Dissertations / Theses on the topic 'Interfacial Debonding'

The problem of a thin elastomeric layer confined between two stiff adherends arises in numerous applications such as microelectronics, bio-inspired adhesion and the manufacture of soft biomedical products. A common requirement is that the debonding of the elastomeric layer from the adherends be controlled to avoid undesirable failure modes. This level of control may necessitate understanding the collective role of the interfacial adhesion, material properties, part geometries, and loading conditions on the debonding. Analytical and numerical approaches using the finite element method and a cohesive zone model (CZM) for the interfacial debonding are used in this dissertation to delineate the role of the afore-mentioned parameters on the initiation and propagation of debonding for both rigid and non-rigid adherends. Extensively studied in the dissertation is the debonding of a semi-infinite relatively stiffer adherend from an elastomer layer with its other surface firmly bonded to a rigid base. The adherend is pulled upwards by applying normal displacements either on its entire unbonded surface or on the edge of its part overhanging from the elastomer layer. The adherend and the elastomeric layer materials are assumed to be linear elastic, homogeneous and isotropic and the elastomer is assumed to be incompressible. Viscoelasticity of the elastomer is considered in the first part of the work. Plane strain deformations of the system with a bilinear traction-separation (TS) relation in the CZM are analyzed. Two non-dimensional numbers, one related to the layer confinement and the other to the interfacial TS parameters, are found to determine if debonding initiates at interior points in addition to at corner points on the adherend/elastomer interface, and if adhesion-induced instability is exhibited. This work is extended to axisymmetric problems in which debonding can take place at both interfaces. Motivated by an industrial demolding problem, numerical experiments are conducted to derive insights into preferential debonding at one of the two interfaces, including for curved adherends. Results reported herein should help engineers design an elastomer layer sandwiched between two adherends for achieving desired failure characteristics.
Ph. D.

Extensive research and recent developments in structural engineering has shown that adhesive bonding of fibre-reinforced polymer (FRP) composite, steel or any other metallic plate to the tension face of a reinforced concrete (RC), metallic or timber beam can effectively enhance its strength and other aspects of structural performance. This technique is now popularly adopted for retro-fitment and rehabilitation of existing structures. These plated beams often fail prematurely well before attaining the full flexural capacity by either plate end debonding (PED) or intermediate crack-induced interfacial debonding (ICD) failure. Concentration of higher interfacial shear and normal stresses at the plate end due to a geometric discontinuity is believed to be responsible for PED that initiates at the plate end and propagates inwards. PED includes concrete cover separation and interfacial debonding initiated at the plate end; and such failure initiated at a critical diagonal crack. ICD initiates at an intermediate major flexural or flexural-shear crack in the soffit of the original beam due to high bond stress and propagates towards one of the plate ends (type-1) or an adjacent crack (type-2). This thesis presents a study of interfacial stresses and debonding failures in plated beams. It first presents a simple and novel theoretical solution of interfacial stresses applicable to any loading considering major deformations like axial and flexural deformations in the beam and plate within linear elastic range. This solution is then enhanced with the inclusion of the effect of adherends’ shear deformation by approximating the displacement field for interfacial shear stress and using Timoshenko’s beam theory for interfacial normal stress, achieving a better understanding of the effect of shear deformation which is ill-understood. This resulted in a first ever solution to include the effect of adherends’ shear deformation under both interfacial shear and normal stresses. This solution is further advanced by developing a rigorous and a versatile closed-form solution fully based on Timoshenko’s beam theory that offered a significant insight. Interfacial stresses at the plate end cannot be measured directly using available measurement techniques, and may only be interpreted indirectly from measured plate strains. The conventional interpretation is based on the assumption that the plate is under pure tension. A significant drawback of this is that the interfacial normal stresses iii cannot be deduced. A new technique is developed to deduce both interfacial shear and normal stresses from strain measurements. The thesis presents three PED strength models for the special case of an RC beam with the plate terminated in the constant moment region: a theoretical model based on interfacial fracture mechanics with a reasonable accuracy; a semi-empirical model with greater accuracy; and an empirical model that is slightly less accurate but simpler to apply than the semi-empirical model. This is followed by the development of a shear debonding model to predict the debonding failure in an RC beam with the plate terminated in high shear and a very low or zero moment region. The two models for PED failure in pure bending and pure shear zones are then combined to result in an accurate shear-bending interaction debonding model. An assessment of these models against a carefully constructed large test database shows that they are more accurate than existing models and suitable for implementation in design codes or guidelines. Finally, a structural mechanics formulation for an FRP-to-concrete bonded joint between two adjacent cracks is developed. It considers axial forces, transverse shear forces and bending moments in the adherends and uses a linearly softening bond-slip model. A section analysis with partial interaction and a rotational spring method are used to relate the applied loading to the interfacial deformation. A closed-form solution is obtained that may form the basis of a rational ICD design method.

Les revêtements d'hydrogel sont des réseaux de polymères transparents et hydrophiles capables d’abosrber plusieurs fois leur épaisseur en eau. Cependant, les contraintes induites par le gonflement du film peuvent entraîner un décollement préjudiciable de l'hydrogel ce qui peut limiter l’utilisation pratique des ces revêtements. Dans cette étude, nous proposons de décrire les mécanismes de décollement de films minces d’hydrogel en fonction de leur densité de greffage à l'interface film/substrat. Le but est de pouvoir contrôler et prédire la dégradation des revêtements hydrogel pendant le gonflement ou sous des contraintes de contact. Dans ce but, nous avons développé une méthodologie permettant de mesurer l'initiation et la propagation de la délamination induite par le gonflement de films minces d’hydrogel à partir de défauts d'interface préexistants bien contrôlés.Des films minces d'hydrogel de poly(diméthylacrylamide) (PDMA) attachés à la surface sont préparés sur des plaquettes de silicium à partir de la réticulation et du greffage simultanés (CLAG) de chaînes polymères fonctionnalisées par la chimie click thiol-ène. Cette stratégie permet de faire varier l'épaisseur du film (0.1 - 2 µm) et de contrôler le taux de gonflement du réseau, ici fixé à 2, tout en assurant une densité de réticulation homogène. Afin de faire varier la résistance de l'interface film/substrat, le substrat en silicium est greffé avec des mélanges de mercaptosilane (réactif) et de propylsilane (inerte) dans différentes proportions avant le dépôt du film mince. Alors que le mercaptosilane est capable de former des liaisons covalentes avec le réseau PDMA, le propylsilane ne réagit pas, ce qui permet de contrôler le taux de greffage du film mince d’hydrogel sur le substrat. Nous caractérisons la fraction de surface de mercaptosilane ainsi obtenue par des analyses XPS et TOF-SIMS. Par ailleurs, toujours à l’interface subtrat/film, des défauts linéaires bien contrôlés ayant une faible adhérence (largeur entre 10 et 100 µm) sont créés sur le substrat en passivant de façon localisée les groupes thiol réactifs par microlithographie. Ces défauts nucléent le décollement des films de façon bien localisée, ce qui permet ensuite de suivre la propagation de la décohésion à partir de ces défauts.Le décollement du film induit par le gonflement est réalisé sous un flux de vapeur constant assurant la saturation du film en eau. En observant le décollement progressif du film à partir des défauts linéaires préexistants, nous retrouvons un motif d’instabilité classique dit de fil de téléphone et nous montrons que le décollement résulte de contraintes de gonflement localisées proche de la ligne de décollement. Nous mesurons la vitesse de propagation du décollement dans la zone où le film est greffé sur le substrat et nous observons qu’elle augmente de deux ordres de grandeur lorsque la quantité de propylsilane dans le mélange de silanes réactifs passe de 0 à 90 %, c’est-à-dire lorsque le taux de greffage du film décroit. Un seuil d'épaisseur pour le décollement est également observé, les films pouvant se décoller étant d’autant plus minces que le taux de greffage du film ets faible. Les mesures de ce seuil sont discutées à partir d'un argument simple de mécanique de la rupture qui permet de rendre compte semi quantitativement de nos mesures
Hydrogel coatings are transparent and hydrophilic polymer networks that absorb a lot of water and can be suitable candidates for anti-mist coatings. However, swelling-induced stresses within the film can result in detrimental debonding of hydrogel and may fail. In this study, these debonding processes are investigated in the relation to the grafting density at the film/substrate interface, so as to control and predict the failure of the coatings during swelling or under contact stresses. For that purpose, we have developed a methodology consisting in monitoring the initiation and the propagation of swelling-induced delamination from well-controlled preexisting interface defects.Surface-attached poly(dimethylacrylamide) (PDMA) hydrogel thin films are prepared on silicon wafers from the simultaneous Cross-Linking And Grafting (CLAG) of functionalized polymer chains by thiol-ene click chemistry. This strategy allows to tune the film thickness (0.1-2 µm) while ensuring a homogeneous crosslinking density. In order to vary the strength of the film/substrate interface, the silicon wafer is grafted by mixing reactive mercaptosilane and unreactive propylsilane in various proportions prior to the formation of the hydrogel film. We characterize the mercaptosilane surface fraction thus obtained by XPS and TOF-SIMS analyses. Well-controlled line defects (width between 2 and 100 µm) are also created to nucleate delamination of the hydrogel from the substrate.Swelling-induced debonding of the film is achieved under a constant vapor flow ensuring water saturation. Optical observations show the progressive debonding of the film from the pre-existing line defects under the action of localized swelling stresses. We obtain a delamination pattern of typical so-called telephone cord instability. We measure the debonding propagation velocity where the hydrogel is grafted to the substrate. The debonding rate is found to decrease over two orders of magnitude when the amount of mercaptosilane in the reactive silane mixture is increased from 10% to 100% while increasing the covalent bonds between hydrogel and substrate. A threshold thickness for debonding is also observed. This threshold thickness increases with the amount of mercaptosilane used to graft the substrate. We derived quantitative values of the interface fracture energy from the measured thickness threshold with a simple fracture mechanics model

Kyoto University (京都大学)
0048
新制・課程博士
博士(工学)
甲第14575号
工博第3043号
新制||工||1453(附属図書館)
26927
UT51-2009-D287
京都大学大学院工学研究科材料工学専攻
(主査)教授 落合 庄治郎, 教授 粟倉 泰弘, 准教授 奥田 浩司
学位規則第4条第1項該当

Thermally induced interfacial stress states between fiber and matrix at cryogenic temperature were studied using three-dimensional finite element based micromechanics. Mismatch of the coefficient of thermal expansion between fiber and matrix, and mismatch of coefficient of thermal expansion between plies with different fiber orientation were considered. In order to approximate irregular fiber distributions and to model irregular fiber arrangements, various types of unit cells, which can represent nonuniformity, were constructed and from the results the worst case of fiber distributions that can have serious stress states were suggested. Since it is difficult to measure the fiber transverse coefficient of thermal expansion at the micro scale, there is an uncertainty problem for stress analysis. In order to investigate the effect of error in assumed fiber transverse coefficient of thermal expansion on thermally induced interfacial stresses, systematic studies were carried out. In this paper, the effect of measurement errors on the local stress states will be studied. Also, in order to determine fiber transverse CTE values from lamina properties, a back calculation method is used for various composite systems.

In the last decades the theme of structural rehabilitation has acquired great importance and the adoption of composite materials in civil engineering applications has been a turning point in this field. The cement-based matrix of FRCM composites presents many advantages for their application to historical buildings. This dissertation presents a study of the influence of composite bonded length and width on the load response and failure mode. Two types of mortar matrix and two different steel densities were employed. The classical push pull configuration is adopted where fibers are pulled while the masonry block is restrained. Based on the experimental results and through a fracture mechanics approach, the cohesive material laws for mode II was obtained. For the completeness of the work, the characterization of each material involved in the single-lap shear test has been achieved.

As hydrogel products are manufactured and used for applications ranging from biomedical to agricultural, it is useful to characterize their behavior and interaction with other materials. This thesis investigates the adhesion between two different solvated semi-interpenetrating polymer network (S-IPN) silicone hydrogels and a cyclo-olefin (COP) polymer through experimental, analytical, and numerical methods.

Interfacial fracture data was collected through the application of the wedge test, a relatively simple test allowing for the measurement of fracture properties over time in environments of interest. In this case, the test was performed at discrete temperatures within range of 4Ë C to 80Ë C. Two COP adherends were bonded together by a layer of one of the S-IPN silicone hydrogels. Upon the insertion of a wedge between the two adherends, debonding at one of the two interfaces would initiate and propagate at a decreasing rate. Measurements were taken of the debond length over time and applied to develop crack propagation rate versus strain energy release rate (SERR) curves. The SERR values were determined through the application of an analytical model derived for the wedge test geometry and to take into account the effects of the hydrogel interlayer. The time-temperature superposition principle (TTSP) was applied to the crack propagation rate versus SERR curves by shifting the crack propagation rates with the Williams-Landel-Ferry (WLF) equation-based shift factors developed for the bulk behavior of each hydrogel. The application of TTSP broadened the SERR and crack propagation rate ranges and presented a large dependency of the adhesion of the system on the viscoelastic nature of the hydrogels. Power-law fits were applied to the master curves in order to determine parameters that could describe the adhesion of the system and be applied in the development of a finite element model representing the interfacial fracture that occurs for each system. The finite element models were used to validate the analytical model and represent the adhesion of the system such that it could be applied to future geometries of interest in which the S-IPN silicone hydrogels are adhered to the COP substrate.

[Files modified per J. Austin, July 9, 2013 GMc]
Master of Science

Les travaux menés dans le cadre de cette thèse ont pour objectif le développement d'une approche numérique performante, basée sur la Méthode des Éléments Discrets (MED) pour simuler le comportement hygro-thermo-mécanique d'un matériau composite à fibres de verre courtes. La modélisation discrète proposée est mise en œuvre dans le cas d'un matériau composite Polyamide 6 renforcé avec 30% de fibres de verre (PA6/GF30). Tout d'abord, les propriétés mécaniques ainsi que les mécanismes d'endommagement du PA6/GF30 sont évalués expérimentalement. Ensuite, un modèle 3D par Éléments Discrets(ED), en s'appuyant sur une méthodologie originale, est développé et validé par comparaison avec des approches micromécaniques et des résultats expérimentaux,en termes de propriétés élastiques. Par ailleurs, le modèle discret mis au point est exploité afin de simuler le processus de délamination en mode I, II et mixte en utilisant un modèle de zone cohésive 3D définit selon une loi de traction-séparation bilinéaire. La décohésion interfaciale fibre/matrice sous sollicitations mécaniques, respectivement dans le cas d'un composite mono-fibre et multifibre est également étudiée. Compte tenu du caractère hydrophile du PA6, l'introduction du modèle de décohésion trouve son intérêt dans la prise en compte de l'endommagement interfacial dû à l'absorption d'eau à l'interface fibre/matrice en présence d'humidité. Par conséquent, des paramètres hygro-thermo-mécaniques sont intégrés au modèle ED afin de tenir compte du gonflement hygroscopique et de l'endommagement du PA6/GF30 dans une large gamme de conditions environnementales. Des comparaisons avec la Méthode des Éléments Finis (MEF) ont été établies afin de vérifier la validité du modèle ED proposé
This thesis work aims at developing a powerful numerical tool based on the Discrete Element Method (DEM) to simulate the hygro-thermo-mechanical behaviour of a short glass fibre composite material. The proposed discrete modelling is performed in the case of a Polyamide 6 composite material reinforced with 30% of glass fibres (PA6/GF30). First of all, mechanical properties as well as damage mechanisms of PA6/GF30 are evaluated using experimental campaign. Then, a 3D Discrete Element (DE) model based on an original methodology is developed and validated by comparison with micromechanical approaches and experimental results in terms of elastic behaviour of PA6/GF30. Furthermore, the developed discrete model is exploited to simulate delamination process on mode I, II and mixed mode using a 3D cohesive zone model with a bilinear tractionseparation law. The fibre/matrix interfacial decohesion under mechanical stress,respectively in the case of a single-fibre and multi-fibre composite is also studied. Given the hydrophilic nature of PA6, the introduction of the decohesion model is interesting in order to take into account the interfacial damage due to water absorption at the fibre/matrix interface in the presence of moisture. Therefore, hygro-thermo-mechanical parameters are integrated into the discrete model in order to take into account the hygroscopic swelling and the damage of PA6/GF30 material under a wide range of environmental conditions. Comparisons with the Finite Element Method (FEM) have been established to check out the validity of the proposed DE model

Cette thèse traite de la modélisation multi-échelle de composites particulaires fortement chargés. La méthode d’estimation, qualifiée d’“Approche Morphologique” (A.M.), repose sur une double schématisation géométrique et cinématique du composite permettant de fournir la réponse aux deux échelles. Afin d’évaluer les capacités prédictives de l’A.M. en élasticité linéaire avec évolution de l’endommagement, l’A.M. est testée vis-à-vis de ses aptitudes à rendre compte des effets de taille et d’interaction de particules sur la chronologie de décohésion. Pour cela, différentes microstructures périodiques simples, aléatoires monomodales et bimodale générées numériquement sont considérées. Les résultats obtenus sont cohérents avec les données de la littérature : la décohésion des grosses particules précède celle des plus petites et est d’autant plus précoce que le taux de charges est important. Puis, l’objectif est de coupler deux non-linéarités traitées séparément dans deux versions antérieures de l’A.M : l’endommagement par décohésion charges/matrice et les grandes déformations. La formulation du problème de localisation-homogénéisation est reprise à la source de manière analytique. Le critère de nucléation de défauts est étendu en transformations finies. Le problème obtenu, fortement non-linéaire, est résolu numériquement via un algorithme de Newton-Raphson. Les étapes sous-jacentes à la résolution (calcul de la matrice tangente, codage en langage Python®) sont explicitées. Des évaluations progressives (matériaux sain et endommagé)permettent de valider la mise en oeuvre numérique. Les effets de taille et d’interaction sont alors restitués en transformations finies
This study is devoted to multi-scale modeling of highly-filled particulate composites.This method, the “Morphological Approach” (M.A.), is based on a geometrical and kinematicalschematization which allows the access to both local fields and homogenized response. In order toevaluate the predictive capacities of the M.A. considering a linear elastic behavior for the constituentsand evolution of damage, analysis is performed regarding the ability of the M.A. to accountfor particle size and interaction effects on debonding chronology. For that purpose, simple periodic,random monomodal and bimodal microstructures are considered. The results are consistent withliterature data : debonding of large particles occurs before the one of smaller particles and thehigher the particle volume fraction, the sooner the debonding. Finally, the objective is to operatethe coupling of two non linearities which were separately studied in previous versions of the M.A. :debonding between particles and matrix, and finite strains. The whole analytical background of theapproach is reconsidered in order to define the localization-homogenization problem. The nucleationcriterion is extended to the finite strains context. The final problem, strongly non linear, is numericallysolved through a Newton-Raphson algorithm. The different solving steps (jacobian matrix,coding with Python®) are developed. Progressive evaluations (sound and damage materials) allowthe validation of numerical implementation. Then, size and interaction effects are reproduced infinite strains

In this thesis, the focus has been on micro-mechanical mechanisms in polymer-based materials and structures. The first part of the thesis treats length-scale effects on polymer materials. Experiments have showed that the smaller the specimen, the stronger is the material. The length-scale effect was examined experimentally in two different polymers materials, polystyrene and epoxy. First micro-indentations to various depths were made on polystyrene. The experiments showed that length-scale effects in inelastic deformations exist in polystyrene. It was also possible to show a connection between the experimental findings and the molecular length. The second experimental study was performed on glass-sphere filled epoxy, where the damage development for tensile loading was investigated. It could be showed that the debond stresses increased with decreasing sphere diameter. The debonding grew along the interface and eventually these cracks kinked out into the matrix. It was found that the length to diameter ratio of the matrix cracks increased with increasing diameter. The experimental findings may be explained by a length-scale effect in the yield process which depends on the strain gradients. The second part of the thesis treats mechano-sorptive creep in paper, i.e. the acceleration of creep by moisture content changes. Paper can be seen as a polymer based composite that consists of a network of wood fibres, which in its turn are natural polymer composites. A simplified network model for mechano-sorptive creep has been developed. It is assumed that the anisotropic hygroexpansion of the fibres leads to large stresses at the fibre-fibre bonds when the moisture content changes. The resulting stress state will accelerate creep if the fibre material obeys a constitutive law that is non-linear in stress. Fibre kinks are included in order to capture experimental observations of larger mechano-sorptive creep effects in compression than in tension. Furthermore, moisture dependent material parameters and anisotropy are taken into account. Theoretical predictions based on the developed model are compared to experimental results for anisotropic paper both under tensile and compressive loading at varying moisture content. The important features in the experiments are captured by the model. Different kinds of drying conditions have also been examined.
QC 20100910

The performance of smart structures depends on the dynamic electromechanical behavior of piezoelectric sensors/actuators and the bonding condition along the interface. This thesis contents a theoretical study of the coupled electromechanical characteristics of a surface-bonded piezoelectric sensor with interfacial debonding, which is subjected to high frequency mechanical loads. A one dimensional sensor model is proposed. Analytical solutions based on the integral equation method are provided. Numerical simulation is conducted to evaluate the effects of different parameters upon the dynamic load transfer between the sensor and the host medium. The results indicate that, the material combination, the sensor geometry, and the loading frequency, affect the load transfer significantly. The analytical solution of the elastic wave field in the host medium is obtained and used to evaluate the effects of different parameters upon the resulting wave field. The theoretical solution demonstrates the basic properties of wave propagation under current loading conditions.

Thesis (M. Sc.)--University of Alberta, 2009.
Title from pdf file main screen (viewed on Aug. 14, 2009). "A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Master of Science, Department of Mechanical Engineering, University of Alberta." Includes bibliographical references.

碩士
長庚大學
顱顏口腔醫學研究所
98
Purpose: To evaluate the bracket/enamel interfacial mechanics withdifferent adhesives and debonding techniques by using finite element analysis, and to predict which kind of adhesive or debonding technique will most likely to cause enamel damage. Material and methods：(1)Measure the Young’s modulus, Possion’s ration and fracture strength of Transbond XT and Unite by shear force testing. The results would be used in FEA in this study. (2)Create a premolar finite element model; this model was consisted with 6240 nodes and 6157 elements. We recorded the stress distribution when we applied 1N in 2 type of adhesives (Transbond XT & Unite) and 3 type of loading modes(tensile, shear, and torsion forces). (3) To test and verify the results of FEA by shear force testing. Results: (1)The Young’s modulus, Possion’s ration, and fracture strength of Transbond XT and Unite was 8823MPa, 0.25, 52.58±5.59 MPa and 9470MPa, 0.26, 14.58±2.84 MPa, respectively. (2)The tensile, shear, torsion debonding force of Transbond XT and Unite was 57.32N, 103.65N, 105.35N and15.47 N, 28.45N, 28.97N, respectively; the stress concentrated area for tensile force was within the adhesive layer; for shear force was in the enamel-adhesive interface; for torsion force was in the adhesive-bracket interface. (3)Shear force testing showed that the debonding force of Transbond XT was larger than Unite. Conclusions: (1)Because the shear debonding force was large and the stress was concentrated in enamel-adhesive interface, shear force was most likely to induce enamel damage. (2)Transbond XT was most likely to induce enamel damage than Unite due to larger debonding force.