Dissertations / Theses: 'Delamination mechanism'

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Blandon, Omar Ali. "Mechanism of Delamination of Electrospun Adhesive Nanofibers." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1446477512.

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Yamanaka, Tadayoshi. "Delamination modelling and toughening mechanism of a woven fabric composite." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104701.

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Efficient and accurate numerical simulation methods for the damage tolerance analysis and fatigue life prediction of fibre reinforced polymers are in high demand in industry. Problems arise in the development of such a simulation method due to the limitations from numerical methods, i.e., delamination modelling, and understanding of damage mechanism of woven fabric composites. In order to provide effective and accurate delamination modelling, a new crack modelling method by using the finite element method is proposed in this study. The proposed method does not require additional degrees-of-freedom in order to model newly created crack/delamination surfaces. The accuracy of delamination growth simulation by the proposed method and that of a commercial FEA package are in good agreement. The damage mechanisms of five harness satin weave fabric composite is studied by creating a multiscale finite element model of a double cantilever beam specimen. The weft and warp yarns, where the gaps are filled with matrix, are individually modeled. Cohesive zone model elements are pre-located within the matrix and interfaces of matrix-yarns and weft-yarns and warp yarns. These meso-scale parts are bonded with homogeneous parts that are used to model regions where no damage is expected. This constitutes a multiscale model of a DCB specimen. The simulation results are in good agreement with the lower bound of experimental results. The toughening mechanism contributed from the weave structure was revealed. This study contributes to knowledge by introducing crack modelling methods and by providing more information in order to understand damage mechanisms of 5HS weave fabric composite laminates during delamination growth.
Les méthodes de simulation numériques efficaces et exactes pour l'analyse de l'endommagement et la prédiction de vie en fatigue des matériaux composites sont essentielles pour l'industrie. Les problèmes surviennent dans le développement d'une telle méthode de simulation en raison des restrictions des méthodes numériques, c'est-à-dire, modélisation de la délamination et compréhension des mécanismes de rupture de composites à base de fibres tissées.Pour developer un modèle de délamination efficace et précis, une nouvelle méthode est proposée dans cette étude en utilisant la method des éléments finis. La méthode proposée n'exige pas de degrés-de-liberté supplémentaires pour créer de nouvelles sufaces de fissures/ délaminations. Le résultat de simulation de délamination par la méthode proposée est comparé avec un logiciel d'éléments finis commercial, et les résultats se comparent bien.Les mécanismes d'endommagement d'un composite tissé typique "five-harness satin" sont le sujet d'une étude. Ceci est fait en créant un modèle d'éléments finis "méso-échelle" en utilisant l'exemple d'un spécimen d'essais Mode 1 (spécimen DCB). Le tissu est modélisé avec les trajectoires exactes des fibres dans les deux directions, et les espaces entre les fibres sont remplis de la matrice. Des éléments cohésifs sont insérés entre la matrice et les interfaces des fibres. Les composants méso-échelles sont joints avec des parties homogènes qui sont utilisées pour modéliser des régions où aucun endommagement n'est prévu. La combinaison des ces parties constitue un modèle multiéchelle d'un spécimen DCB. Les résultats de simulation d'un essai sont en accord avec les résultats expérimentaux, du côté conservateur. Le mécanisme renforçant des ultant du type de tissage a été démontré.Cette étude contribue à la science en présentant de nouvelles méthodes pour modéliser les fissures et pour comprendre les mécanismes d'endommagement des composites tissés pendant la croissance des délaminations.

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Tran, Tony D. "An Investigation of Initially Delaminated Composite Sandwich with Delamination Arrest Mechanism under Buckling Loading." DigitalCommons@CalPoly, 2010. https://digitalcommons.calpoly.edu/theses/428.

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This thesis involves the development of a fiberglass-foam composite sandwich structure with the introduction of delamination arrestment keys; therefore, a study of an initially delaminated composite sandwich structure was the experimental analysis on multiple configurations in how the arrestment keys are placed. The first part of this thesis research was to the experimental design and manufacturing of the composite sandwich plates. These plates were later cut down to the specific test dimensions and manufacturing processes for the composite sandwich plates and test specimens were created. The composite sandwich plates were manufactured using a vacuum resin infusion process. The dimensions of the composite layup are 14 inches in length with a width of 10.75 inches. The width size has margin to account for machining. The actual dimensions of the test specimen after it is prepared are 14 inches by 0.75 inches. The test anvil length is 11 inches and is used to perform tests to determine mechanical characteristics of the structures under buckling loading. These plates provide approximately 9 to 13 specimens per each case. All the test specimens have 4 plies of 18 oz fiberglass woven roving fabric from Jamestown Distributors, a LAST-A-FOAM FR-6710 foam core, and 5 to 1 ratio of West Systems 105/206 epoxy. Also, a non-porous material was integrated into the structure to create an initial delamination in some of the case studies. The integration of the delamination arrestment keys involve milling the foam core to provide the necessary grooves for key placements before the structure is vacuumed and epoxy is flowed. The arrestment keys are made of unidirectional fiberglass strand and the West Systems 105/206 epoxy using a wet layup process. In addition, fiberglass woven roving specimens were created to see the material characteristics under compression and tensile loading. The same is created to determine the material properties of the foam core, wood boundary core, and arrestment keys under compression loading. The second part to this thesis investigation is the experimental testing of the test specimens with all different variables considered. Those variables includes determining the final solid cure duration of the fiberglass skin, the geometric lengths between pure compression and pure buckling, behaviors of different initial delamination size, effects of continuous and discontinuous arrestment keys parallel and perpendicular to the in-plane loading, and material properties. The final solid cure duration differ from what the manufacturer gave on their epoxy. This experiment testing followed ASTM D-3039 standard to see the differences in elastic modulus over duration of 15 days. The resulting data shows that the test specimen fully cures after 13 to 14 days. The test specimens in search of the geometric buckling length for this investigation did not follow ASTM C-364 standard in full, but follows a variation of the ASTM C-364 standard in order to support buckling loading condition and the limited accessibility of the test equipments. Instead, the modifications are found with a different test jig design and test specimen configuration. The test jig was created to provide a pinned condition with a 0.25 inch diameter. The test specimen is laid up with a foam and wood cores. Two wood cores are laid at each edge of the foam core to increase loading capacity and holes are drilled through the wood cores to create a pinned-pinned case for the optimum buckling condition. The results detailing the geometric buckling show that after 9 inches anvil length there is no compression; only buckling occurs with a cross-sectional dimension of 0.75 inch by 0.575 inch. The 11 inch foam length was chosen for convenience of machining. This modified setup was also used for testing the different configuration with the embedded arrestment keys. The multiple different configurations completed for these test specimens under unstable loading, the experiment results show that a continuous arrestment key embedded significantly improve the loading capacity over a perfectly sound non-delaminated specimen and maintain the majority of loading capacity even with an introduced delamination. The embedded continuous key also provided a higher horizontal displacement capability before fracture in comparison to the initially delaminated test specimens. As for the test specimens used to determine the material characteristics, ASTM D-3410 and modified ASTM C-364 standards were followed. The test specimens had a fiber volume fraction of approximately 0.60, which details the brittle failure under tensile and compression loading. The results also show that the fibrous fiberglass test specimens have a higher ultimate strength in compression or buckling then in tension. All of the experimental testing was completed in the Aerospace Engineering Structural/Composite Lab at California Polytechnic State University at San Luis Obispo, California. Therefore, an introduction of a continuous arrestment key parallel to the in-plane loading and embedded into the composite sandwich structure provided a significant increase in loading and buckling capabilities in comparison to the control test specimens with and without an initial delamination and no embedded key. The continuous key placed parallel to the load vector increased the structural strength with an increase of 126% from a 1-inch delaminated structures and only an 11% drop from non-delaminated structures. That is, 1-inch and 2-inch delaminated structures showed a 61% drop and 81% drop from non-delaminated structures. Some configurations have reduced or arrested of the delaminated region.

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Whitcomb, J. D. "Instability-related delamination growth of embedded and edge delaminations." Diss., Virginia Polytechnic Institute and State University, 1988. http://hdl.handle.net/10919/77755.

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Compressive loads can cause local buckling in composite laminates that have a near-surface delamination. This buckling causes load redistribution and secondary loads, which in turn cause interlaminer stresses and delamination growth. The goal of this research effort was to enhance the understanding of this instability-related delamination growth in laminates containing either an embedded or an edge delamination. There were three primary tasks: 1) development of a geometrically nonlinear finite element analysis named NONLIN3D; 2) performance of a parametric analytical study to determine the effects of strain, delamination shape, and delamination size on the distribution of the strain energy release rate components along the delamination front; and 3) performance of a combined experimental and analytical study of instability-related delamination growth (IRDG). Two material systems (AS4/PEEK and IM7/8551-7) and two stacking sequences (0/90/90/0)₆ and (90/0/0/90)₆ were examined. The laminates were fabricated with Kapton inserts between the fourth and fifth plies from the top surface to give an initial delamination. The analysis predicted a large variation of G_I and G_II along the delamination front. The G_III component was always small. The location of maximum G_I and G_II depended on the delamination shape and applied strain. In general, the strain-energy release rates were small except in a small region. Hence, delamination growth was expected to occur over only a small portion of the delamination front. Experiments corroborated this prediction. The laminate stacking sequence had a large effect on the shape of the deformed region, the direction of delamination growth, and the strain at which delamination growth occurred. These effects were predicted by the analysis. The G_I component appeared to govern initial delamination growth in the IM7/8551-7 laminates. Matrix ply cracking generally accompanied delamination growth. In some cases fiber micro-buckling also occurred shortly after delamination growth occurred.
Ph. D.

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Xia, Qingxi 1973. "Mechanics of inelastic deformation and delamination in paperboard." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/8334.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2002.
Includes bibliographical references (p. 233-236).
Paperboard is one of the most widely used materials. The inelastic deformation of paperboard plays a crucial role during many manufacturing processes (e.g., the converting process whereby paperboard is converted into a product such as a milk carton by punching and subsequent folding) and during in-service applications. There is a scarcity of constitutive models describing inelastic behavior of paperboard under complex loading, despite the paper industry's great need of analytical tools to aid the design and manufacturing of better paperboard products. In this thesis, two constitutive models are developed to model the highly anisotropic, elastic-plastic behavior of paperboard/paper: (1) A three-dimensional elastic-plastic interface constitutive model is developed to model the out-of-plane delamination behavior of paperboard. The onset of interface separation is controlled by a limit surface in the normal-shear traction space. The limit surface is taken to shrink with a monotonically-increasing scalar internal variable reflecting damage associated with the history of inelastic relative interface displacement. (2) A three-dimensional, anisotropic continuum constitutive model is developed to model the in-plane elastic-plastic deformation of paper and paperboard. The proposed initial yield surface is directly constructed from the yield strengths measured in various loading directions and the corresponding ratios of plastic strain components. An associated flow rule is used to model the plastic flow of the material. Anisotropic strain-hardening of yield strengths is introduced to model the evolution of the yield surface with inelastic strain.
(cont.) The two constitutive models are implemented into finite element software to enable the simulation of paperboard mechanical behavior under complex, finite deformation. The models are shown to be capable of accurately capturing both the out-of-plane delamination (via the interface model) and the anisotropic in-plane elastic-plastic (via the continuum in-plane model) behavior of paperboard under complex loading. The two models are combined to simulate the mechanics of a converting process (creasing and subsequent folding) of paperboard. The simulations agree well with corresponding experimental observations. In particular, the underlying mechanisms of damage and delamination development during creasing and subsequent folding are predicted well; the macroscopic response of the bending moment vs. bending angle also agrees with experimental data. This research provides physically based three-dimensional material models of the anisotropic, elastic-plastic deformation of paperboard that enable the computational design of paperboard process and product design.
by Qingxi Steve Xia.
Ph.D.

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Johansson-Näslund, Markus. "Numerical analysis of paperboard delamination using cohesive elements." Thesis, KTH, Hållfasthetslära, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-277779.

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A new test method for measuring the shear strength associated with mode III delamination of paperboard is studied with the purpose of reducing the size of the test configuration. The method, which uses a split cantilever beam (SCB) specimen, measures the shear strength indirectly through the fracture resistance. The methodology is based on the double cantilever beam (DCB) specimen, used for measuring the normal delamination strength of paperboard. The study is based on finite element analyses, where cohesive elements are implemented for predicting the fracture response. An experimental evaluation of the test method was carried out in a pre-study conducted between Karlstad, Skövde and Lund University together with Tetra Pak. The experiments considered both the SCB-specimen and the standardised DCB-specimen, and for determination of the fracture behaviour the cohesive law presented by Tryding & Ristinmaa (2017) were considered. The result obtained from the experiments is used as a basis for evaluating the analyses. To model the fracture development, the relation presented by Tryding & Ristinmaa (2017) is implemented in the commercial finite element software Abaqus through a user-specified element. From the analyses of the DCB-specimen it is shown that through implementation of a specified cohesive law, it is possible to simulate mode I fracture development of paperboard in an accurate manner. The results for the DCB analyses correlate well with the experimental results. The result for the SCBspecimen shows a deviating behaviour from the experimental result by underestimating the shear strength. It is noted that the specimen is subjected to notable deformations in both the first shear direction and the normal direction, preventing pure shear loading from being obtained. Based on the analyses, it is indicated that the current test configuration does not obtain pure shear separation in mode III, and thereby underestimates the actual shear strength of the paperboard. It is also shown that reducing the specimen length with 400 mm has no significant impact on the properties related to the cohesive law. By altering the initial crack length, it is possible to further reduce the length of the specimen. However, to prevent development of unstable fracture, the length of the paperboard should exceed 300 mm. Alternating the crack length and the width of the paperboard also seems to contribute to lower displacements in the normal direction and provides a better fit with the experiments. Tryding, J. & Ristinmaa, M. (2017). Normalization of cohesive laws for quasi-brittle materials. Engineering Fracture Mechanics, 178, 333-345. doi:10.1016/j.engfracmech.2017.03.020
En ny testmetod för att mäta skjuvstyrkan för modus III delaminering av kartong studeras i syftet att reducera testutrustningens storlek. Testmetoden, som använder sig av en delad konsolbalk (SCB), mäter skjuvstyrkan indirekt genom brottresistansen. Metodiken är baserad på det standardiserad konsolbalks testet DCB, var två balkar är sammankopplade och som används för att mäta delaminering styrkan i kartongens normala riktning. Studien baseras på analyser med finita element, var kohesiva element implementeras för att prediktera brottbeteendet. En experimentell utvärdering av testmetoden genomfördes i en förstudie mellan Karlstads, Skövdes och Lunds universitet tillsammans med Tetra Pak. Experimenten gjordes både för DCB- och SCB-testet, och för att utvärdera brottbeteendet användes de kohesiva lagarna som presenterats av Tryding & Ristinmaa (2017). De experimentella resultaten används som bas vid utvärdering av analyserna. För att modellera spricktillväxten implementeras de kohesiva lagarna i det kommersiella FEM programmet Abaqus genom ett användar specificerat element (UEL). Från analyserna av DCB-testet visas det att det är möjligt att simulera modus I sprickbildning i kartong genom implementering av en specifik kohesive lag. Simuleringarna av DCB-testet stämmer väl överens med de experimentella resultaten. Resultaten från SCB-analyserna visar däremot på ett avvikande beteende från experimenten genom att underskatta skjuvstyrkan. Det noteras i analyserna av SCB-testet att märkbara deformationer i både den första skjuvriktningen och normal riktningen uppkommer, vilket förhindrar att ren skjuvbelastning i modus III erhålls. Baserat på analysernas resultat indikeras det att den nuvarande konfiguration för SCB-testet inte ger ren skjuvbelastning i modus III och underskattar därför kartongens faktiska skjuvstyrka. Det visas också att en 400 mm reducering av SCB-geometrins längd inte har någon märkbar påverkan på de kohesiva egenskaperna. Genom att ändra den initiala spricklängden är det möjligt att ytterligare reducera SCBgeometrins längd. För att försäkra sig om att sprickas tillväxt förblir stabil bör däremot längden på kartongen överstiga 300 mm. Att minska den initiala spricklängden och bredden på kartongen verkar generellt bidra till lägre deformationer i normal riktningen och ett resultat som ligger närmare de experimentella. Tryding, J. & Ristinmaa, M. (2017). Normalization of cohesive laws for quasi-brittle materials. Engineering Fracture Mechanics, 178, 333-345. doi:10.1016/j.engfracmech.2017.03.020

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Dávila, Carlos G. "Delamination initiation in postbuckled dropped-ply laminates /." This resource online, 1991. http://scholar.lib.vt.edu/theses/available/etd-07282008-134842/.

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8

Wang, Bin. "Local delamination failure of thin material layers." Thesis, Loughborough University, 2017. https://dspace.lboro.ac.uk/2134/25128.

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Thin material layers have found various applications with various roles of functions, such as in fibre reinforced laminated composite materials, in integrated electronic circuits, in thermal barrier coating material system, and etc. Interface delamination is a major failure mode due to either residual stress or applied load, or both. Over the past several decades, extensive research works have been done on this subject; however, there are still uncertainties and unsolved problems. This thesis presents the new developed analytical studies on local delamination failure of thin material layers. Firstly, the analytical theories are developed for post-local buckling-driven delamination in bilayer composite beams. The total energy release rate (ERR) is obtained more accurately by including the axial strain energy contribution from the intact part of the beam and by developing a more accurate expression for the post-buckling mode shape. The total ERR is partitioned by using partition theories based on the Euler beam, Timoshenko beam and 2D-elasticity theories. By comparing with independent test results, it has been found that for macroscopic thin material layers the analytical partitions based on the Euler beam theory predicts the propagation behaviour very well and much better than the others. Secondly, a hypothesis is made that delamination can be driven by pockets of energy concentration (PECs) in the form of pockets of tensile stress and shear stress on and around the interface between a microscopic thin film and a thick substrate. Both straight-edged and circular-edged spallation are considered. The three mechanical models are established using mixed-mode partition theories based on classical plate theory, first-order shear-deformable plate theory and full 2D elasticity theory. Experimental results show that all three of the models predict the initiation of unstable growth and the size of spallation very well; however, only the 2D elasticity-based model predicts final kinking off well. Based on PECs theory, the room temperature spallation of α-alumina oxidation film is explained very well. This solved the problem which can not be explained by conventional buckling theory. Finally, the analytical models are also developed to predict the adhesion energy between multilayer graphene membranes and thick substrates. Experimental results show that the model based on 2D elasticity partition theory gives excellent predictions. It has been found that the sliding effect in multilayered graphene membranes leads to a decrease in adhesion toughness measurements when using the circular blister test.

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Dimant, Ron A. "Damage mechanics of composite laminates." Thesis, University of Cambridge, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338020.

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Huang, Haiying. "Single and multiple delamination behavior in composite plates." Diss., Georgia Institute of Technology, 1998. http://hdl.handle.net/1853/12541.

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Dávila, Carlos G. "Delamination initiation in postbuckled dropped-ply laminates." Diss., Virginia Tech, 1991. http://hdl.handle.net/10919/38915.

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12

劉英傑 and Yingjie Liu. "Damage characterization of multi-directional laminates with matrix cracks and delamination." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1996. http://hub.hku.hk/bib/B31235104.

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Liu, Ying-jie. "Damage characterization of multi-directional laminates with matrix cracks and delamination /." Hong Kong : University of Hong Kong, 1996. http://sunzi.lib.hku.hk/hkuto/record.jsp?B16504434.

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Chen, Zi Qi. "Delamination buckling of pressure-loaded laminated cylindrical shells and panels." Diss., Georgia Institute of Technology, 1987. http://hdl.handle.net/1853/21227.

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Zhang, Qiuting. "Mechanics and Functionality of Extreme Mechanical Instabilities through Buckling Driven Delamination." Diss., Temple University Libraries, 2019. http://cdm16002.contentdm.oclc.org/cdm/ref/collection/p245801coll10/id/587760.

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Mechanical Engineering
Ph.D.
Mechanical instabilities such as wrinkling and buckling-driven delamination in thin film-substrate systems have historically been considered as one of structural failure mechanisms, which should be avoided. The past decade has witnesssed rapid growth in harnessing such surface instabilities for a wide range of tunable surface related properties and functionalities, especially in soft materials on small scales. Compared to extensively studied wrinkling on soft substrates and localized buckling driven delamination on stiff substrates, the fundamental mechanics underpinning ordered buckle-delamination on soft substrate over large area and its guidance for potential implications in engineering innovation remain largely to be explored. This thesis aims to partially bridging such a knowledge gap. In this thesis, I exploit how to generate the controllable and globally periodic delaminated buckling patterns in thin films on highly prestrained elastomeric substrates, and then explore the fundamental mechanics of this spontaneous extreme buckling driven periodic delamination, as well as its implications in design of extremely stretchable electronics and interfacial mechanical properties measurement. Compared to wrinkling, one of the benefits of extremely buckling driven delamination is the extraordinarily high aspect ratio of buckles. The large surface roughness and high local curvature could potentially enable extreme surface topographies related properties, such as adhesion, wetting, friction, and optics, as well as augment the extreme stretchability in stretchable optical and electronic devices. In the aim of harnessing this extreme buckling driven delamination, I first explore the formation and evolution of extraordinarily high-aspect-ratio delaminated buckles of thin films on 400% pre-strained elastomers, as well as uncovered the underlying deformation mechanism through combining quantitative theoretical analysis and experimental and numerical approaches. A theoretical framework is developed to describe the formation and evolution process of periodic delaminated buckles, which includes three deformation stages, i.e. onset of localized blisters (Stage I), growth and propagation of delamination (Stage II), and post-buckling after delamination arrest (Stage III). I show that under extreme large compressive strain, the profile of periodic blisters changes from sinusoidal shape to jig-saw-like shape with relative high aspect ratio, which have potential applications for design of extremely stretchable electronics. Equipped with the fundamental mechanics of buckle-delamination in thin films, I then exploit harnessing the spontaneous buckling driven periodic delamination to achieve high stretchability in both metal and silicon films. Experimentally I observe periodic buckle-delaminated patterns over large area, accompanied by highly ordered transversely cracking patterns, which can be theoretically predicted by simple crack fragments model. I hypothesize that when the width of ribbons is set to be equal or smaller than the theoretically predicted crack fragment width, there would be no cracking fragmentation. This criteria for designing crack-free micro-ribbons is further validated by related experiments. Guided by the validated criteria, I successfully design crack-free and spontaneous delaminated ribbons on highly prestrained elastomer substrates, which provides a high stretchability of about 120% and 400% in Si and Au ribbons, respectively. I further extend the buckling instability-based metrology to systematically measure the mechanical properties of 2D organic conjugated polymer nano-films, which have tremendous promising applications in organic integrated circuits, solar cells, and stretchable devices. I develop a new fabrication strategy to generate buckle-delaminated free-standing organic conjugated polymeric (P3BT/C60) nanosheets. Through both experiments and theoretical analysis, I show that the free-standing buckle-delaminated organic P3BT/C60 nanosheets have significant advantages over the traditional spin-coated wrinkled nanosheets, including the enhanced mechanical properties, a higher level of stretchability with lower electrical resistance, and a wider range of controllable wettability modulation.
Temple University--Theses

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Yilmaz, Suphi. "Buckling Driven Delamination Of Orthotropic Functionally Graded Materials." Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/3/12607836/index.pdf.

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In today'
s technology severe working conditions increase demands on structural materials. A class of materials which are developed to meet these increased demands is Functionally Graded Materials (FGMs). These are inhomogeneous structural materials which are able to withstand large temperature gradients and corrosive environment. Application areas of FGMs are in aerospace industry, nuclear reactors, chemical plants and turbine systems. FGMs have gradual compositional variation from metal to ceramic which give them mechanical strength, toughness and heat resistance. However under high temperature gradients, cracking problems may arise due to thermal stresses. In layered structures the final stage of failure may be delamination due to crack extension. The objective of this study is to model a particular type of crack problem in a layered structure consisting of a substrate, a bond coat and an orthotropic FGM coating. There is an internal crack in the orthotropic layer and it is perpendicular to material gradation of coating. The position of the crack inside the coating is kept as a variable. The steady-state temperature distribution between the substrate and the coating causes a buckled shape along crack face. The critical temperature change, temperature distribution, mixed mode stress intensity values and energy release rates are calculated by using Displacement Correlation Technique. Results of this study present the effects of geometric parameters such as crack length, crack position, etc as well as the effects of the type of gradation on buckling behavior and mixed mode stress intensity factors.

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Loveridge, M. J. "The Scanning Kelvin probe applied to mechanisms of delamination in organic coated steels." Thesis, Swansea University, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637953.

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The objectives set out for the work detailed within this thesis can be considered on two levels. First of all a principal objective was to obtain a detailed understanding of the kinetics and mechanism of coating delamination as it affects prepainted and laminated organic coated steels. The second part involves identification of new corrosion inhibitors, pretreatments, adhesives and primer systems which will greatly improve delamination resistance, and hence corrosion resistance in steel products. A thorough, systematic study of the above has enabled the project to deliver quantitative mechanistic models of delamination phenomena as they affect coated steel products. Also obtained has been valuable, detailed information on the influence of conventional and novel corrosion inhibitors and pretreatments. Insight gained from the study has enabled us to identify new materials for incorporation into organic coated steel with greatly improved delamination resistance. The pigments investigated were alkali earth-exchanged bentonite, phosphate-exchanged hydrotalcite and the Polyaniline Emeradine salts of para-Toluene sulphonate, Camphor sulphonate and Phenyl phosphate. Fresh insight has recently been obtained into the Scanning Kelvin probe Technique (SKP) and its application of the investigation of the kinetics and mechanism of coating delamination processes occurring concurrently with corrosion at cut-edges and defects in prepainted and laminated organic coated steel products. SKPT is capable of following the progress of a delamination front beneath apparently intact coatings. The SKP was used to systematically investigate the influence of several novel corrosion inhibitor pigments and pigment-pretreatment synergy on the kinetics and mechanism of coating delamination. This approach has enabled a better characterisation of existing materials and to identify new, high performance materials for the manufacture of improved coated steel products. Where possible the SKP findings have been supported by parallel investigations using SIMS (Secondary Ion Mass Spectroscopy).

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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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Messenger, C. R. "Investigation of delamination and matrix cracking in quasi-isotropic GFRP laminates." Thesis, University of Surrey, 1996. http://epubs.surrey.ac.uk/842699/.

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Intra-laminar and inter-laminar cracking in GFRP laminates has been studied. The epoxy matrix used gave a transparent composite and was compatible with polyurethane, enabling a modified system (containing 20% urethane) to be investigated in addition to the standard epoxy. Three stacking sequences of quasi-isotropic laminates, (+45/-45/0/90)s, (0/90/-45/+45)s and (+45/90/-45/0)s were tested. Data were obtained for the growth of damage and its effect on laminate stiffness under increasing quasi-static load and as a function of number of fatigue cycles at two different stress levels. Using the transparent systems enabled a more complete set of damage data to be obtained than by previous workers. The damage comprised 90-ply cracking followed by +45 and -45 cracking and then for (+45/-45/0/90)s [and to a limited extent in (+45/90/-45/0)s], delamination. The initiation and growth of damage was examined with regard to matrix type and stacking sequence. The onset of matrix cracking and delamination are both delayed in the urethane-containing laminates; fracture mechanics tests showed that the urethane system was significantly tourer. Moreover, at a given quasi-static stress or number of fatigue cycles the urethane-modified laminates retain a greater proportion of their initial modulus. The stacking sequence influences interlaminar stresses (thereby controlling delamination) and determines parameters such as ply thickness and neighbouring ply orientation which in turn influence intralaminar cracking. Fracture mechanics has been applied to model the initiation and growth of delamination under quasi-static and cyclic loading using a modified compliance technique. Shear-lag models have been used to determine the stiffness loss due to intralaminar cracking, enabling the stiffness reduction associated with delamination to be deduced empirically. This enables the energy release rates associated with delamination to be derived leading to more sensible results than those obtained using an unmodified technique.

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20

Ilomäki, M. (Marko). "Application of fracture mechanics in analyzing delamination of cyclically loaded paperboard core." Doctoral thesis, University of Oulu, 2004. http://urn.fi/urn:isbn:9514274008.

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Abstract The primary objective of this work is to study and model the fracture process and durability of paperboard cores in cyclic loading. The results are utilized in creating analytic model to estimate the life time of cores in printing industry. The life time means here the maximum number of winding-unwinding cycles before the core delaminates. This study serves also as an example of use of board as a constructional engineering material. Board is an example of complicated, fibrous, porous, hydroscopic, time dependent and statistic material. Different core board grades are typically made of recycled fibers. The material model in this work is linear-elastic, homogeneous and orthotropic. The material characteristics, elastic and strength properties are studied first. Then the material is studied from the points of view of fracture and fatigue mechanics. Some of the analysis and test methods are originally developed for fiber composites but have been applied successfully here also for laminated board specimen. An interesting finding is that Scott Bond correlates well with the sum of mode I and mode II critical strain energy release rates. It was also possible to apply Paris' law and Miner's cumulative damage theory in the studied example situations. The creation of the life time model starts by FEM-analysis of cracked and non cracked cores in a typical loading situation. The elastic-linear material model is used here. The calculated stresses are utilized in analytic J-integral model. The agreement between analytic and numerical J-integral estimations is good. The analytic life time model utilizes the analytic J-integral model, Miner's cumulative damage theory and analytically formulated Wöhler-curves which were constructed by applying the Paris' law. The Wöhler-curves were constructed also by testing cores to validate the theoretical results. The testing conditions are validated by FEM-analysis. The cores heat up when tested or used with non expanding chucks and a temperature correction was needed in the life time model to consider this. Also, single or multi crack model was used depending on the studied case. The calculated and tested durability prediction curves show good correspondence. The results are finally reduced to correspond to certain confidence level.

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Cardanini, Alisha Ann. "Finite Element Analysis of Bi-Metallic Structures with Adhesive Delamination." The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu150185598849201.

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22

Okubo, Hitoshi, Fumihiro Endo, Naoki Hayakawa, Hiroki Kojima, and Diaa-Eldin A. Mansour. "Partial Discharges and Associated Mechanisms for Micro Gap Delamination at Epoxy Spacer in GIS." IEEE, 2010. http://hdl.handle.net/2237/14531.

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23

Okubo, Hitoshi, Masahiro Hanai, Naoki Hayakawa, Hiroki Kojima, and Diaa-Eldin A. Mansour. "Physical Mechanisms of Partial Discharges at Nitrogen Filled Delamination in Epoxy Cast Resin Power Apparatus." IEEE, 2013. http://hdl.handle.net/2237/20739.

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24

Goyal, Vinay K. "Analytical Modeling of the Mechanics of Nucleation and Growth of Cracks." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/30006.

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With the traditional fracture mechanics approaches, an initial crack and self-similar progression of cracks are assumed. In this treatise, theoretical and numerical tools are developed to mathematically describe non-self-similar progression of cracks without specifying an initial crack. A cohesive-decohesive zone model, similar to the cohesive zone model known in fracture mechanics as Dugdale-Barenblatt model, is adopted to represent the degradation of the material ahead of the crack tip. This model unifies strength-based crack initiation and fracture based crack progression. The cohesive-decohesive zone model is implemented with an interfacial surface material that consists of an upper and lower surface connected by a continuous distribution of normal and tangential nonlinear elastic springs that act to resist either Mode I opening, Mode II sliding, Mode III sliding, or mixed mode. The initiation of fracture is determined by the interfacial strength and the progression of fracture is determined by the critical energy release rate. The material between two adjacent laminae of a laminated composite structure or the material between the adherend and the adhesive is idealized with an interfacial surface material to predict interfacial fracture. The interfacial surface material is positioned within the bulk material to predict discrete cohesive cracks. The proper work-conjugacy relations between the stress and deformation measures are identified for the interfacial surface theory. In the principle of virtual work, the interfacial cohesive-decohesive tractions are conjugate to the displacement jumps across the upper and lower surfaces. A finite deformation kinematics theory is developed for the description of the upper and lower surface such that the deformation measures are invariant with respect to superposed rigid body translation and rotation. Various mechanical softening constitutive laws thermodynamically consistent with damage mechanics are postulated that relate the interfacial tractions to the displacement jump. An exponential function is used for the constitutive law such that it satisfies a multi-axial stress criterion for the onset of delamination, and satisfies a mixed mode fracture criterion for the progression of delamination. A damage parameter is included to prevent the restoration of the previous cohesive state between the interfacial surfaces. In addition, interfacial constitutive laws are developed to describe the contact-friction behavior. Interface elements applicable to two dimensional and three dimensional analyses are formulated for the analyses of contact, friction, and delamination problems. The consistent form of the interface element internal force vector and the tangent stiffness matrix are considered in the formulation. We investigate computational issues related to interfacial interpenetration, mesh sensitivity, the number of integrations points and the integration scheme, mathematical form of the softening constitutive law, and the convergence characteristics of the nonlinear solution procedure when cohesive-decohesive constitutive laws are used. To demonstrate the predictive capability of the interface finite element formulation, steadystate crack growth is simulated for quasi-static loading of various fracture test configurations loaded under Mode I, Mode II, Mode III, and mixed-mode loading. The finite element results are in agreement with the analytical results available in the literature and those developed in this work. A progressive failure methodology is developed and demonstrated to simulate the initiation and material degradation of a laminated panel due to intralaminar and interlaminar failures. Initiation of intralaminar failure can be by a matrix-cracking mode, a fiber-matrix shear mode, and a fiber failure mode. Subsequent material degradation is modeled using damage parameters for each mode to selectively reduce lamina material properties. The interlaminar failure mechanism such as delamination is simulated by positioning interface elements between adjacent sublaminates. The methodology is validated with respect to experimental data available in the literature on the response and failure of quasi-isotropic panels with centrally located circular cutouts. Very good agreement between the progressive failure analysis and the experiments is achieved if the failure analyses includes the interaction of intralaminar and interlaminar failures in the postbuckling response of the panels. In addition, ideas concerning the implementation of a fatigue model incorporated with a cohesive zone model are discussed.
Ph. D.

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25

Garcia, Jorge David Aveiga. "A delamination propagation model for glass fiber reinforced laminated composite materials." Universidade de São Paulo, 2018. http://www.teses.usp.br/teses/disponiveis/18/18148/tde-31072018-143609/.

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The employment of composite materials in the aerospace industry has been gradually considered due to the fundamental lightweight and strength characteristics that these type of materials offer. The science material and technological progress that has been reached, matches perfectly with the requirements for high-performance materials in aircraft and aerospace structures, thus, the development of primary structure elements applying composite materials became something very convenient. It is extremely important to pay attention to the failure modes that influence composite materials performances, since, these failures lead to a loss of stiffness and strength of the laminate. Delamination is a failure mode present in most of the damaged structures and can be ruinous, considering that, the evolution of interlaminar defects can carry the structure to a total failure followed by its collapse. Different techniques are usually adopted to accurately predict the behavior of damaged structures but, due to the complex nature of failure phenomena, there is not an established pattern. The present research project aims to develop a delamination propagation model to estimate a progressive interlaminar delamination failure in laminated composite materials and to allow the prediction of material\'s degradation due to the delamination phenomenon. Experimental tests assisted by ASTM Standards were performed to determine material\'s parameter, like the strain energy release rate, using GFRPs laminated composites. The delamination propagation model proposed was implemented as subroutines in FORTRAN language (UMAT-User Material Subroutine) with formulations based on the Fracture Mechanics. Finally, the model was compiled beside with the commercial Finite Element program ABAQUSTM.
O emprego de materiais compósitos na indústria aeroespacial tem sido gradualmente utilizado devido às suas características fundamentais, como peso leve e alta rigidez, que este tipo de material oferece. Tanto a ciência do material como o desenvolvimento tecnológico que se tem logrado, possibilitaram que estes materiais cumprissem com os requisitos de desempenho para aplicações em estruturas aeronáuticas e aeroespaciais, por tanto, o desenvolvimento de elementos de estruturas primárias usando materiais compósitos, passou a ser muito conveniente. É de extrema importância prestar atenção aos modos de falha que comprometem a performance dos materiais compósitos, uma vez que, estas falhas levam a uma perda de resistência e rigidez do laminado. A delaminação é um modo de falha presente na maioria de estruturas danificadas e pode ser desastroso, considerando que, a evolução dos defeitos interlaminares podem levar a estrutura a falhar seguido pelo colapso estructural. Diferentes técnicas são geralmente adotadas para prever, de maneira correta, o comportamento de estruturas danificadas, porém, devido à natureza complexa do fenômeno de falha, não existe um padrão estabelecido. O presente trabalho de pesquisa visa desenvolver um modelo de delaminação e de propagação da delaminação para estimar a evolução da falha interlaminar em materiais compósitos laminados e permitir a predição do comportamento do material com a evolução da delaminação. Ensaios experimentais auxiliados por normas ASTM foram realizados para determinar parâmetros do material, tais como, as taxas de liberação de energia de deformação, usando materiais compósitos laminados de matriz polimérica reforçada com fibra de vidro. O modelo de propagação da delaminação proposto, foi implementado como uma sub-rotina em linguagem FORTRAN (UMAT – User Material) com formulações baseadas na Mecânica da Fratura. Finalmente, o modelo foi compilado com o software comercial de Elementos Finitos, ABAQUSTM.

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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.

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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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27

Pilhagen, Johan. "The fracture mechanisms in duplex stainless steels at sub-zero temperatures." Doctoral thesis, KTH, Materialteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-133677.

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The aim of the thesis was to study the susceptibility for brittle failures and the fracture process of duplex stainless steels at sub-zero temperatures (°C). In the first part of the thesis plates of hot-rolled duplex stainless steel with various thicknesses were used to study the influence of delamination (also known as splits) on the fracture toughness. The methods used were impact and fracture toughness testing. Light optical microscopy and scanning electron microscopy were used to investigate the microstructure and fracture surfaces. It was concluded that the delaminations caused a loss of constraint along the crack front which resulted in a stable fracture process despite the presence of cleavage cracks. These delaminations occurred when cleavage cracks are constrained by the elongated austenite lamellae. The pop-in phenomenon which is frequently observed in duplex stainless steels during fracture toughness testing was shown to occur due to these delaminations. The susceptibility for pop-in behaviour during testing increased with decreasing plate thickness. The toughness anisotropy was also explained by the delamination phenomenon.In the second part of the thesis duplex stainless steel weld metals from lean duplex and super duplex were investigated. For the lean duplex weldments with different nickel contents, tensile, impact and fracture toughness testing were conducted from room temperature to sub-zero temperatures. The result showed that increased nickel content decreased the susceptibility for critical cleavage initiation at sub-zero temperatures. The super duplex stainless steel weldment was post weld heat treated. The fracture sequence at low temperature was critical cleavage fracture initiation after minor crack-tip blunting and ductile fracture. Energy-dispersive X-ray spectroscopy investigation of the weld metals showed that substitutional element partitioning is small in the weld metal. However, for the post weld heat treated weldments element partitioning occurred which resulted in decreased nickel content in the ferrite.

QC 20131108

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28

Kuriakose, Sunil. "Analysis of damage in composite laminates under bending." Diss., Georgia Institute of Technology, 2002. http://hdl.handle.net/1853/12054.

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Barbieri, Ettore. "Meshfree methods for the analysis of composite materials." Thesis, University of Bath, 2010. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.558846.

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The proposed research is essentially concerned on numerical simulation of materials and structures commonly used in the aerospace industry. The work is primarily focused on the study of the fracture mechanics with emphasis to composite materials, which are widely employed in the aerospace and automotive industry. Since human lives are involved, it is highly important to know how such structures react in case of failure and, possibly, how to prevent them with an adequate design. It has become of primary importance to simulate the material response in composite, especially considering that even a crack, which could be invisible from the outside, can propagate throughout the structure with small external loads and lead to unrecoverable fracture of the structure. In addition, structures made in composite often present a complex behaviour, due to their unconventional elastic properties. A numerical simulation is then a starting point of an innovative and safe design. Conventional techniques (nite elements for example) are not su-cient or simply not ecient in providing a satisfactory description of these phenomena. In fact, being based on the continuum assumption, mesh-based techniques suer of a native incapacity of simulating discontinuities. Novel numerical methods, known as Meshless Methods or Meshfree Methods (MM) and, in a wider perspective, Partition of Unity Methods (PUM), promise to overcome all the disadvantages of the traditional finite element techniques. The absence of a mesh makes MM very attractive for those problems involving large deformations, moving boundaries and crack propagation. However, MM still have signicant limitations that prevent their acceptance among researchers and engineers. Because of the infancy of these methods, more efforts should be made in order to improve their performances, with particular attention to the computational time. In summary, the proposed research will look at the attractive possibilities offered by these methods for the study of failure in composite materials and the subsequent propagation of cracks.

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Chadha, Harpreet Singh. "Quantitative evaluation of thin film adhesion using the probe test." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/35426.

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In this study, a test technique, referred to as the probe test, has been developed as a quantitative tool for measuring the adhesion in thin adhesive films and coatings. The technique was initially developed as a qualitative test by the Hewlett-Packard Company for measuring adhesion of thin film microelectronic coatings. In the probe test method, an inclined needle-like probe with a conical tip is advanced underneath the free edge of a thin polymeric coating bonded to a substrate, causing the edge to lift-up from the surface of the substrate. A debond is thus initiated at the loading point and propagates as a semi-circular crack at the interface as the probe slides under the coating. A standard test procedure has been developed for testing thin adhesive coating/substrate systems. The sample system used is a thin film epoxy polymer coated silicon system. The interfacial fracture energy (Gc) (or critical strain energy release rate) has been used as a quantitative measure of adhesion for the given adhesive coating/substrate system. The probe test experiments were conducted using an optical microscope and a WYKO optical profiler. Using the optical microscope, the debond radius was measured for different debond sizes. Using the WYKO optical profiler, the three-dimensional surface topography of the debonded coating around the crack front was measured for different debond sizes. Using the experimental data from the probe test, analytical and numerical (finite element-based) techniques have been developed to determine the interfacial fracture energy (Gc) for the given adhesive coating/substrate system. The analytical techniques were developed based on different plate theory formulations (thin/thick plate - small/large deflection) of the probe test geometry and local curvature measurement at the crack tip. The finite element based techniques were developed using a hybrid numerical-experimental approach and surface-based contact interaction analysis in ABAQUS. The results obtained using thick plate-large deflection formulation correlated with finite element contact interaction analysis results. The probe test can be used with transparent or opaque coatings and thus offers a promising alternative to indentation and other tests methods for characterizing thin film and coating adhesion.
Master of Science

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31

Ghazali, Habibah. "Dual-Capsule Based Self-Healing of Epoxy and Carbon-Epoxy Laminated Composite." Thesis, The University of Sydney, 2016. http://hdl.handle.net/2123/15387.

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Since the year 2000, researchers have made extensive efforts to develop novel materials with self-healing ability by embedment of microencapsulated self-healing agents. The motivation behind these studies is to heal the crack once it occurs and to slow down crack growth in the materials. These materials were designed with the capability of repairing damage/fracture autonomously whenever it happens, and the materials subsequently recover their original properties. Many of the early-developed healing systems focused on the healing of polymers and their fibre-reinforced composites with a room temperature-curing system. Because of the difficulty in applying resins with microcapsules normally around 100 μm in size to reinforcing fibres during the fabrication process of composites and due to the limited space between the plies, most studies have adopted a low fibre volume fraction for ease of processing and fabrication. The realisation to structural composites containing a high fibre volume fraction was less studied. In general, a high fibre volume fraction is a critical factor for achieving high specific strength and high specific modulus of the resultant composites. Firstly, this study aims to develop a diglycidyl ether of bisphenol A (DGEBA) epoxy as the self-healing agent and characterise its capability in healing the elevated temperature-cured epoxy, epoxy-based adhesive joints, and carbon-fibre reinforced epoxy composites. A dual-capsule self-healing system containing DGEBA epoxy and mercaptan as its hardener, microencapsulated in similar sizes, was developed to be embedded into the base epoxy resin. This healing system was chosen to match that of the matrix of composite laminates fabricated in this study for its superior thermal stability. Although the DGEBA epoxy/mercaptan self-healing system has been reported to provide the epoxy with room temperature healing, the high viscosity imposed by the healing agent has made room temperature healing conditions less reliable for healing of composite laminates of a high fibre volume fraction, where the amount of the embedded microcapsules is constrained by fibres. Therefore, the effect of healing temperature on viscosity and healing efficiency in the base epoxy is studied to obtain the improved healing conditions. It was found that the better healing performance for this healing system is achieved at 70°C since the viscosity of DGEBA epoxy is much lower at this temperature. With a better flow behaviour, the healing agent has a better capacity to flow and spread onto crack surfaces. Apart from that it was also found that the formed healant film covering thin cavity between two crack surfaces is critical for the healing performance, and at the elevated temperature of 70°C, the full recovery in fracture toughness (KIC) is achieved for Mode I fracture in the epoxy. The dual-capsule self-healing system was then extended to heal delamination in carbon fibre (CF)/epoxy (EP) composite laminates after Mode I interlaminar fracture. One of the main focuses of this study is centred on CF/EP composite laminates embedded with the dual-capsule and with a high fibre volume fraction fabricated using the vacuum assisted resin infusion technique, with the aims to effectively heal delamination as well as matrix microcracking once they occur. Here, it was demonstrated that by properly modulating the amount of microcapsules dispersed on reinforcing CF fabrics, CF/EP composite laminates with a fibre volume fraction as high as 65% can be achieved. The self-healing performance after Mode I delamination in CF/EP composite laminates with the dual-capsule self-healing system of two different sizes (average 123 µm and 65 µm, respectively) of microcapsules was investigated. Effects of incorporating microcapsules on baseline properties of the composite laminates were investigated, and it was found that such incorporation first leads to some reduction in the baseline properties of the laminates. The CF/EP laminate with large size (123 µm) microcapsules shows 4.6% reduction in the original Mode I interlaminar fracture toughness (GIC) as compared to that of the base laminate; while the CF/EP laminate with small size (65 µm) microcapsules shows a reduction of 36.9%. Healing efficiency is characterised by the recovery in the Mode I critical stress intensity factor (KIC) measured using width-tapered double cantilever beam (WTDCB) specimens. Although the full recovery was achieved for the base laminate injected with the same healing agent, the healing efficiency with only 54% recovery was achieved for the laminate with the small size microcapsules, with the maximum being 57% in some cases. In the case of large size microcapsules, the healing efficiency increased to 69% recovery with the maximum being 80% in some cases. It was also observed that the recovery in Mode I interlaminar fracture toughness was directly correlated with the amount of healant film covering the fracture surfaces, with the highest healing efficiency obtained for the laminate with the largest film. In the following study, the self-healing performance after Mode II delamination in CF/EP laminates containing the dual-capsule self-healing system was investigated. The effect of incorporation of the microcapsules on Mode II interlaminar fracture toughness (GIIC) of CF/EP laminates was characterised using end-notched flexure (ENF) specimens. In contrast to the Mode I delamination tests, the results indicated that the Mode II interlaminar fracture toughness (GIIC) of the base CF/EP laminate was improved (up to 48%) with the incorporation of the dual-capsule self-healing system. When healed at 70°C, the dual-capsule self-healing system also provided the laminate with healing capability on Mode II delamination with 63% recovery in GIIC. Observation on the fracture surfaces also revealed that the healing efficiency varies directly with the concentration of healant and the healing of interlaminar region after Mode II fracture. Finally, the self-healing epoxy adhesive was developed using this dual-capsule self-healing system. The healing system was incorporated into a commercial two-part room temperature-cured epoxy adhesive. The addition of 3 wt% microcapsules in concentration into adhesive of 172 (± 50) μm in thickness was shown to increase the baseline lap-shear strength by 28%. The results also revealed an increment to the baseline fracture toughness (GIC) of the epoxy adhesive, with improvement as high as 80% for adhesive with thickness of 273 (±66) μm, measured using tapered-double cantilever beam (TDCB) specimens. The increase in fracture toughness was mainly attributed to enhanced plastic deformation of the host adhesive as well as the crack path deflection caused by the poor adhesion between the microcapsules and the epoxy adhesive. The healing efficiency based on the recovery in the original crack initiation and crack propagation fracture toughness is 52% and 74% respectively.

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32

Abdelal, Nisrin Rizek. "Effects of Voids on Delamination Behavior Under Static and Fatigue Mode I and Mode II." University of Dayton / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1365418463.

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33

CERIONI, AGOSTINO. "Simulation of delamination in composite materials under static and fatigue loading by cohesive zone models." Doctoral thesis, Università degli Studi di Cagliari, 2009. http://hdl.handle.net/11584/266000.

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This thesis is a dissertation focusing on the mechanics of delamination in laminated composites. Delamination, one of the most critical forms of failure in composite materials, may occur as a result of many causes and different types of loading, such as, for example, static or cyclic loading. This work presents an examination of the potential of cohesive interface elements for the prediction of delamination propagation under quasi-static mode I, mode II and mixed mode (I and II) loading, by a comparison between experimental tests and parametric analyses in order to evaluate the sensitivity of the elements to some parameters. The results of the comparison show that a rather good accordance may be obtained between experimental data and numerical simulations with a proper choice of the main model parameters. Moreover, a simplified mathematical model for the study of fatigue driven delamination is described. This model is particularly useful for investigating the performance of various formulations of interface elements that are used to simulate delamination under cyclic loading, because of its simplicity and efficiency that allow evaluating a large number of sets of parameter values. The model has been studied with different static constitutive laws and damage definitions, coupled with a particular fatigue degradation strategy. In particular, the sensitivity of the model, with the different proposed constitutive laws, has been evaluated with respect to some its key parameters.

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Aminjikarai, Vedagiri Srinivasa Babu. "An Automated Dynamic Fracture Procedure and a Continuum Damage Mechanics Based Model for Finite Element Simulations of Delamination Failure in Laminated Composites." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1242963775.

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35

Mikulik, Zoltan Mechanical &amp Manufacturing Engineering Faculty of Engineering UNSW. "Application of fracture mechanics to predict the growth of single and multi-level delaminations and disbonds in composite structures." Publisher:University of New South Wales. Mechanical & Manufacturing Engineering, 2008. http://handle.unsw.edu.au/1959.4/41560.

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The high stiffness to weight ratio and fatigue resistance make carbon fibre composites suitable for both military and large civil aircraft. The limited ability of current numerical methods to capture the complex growth of damage in laminated composites leads to a conservative design approach applied in today??s composite aircraft structures. The aim of the presented research was to develop an improved methodology for the failure prediction of laminated composites containing delaminations located between arbitrary layers in the laminate, and to extend the investigations to composite structures subjected to barely visible impact damage (BVID). The advantages of fracture mechanics-based methodologies to predict interlaminar failure in composite structures were identified, from which the crack tip element (CTE) approach and the virtual crack closure technique (VCCT) were selected for assessment. Extensive validation of these fracture mechanics methods is presented on a number of composite structures ranging from coupons to large stiffened panels. It was shown that the VCCT was relatively insensitive to the crack front mesh size, whilst predictions using the CTE methodology were significantly influenced by the element size. Based on the obtained results modelling guidelines for the VCCT and CTE were established. Significant contribution of this research to the field of the analysis of composite structures was the development of a novel test method for the evaluation of embedded single and multi-level delaminations. The test procedure of the single delamination specimen was proposed as an analogous test to conventional compression experiments. The transverse test overcame the inherent problems of in-plane compression testing and produced less scatter of experimental measurements. Quantitative analysis of numerical results employing the validated finite element modelling approaches showed that the failure load and location were in agreement with experiments. Furthermore, new modelling techniques for composite structures containing BVID proposed in this research produced good correlation with test data from the compression after impact (CAI) test. The study of BVID provided a significant contribution toward the knowledge of the applicability of implicit FE solvers to predict failure of CAI specimens as well as the criticality of centrally impacted specimens.

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36

Renault, Michel. "Tolerance a l'endommagement de composites carbone-resine et stratifies t300-914." Paris, ENMP, 1988. http://www.theses.fr/1988ENMP0109.

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Etude experimentale (essais de fatigue, essais de traction, de compression) sur des eprouvettes entaillees ou non, trouees ou non de stratifies resine epoxyde/carbone. Analyse mathematique avec des calculs par elements finis

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37

Ng, Annie Yuhn-Chee. "The mechanics of cam-type femoroacetabular impingement." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:390fbe37-77a5-42da-aa61-5be8e9b90955.

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Cam-type Femoro-Acetabular Impingement (FAI) is a common cause of hip osteoarthritis (OA). In this condition a bony abnormality at the head-neck junction of the femoral head, called the “cam”, abuts against the acetabulum causing labral damage and articular cartilage delamination, which in turn may lead to progressive degeneration and OA. The understanding of the damage mechanism is currently at a conceptual level. The aim of the thesis is to develop a more detailed understanding of the underlying mechanism so as to improve methods of detection and treatment of cam-type FAI and thus to help prevent hip OA. A geometric-kinematic model combining hip joint motion and hip joint geometry was cre- ated to determine what motions, activities or cam shapes give rise to cam-type impingement, which was quantified by the proximity of the acetabular and femoral bony surfaces. Five normal subjects and five symptomatic cam-type FAI patients were modelled. The FAI patients experienced early impingement during the impingement test but did not have impingement during common functional activities. The early impingement was possibly due to the larger coverage and protrusion of their cams and the smaller overall proximity in their hip joints. A 2D finite element (FE) model was created to simulate cam-type FAI. As idealised 2D rectangular and circular geometries did not reproduce the damage seen clinically, subject- specific geometry, loads, and motions were introduced. Under some circumstances, as the cam entered the hip joint, large shear strains developed near the cartilage-bone interface of the acetabulum which would result in cartilage delamination. In vitro experiments were undertaken to validate the FE model and verify the damage mech- anism by which cam-type FAI leads to cartilage delamination. Porcine cartilage-bone samples were loaded under conditions similar to those generated by a cam (shear and compression). A validation FE model was created that used the same material and contact representations and analysis framework as the impingement FE model but mimicked the experimental setup. The cartilage shear strains assessed with a video-based method were similar to predicted FE results. In vitro damage experiments demonstrated that delamination can be caused by repetitive shear and compressive loading that lead to large shear strains near the cartilage-bone interface. The impingement FE model was used to further explore the effect of cam anatomy. In hips with low clearance, cams with large protrusions (75% hip joint clearance) would not enter into the hip joint, but caused high shear strains in the labrum, which would result in labral tears. A narrower cam caused damage to the labral tip, whereas a wider cam caused damage to the labral-bone junction. In contrast, cams with small protrusion (25% hip joint clearance) were able to enter the joint and caused damage at the articular cartilage-bone interface, which would result in cartilage delamination. The wider the cam, the further into the hip joint the damage was initiated. The FE model was used to explore the effect of different labral anatomy and of reshaping surgery. A labrum connected to the articular cartilage resulted in shear strains of up to five times greater in the articular cartilage and labrum compared to an unconnected labrum and was more likely to cause articular cartilage delamination. For a cam that damages the articular cartilage, surgical removal of the cam reduced shear strains. For a cam that abuts the labrum, surgical removal of the cam eliminated labral abutment and increased the range of motion of the hip, but resulted in greater shear strains in the articular cartilage. It is not known whether these shear strains are normal or could possibly be damaging. Also, reshaping the head to be spherical resulted in slightly reduced shear strains in the articular cartilage compared to the current surgical practice of cutting deeper into the femoral head when removing the cam. This study has, for the first time, using a validated FE model demonstrated the mechanism by which a cam can cause articular cartilage delamination and labral tearing. Further analysis using the geometric and FE model should help identify cam deformities that would be likely to cause OA and the best way to treat them surgically so as to prevent OA.

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Swindeman, Michael James. "A Regularized Extended Finite Element Method for Modeling the Coupled Cracking and Delamination of Composite Materials." University of Dayton / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1324605778.

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Neely, Jared A. "Correlation of Stress Intensity Range with Deviation of the Crack Front from the Primary Crack Plane in both Hand and Die Forged Aluminum 7085-T7452." University of Dayton / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1557162451907811.

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40

Bouquet, Jean-Baptiste. "Implementation of a robust solver for predicting highly localized deformations in microelectronics." Thesis, Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41112.

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Fracture of polymer-metal interfaces is one of the main failure modes occurring in micro-electronic components. This phenomenon is particularly true when considering the delamination of several layers of an interconnect structure. In order to predict the failure nucleation and the crack propagation into the composite material, the finite element analysis is one of the key procedures. Even though simple linear models have been considered for years, we are now facing the necessity of using more complex models including non-linearity which can occur, in this case, with the presence of high local stresses near the crack front. However, the computational time can sometimes be incredibly long. Moreover, the fact that the considered materials are quasi-brittle brings some numerical difficulties such as sharp snap-back and snap-through. The actual challenge resides in obtaining a reliable result in a reasonable time of calculation. The present work considers the implementation of a new non-linear finite element solver, developed for the MSc. Marc/Mentat package software. It is based on a general arc-length constraint which considers the energy released during the propagation of the crack. This offers the advantage of being directly linked to the failure process, and no previous knowledge of the failure behavior is required. The models considered in this work represent the simulation of crack propagations in multilayer electronic systems, such as SIP devices, and are based on a cohesive zone approach. In order to clearly understand the issues of this problem, this work includes a brief description of the fracture mechanics and reviews the existing nonlinear finite element solvers. After explaining the principle of the energy release solver and the different issues due to its implementation, its efficiency is compared to pre-implemented solvers, such as the Crisfield method. The results show a significant improved robustness of the new energy released method compared to the previous arc-length methods.

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Ge, Yangyang. "Development of testing methods for characterization of delamination behavior under pure mode III and mixed modes in a laminated composite." Thesis, Toulouse 3, 2016. http://www.theses.fr/2016TOU30130/document.

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Le but de ce travail est la caractérisation du comportement au délaminage des composites stratifiés en mode mixte I+II+III, en se focalisant en particulier sur le verrou scientifique que représente le mode III pur. Cette thèse repose sur un travail à la fois expérimental et numérique, validant numériquement les tests existants et ceux développés. La mise en perspective des résultats obtenus a permis, d'un coté, de mieux appréhender l'importance de la distribution des taux de restitution d'énergie, GI, GII et GIII, le long du front de fissure sur le la détermination de la ténacité du composite et d'un autre coté, de proposer et d'améliorer les méthodes de caractérisation. Avant d'évoquer le délaminage en mode mixte, nos efforts se sont d'abord concentrés sur la caractérisation du délaminage en mode III pur. Deux essais de type " Edge Crack Torsion " (ECT) disponibles dans la littérature ont été réalisés. La distribution de GIII le long du front de fissure a été déterminée par la méthode des éléments finis (MEF) en utilisant la technique de fermeture virtuelle de fissure (VCCT). La capacité de ces tests est compromise par : 1. La participation du mode II non nul ; 2. La forte variation de GIII près des bords de l'éprouvette. Ces problèmes rendent la détermination de la ténacité en mode III pur, GIIIC, difficile et imprécise. Par la suite, un nouveau test a été proposé, nommé "Edge Ring Crack Torsion" test (ERCT ou ERT-III). Il s'appuie sur une éprouvette possédant une fissure de front circulaire, l'absence d'extrémités sur le front de fissure permet de supprimer les effets de bords. Après l'optimisation et la modification de la géométrie du dispositif dans le test ERCT original, GIII le long du front de fissure reste presque constant avec très peu de modes parasites. La formule proposée par Tada est appliquée pour déterminer GIIIC. Il est démontré qu'en général, si la variation de GIII est faible le long du front de fissure, la ténacité déterminée par une solution " closed-form " concorde bien avec celle obtenue numériquement. En fait, la répartition de GIII peut être influencée par divers facteurs, tels que la nature des stratifiés, la géométrie du dispositif expérimental et la géométrie des éprouvettes. L'interaction de ces facteurs a été aussi abordée dans cette étude. En outre, une étude numérique de sensibilité aux défauts a permis de vérifier la robustesse de l'essai proposé vis-à-vis de différents défauts qui sont inhérent à tout travail expérimental. Enfin, une géométrie d'éprouvette optimisée est donnée avec une méthodologie permettant de réduire les fluctuations de GIII. L'utilisation de l'éprouvette ERC a été généralisée à la caractérisation du délaminage pour deux autres modes purs : l'essai de traction permet de solliciter ERC en mode I pur et celui de flexion sollicite ERC en mode II pur, nommé ERCTE ou ERC-I et ERCF ou ERC-II, respectivement. Les avantages du test ERCT sont bien conservés. La réalisation des essais ERC-I, ERC-II et ERC-III permet de mesurer la ténacité de chacun des trois modes purs sur des éprouvettes ayant la même géométrie. Finalement, nous avons étudié numériquement la faisabilité de réaliser les essais de délaminage en mode mixte I + II, I + III et I + II + III sur les éprouvettes ERC. Il s'avère que le rapport modal en mode mixte peut être obtenu dans une large gamme en faisant varier la géométrie de l'éprouvette et en combinant les modes de chargement. Aucun mode indésirable n'est présent lors des essais en mode mixte I+II ou en mode mixte I+III. Cependant la distribution de GI, GII et GIII ne sont pas complètement uniforme, mais sa variation reste assez petite. En conclusion, les tests ERC proposés dans cette étude sont prometteurs pour la caractérisation du comportement au délaminage en mode mixte des composites. Il serait possible, dans un avenir proche, de proposer un critère de délaminage en mode mixte I+II+III basé sur une étude utilisant des essais sur éprouvettes ERC
The aim of this research work is to characterize the delamination behavior of laminate composite materials under the three pure modes and mixed modes, focusing especially on the complex issue of mode III. Both experimental and numerical works were performed, validating the existing and new testing methods. Correlation between the results obtained aims, on the one hand to better understand the distribution of strain energy release rates (GI, GII, GIII) along the crack front; on the other hand, to propose and improve testing methods, and to propose and validate simple approaches for determination of delamination toughness. Pure mode III testing methods are studied. Firstly, two kinds of Edge Crack Torsion tests were carried out, the distribution of GIII along the crack front were determined by finite element analysis (FEA) using virtual crack closure technique (VCCT). The performances of these tests are compromised by the drawbacks: (1) A participation of mode II component cannot be completely eliminated; (2) The distribution of GIII along the crack front is not uniform especially near the sides. After a study of existing tests, a novel mode III testing method was proposed, named Edge Ring Crack Torsion test (ERCT or ERC-III later). In the ERC specimen, the total absence of sides in the circular crack front leads to no edge effects. As a result, pure mode III delamination is achieved and the distribution of GIII along the crack front is quite uniform. In fact, the values of GIII along the crack front are nearly constant after optimizing and modifying the geometry of device in the original ERCT test. A closed-form solution proposed by Tada is applied to determine mode III delamination toughness. In ERCT test, the results calculated by Tada formula agree well with the ones calculated by VCCT when the distribution of GIII is relatively uniform. Actually, a numerical study shows that the distribution of GIII can be affected by different factors related to the nature of laminates tested, the geometry of test device and the geometry of the specimens. The interactive effect of above factors was also discussed in this study. In order to understand the influence of potential defaults on the performance of ERCT test, sensitivity study has been performed on the relative position of the crack front, the circularity of the crack front and the specimen shape. Optimum specimen's relative pre-crack geometry is given and a method for reducing the variation is provided. Then the application of ERC specimen was generalized to other pure delamination modes characterization. Pure mode I can be realized if ERC specimens are loaded in tension, named ERCTE or ERC-I, so can pure mode II if ERC specimens are loaded in flexion, named ERCF or ERC-II. The distribution of the strain energy release rates was also evaluated by FEA using VCCT. These tests keep most advantages of ERC-III test. Pure mode I and pure mode II delamination are achieved respectively and the distribution of GI or GII along the crack front is quite uniform. The realization of ERC-I, ERC-II and ERC-III allows to measure the toughness of each of three pure modes without any interference from geometry of specimens. Finally, we have studied numerically the feasibility to realize the delamination tests in mixed mode I+II, I+III and I+II+III by using ERC specimen. Firstly, the mixed mode ratio can be obtained in a large range by varying the geometry of the specimen and by combining loading modes. Secondly, no unwanted mode is presented for mixed mode I+II and mixed mode I+III; Thirdly, the distribution of strain energy release rates are not completely uniform but its variation is small enough to be accepted. In conclusion, ERC tests are promising testing methods for characterization of mixed mode delamination behavior. It will be possible to propose a mixed mode I+II+III delamination criterion based on the investigation by ERC tests in a close future

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42

Seon, Guillaume. "Finite element-based failure models for carbon/epoxy tape composites." Thesis, Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/28117.

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43

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.

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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 industrielle
Carbon 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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44

Rodriguez, George IV. "Finite Element Modeling of Delamination Damage in Carbon Fiber Laminates Subject to Low-Velocity Impact and Comparison with Experimental Impact Tests Using Nondestructive Vibrothermography Evaluation." DigitalCommons@CalPoly, 2016. https://digitalcommons.calpoly.edu/theses/1583.

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Carbon fiber reinforced composites are utilized in many design applications where high strength, low weight, and/or high stiffness are required. While composite materials can provide high strength and stiffness-to-weight ratios, they are also more complicated to analyze due to their inhomogeneous nature. One important failure mode of composite structures is delamination. This failure mode is common when composite laminates are subject to impact loading. Various finite element methods for analyzing delamination exist. In this research, a modeling strategy based on contact tiebreak definitions in LS-DYNA®was used. A finite element model of a low-velocity impact event was created to predict delamination in a composite laminate. The resulting delamination relative size and shape was found to partially agree with analytical and experimental results for similar impact events, while the force-time plot agreed well with experimental results. A small difference in contact time in the simulation compared to experimental testing is likely due to the omission of composite failure modes other than delamination. Experimental impact testing and subsequent vibrothermography analysis showed delamination damage in locations shown in previous research. This confirmed the validity of vibrothermography as a nondestructive evaluation technique for analyzing post-impact delamination.

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45

Kulkarni, Mandar Madhukar. "Prediction of Elastic Properties of a Carbon Nanotube Reinforced Fiber Polymeric Composite Material Using Cohesive Zone Modeling." University of Cincinnati / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1235433423.

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46

Matheas, Jan. "Entwicklung von Finiten Schalenelementen zur Berechnung von Verstärkungen aus Textilbeton bei Flächentragwerken." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2007. http://nbn-resolving.de/urn:nbn:de:swb:14-1177589904936-74048.

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In der vorliegenden Dissertation wird auf der Grundlage einer kontinuumsmechanischen Herangehensweise die Formulierung eines mechanischen Modells in Verbindung mit der Umsetzung in ein Schalenelement im Rahmen der Finite-Element-Methode zur Simulation des Tragverhaltens geschichteter Flächentragwerksstrukturen unter Berücksichtigung der Schädigungsart Delamination vorgestellt. Grundlage des Mehrschichten-Modells ist die Entwicklung einer geometrisch nichtlinearen oberflächenorientierten Schalentheorie mit schub- und dickenelastischem Verhalten ausgehend von der vollständigen Kinematik einer Multidirektor-Theorie. Der Oberflächenbezug gewährleistet eine auf Kontaktprobleme angepasste mechanische Modellbildung. Innerhalb der Schichten wurde ein Materialgesetz für linear elastisches, orthotropes Material verwendet, dessen Dreidimensionalität durch die Schalenformulierung nicht eingeschränkt wird. Das Hauptaugenmerk der Arbeit liegt auf der Entwicklung eines auf verschiedene Materialien anpassbaren Schichten-Verbundmodells. Das Versagen des Schichtenverbundes – Delamination genannt – wurde durch ein einfaches Spannungskriterium beschrieben. Die Delamination wird durch Modifikation der kinematischen Bedingungen diskret berücksichtigt. Zur Beschreibung des Tragverhaltens nach Ausbildung der Delamination wurde ein als „innerer Kontakt“ bezeichnetes Kontakt-Modell entwickelt, durch das Adhäsion zwischen den Schichten berücksichtigt werden kann. Das vorliegende Schalenmodell kann bei Berücksichtigung von Delamination auf Probleme, in denen kleine Relativverschiebungen zu erwarten sind, für beliebige elastische Materialien angewendet werden. Der Rahmen, in dem diese Arbeit entstand, gab den hauptsächlichen Einsatzbereich, die Simulation von Flächentragwerksstrukturen mit einer Verstärkungsschicht aus textilbewehrtem Feinbeton, vor
This publication introduces, in a continuum-mechanical approach, the formulation of a mechanical model in connection with the transformation into a shell element using the finite element method for the simulation of the load-bearing behaviour of laminated shell structures thereby considering delamination as a type of damage. This multi-layer model is based upon the development of a geometrically nonlinear surface-related shell theory with shear-elastic behaviour and variable thickness, beginning with the complete kinematics of a multi-director theory. The surface relationship ensures a mechanical modelling which is adaptable for contact problems. A linear-elastic orthotropic material law, whose three-dimensionality is not restricted by the shell formulation, applies within the layers. The main focus of the thesis is on the development of a layer-bond model that can be adjusted for different materials. The debonding of layers – called delamination – is described by a simple stress criterion. Delamination is discretely taken into account by modifying the kinematic conditions. A contact model, called „inner contact“, that can be used to account for adhesion between layers, has been developed to describe the load-bearing behaviour after delamination has occurred. The present shell model is restricted to elastic material behaviour and can preferably be applied to such problems where small relative displacements are expected. The environment, in which this research has been conducted, established the primary of application area, which is the simulation of shell structures within a strengthening layer comprised of textile-reinforced concrete

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47

Matheas, Jan. "Entwicklung von Finiten Schalenelementen zur Berechnung von Verstärkungen aus Textilbeton bei Flächentragwerken." Doctoral thesis, Technische Universität Dresden, 2005. https://tud.qucosa.de/id/qucosa%3A24873.

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In der vorliegenden Dissertation wird auf der Grundlage einer kontinuumsmechanischen Herangehensweise die Formulierung eines mechanischen Modells in Verbindung mit der Umsetzung in ein Schalenelement im Rahmen der Finite-Element-Methode zur Simulation des Tragverhaltens geschichteter Flächentragwerksstrukturen unter Berücksichtigung der Schädigungsart Delamination vorgestellt. Grundlage des Mehrschichten-Modells ist die Entwicklung einer geometrisch nichtlinearen oberflächenorientierten Schalentheorie mit schub- und dickenelastischem Verhalten ausgehend von der vollständigen Kinematik einer Multidirektor-Theorie. Der Oberflächenbezug gewährleistet eine auf Kontaktprobleme angepasste mechanische Modellbildung. Innerhalb der Schichten wurde ein Materialgesetz für linear elastisches, orthotropes Material verwendet, dessen Dreidimensionalität durch die Schalenformulierung nicht eingeschränkt wird. Das Hauptaugenmerk der Arbeit liegt auf der Entwicklung eines auf verschiedene Materialien anpassbaren Schichten-Verbundmodells. Das Versagen des Schichtenverbundes – Delamination genannt – wurde durch ein einfaches Spannungskriterium beschrieben. Die Delamination wird durch Modifikation der kinematischen Bedingungen diskret berücksichtigt. Zur Beschreibung des Tragverhaltens nach Ausbildung der Delamination wurde ein als „innerer Kontakt“ bezeichnetes Kontakt-Modell entwickelt, durch das Adhäsion zwischen den Schichten berücksichtigt werden kann. Das vorliegende Schalenmodell kann bei Berücksichtigung von Delamination auf Probleme, in denen kleine Relativverschiebungen zu erwarten sind, für beliebige elastische Materialien angewendet werden. Der Rahmen, in dem diese Arbeit entstand, gab den hauptsächlichen Einsatzbereich, die Simulation von Flächentragwerksstrukturen mit einer Verstärkungsschicht aus textilbewehrtem Feinbeton, vor.
This publication introduces, in a continuum-mechanical approach, the formulation of a mechanical model in connection with the transformation into a shell element using the finite element method for the simulation of the load-bearing behaviour of laminated shell structures thereby considering delamination as a type of damage. This multi-layer model is based upon the development of a geometrically nonlinear surface-related shell theory with shear-elastic behaviour and variable thickness, beginning with the complete kinematics of a multi-director theory. The surface relationship ensures a mechanical modelling which is adaptable for contact problems. A linear-elastic orthotropic material law, whose three-dimensionality is not restricted by the shell formulation, applies within the layers. The main focus of the thesis is on the development of a layer-bond model that can be adjusted for different materials. The debonding of layers – called delamination – is described by a simple stress criterion. Delamination is discretely taken into account by modifying the kinematic conditions. A contact model, called „inner contact“, that can be used to account for adhesion between layers, has been developed to describe the load-bearing behaviour after delamination has occurred. The present shell model is restricted to elastic material behaviour and can preferably be applied to such problems where small relative displacements are expected. The environment, in which this research has been conducted, established the primary of application area, which is the simulation of shell structures within a strengthening layer comprised of textile-reinforced concrete.

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48

Singh, Hitendra Kumar. "Determining Interfacial Adhesion Performance and Reliability for Microelectronics Applications Using a Wedge Test Method." Thesis, Virginia Tech, 2004. http://hdl.handle.net/10919/30973.

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Fracture mechanics is an effective approach for characterizing material resistance to interfacial failure and for making interface reliability predictions. Because interfacial bond integrity is a major concern for performance and reliability, the need to evaluate the fracture and delamination resistance of an interface under different environmental conditions is very important. This study investigates the effects of temperature, solution chemistry and environmental preconditioning, in several solutions on the durability of silicon/epoxy and glass/epoxy systems. A series of experiments was conducted using wedge test specimens to investigate the adhesion performance of the systems subjected to a range of environmental conditions. Both silicon and glass systems were relatively insensitive to temperature over a range of 22-60Â°C, but strongly accelerated by temperatures above 60Â°C, depending on the environmental chemistry and nature of the adhesive system used. Silicon/commercial epoxy specimens were subjected to preconditioning in deionized (DI) water and more aggressive solution mixtures prior to wedge insertion to study the effect of prior environmental exposure time on the system. The wedge test data from preconditioned specimens were compared with standard wedge test results and the system was insensitive to preconditioning in DI water but was affected significantly by preconditioning in aggressive environments. Plots describing - G (crack velocity versus applied strain energy release rate) characteristics for a particular set of environmental conditions are presented and a comparison is made for different environmental conditions to quantify the subcritical debonding behavior of systems studied. A kinetic model to characterize subcritical debonding of adhesives for microelectronic applications is also proposed based on molecular interactions between epoxy and a silane coupling agent at the interface and linear elastic fracture mechanics, which could help predict long-term deterioration of interfacial adhesion.
Master of Science

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Pour, Shahid Saeed Abadi Parisa. "Mechanical behavior of carbon nanotube forests under compressive loading." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47699.

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Carbon nanotube (CNT) forests are an important class of nanomaterials with many potential applications due to their unique properties such as mechanical compliance, thermal and electrical conductance, etc. Their deformation and failure in compression loading is critical in any application involving contact because the deformation changes the nature of the contact and thus impacts the transfer of load, heat, and charge carriers across the interface. The micro- and nano-structure of the CNT forest can vary along their height and from sample to sample due to different growth parameters. The morphology of CNTs and their interaction contribute to their mechanical behavior with change of load distribution in the CNT forest. However, the relationship is complicated due to involvement of many factors such as density, orientation, and entanglement of CNTs. None of these effects, however, are well understood. This dissertation aims to advance the knowledge of the structure-property relation in CNT forests and find methodologies for tuning their mechanical behavior. The mechanical behavior of CNT forests grown with different methodologies is studied. Furthermore, the effects of coating and wetting of CNT forests are investigated as methods to tailor the degree of interaction between CNTs. In situ micro-indentation of uncoated CNT forests with distinct growth-induced structures are performed to elucidate the effects of change of morphology along the height of CNT forests on their deformation mechanism. CNT aerial density and tortuosity are found to dictate the location of incipient deformation along height of CNT forests. Macro-compression testing of uncoated CNT forests reveals mechanical failure of CNT forests by delamination at the CNT-growth substrate. Tensile loading of CNT roots due to post-buckling bending of CNTs is proposed to be the cause of this failure and simple bending theory is shown to estimate the failure load to be on the same order of magnitude as experimental measurements. Furthermore, delamination is observed to occur in the in situ micro-indentation of CNT forests coated with aluminum on the top surface, which demonstrates the role of the mechanical constraints within the CNT forest in the occurrence of delamination at the CNT-substrate interface. In addition, this dissertation explores the mechanical behavior of CNT forests coated conformally (from top to bottom) with alumina by atomic layer deposition. In situ micro-indentation testing demonstrates that the deformation mechanism of CNT forests does not change with a thin coating (2 nm) but does change with a sufficiently thick coating (10 nm) that causes fracturing of the hybrid nanotubes. Ex situ flat punch and Berkovich indentations reveal an increase in stiffness of the CNT forests that are in range with those predicted by compression and bending theories. An increase in the recoverability of the CNTs is also detected. Finally, solvent infiltration is proposed as a method of decreasing stiffness of CNT forests and changing the deformation mechanism from local to global deformations (i.e., buckling in the entire height). Presence of solvents between CNTs decreases the van der Waals forces between them and produces CNT forests with lower stiffness. The results demonstrate the effect of interaction between CNTs on the mechanical behavior. This dissertation reveals important information on the mechanical behavior of CNT forests as it relates to CNT morphology and tube-to-tube interactions. In addition, it provides a framework for future systematic experimental and theoretical investigations of the structure-property relationship in CNT forests, as well as a framework for tuning the properties of CNT forests for diverse applications.

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Zheng, Jiantao. "Interfacial fracture of micro thin film interconnects under monotonic and cyclic loading." Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/26489.

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Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2009.
Committee Chair: Sitaraman, Suresh; Committee Member: Degertekin, Levent; Committee Member: McDowell, David; Committee Member: Tummala, Rao; Committee Member: Vandentop, Gilroy; Committee Member: Wang, Zhong Lin. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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Dissertations / Theses on the topic 'Delamination mechanism'

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