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Open-mode cracks could be commonly observed in layered rocks. A concept model is firstly used to explore the mechanism of the vertical cracks (VCs) in the top layer. Then the crack behaviour of the two-layer model is simulated based on a cohesive zone model (CZM) for layer interfaces and a plastic-damage model for rocks. The model indicates that the tensile stress normal to the VCs changes to compression if the crack spacing to layer thickness ratio is lower than a threshold. The results indicate that there is a threshold for interfacial shear strength that controls the crack patterns of the layered system. If the shear strength is lower than the threshold, the top layer is meshed by the VCs and interfacial cracks (ICs). When the shear strength is higher than the threshold, the top layer is meshed by the VCs and parallel cracks (PCs). If the shear strength is comparative to the threshold, a combining pattern of VCs, PCs and ICs for the top layer can be formed. The evolutions of stress distribution in the crack-bound block indicate that the ICs and PCs can reduce the load transferred for the substrate layer, and thus leads to a crack saturation state. [ABSTRACT FROM AUTHOR]

This paper aims to propose a simulation procedure to predict the interlaminar fracture toughness of stitched flax fiber composites through a virtual double cantilever beam test. The proposed procedure is constituted of two steps. First, the interlaminar failure of unstitched flax fiber laminate, as the parent laminate, is modeled using cohesive elements with a nonlinear softening law in order to model the large-scale fiber bridging occurred during delamination. The experimental results are used to calibrate the parameters of the cohesive law. Second, two-node beam elements are superposed onto the cohesive interface of the parent laminate at a prescribed stitch density and distribution to model the bridging stitches present in the validation samples. The stitch material behavior and properties are obtained from the tensile test of impregnated stitch fibers. The out-of-plane flax yarn stitching was found to generate a twofold increase in the delamination resistance of the composite laminate at a medium stitch density. The FE analysis results agreed well with the experimental results, where a good fit between the predicted and experimental R-curves was achieved. [ABSTRACT FROM AUTHOR]

Material flow during welding is an important factor that affects the quality of friction stir welding (FSW) joints. In this study, a new welding tool/work piece contact model is proposed to simulate material flow near the FSW tool. The material around the tool flows under the driving force of friction non-uniformly distributed on the interface. Friction force is calculated based on modified Coulomb friction law in this model. Wormhole defects under various welding parameters are graphically predicted by the distribution of tracing particles added in numerical models. Five groups of FSW experiments were conducted to obtain temperature and joint morphology results. Simulation results, including temperature and wormhole defects prediction, corresponded with the experimental results. Further analyses imply that under the process parameters selected in this study, an area with very low friction force occurred behind the tool pin. When the material in front of the tool pin moved to this area from the retreating side, the material speed significantly decreased due to the insufficient driving force, and it became difficult for the material to move to the advancing side along the circular path. The study reveals that the non-uniform friction force model provides a potential tool for predicting FSW defects. [ABSTRACT FROM AUTHOR]

Damage and failure process of the unidirectional fiber-reinforced ceramic matrix composites (FRCMCs) under tensile stress had been studied by many researchers in theoretical method. But because of some assumptions made in the theoretical model, it canot describe the performance of interface accurately. In this paper, evolving compliant interface (ECI) is employed to describe the properties of weak bonding interface. The ECI can respond the failure of debonding and sliding of interface efficiently. The whole damage evolution process of the material has been simulated by finite element method (FEM) and the stress-strain curve, the space of cracks at saturated state and the stress of components are discussed. The stress-strain curves of several ceramic composites were predicted by the model and compared with the experimental data. The results indicate that the tensile stress-strain curves agree well with the experimental data on consideration of Evolving compliant interfacial debonding model. [ABSTRACT FROM AUTHOR]

In this paper, a doubly periodic interfacial cracking problem in a layered periodic composite is analyzed under antiplane shear loads. To further understand the interaction effect among the periodic interfacial cracks, four crack configurations are considered, namely a bilayered composite containing a single crack and a periodic array of collinear cracks, a layered periodic composite with a periodic array of parallel cracks and a doubly periodic rectangular array of cracks. In view of the periodic symmetry, the three periodic problems are transformed to a mixed boundary value problem for a single crack problem in an appropriate cell with the suitable periodic boundary conditions on its boundaries. The treatment skills for the periodic array of collinear cracks and the disposal techniques for the periodic array of parallel cracks are used together to solve the doubly periodic rectangular array of cracking problem. To demonstrate the computational accuracy of the present method, detailed comparative analyses are carried out. Numerical results are presented to show the interaction effect among the periodic interfacial cracks. For the doubly periodic rectangular array of cracking problem, parametric studies on the stress intensity factors leads out the following rule: the shielding effect of multiple parallel cracks and the amplifying effect of multiple collinear cracks exist simultaneously, and a coupled effect between geometrical and physical parameters on the interfacial fracture behavior exists clearly. [ABSTRACT FROM AUTHOR]

The focus of this work is to investigate spall fracture in polycrystalline materials under high-speed impact loading by using an atomistic-based interfacial zone model. We illustrate that for polycrystalline materials, increases in the potential energy ratio between grain boundaries and grains could cause a fracture transition from intergranular to transgranular mode. We also found out that the spall strength increases when there is a fracture transition from intergranular to transgranular. In addition, analysis of grain size, crystal lattice orientation and impact speed reveals that the spall strength increases as grain size or impact speed increases. [ABSTRACT FROM AUTHOR]

A finite element approach for calculating the energy release rate ( G ) and individual modes ( G I and G II ) when simulating crack growth through a two-dimensional composite material is presented. A new mesh-substitution scheme is used with basic fracture mechanics concepts to automatically calculate G , G I , and G II for potential growth along material interfaces and at different kink angles. The method is general and can be used when investigating interface cracks, substrate cracks (i.e., cracks contained in a material region), and substrate cracks with tips touching one or more interfaces. For bimaterial interface cracks, a coupled energy release rate ( G I–II ) is determined, and complex stress intensity factor components are calculated. A complete crack propagation framework, which includes the developed methods, is presented and then used to simulate crack growth through a composite material. [ABSTRACT FROM AUTHOR]

A NURBS enhanced extended finite element approach is proposed for the unfitted simulation of structures defined by means of CAD parametric surfaces. In contrast to classical X-FEM that uses levelsets to define the geometry of the computational domain, exact CAD description is considered here. Following the ideas developed in the context of the NURBS-enhanced finite element method, NURBS-enhanced subelements are defined to take into account the exact geometry of the interface inside an element. In addition, a high-order approximation is considered to allow for large elements compared to the size of the geometrical details (without loss of accuracy). Finally, a geometrically implicit/explicit approach is proposed for efficiency purpose in the context of fracture mechanics. In this paper, only 2D examples are considered: It is shown that optimal rates of convergence are obtained without the need to consider shape functions defined in the physical space. Moreover, thanks to the flexibility given by the Partition of Unity, it is possible to recover optimal convergence rates in the case of re-entrant corners, cracks and embedded material interfaces. [ABSTRACT FROM AUTHOR]

Abstract: A numerical study has been performed to investigate the failure process of single fiber composite materials considering interface properties under uniaxial tensile load. In the study, ABAQUS–USDFLD is used to simulate the fiber break and ABAQUS–UMAT is employed to simulate the matrix cracking. In particular, cohesive element is used to simulate the interface properties. From the study, we can see that the degradation factor d involved in the subroutine USDFLD and UMAT has significant effects on the damage initiation. We also found the fiber and matrix affect single fiber composite performance obviously and interface properties affect single fiber composites performance via failure models. [Copyright &y& Elsevier]

Abstract: Thermal barrier coatings, frequently used in turbine blades, comprise a corrosion-protecting bond coat, a ceramic top coat and a growing oxide layer in between. Failure mechanisms of these coating systems are still not satisfactorily understood. In this paper, crack initiation and propagation in thermal barrier coatings is studied with two-dimensional finite element simulations. Cracks are propagated at the interface between the TGO and the TBC either at the peak or at the valley position of asperities for different values of the creep strength of the materials. It is shown that, usually, cracks starting in the valley position have a larger energy release rate than those starting at peaks. Cracks in the peak position propagate in mode II even with rather thin TGO and thus do not relax stresses as effectively as cracks in the valley position. Whether cracks are arrested or not strongly depends on the creep properties. Additional effects that may have to be taken into account to model crack arrest more realistically are also discussed. [Copyright &y& Elsevier]

Abstract: Assessing the healing rate of a fault is relevant to the knowledge of the seismic machinery. However, measuring fault healing at the depths where it occurs still remains inaccessible. We have designed an analog laboratory experiment of a simulated rough fault that undergoes healing and investigate the relative roles of interface chemical reactivity and sliding velocity on the healing rate. Slide-hold-slide experiments are conducted on a bare interface with various materials in contact (glass/glass, salt/glass, and salt/salt) with or without the presence of a reactive fluid and the slider-surface pull-off force is measured. Our results show that the interface strengthens with hold time, whatever the conditions of the experiments. In addition, we quantify the effect of chemical reactivity on the healing rate. Considering the glass/glass case as a reference, we show that the healing rate is increased by a factor of 2 for the salt/glass case; by a factor of 3 for the salt/salt case; and by about a factor of 20 when saturated brine is added on a salt/salt interface. We also measure that the sliding velocity affects the healing rate for salt/salt interfaces at room humidity. A careful optical monitoring of the interface allows a direct observation of the contact growth characteristics associated to each type of materials. Finally, the large differences of healing rate are interpreted through a mechanistic approach, where the various experimental conditions allow separating different healing mechanisms: increase of adhesion of the contacts by welding, contact growth due to creep or due to neck growth driven by surface tension. [Copyright &y& Elsevier]

Abstract: The axisymmetric cell model consisting of interface, matrix and reinforced particle is used to simulate the tensile test of particle reinforced metal matrix composite for predicting the micro stress/strain field and macro tensile stress/strain curve. In simulation of the tensile test, the cohesive element model is selected to model interfacial crack growth. It mainly analyzed the effects of interfacial properties, reinforcement volume fractions and aspect ratios on the stress–strain states of particle reinforced metal matrix composite. The results show that the peak micro stress and plastic strain occur at the interface in which it is a certain angle from the tensile stress direction; with the interfacial fracture toughness and reinforcement volume fraction increasing, the flow stress increases firstly and then decreases. The tensile stress–strain properties of SiC/6064Al are good when the interfacial fracture toughness is equal to 60J/m and the reinforcement fraction volume is equal to 20%. Smaller reinforcement aspect ratio leads to smaller micro stress in composites. [Copyright &y& Elsevier]

Abstract: Experimental simulations of dynamic crack growth past inclusions of two different elastic moduli, stiff (glass) and compliant (polyurethane) relative to the matrix (epoxy), are carried out in a 2D setting. Full-field surface deformations are mapped in the crack–inclusion vicinity optically. The crack growth behavior as a function of inclusion–matrix interfacial strength and the inclusion location relative to the crack is studied under stress-wave loading conditions. An ultra high-speed rotating mirror-type digital camera is used to record random speckle patterns in the crack–inclusion vicinity to quantify in-plane displacement fields. The crack-tip deformation histories from the time of impact until complete fracture are mapped and fracture parameters are extracted. The crack front is arrested by the symmetrically located compliant inclusion for about half the duration needed for complete fracture event. The dynamically propagating crack is attracted and trapped by the weakly bonded inclusion interface for both stiff and compliant symmetrically located inclusion cases, whereas it is deflected away by the strongly bonded stiff inclusion and attracted by strongly bonded compliant inclusion when located eccentrically. The crack is arrested by a strongly bonded compliant inclusion for a significant fraction of the total dynamic event and is longer than the one for the weakly bonded counterpart. The compliant inclusion cases show higher fracture toughness than the stiff inclusion cases. Measured crack-tip mode-mixities correlate well with the observed crack attraction and repulsion mechanisms. Macroscopic examination of fracture surfaces reveals much higher surface roughness and ruggedness after crack–inclusion interaction for compliant inclusion than the stiff one. Implications of these observations on the dynamic fracture behavior of micron size A-glass and polyamide (PA6) particle filled epoxy is demonstrated. Filled-epoxy with 3% V f of PA6 filler is shown to produce the same dynamic fracture toughness enhancement as the one due to 10% V f glass. [Copyright &y& Elsevier]

Abstract: Thermal barrier coatings (TBCs) systems are widely used in gas turbines. However, the potential of thermal barrier coatings cannot be fully exerted due to the lack of a reliable life prediction of the coating, which requires the better understanding of the TBC failure mechanisms. In the present work, the failure mechanism of atmospheric plasma spraying (APS) was studied. The FE simulation was adopted to explore the stress distribution in TBC, and then thermal fatigue experiments were carried out. Two advanced constitutive models have been developed and implemented into ABAQUS through UMAT in order to simulate the mechanical behaviors of TBC system under thermal cyclic load. The constitutive model for ceramic top coat (TC) could model the non-symmetry of tensile and compressive loading, and viscoplastic constitutive model was used for the substrate. The stress distributions along the interfaces between TC and bond coat (BC) were obtained. For as-deposited APS–TBC, the thermally grown oxide (TGO) is very thin, which is less than 0.3μm, the small cracks only initiate in the ceramic top coat not in TGO. The crack imitates at the off-peak and propagates to the peak in TC. Finally the crack will have tendency to occur in internal top coat and be spallation. Meanwhile, the FE simulation and experiment data can provide a basis to develop a more accurate life prediction model. [Copyright &y& Elsevier]

Abstract: This work was motivated by the desire to improve the long-term durability of E-glass/Hysol 9394 epoxy/Al-6XN stainless steel joints whose fracture energy in a previous study was shown to fall from ∼950J/m2 (ambient) to a mere ∼88J/m2 after only two days of exposure to a 90%RH, 50°C environment. This paper reports a new polyurea chemistry to bond the E-glass and steel sections with very promising results. The fracture energy under ambient condition was measured to be 1232±15J/m2 using a double cantilever beam experiment. This value degraded by only 13% to 1070±35J/m2 in samples that were conditioned for 30days at 90%RH and 50°C. The failure in all samples was cohesive, within the first ply of the E-glass composite that neighbored the polyurea interface. The intrinsic fracture energy measurements, devoid of inelastic effects, were also carried out by submerging samples in a liquid nitrogen bath. Values of 590±25J/m2 were obtained, which can be used by the designers to set the local failure condition in design simulations of large-scale structures. [Copyright &y& Elsevier]

Abstract: A method for accelerated simulation of fatigue crack growth in a bimaterial interface (e.g. in a face/core sandwich interface) is proposed. To simulate fatigue crack growth, a routine is incorporated in the commercial finite element program ANSYS and a method to accelerate the simulation is implemented. The proposed method (the cycle jump technique) is based on conducting finite element analysis for a set of cycles to establish a trend line, extrapolating the trend line spanning many cycles, and use the extrapolated state as initial state for additional finite element simulations. A control criterion is utilized to ensure the accuracy of the cycle jumps. The inputs of the developed scheme are the crack growth rate as a function of energy release rate for discrete mode-mixities. If these relationships are available for a specific interface, interface fatigue crack growth in any structure with the same interface can be simulated. Using this approach, fatigue crack growth in the face/core interface of a sandwich beam is simulated. Results of the simulation show that with fair accuracy, using the cycle jump technique, more than 65% reduction in computation time can be achieved. Results show that in highly nonlinear problems the control parameter needs to be chosen with care. [Copyright &y& Elsevier]

Abstract: The morphology of telephone cord buckles of elastic thin films can be used to evaluate the initial residual stress and interface toughness of the film–substrate system. The maximum out-of-plane displacement , the wavelength and amplitude of the wave buckles can be measured in physical experiments. Through , , and , the buckle morphology is obtained by an annular sector model established using the von Karman plate equations in polar coordinates for the elastic thin film. The mode-mix fracture criterion is applied to determine the shape and scale parameters. A numerical algorithm combining the Newmark- scheme and the Chebyshev collocation method is adopted to numerically solve the problem in a quasi-dynamic process. Numerical experiments show that the numerical results agree well with physical experiments. [Copyright &y& Elsevier]

Abstract: The cohesive strength is an important parameter in numerically modeling composite delamination via CZM (cohesive zone model) based FEM. A micromechanical model is proposed to predict the cohesive strength based on the periodic RVE technique. A periodic displacement boundary condition has been presented on the assumption that the RVE is orthotropic in the sense of overall response. The cohesive strengths of T700/QY8911 and AS4/PEEK laminates at various fibers cross-angles are gained by FEM. With the predicted cohesive strengths the FEM simulations on Mixed-Mode bending (MMB) and seven-point bending test are presented, and the results are in fair agreement with experimental observation. [Copyright &y& Elsevier]

Abstract: The fracture behaviour of concrete is complex due to highly heterogeneous nature of the material. The heterogeneity of concrete manifests itself at various scales. At mesoscale, the presence of aggregates influences the strength of concrete by developing a zone of weakness in the form of aggregate–matrix interface. These lead to an increased distributed micro-cracking and enhances the energy absorption capacity of the material. The energy absorption capacity of structure is dependent not only on material properties but also on structural geometry and loading conditions. The present work attempts to identify the material and structural parameters that influence the overall behaviour, by using discrete numerical modelling of the material at mesoscale. Lattice modelling, a technique to model the heterogeneity using lattice elements is used to study the fracture behaviour of the material. Effect of aggregate volume fraction, specimen thickness and depth on the global behaviour is studied. [Copyright &y& Elsevier]

A new three-dimensional finite-element model of two-dimensional, triaxially braided composites is presented in this paper. This mesoscale modeling technique is used to examine and predict the deformation and damage observed in tests of straight-sided specimens. A unit cell-based approach is used to consider the braiding architecture and the mechanical properties of the fiber tows, the matrix, and the fiber tow-matrix interface. A 0°/±60° braiding configuration has been investigated by conducting static finite-element analyses. Failure initiation and progressive degradation has been simulated in the fiber tows by using the Hashin failure criteria and a damage evolution law. The fiber tow-matrix interface was modeled by using a cohesive zone approach to capture any fiber-matrix debonding. By comparing the analytical results with those obtained experimentally, the applicability of the developed model was assessed and the failure process was investigated. [ABSTRACT FROM AUTHOR]

Abstract: Cyclic mixed mode delamination in multidirectional composite laminates subjected to high cycle fatigue loading has been investigated by numerical simulations and cyclic mixed mode bending experiments. The numerical model includes lamina and interface elements. The description of the delamination crack growth rate is based on the cyclic degradation of bilinear interface elements linking the evolution of the damage variable with the delamination crack growth rate. The constitutive cyclic damage model is calibrated by means of mixed mode fatigue experiments and reproduces the experimental results successfully and with minor error. It is concluded that only with implementing a cyclic damage variable in the cohesive interface element the experimentally observed crack growth and stiffness degradation can be captured properly. Scanning electron microscopy of fracture surfaces after cyclic loading revealed that abrasion of crack bridging surface roughness is the main microscopical cause of weakening and degradation of the interface. [Copyright &y& Elsevier]

A straightforward procedure is described for utilizing experimentally evaluated bridging laws that characterize Mode II fracture growth of composite materials into numerical simulations. Unidirectional glass/epoxy end notch flexure (ENF) coupons have been fabricated and tested. Three data reduction schemes available in the literature were used for the construction of the R-curves together with the J-integral approach for the derivation of the bridging laws. Two traction— separation models have been utilized for the characterization of the fracture process zone (FPZ) developing during the delamination propagation process. The first model considers only the existence of a bridging zone behind the physical crack tip, whereas the proposed model considers both the existence of a bridging zone and of a cohesive zone in front of the physical crack tip. The traction—separation models were implemented into interface elements for the simulation of the ENF tests. Numerical results have shown that the proposed procedure together with the proposed traction— separation model is quite promising for simulations that involve Mode II fracture growth. [ABSTRACT FROM AUTHOR]

Abstract: We study density-driven flow in a fractured porous medium in which the fractures are represented as manifolds of reduced dimensionality. Fractures are assumed to be thin regions of space filled with a porous material whose properties differ from those of the porous medium enclosing them. The interfaces separating the fractures from the embedding medium are assumed to be ideal. We consider two approaches: (i) the fractures have the same dimension, d, as the embedding medium and are said to be d-dimensional; (ii) the fractures are considered as (d −1)-dimensional manifolds, and the equations of density-driven flow are found by averaging the d-dimensional laws over the fracture width. We show that the second approach is a valid alternative to the first one. For this purpose, we perform numerical experiments using finite-volume discretization for both approaches. The results obtained by the two methods are in good agreement with each other. [ABSTRACT FROM AUTHOR]

Abstract: The concept of configurational forces is applied to demonstrate the application of the concept of configurational forces in the numerical simulation of crack growth and fracture processes. It is shown, how material property variations at an interface affect the crack driving force and how the criterion of maximum dissipation is used to evaluate the direction of crack propagation. Fatigue crack growth experiments were conducted on diffusion welded bimaterial specimens consisting of a high-strength steel and soft ARMCO iron. Two cases are considered: (1) specimens with an interface perpendicular to the initial crack orientation, and (2) specimens with an inclined interface. The numerical simulation with the concept of configurational forces show that not only variations of the elastic modulus and/or the yield stress have a tremendous influence on the crack driving force, the crack growth rate, and the curvature of the crack path, but also the thermal residual stresses that resulted from a rather small difference of the coefficient of thermal expansion. [ABSTRACT FROM AUTHOR]

Abstract: The combined analysis of the fracture toughness enhancement of carbon nanotube (CNT)-reinforced composites is herein carried out on the basis of atomistic simulation, shear-lag theory and facture mechanics. It is found that neither longer reinforced CNTs nor stronger CNT/matrix interfaces can definitely lead to the better fracture toughness of these composites. In contrast, the optimal interfacial chemical bond density and the optimal CNT length are those making the failure mode just in the transition from CNT pull-out to CNT break. To verify our theory, an atomic/continuum finite element method (FEM) is applied to investigate the fracture behavior of CNT-reinforced composites with different interfacial chemical bond densities. Our analysis shows that the optimal interfacial chemical bond density for (6,6) CNTs is about 5–10% and that increasing the CNT length beyond 100nm does not further improve fracture toughness, but can easily lead to the self-folding and clustering of the CNTs. The proposed theoretical model is also applicable to short fiber-reinforced composites. [Copyright &y& Elsevier]

Abstract: Patch repair is a commonly used method for rectifying localized corrosion damage in reinforced concrete members. However, the ring-anode effect, which is corrosion at the intersection between the substrate and the repaired concrete, is a commonly observed failure mechanism after patch repairs. In this study, the kinetics of the corrosion in the ring-anode zones of repaired concrete structures is investigated by numerical modeling. All simulations, in agreement with the existing experimental and in situ observations, have demonstrated the formation of a ring-anode zone in the 2–5cm portion of the substrate from the interface between the substrate and the repaired concrete. Furthermore, the anodic current density in the ring-anode zone is found to have a peak near the repaired concrete and to asymptotically approach to the corrosion current density observed in the substrate before the patch repair. More importantly, the simulations demonstrate quantitatively how various parameters affect the ring-anode corrosion. It was found that the resistivities of substrate and repair concretes are the most significant factors that influence the magnitude of macrocell corrosion, followed by the availability of oxygen in the patch. It was observed that the ring-anode effect is a localized problem that occurs in the substrate near the repair bond line, and the size of the patch and the cover thickness are not significant factors affecting the phenomenon. [Copyright &y& Elsevier]

Abstract: A fuselage representative carbon fibre-reinforced multi-stiffener panel is analysed under compressive loading. An intact and pre-damaged configuration is loaded into the postbuckling region and further on until collapse occurs. An analysis tool is applied that includes an approach for predicting interlaminar damage initiation and degradation models for capturing interlaminar damage growth as well as in-plane damage mechanisms. Analysis of the intact panel configuration predicts collapse due to fibre fracture in the stiffeners close to the panel clamps, which agrees well with the results from experimental testing. The pre-damaged configuration was proposed containing Teflon-coated layers to generate the initial debonds in the skin-stiffener interface. The outcome of the simulation of this configuration shows that crack growth is not predicted to occur, which agrees with the observations of the experiment. A parametric study is conducted to investigate the effect of the skin-stiffener debond parameters such as length, width and location on crack growth and the collapse behaviour of the panel. It is found that the sensitivity of the panel design to the damage parameters is highly dependent on the postbuckling mode shape or displacement pattern, and particularly the extent to which this influences the conditions at the crack front. More broadly, the analysis tool is shown to be capable of capturing the critical damage mechanisms leading to structural collapse of stiffened composite structures in the postbuckling region. [Copyright &y& Elsevier]

Abstract: Fretting fatigue initiation was studied for a shrink-fit pin at rotating bending. Eight assemblies with four different grips were manufactured from soft normalized steel and tested at loads well below bending endurance. All pins displayed rust-red fretting oxides deep into the contact and black oxidised fretting scars with fretting fatigue cracks at the rim. The slip evolution was simulated in a three-dimensional FE model including assembly, bending and sufficiently many rotations to reach a steady-state. The extension of cyclic slip agreed with the black oxidised scar. Deeper into the contact a monotonic slip developed to the positions with rust-red oxides. Asymmetric slip and traction on the interface sides together with a slight twist of the pin in the hub and the slip development process, illustrated that a three-dimensional analysis was required for the interface. Both the stress amplitude and the Findley multi-axial criterion predicted fretting fatigue of the pin although the rotating bend stress was well below the endurance limit. [Copyright &y& Elsevier]

Abstract: Interface delamination and arching of a ductile thin film on a hard substrate subject to microwedge indentation were investigated systematically using a three-dimensional finite element method. A traction–separation law was introduced to simulate the cohesion and failure behavior of the interface between the film and the substrate. The effects of the interface strength and the length of the microwedge indenter on the onset and growth of interface delamination and film arching were analyzed. It was shown that a two-dimensional to three-dimensional transition of stress state occurs during indentation, depending on the indenter length and indentation depth. Conditions for using two-dimensional and three-dimensional models were suggested. [Copyright &y& Elsevier]

Abstract: The paper investigates the capability of a finite element model based on cohesive interface elements to simulate complex three-dimensional damage patterns in composite laminates subjected to low-velocity impact. The impact response and the damage process of cross-ply laminated plates with grouped ([03/903]s and [903/03]s) and interspersed ([0/90]3s) ply stacking was simulated using a FE model developed by the authors in a previous study and the numerical results were compared to experimental observations. The model provided a correct simulation of size, shape and location of the principal fracture modes occurring in impacted [03/903]s and [903/03]s laminates. In [0/90]3s laminates, characterized by a complex spatial damage distribution, the model was able to predict the approximately circular shape of the overall projected damage area and to capture the typical shape features of individual delaminations; significant discrepancies between experiments and predictions were however observed in terms of delamination sizes at single interfaces. Further investigations are needed to clarify the main reasons of these discrepancies. [Copyright &y& Elsevier]

Abstract: The elastostatic problem of a mode-I crack embedded in a bimaterial with an imperfect interface is investigated. The crack is in proximity to and perpendicular to the imperfect interface, which is governed by linear spring-like relations. The Fourier transform is applied to reduce the associated mixed-boundary value problem to a singular integral equation with Cauchy kernel. By numerically solving the resulting equation, stress intensity factors near both crack tips are evaluated. Obtained results reveal that the stress intensity factors in the presence of the imperfect interface vary between that with a perfect interface and that with a completely debonding interface. Moreover, an increase in the interface parameters decreases the stress intensity factors. In particular, when crack approaches to the weakened interface closer, the stress intensity factors become larger for a sliding interface, and become larger or smaller for a Winkler interface, depending on the crack lying in a stiffer or softer material. The influences of the imperfection of the interface on the stress intensity factors for a bimaterial composed of aluminum and steel are presented graphically. [Copyright &y& Elsevier]

Abstract: In terms of the representative unit cell (RUC) with tri-layers, the time-dependent fracture performance of interfacial crack in multilayered structures was studied by using the finite element method (FEM). The feasibility of integral-type crack driving force parameter C ∗ for interpretation of interfacial creep crack growth (CCG) of multilayered systems were reexamined. Results indicate that the magnitude of the interfacial creep crack growth driving force was related to the mismatch factor of multi-layers and was significantly affected by the thickness of interlayer. [Copyright &y& Elsevier]

The hybrid time-domain boundary element method (BEM), together with the multi-region technique, is applied to simulate the dynamic process of crack deflection/ penetration at an interface in a bi-material. The whole bi-material is divided into two regions along the interface. The traditional displacement boundary integral equations (BIEs) are employed with respect to the exterior boundaries; meanwhile, the non-hypersingular traction BIEs are used with respect to the part of the crack in the matrix. Crack propagation along the interface is numerically modelled by releasing the nodes in the front of the moving crack tip and crack propagation in the matrix is modeled by adding new elements of constant length to the moving crack tip. The dynamic behaviours of the crack deflection/penetration at an interface, propagation in the matrix or along the interface and kinking out off the interface, are controlled by criteria developed from the quasi-static ones. The numerical results of the crack growth trajectory for different inclined interface and bonded strength are computed and compared with the corresponding experimental results. Agreement between numerical and experimental results implies that the present time-domain BEM can provide a simulation for the dynamic propagation and deflection of a crack in a bi-material. [ABSTRACT FROM AUTHOR]