between plies of the laminate. In aeronautical applications, composite plates are sensitive to impact and delamination occurs readily in composite laminates on impact. Many composite components have curved shapes, tapered thickness and plies with different orientations, which make the delamination grow with a mode mix that depends on the extent of the crack. Thus, delaminations generally grow under varying mode mix. It is therefore important to develop methods that can characterise subcritical, mixed-mode growth in fatigue delamination. The main objective of the present investigation is the characterisation of the variable mixed-mode delamination in composite laminates under fatigue conditions. To this end, a mixed-mode fatigue delamination model is proposed. Oppositely to the mixed-mode fatigue delamination models present in the literature, the proposed model takes into account the non-monotonic variation of the propagation parameters with the mode mix observed in different experimental data. Moreover, the mixed-mode end load split (MMELS) test, which main characteristic is that the propagation mode of the interlaminar crack varies with the crack extent, is analysed. Two theoretical approaches present in the literature are considered. However, the resulting expressions for the MMELS test are not equivalent and the differences between approaches can be up to 50 times. A more accurate alternative analysis of the MMELS test is carried out in the present study for comparison. The alternative analysis is based on the finite element method and the virtual crack closure technique. Significant findings are found for precise materials characterisation using the MMELS test. A MMELS test rig is also designed and built. Different specimens of essentially unidirectional carbon/epoxy laminates are tested for the experimental characterisation of fatigue delamination under varying mode mix. A fractographic analysis is also conducted in some of the delaminated fracture surfaces. The experimental results are compared to the predictions of a proposed model for the fatigue propagation of interlaminar cracks.
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Charalambous, Georgia. "The effect of temperature on mixed-mode fracture toughness and fatigue delamination growth of fibre-reinforced composites." Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.682234.
Повний текст джерелаАнотація:
A significant part of composite structures in service are made of Fibre-Reinforced Polymers (FRPs). These are exposed to complex static and time-dependent loading, often in aggressive environments. In pristine condition, FRPs can have very high fatigue strength. However FRP components that have undergone prior damage (e.g. impact) are particularly susceptible to fatigue and fail primarily under delamination. The latter is the progressive disbond of contiguous plies driven by a combination of fracture modes. As preventing delamination initiation is somewhat unavoidable, a damage tolerance (DT) design philosophy is commonly adopted for mitigating the impact of delamination on the long-term durability of composite structural elements. In the literature, characterisation data for Fatigue Delamination Growth (FDG) in composite materials is sparse, particularly for mixed-mode regimes. This is partially due to the fact that there are no standardised methodologies for performing fatigue characterisation tests on composites. Since most of primary composite structures are exposed to variable temperature conditions, it is vital that the characterisation tests are carried-out in representative environments. However, practical challenges in testing make the investigation of environmentally assisted fatigue extremely difficult. From limited references in literature, there is no general consensus whether an increasing temperature delays or accelerates FDG. This study proposes a novel methodology for mixed-mode FDG characterisation under variable temperature conditions. A new four-point bending test fixture, which can also be installed into an environmental chamber, has been designed and built. Asymmetric Cut-Ply specimens have been employed to characterise the fracture toughness and FDG in a second-generation toughened carbon/epoxy, namely IM7/8552. Tests were performed at -50°C, Room Temperature (RT), 50°C and 80°C and a constant mode-mixity of 0.43 has been applied throughout the testing campaign. In Asymmetric cut-ply coupons, the mode mixity is controlled solely by the geometry of the specimen, i.e. the ratio of number of cut plies to continuous layers in the specimens. The proposed testing protocol has been validated against other mixed-mode testing techniques, using RT data. It is demonstrated that the testing method proposed here does not require a compliance calibration and yield 'results in agreement with the widely employed mixed-mode bending coupons. Quasi-static results highlight that at 80°C the fracture toughness increases with respect to that at RT. On the contrary, an increase in temperature accelerates the FDG at relatively low severities, i.e. in the near-threshold regime. A semi-empirical equation has been introduced in order to represent the effect of temperature on the Fatigue Delamination Growth Rate (FDGR) as a function of the Strain Energy Release Rate (SERR) at the crack tip. The equation is in the Power law form and it comprises temperature-dependent pre-factor and exponent. The semi-empirical equation has been implemented in a cohesive zone formulation for finite element analysis (FEA) purposes. The results point out the importance of considering representative temperature conditions in obtaining fundamental material properties for DT design. Experimental and numerical investigations have been also performed to study the influence of temperature on delamination growth at a sub-element scale, by employing tapered specimens.
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Jorcin, Jean-Baptiste Pébère Nadine. "Spectroscopie d'impédance électrochimique locale caracterisation de la delamination des peintures et de la corrosion des alliages Al-Cu /." Toulouse : INP Toulouse, 2007. http://ethesis.inp-toulouse.fr/archive/00000494.
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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.
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Careddu, Matteo. "Characterization of mode I disbonding behaviour of carbon/epoxy composites bonded with two adhesion qualities." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/6355/.
Повний текст джерелаАнотація:
La mancanza di procedure standard per la verifica delle strutture in compositi, al contrario dei materiali metallici, porta all’esigenza di una continua ricerca nel settore, al fine di ottenere risultati significativi che culminino in una standardizzazione delle procedure.
In tale contesto si colloca la ricerca svolta per la stesura del presente elaborato, condotta presso il laboratorio DASML del TU Delft, nei Paesi Bassi. Il materiale studiato è un prepreg (preimpregnated) costituito da fibre di carbonio (M30SC) e matrice epossidica (DT120) con la particolare configurazione [0°/90°/±45°/±45°/90°/0°]. L’adesivo utilizzato per l’incollaggio è di tipo epossidico (FM94K). Il materiale è stato assemblato in laboratorio in modo da ottenere i provini da testare, di tipo DCB, ENF e CCP. Due differenti qualità dello stesso materiale sono state ottenute, una buona ottenuta seguendo le istruzione del produttore, ed una povera ottenuta modificando il processo produttivo suggerito, che risulta in un incollaggio di qualità nettamente inferiore rispetto al primo tipo di materiale.
Lo scopo era quello di studiare i comportamenti di entrambe le qualità sotto due diversi modi di carico, modo I o opening mode e modo II o shear mode, entrambi attraverso test quasi-statici e a fatica, così da ottenere risultati comparabili tra di essi che permettano in futuro di identificare se si dispone di un materiale di buona qualità prima di procedere con il progetto dell’intera struttura.
L’approccio scelto per lo studio dello sviluppo della delaminazione è un adattamento della teoria della Meccanica della Frattura Lineare Elastica (LEFM)
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Satthumnuwong, Purimpat. "Approche expérimentale et numérique de la rupture des assemblages collés de composites stratifiés." Thesis, Dijon, 2011. http://www.theses.fr/2011DIJOS052/document.
Повний текст джерелаАнотація:
L’assemblage des matériaux composites par collage présente des avantages incontestés par rapport à d’autres méthodes telles que le boulonnage ou le rivetage. Cependant, la principale difficulté que rencontrent les concepteurs est celle de la prévision du niveau et du mode de rupture de ces collages. Dans le cas des composites stratifiés, un des facteurs influents sur le comportement des joints collés est la séquence d'empilement, mais les travaux présentés dans la littérature ne séparent pas les effets globaux (modification des rigidités de membrane et de flexion) et les effets locaux (orientation des plis au contact de la colle). La présente étude s'intéresse à la caractérisation de ces effets dans le cas de joints de type simple recouvrement de stratifiés carbone/epoxy. Pour isoler les effets locaux, des séquences d'empilement spécifiques quasi isotropes quasi homogènes sont utilisées. A propriétés de raideur globale égales, des différences de résistance de plus de 30% sont observées selon les séquences considérées. Les essais réalisés avec un stratifié symétrique anisotrope en flexion montrent également que la raideur en flexion joue un rôle important dans le comportement des joints. Les modèles analytiques utilisés prédisent les effets globaux avec une bonne précision mais sont inappropriés lorsque des phénomènes locaux se produisent. Une approche par éléments finis permet de prendre en compte ces phénomènes, en modélisant explicitement les plis au contact de la colle et en rendant possible le décollement interlaminaire de ces plis à l'aide d'un modèle de zone cohésive. Cette modélisation est mise en œuvre pour réaliser une étude paramétrique de la géométrie du joint et pour produire une enveloppe de rupture en fonction de la direction de sollicitationAdhesive bonding of composite materials has undeniable advantages over other methods such as bolting or riveting. However, one of the difficulties encountered by designers is the prediction of the failure level and failure mode of these adhesively bonded assemblies. In the case of composite laminates, one of the factors acting on the bonded joint behaviour is the stacking sequence, but works presented in the literature do not separate global effects (membrane and bending stiffness modification) and local effect (ply orientation near the adhesive layer). This study deals with the characterization of such effects in the case of single lap joints of carbon/epoxy laminates. In order to isolate the local effects, specific quasi isotropic quasi homogeneous stacking sequences are used. When stiffness properties are maintained constant, strength variations of more than 30 % are observed. Tests performed with a symmetric laminate with bending anisotropy show that the bending stiffness plays also an important role in the joint behaviour. Closed form models are able to predict global effects with a good accuracy but are inappropriate when local effects occur. The use of finite element models can account for these phenomena, by explicitly modelling the laminate plies near the adhesive layer and introducing delamination between these plies with a cohesive zone model. This model is used to perform a parametric study of the joint geometry and to produce a failure envelope according to the orientation of the loading
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Vandellos, Thomas. "Développement d’une stratégie de modélisation du délaminage dans les structures composites stratifiées." Thesis, Bordeaux 1, 2011. http://www.theses.fr/2011BOR14380/document.
Повний текст джерелаАнотація:
Les composites stratifiés de plis unidirectionnels en carbone/époxy sont fortement utilisés pour alléger les structures aéronautiques tout en conservant de bonnes propriétés structurales. Toutefois, les avantages de ce type de matériau ne sont pas encore pleinement exploités de par le manque de confiance accordée aux modèles de prévision de l’endommagement, dont notamment ceux concernant le délaminage. C’est pourquoi l’objectif de cette thèse était de développer une stratégie de modélisation du délaminage adaptée aux structures composites stratifiées. Cette stratégie s’est appuyée sur le développement d’un modèle de zone cohésive prenant en compte les ingrédients nécessaires à la bonne description de l’amorçage et de la propagation de la fissure : (i) un critère d’amorçage avec un renforcement en compression/cisaillement hors-plan, (ii) une loi de propagation décrivant l’évolution de la ténacité en fonction de la mixité de mode et (iii) la prise en compte du couplage inter/intralaminaire. Pour identifier ce nouveau modèle, une procédure d’identification efficace, s’appuyant sur un essai de traction sur plaque rainurée, a été mise en place. Cette procédure d’identification a permis de démontrer que la ténacité semble indépendante (i) de l’orientation des plis adjacents à l’interface et (ii) de l’empilement étudié. De même, pour décrire l’évolution de la ténacité, une nouvelle loi de propagation adaptée au matériau carbone/époxy a été proposée. Pour finir, la stratégie de modélisation, complétée par une stratégie de calcul, a été appliquée sur différents cas structuraux pour mettre en avant ses apports et ses premières limitesThe carbon/epoxy laminated composites of unidirectional plies are strongly used in order to reduce the weight of aeronautical structures while at the same time proposing good structural properties. However, the advantages of this kind of material are not fully exploited due to the lack of confidence in damage models, like ones concerning delamination. Then, the purpose of this work was the development of a strategy to model delamination in laminated composite structures. This strategy was based on the development of a cohesive zone model taking into account the ingredients necessary to the well description of the onset of delamination and the crack growth: (i) an onset criterion with an out-of-plan compression/shearing reinforcement, (ii) a propagation law describing the evolution of the fracture toughness as a function of mixed mode ratio and (iii) the inter/intralaminar coupling. To identify this new model, an efficient identification procedure, basing on a tensile test on notched specimen, has been proposed. This identification procedure has demonstrated that the fracture toughness seems to be independent of (i) the orientation of plies closed to the interface and (ii) the stacking sequence. Furthermore, to describe the evolution of the fracture toughness, a new propagation law adapted to carbon/epoxy material has been proposed. Finally, the strategy to model delamination, completed by a calculation strategy, has been applied on several structural cases to prove its contributions and its first limitations
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Motamedi, Damoon. "Nonlinear XFEM modeling of delamination in fiber reinforced composites considering uncertain fracture properties and effect of fiber bridging." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/44630.
Повний текст джерелаАнотація:
Initiation and propagation of a crack in composite materials can affect their global mechanical properties severely. From a numerical modeling perspective, most conventional macro-level methods reported for composite laminates are based on the assumption that a Representative Volume Element (RVE) of the material is periodically repeated over the entire sample. However, a considerable amount of spatial non-uniformity in material and geometrical parameters can exist in both unidirectional (UD) and woven fabric composites. The scattered distribution of fibers, fibers penetration between composite layers, voids within the matrix, human errors during sample preparation, and imperfect thickness distribution can be among the most common sources of such non-uniformity. In turn, these non-uniformities can make the numerical simulation of composites under the assumption of a periodic RVE unreliable, and thereby, the stochastic modeling of effective material properties becomes essential for a more precise assessment of composites’ mechanical behaviour.
In the present work, a new three-dimensional (3D) stochastic extended finite element method (XFEM) is proposed and implemented to model the delamination surface in composite samples by integrating the capabilities of the finite element method (FEM) commercial software (ABAQUS) into a user-defined FORTRAN code and MATLAB package. XFEM is known to offer significant advantages over conventional FEM by enabling optimal convergence rates in the presence of pronounced discontinuities/singularities such as cracks. The effect of nonlinear modeling parameters such as cohesive zone length, penalty stiffness factor and large deformation are also considered in the proposed approach to add to the accuracy of simulations. The XFEM model is first tested and validated against previously reported data in the literature. Next, a statistical distribution is sought from data non-repeatability during a set of double cantilever beam (DCB) and end-notched flexure (ENF) tests conducted on Poly (phenylene Sulfide) PPS/Glass thermoplastic composite samples. Results from the experiments and XFEM are compared and demonstrate the capability of the new numerical approach in capturing non-repeatable material response, often seen during the fracture testing of UD composites to characterize their mode I and mode II fracture properties.
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Durix, Lucas. "On the design of a new test method to characterize the delamination of thermosetting polymer under thermal mixed mode loading." Valenciennes, 2010. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/bd1267ad-5bd0-4890-b878-4443d6031356.
Повний текст джерелаАнотація:
Crack propagation in integrated circuits is a major failure cause of electronic components. In the automotive branch, a highly competitive market, failure is not allowed and reliability can make the difference to gain market shares. For this reason, many efforts and researches were conducted in this field during the last decades. In automotive applications, electronic parts have to challenge heavy life conditions, such as vibrations, wide temperature variations, humidity, oil aggressions, etc. In particular, cyclic thermal variations bring incompatible thermal strains along materials interfaces, and leads to interfacial crack propagation (delamination) between copper leadframes used as conductor and polymeric molding compound used to encapsulate devices. Delamination causes then the cracking of the encapsulant and finally the failure of the electronic component. Predicting the interfacial delamination in electronic packages is key to enhance reliability. As detailed in this work, delamination strength of interfaces involving molding compounds depends on many influences. Its characterization required numerous kinds of test, involving heavy costs and long testing periods. In this work, a low cost test setup is proposed to characterize the molding compound/copper interface regarding the different influences already mentioned. The delamination toughness of the copper/polymeric molding compound is characterized with a classic molding compound of the market with respect to the mode mixity (ratio of loading mode II/mode I), temperature, and load rate. Moisture effect is also investigated. The critical energy release rate for the investigated interface is estimated using the classical numerical-experimental correlation used in fracture mechanics. For the investigated material pair, the interfacial toughness exhibits viscoelastic properties and an own time-temperature superposition principle. Obtained interfacial parameters are defined in Abaqus. The latter is widely benchmarked for problems involving delamination and viscoelastic materials. In the case of cracking between two dissimilar materials, the analytical solution of the stress and strain fields at delamination front depends on a characterisctic reference length. The choice of this refence length, conditioning the the mode mixity estimation, is also addressed. The reference length is experimentally characterized for the different investigated temperatureLa propagation des fissures dans les circuits intégrés est l’une des causes principales de défaillance de ces circuits. Sur le marché automobile fortement concurrentiel, les défaillances ne sont pas permises, et la fiabilité demeure un critère pouvant faire la différence pour gagner des parts de marché. Pour cette raison, de nombreux efforts et recherches ont vu le jour durant les dernières décennies. Dans le cas des applications liées à l’automobile, les composants électroniques sont confrontés à de lourdes contraintes, telles que vibrations, importants changements de température, projections d’eau ou de dérivés pétroliers, etc. Les variations de température génèrent en particulier des déformations thermiques souvent incompatibles au niveau des interfaces entre matériaux, ce qui provoque dans les circuits intégrés le décollement des conducteurs cuivrés de l’enrobage polymérique utilisé pour la protection du composant (délaminage). Le délaminage aboutit par la suite à la fissuration propre de l’encapsulant puis à la défaillance du composant. L’amélioration de la fiabilité des composants requiert par conséquent de pouvoir prédire le délaminage aux interfaces cuivre/matériau d’encapsulation. Tel que démontré dans ces travaux, la ténacité interfaciale dépend de plusieurs influences. Une caractérisation complète requiert de nombreux tests, mettant en jeu différents types d’appareillages et d’éprouvettes, ce qui génère de nombreux coûts et un temps d’exécution important. Une méthode de test à faible coût est proposée dans ce document pour la caractérisation des interfaces cuivre/encapsulant dans les différentes conditions évoquées. Cette méthode a été mise en pratique avec succès pour caractériser un matériau d’encapsulation classiquement utilisé dans l’industrie automobile. L’influence de la mixité des modes de rupture, de la température, de la vitesse de chargement ainsi que de l’humidité ont été étudiées. Les techniques habituelles en mécanique de la rupture de corrélation résultats expérimentaux-simulations ont été utilisées pour déterminer le taux de restitution d’énergie critique dans les différents cas. La ténacité de l’interface cuivre/matériau d’encapsulation s’est révélée suivre un comportement viscoélastique, incluant des propriétés propres de superposition temps-température. Les paramètres interfaciaux obtenus ont finalement été définis dans l’outil de simulation MEF Abaqus. Ce dernier a d’ailleurs été l’objet de nombreuses vérifications en ce qui concerne la simulation des problèmes de délaminage des matériaux viscoélastiques. Dans le cas de la fissuration entre deux matériaux hétérogènes, la description analytique des champs de contrainte et de déformation en pointe de fissure fait appel à une longueur de référence. Le choix de cette longueur de référence est abordé dans ce document. Cette dernière est déterminée expérimentalement pour les différentes températures testées
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Mahmood, Ali Hasan. "Optimising the lamination properties of textile composites." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/optimising-the-lamination-properties-of-textile-composites(6a215f92-e200-4e30-8b72-7f599a5e95f3).html.
Повний текст джерелаАнотація:
Woven glass composites have been used for many years in commercial applications due to their light weight, competitive price and good engineering properties. Absorption of energy by laminated composite material results in damage in various forms, the most common of which is delamination. Inter-laminar fracture causes the layers of composite to separate, resulting in a reduction in stiffness and strength of the composite structure, matrix cracking and in some cases fibre breakage takes place. The aim of this project was to improve the inter-laminar bond strength between woven glass fabric and resin. Air jet texturing was selected to provide a small amount of bulk to the glass yarn. The purpose was to provide more surface contact between the fibres and resin and also to increase the adhesion between the neighbouring layers. These were expected to enhance the resistance to delamination in the woven glass composites.Glass yarns were textured by a Stähle air jet texturing machine. Core-and-effect yarn was produced instead of a simple air textured yarn. Hand loom and vacuum bagging techniques were used for making the fabric and composite panels from both textured and non-textured yarns. Density and fibre volume content were established for physical characterisation. Breaking strength (tenacity) of the yarns and tensile, flexure, inter-laminar shear strength (ILSS) and fracture toughness (mode 1) properties of the composites were determined. Projection microscopy and SEM imaging techniques were used to assess the fractured surfaces of the composite specimens. The yarn tenacity and the tensile properties of the composites were significantly reduced after the texturing process, whereas flexure properties were unchanged. However, significant improvement was observed in the ILSS and fracture toughness of the composites after the texturing process. It was also observed that the composites made from the fabrics with textured yarns in only the weft direction are the most advantageous as they maintained the tensile and flexure properties but have significantly higher inter-laminar shear strength.
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Simlissi, Essossinam. "Modeling of delamination and interface strength in printed circuit boards." Electronic Thesis or Diss., Université de Lorraine, 2019. http://www.theses.fr/2019LORR0326.
Повний текст джерелаАнотація:
Dans cette thèse, la résistance des interfaces dans les circuits imprimés (PCB) est étudiée. Un PCB est un élément passif permettant d’interconnecter des composants électroniques soudés sur les couches externes. Un PCB est un assemblage multicouche, multi-matériaux fait de composites tissés et de feuillards de cuivre. Le cuivre joue un rôle majeur dans les circuits imprimés car il est le support de l’information électrique. Pendant son cycle de vie, le PCB subit un grand nombre de cycles thermiques pouvant entraîner la rupture des fûts de cuivre. Par ailleurs, l’utilisation de certaines combinaisons de matériaux peut entraîner du délaminage ce qui limite la durée de vie du PCB. La mesure de la résistance de l'interface entre la couche de cuivre et le substrat composite est alors très importante. Pour l’industrie du PCB, le test de pelage reste la méthode courante pour mesurer les propriétés de l’interface entre deux matériaux. Cette thèse comporte trois parties. Premièrement des tests de pelage sont réalisés pour différents angles de pelage et à température ambiante. Les échantillons étudiés et testés sont constitués d'un feuillard de cuivre assemblé à un substrat composite tissé. Lors de l’essai, la décohésion au niveau de l’interface est bien observée. Par ailleurs, la force de pelage et le rayon de courbure du film de cuivre sont mesurés en régime stationnaire. En parallèle, une analyse théorique du test de pelage est conduite pour des matériaux élasto-plastiques. Le chemin de déformation du film de cuivre lors du test de pelage est assimilé à un mode de flexion – flexion inverse. Nous proposons une analyse théorique de ce trajet de chargement pour un matériau élasto-plastique obéissant à une loi d’écrouissage de type Voce. Enfin, des simulations de pelage par éléments finis sont effectuées pour différents angles. Le comportement du cuivre identifié à l’aide d’un essai de traction est considéré comme élasto-plastique. Une loi d’écrouissage de type Voce est utilisée. Le substrat est supposé élastique orthotrope. L’interface est modélisée par des éléments cohésifs en utilisant une loi de type traction séparation bilinéaire. Les résultats des simulations (EF) sont comparés aux données expérimentales de la thèse. On observe un bon accord au niveau à la fois de la force de pelage mais aussi du rayon de courbure. Au final, ce travail de thèse permet de proposer un dialogue essai / simulations numériques pour définir précisément l’énergie de rupture de l’interfaceIn this thesis, the identification of the interface strength in Printed Circuit Boards (PCBs) is assessed. A PCB is a passive component, which allows to interconnect electronic components soldered on the outer layers in order to realize a complex electronic system. It is a multiple layer assembly made of woven composite and copper foil. Copper plays a major role in Printed Circuit Boards (PCBs) since it is the carrier of the electrical information. During its lifetime, the PCB undergoes a large number of thermal cycles, which can lead to the failure of copper path. In addition, it has been detected that the use of certain combinations of based materials leads to delamination, which limits the PCB service-life. The measurement of interface strength between copper layer and composite substrate is critical and the usual method for measuring the interface properties in PCB industry is the peel test. The PhD is divided in three main parts. In the first experimental part, peel tests at various peel angles are performed using specimens, which consist of a copper foil bonded on a woven composite substrate. Interface separation between the copper film and the composite substrate is observed. During the test, the peel force per unit width and the copper film radius at steady state are measured. Next, a theoretical analysis of the peel test for an elastic-plastic material is proposed. A precise definition of the work done by bending plasticity for a particular class of material response is established. Indeed, we have extended previous works of the literature by considering that the plastic hardening behavior of the film is modeled by a Voce type law. Finally, finite element (FE) simulations of peeling are conducted at various peel angles by considering that the copper material response is elastic-plastic. The isotropic hardening is identified based on uni-axial tensile tests. The woven composite is assumed to remain elastic with an orthotropic response. The interface is modeled by cohesive elements using a bilinear traction separation law. FE results are compared to experimental data. It is shown that the peel force and the film curvature are predicted accurately, for a large range of peel angles. 125 Therefore, from the dialog between finite element calculations and experiments, the interface fracture energy is obtained