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In this paper, dynamically propagating cracks in anisotropic plates exposed to a generalised thermal shock are investigated. Here, the governing equations are considered according to the Lord-Shulman (LS) model as a fully coupled generalised thermoelasticity theory. The crack is modelled in the context of the eXtended Finite Element Method (XFEM). To evaluate Stress Intensity Factors (SIFs), a technique based on the J integral and crack tip opening and sliding displacements, previously applied for stationary cracks, is developed for a dynamically propagating crack in orthotropic solids. Besides, a variety of functions for enriching the displacement field are derived relying on the behaviour near the tip of a dynamically propagating crack in anisotropic materials. The maximum hoop stress criterion is also modified by using the asymptotic stress field for a dynamically propagating crack. In addition, the effect of the angular variation of fracture toughness in orthotropic materials is accounted in computing the crack propagation speed. In some examples, dynamic crack growth in complex cracked orthotropic structures subjected to LS thermal shock is studied in detail. The impacts of fibre orientations and LS relaxation time are also investigated in these examples. In conclusion, applying non-Fourier thermal shock for modelling dynamically propagating cracks in orthotropic structures is recommended to obtain more realistic results. In addition, by increasing the LS relaxation time, the crack grows less oscillatory and is more aligned along the material fibres. [ABSTRACT FROM AUTHOR]

Carter's model of fluid loss is used in the oil and gas industry performing the numerical approach of leak-off. Its deduction applies some simplifying assumptions, such as the difference between fluid pressure and constant pore pressure and filtration process approximation to a unidirectional flow, perpendicular to the fracture plane. For this paper, the so-called Chimas is an hydromechanical simulator of oil reservoirs, fully coupled and implicit, in a way that considers the poroelastic effects on the propagation of fractures. The leak-off process is explicitly treated in the fracture boundary conditions using Darcy's law. The objective of this work is to validate the filtration phenomenon of Chimas hydromechanical simulator comparing the parameters of length, width and injection pressure with those obtained using an iterative method implemented in MatLab and which includes Carter's analytical equation. Numerical accuracy was validated against asymptotic analytical solutions. The agreement between the iterative method and the analytical solutions was particularly good in relation the length fracture and injection pressure. [ABSTRACT FROM AUTHOR]

Glued-in rods (GiR) represent a very successful type of adhesively bonded joints in timber engineering. Despite their apparent geometrical simplicity, their dimensioning still challenges practitioners. A major source of mechanical complexity resides in the orthotropic nature of the wood, or engineered wood products, as laminated veneer lumber (LVL). This paper presents a relatively simple design approach based upon fracture mechanics (FM) and associated double-cantilever beam (DCB) tests that complemented tensile tests for material characterisation. In comparison with the state-of-the-art related to FM in timber engineering, the paper presents a practitioner oriented approach of a yet complex set of GiR geometries involving beech LVL (M16-8.8 threaded rods embedded in cross sections of 120 × 120 mm2 and embedment lengths of 96mm, 128mm and 160mm). The developed numerical model resulted in a good description of the load-displacement of a series of full scale, including very good estimates of their load capacities. Additionally, it allowed for significant insights regarding the complicated relationship between geometry, orthotropy, strength of the component and failure of the GiR, as for examples the complex fracture process, and the importance of transverse tensile stresses, which play a preponderant role, equal in importance to shear stresses. [ABSTRACT FROM AUTHOR]

This paper derives analytical predictions for notched cross-laminated timber (CLT) plate delamination using fracture mechanics for crack propagation from the notch root. The analysis accounts for both CLT heterogeneity and residual stresses caused by seasonal variations in temperature and humidity. The accuracy of predictions coupled with shear corrections, was confirmed by comparison to finite element analysis. The fracture mechanics approach was validated as appropriate by comparison to recent experiments on notched CLT beams. Residual stress effects are significant and depend strongly on notch depth. Environmental changes that promote swelling, such as increases in temperature or moisture content, are more detrimental to plate integrity than are changes that promote shrinkage. Relatively modest levels of swelling stress can potentially cause spontaneous delamination. A new design guide for notched CLT plates that includes effects of heterogeneity and residual stresses is proposed. [ABSTRACT FROM AUTHOR]

This paper defines in-plane displacement functions of a composite lattice rectangular plate, which is assumed to be a Kirchhoff-Love plate. It presents an approximate method based on the continuous model of conducting a progressive failure analysis for predicting material failure and post-failure behavior of the composite lattice rectangular plate with various boundary and load conditions. To define the approximate method, we use the Ritz method and Hashin's failure criteria. The validity of the present method is verified by comparing the results of the finite element analysis. Finally, we perform parametric and sensitivity analyses to investigate the effects of the design parameters on the failure characteristics of the composite lattice rectangular plates based on the present method. The results allow a database to be obtained on the structural characteristics of composite lattice rectangular plates. Consequently, it is concluded that the present method is well suited to progressive failure analysis of composite lattice rectangular plates due to their relative simplicity and computational efficiency. [ABSTRACT FROM AUTHOR]

In this paper, Composite Repair System (CRS) is applied to repair the circumferential internal surface cracked steel pipes subjected to bending. The Stress Intensity Factor (SIF) is quantitatively analysed by means of numerical simulations, and the crack growth rate is predicted by using the Paris' law. First, the three-dimensional finite element (FE) model is developed, and its reliability of evaluating SIF of internal surface crack in CRS reinforced pipe is validated. Then based on the FE method and combined with Paris' law, a case study is deployed to predict the internal surface crack growth in steel pipes reinforced with CRS. The results show that CRS have significantly reduced the SIF of the internal surface crack and decrease the crack growth rate, while unchanging the variation trend of the crack aspect ratio. Afterwards, a parametric study is performed in order to guide the optimisation design of CRS reinforcement. [ABSTRACT FROM AUTHOR]

In this paper, a combined experimental-numerical method was proposed to study the effect of adhesive thickness on mode I fracture energy of the adhesive layer, using Double Cantilever Beam (DCB) testing and Cohesive Zone Modelling (CZM). A Trapezoidal Cohesive Zone Model (TCZM) was introduced in tabular form into commercial Finite Element (FE) package to simulate the crack propagation behaviour in the adhesive layer and include the ductile characteristics of the selected adhesive. In order to overcome the difficulty in the accurate monitoring and measurement of crack length during loading, the Compliance-Based Beam Method (CBBM) was adopted to deduce the mode I strain energy release rate data. The load–displacement curve, Resistance curve (R curve), and mode I fracture energy data obtained from both experiment and simulation were analysed to validate the established FE model. It was observed that adhesive thickness has a significant influence on the ductile fracture behaviour of adhesive under mode I loading. The mode I fracture energy increases initially, and then decreases with the increase of adhesive layer thickness in the selected thickness range, while obvious transition was also observed in the perspective of micro-scale failure mechanism of the fracture surface through Scanning Electron Microscopy (SEM). [ABSTRACT FROM AUTHOR]

In this paper, a novel technique has been developed by coupling the conventional finite element method (FEM) with the extended iso-geometric approach (XIGA) for modeling crack growth in engineering materials. The new proposed technique, named as the coupled FE-IGA technique, exploits the advantages of both the FEM and the XIGA. XIGA is used for the approximation of the displacement field in the region surrounding the crack surfaces, whereas the rest of the domain is discretized into conventional Lagrange finite elements. The transition elements are used to connect FEM portion of the domain with the XIGA region. The displacement approximations across the transition elements must preserve the continuity between XIGA and FEM solutions. The Ramp function approach is used for the approximation of the displacement field across the transition elements. The discontinuities such as cracks, holes, inclusions and other material interfaces are modeled independent of the mesh in coupled FE-IGA technique. The standard displacement approximations are enriched with appropriate enrichment functions, which introduce the effect of different discontinuities into the formulation. Finally, several numerical problems are solved by the coupled FE-IGA technique to demonstrate the capabilities of this novel approach in modeling fatigue crack growth in engineering materials. [ABSTRACT FROM AUTHOR]

Contour integral method is the conventional approach in order to characterise main crack parameters in fracture studies. This method is used in verity fields in fractures mechanics because of its capability in linear and non-linear fracture mechanics. Whereas, requirements such as mesh singularity in crack tip and refined layers of elements in surrounding contours, which increase computing time and make it prolix for large components. The main aim of this paper is to develop an extended finite element method-linear elastic fracture mechanics (XFEM-LEFM) model to impart XFEM advantages in survey of fracture mechanics of planetary gear sets. At first main crack parameters of root crack of the planet gear have been obtained and compared with conventional method, and after that crack growth path is predicted, and finally effect of rim thickness is investigated and compared with other researches to illustrate the efficiency of the developed model. For this purpose, Python script code is generated to automatically calculate the stress intensity factors of root crack and after that simulate the crack growth path until final fracture. [ABSTRACT FROM AUTHOR]

It is crucial to exactly predict the value of C* in order to predict creep crack growth and assess the creep life of high temperature structures. The coefficient of h1, in the modified General Electric/Electric Power Research Institute (GE/EPRI) method for power-law creep materials with a threshold stress, was determined in this paper using the finite element method for various crack ratios and creep exponents of n. The effects that both the threshold stress and the load level have on the values of h1 were also investigated. The results of the study indicated that the values of h1 were obviously affected by the threshold stress at a low level of C*, but that they remained almost constant with the increased threshold stress at high levels of C*. The discrepancy of the value of h1 between the two levels of C* increased as the threshold stress increased. [ABSTRACT FROM AUTHOR]

Recently, the advent of optical systems has made possible the fast and accurate measurement of roughness discontinuity in three dimensions. In this study, a number of 3D roughness parameters such as fractal parameter (D), amplitude parameter (A), roughness parameter Rs and Grasselli's roughness parameter (2A0θ*max/(C + 1)) have been presented to quantify the geometry of the fracture surfaces. However, all these roughness parameters are scale dependent and their values change with scale. In this paper, the variations in theses parameters have been investigated with regard to scale. For this purpose, initially, three natural fracture surfaces with the dimensions 500 × 500 mm2 were selected and then, the four mentioned roughness parameters were calculated for these three surfaces in the range from 50 × 50 mm2 to 500 × 500 mm2. Finally, to evaluate the accuracy of roughness estimation by these roughness parameters, several joint replicas from the surfaces were constructed and the direct shear tests were carried out on them. Based on the experimental results, the Grasselli's roughness parameter gives more accurate estimation of the variations in surface roughness in regard to scale. Also the effect of small-scale evenness on surface roughness has been investigated. [ABSTRACT FROM AUTHOR]

C* is usually used to describe the creep crack growth. ASTM E1457 allows C* to be calculated from creep load line displacement rate. However in components it is difficult or impossible to measure load line displacement rate. Therefore for the components C* must be determined by finite element methods or reference stress concepts. Estimates of C* obtained by reference stress methods will depend on the collapse mechanism adopted and therefore several estimations are proposed. This paper presents a numerical study of non-linear fracture mechanics parameter predictions under elevated temperature for axially oriented external surface crack in cylinder. Comparison of C* calculated from FE analysis and different reference methods is conducted. The values of C* obtained from the API579 net section solution are also found to be slightly conservative and give the closest agreement to the F.E. contour integral C*. In addition, the comparison between C* of homogeneous material and TYPE IV cracking is conducted. The difference between homogeneous material and TYPE IV cracking is almost negligible and therefore the reference stress solutions for homogenous material could be applied to estimate C* for TYPE IV cracking. [ABSTRACT FROM AUTHOR]

This paper presents a novel integrated approach using the extended finite element method (XFEM) and cohesive elements (CEs) for modeling three-dimensional (3D) delaminations, matrix cracks, and their interactions in progressive failure of composite laminates. In the proposed XFEM-CE approach, the matrix cracks are explicitly modeled by the XFEM through nodal enrichment and element partition, and the inter-ply delaminations are modeled by cohesive elements through traction–separation law. An XFEM-based cohesive element enrichment scheme is developed in order to properly model the interactions between the delaminations and matrix cracks. It is critical to enrich the cohesive elements at the local juncture where cracks meet, in order to obtain the correct crack path interactions. Examples are presented for failure analysis of double-cantilever-beam and end-notch-flexure laminates with different layups. The results show strong explicit matrix crack–delamination interactions in these laminates. This work presents another significant development of a computational platform for realistic modeling of progressive damage in composites. [ABSTRACT FROM AUTHOR]

The debonding of casing/cement or cement/formation interfaces are the representative forms of wellbore integrity failure. In this paper, a 3D finite element model for simulating the growth of fluid-driven debonding fractures along the casing/cement and cement/formation interfaces during hydraulic fracturing treatment is established. The simulation results show that (1) it is easier for the debonding fracture to extend along the casing/cement interface, (2) the fluid invasion induced debonding fractures will not cover the whole circumference of the interfaces, (3) the extent of uncovered circumferential region neighboring the debonding fracture gradually increases with the growth of the fracture height. [ABSTRACT FROM AUTHOR]

Since there are increasing applications for reinforced thermoplastic pipe (RTP) in the oil and gas industry, the mechanical behavior of RTP under various loading conditions has drawn much attention. The combined load of tension and internal pressure should be considered in procedures of RTP’s installation and operation. In this paper, an analytical model derived from Knapp’s optical cable model and finite element method (FEM) are presented to study the behavior of RTP and the reinforcement wires in the pipe under combined tension and internal pressure. Results from two methods are compared and discussed. Additional parametric study is presented to show the influence of important parameters on the behavior of RTP under combined tension and internal pressure. [ABSTRACT FROM AUTHOR]

This paper presents the design and modeling of micro-electromechanical systems (MEMS) on the ternary ferroelectric compounds (PZT) based by using finite element model (FEM) simulation. The conceptual framework establishes five steps to perform the critical analysis: design a novel structure, define the failure mechanisms under the given conditions, analyze different vibrations, analyze the operation principle, and detect resonance modes. In addition, MEMS failure modes were analyzed under different scenarios and the obtained results discussed. [ABSTRACT FROM AUTHOR]

In this paper, a systematic and detailed observation was made of the crack extension behavior of thin 90° layers of cross-ply carbon fiber reinforced plastics (CFRP) laminates. The effect of ply thickness on the crack propagation mechanism was discussed with respect to the energy release rate of the intralaminar transverse crack, calculated using finite element analysis. In a laminate with a 40 μm-thick-ply, the crack gradually extended with increasing strain. Conversely, extreme crack extension was found at around 1.0% strain in a laminate with a standard thick ply. Based on the numerical analysis, the crack suppression effect is verified using a thin ply; the effect is apparently caused by a decrease in the energy release rate at the crack tip in the thin layer. [ABSTRACT FROM PUBLISHER]

Ctis an important parameter in predicting creep crack growth life from the small-scale creep stage to the extensive steady state creep stage. In this paper, weld interface and non-interface creep cracks for compact tension (CT) specimens with heat-affected zone (HAZ) were studied by finite element method (FEM) to systematically research the estimation method ofCtfor weld creep cracks. Simulation results showed thatCtof weld interface cracks could be estimated by Yoon’s method. For weld non-interface cracks,Ctunder the small-scale and transition creep stages could be exactly estimated by a proposed method. The accuracy of the proposed method was not affected by HAZ, but Yoon’s method was slightly affected by HAZ. [ABSTRACT FROM PUBLISHER]

A new adaptive multiscale method for the non-linear fracture simulation of heterogeneous materials is proposed. The two major sources of errors in the finite element simulation are discretization and modelling errors. In the failure problems, the discretization error increases due to the strain localization which is also a source for the error in the homogenization of the underlying microstructure. In this paper, the discretization error is controlled by an adaptive mesh refinement procedure following the Zienkiewicz–Zhu technique, and the modelling error, which is the resultant of homogenization of microstructure, is controlled by replacing the macroscopic model with the underlying heterogeneous microstructure. The scale adaptation criterion which is based on an error indicator for homogenization is employed for our non-linear fracture problem. The control of both discretization and homogenization errors is the main feature of the proposed multiscale method. [ABSTRACT FROM PUBLISHER]

In this paper, the fracture toughness parameters of two types of dentistry cement have been investigated based on numerical and experimental analysis. Dentistry cements are largely applicable and useful when it comes to mending teeth and are used as resin and filler. Composite cement and adhesive resin cement are among the helpful cements in dentistry. As a result of production and the loading conditions in the mouth, the generation of micro-cracks is inevitable. In this research, by producing butterfly Arcan samples including crack and by loading those in different angles, pure mode-I, pure mode-II, and mixed-mode fracture data were obtained. The experiments were conducted by an Arcan fixture and loading device, which had the ability of investigating the fracture parameters of materials in different loading angles. By calculating the geometrical correction factors by using ABAQUS finite element software, fracture toughness and critical energy release rate have been obtained. Also, the effects of crack length, elasticity modulus, and Poisson's coefficient on the fracture parameters and energy release rate in different loading angles have been studied using numerical analysis. [ABSTRACT FROM PUBLISHER]

Free-free beams (FFB) are used to model many structures, such as missiles, rockets, MEMS (Micro Electro Mechanical Systems), etc. This paper aims to illustrate a novel structural health monitoring method—Fourier analysis of mode shapes of damaged beams—and extend it to the case of FFB. The damaged mode shapes of FFB are obtained by a finite element model and then studied using spatial Fourier analysis. The effect of noise in the mode shape data is considered and it is found that the Fourier coefficients provide a useful indication about the location and size of damage. [ABSTRACT FROM AUTHOR]

This paper considers the prediction of creep crack growth (CCG) in different fracture mechanics geometries using finite element (FE) analysis based on a material independent simplified multiaxial failure strain model at the crack tip. The comparison is first made by modelling C(T) specimen tests under plane stress and plane strain conditions using creep properties of a C-Mn steel at 360°C. In addition, in order to examine CCG due to different geometries, a single edge notch specimen (SENT), centre cracked tension specimen (CCT) and three-point bending (3PB) specimen have been modelled and analysed. In all cases, it is found, depending on the geometry, that for this steel at low creep temperatures the applied load develops a high reference stress/yield stress (σref/σy) ratio, which helps reduce constraint at the crack tip. The predictions are analysed under plane stress/plane strain loading conditions identifying the effects of geometry on cracking rates and the implications for predicting long term test or component failure times exceeding where the applied σref/σy<<1. [ABSTRACT FROM AUTHOR]

This paper reports the results of elastic-creep finite element (FE) analyses of a P91 steel pipe weld with two external 'type IV' circumferential cracks, subjected to internal pressure and end (system) load using creep properties obtained at 650°C. Numerical contour integral calculations have been performed to obtain both transient and stationary high temperature fracture mechanics parameters. A mesh sensitivity analysis was performed in order to ensure the accuracy of FE analyses in the transient creep stage. The effects of load magnitude, the material mismatch near the crack surfaces and the crack depth on the stationary creep C* contour integrals have been investigated, and corresponding analytical correlations are presented. [ABSTRACT FROM AUTHOR]

A laboratory simulation of load-induced reflective cracking was carried out using Hamburg wheel tracking tester (HWTT). The simulation, compared with some previous fatigue tests, is more reasonable and applicable because, instead of static load, the cyclic dynamic load is applied to the specimens and the test is relatively time and cost saving. The purpose of this study was to evaluate the effectiveness of various stress-absorbing interlayers to retard the development of reflective cracking, including styrene-butadiene-styrene (SBS)-modified asphalt sand concrete interlayer, asphalt-rubber sand concrete interlayer, fibreglass-polyester paving mat interlayer and stress-absorbing membrane interlayer (SAMI). Specimens without any anti-reflective cracking measure were also included to serve as a control. This paper first describes material properties, aggregate gradations and the simulation apparatus. Then, it assesses the effectiveness of different measures to prevent reflective cracking based on laboratory test results. It reveals that asphalt-rubber sand concrete interlayer performed best and fibreglass-polyester paving mat interlayer ranked next, whereas both SBS-modified asphalt sand concrete interlayer and SAMI showed similar and less sound performances compared with the former two under laboratory test environments. However, SAMI may witness an improved field performance due to the limitation of laboratory test set-up and any of the four measures could prolong the fatigue life of the specimens substantially. A finite element model simulation was followed to explain the anti-reflective cracking mechanism and support the HWTT results. [ABSTRACT FROM AUTHOR]

We have shown that a significant creep occurs at the concrete-fiber reinforced polymer (FRP) interface based on double shear long-term test. The primary test parameters were the shear stress to ultimate shear strength ratio, the epoxy curing time before loading as well as the epoxy thickness. The test results showed that when the epoxy curing time before loading was earlier than seven days the shear stress level significantly affected the long-term behavior of epoxy at the interfaces, and in particular the combined effect of high shear stress and thick epoxy adhesive can result in interfacial failure if subjected to high-sustained stresses. In this paper, based on the previous experimental observations, an improved rheological model was developed to simulate the long-term behavior of epoxy adhesive at the concrete-FRP interfaces. Furthermore, the newly developed rheological creep model was incorporated in finite element (FE) modeling of a reinforced concrete (RC) beam strengthened with FRP sheets. The use of rheological model in FE setting provides the opportunity to conduct a parametric investigation on the behavior of RC beams strengthened with FRP. It is demonstrated that creep of epoxy at the concrete-FRP interfaces increases the beam deflection. It is also shown that consideration of creep of epoxy is essential if part or the entire load supported by FRP is to be sustained. [ABSTRACT FROM AUTHOR]

During thermo-inductive inspection, an eddy current of high intensity is induced into the inspected material and the thermal response is detected using an infrared camera. Anomalies in the surface temperature during and after inductive heating correspond to inhomogeneities in the material. A finite element simulation of the surface crack detection process using active thermography with inductive heating has been developed. The simulation tool was tested and used for investigations on austenitic steel components with different longitudinal orientated cracks. The shape of the crack varies in the crack opening and the depth. The simulation model was based on the finite element programming software ANSYS. The suitability of the developed simulation of the inductive excited thermography for crack detection will be demonstrated by calculations and experiments. This paper focuses on longitudinal orientated cracks in austenitic steel, which are opened to the surface. The results show that depending on the shape of the crack the temperature distribution of the material under test made of austenitic steel is different. It will be shown how the crack size affects the temperature difference between the crack and the surrounding surface. [ABSTRACT FROM AUTHOR]

This paper deals with Finite Element Analysis of bonded Tubular Socket Joints (TSJs) made with laminated Fibre Reinforced Plastic (FRP) composite structures. The effective coupling length for suitable performance of the joint is determined based on the Tsai-Wu failure criterion. The analysis revealed the three-dimensional nature of the stresses and are found to be concentrated in the close vicinity of the free edges and junction of the adherends in the coupling region of the bonded TSJ. Shear stress ( τrθ ), though comparatively small in magnitude, is found to be extremely sensitive to three-dimensional effects as compared to stresses τzr and σr . Failure indices at different critical interfaces are determined using Quadratic Failure Criterion (QFC) within the adhesive and Tsai-Wu coupled stress criterion for the adherend-adhesive and socket-adhesive interfaces. Based on the latter criterion, locations prone to adhesion failure initiation are identified to be existing near the free edges of the adherend-adhesive interfaces in the coupling region of the bonded TSJ. Strain Energy Release Rate (SERR) calculated using Modified Crack Closure Integral (MCCI) vis-à-vis Virtual Crack Closure Technique (VCCT) has been used as the characterizing parameter for assessing the growth of adhesion failures. The adhesion failure damages have been observed to propagate at the same rate in a self-similar manner mainly in the in-plane shearing mode. Quasi-isotropic and angle-ply orientations of the FRP composite laminates are more resistant to opening mode growth of failure, whereas cross-ply and unidirectional oriented socket/adherends offer better resistance to in-plane shearing mode of adhesion failure damage growth. Plies oriented in the direction of the applied load, especially Graphite/Epoxy (Gr/E) [90]16, are found to offer the best resistance to all types of adhesion failure growth modes and hence are the most preferred fibre orientations for the bonded TSJ under tension. Increasing the degree of anisotropy of the composite socket/adherends improves the adhesion failure damage growth resistance of the bonded TSJ. Boron/Epoxy (B/E) FRP composites are found to be the best in slowing down the growth rate of the adhesion failures among the various FRP composite socket/adherends considered in the present study. [ABSTRACT FROM AUTHOR]

In this paper, we develop and implement high-resolution, computationally efficient multi-cell finite-element (FE) models of metallic foams in order to more accurately investigate the collapse behaviour of these emerging materials. The main objective is to investigate the effect of morphological imperfections at the cellular scale on the global response of the cellular material. Attention was therefore devoted to three related aspects of the work. The first is concerned with the development of FE models of metallic foams accounting for morphological imperfections at the cellular level. The second is concerned with conducting parametric studies of different model parameters and examining their effect on the instantaneous load-deformation history, peak collapse loads and energy absorption levels of the foam. The third is devoted to a thorough comparison of the numerical simulations with experimental results. Results revealed the influence of these imperfections on low-density foams, and to a much lesser extent on high-density ones. [ABSTRACT FROM AUTHOR]

This paper investigated the damage transition mechanism between the fiber-breaking mode and the fiber-avoiding crack mode when the fiber-length is reduced in the unidirectional discontinuous carbon fiber-reinforced-plastics (CFRP) composites. The critical fiber-length for the transition is a key parameter for the manufacturing of flexible and high-strength CFRP composites with thermoset resin, because below this limit, we cannot take full advantage of the superior strength properties of fibers. For this discussion, we presented a numerical model for the microscopic damage and fracture of unidirectional discontinuous fiber-reinforced plastics. The model addressed the microscopic damage generated in these composites; the matrix crack with continuum damage mechanics model and the fiber breakage with the Weibull model for fiber strengths. With this numerical model, the damage transition behavior was discussed when the fiber length was varied. The comparison revealed that the length of discontinuous fibers in composites influences the formation and growth of the cluster of fiber-end damage, which causes the damage mode transition. Since the composite strength is significantly reduced below the critical fiber-length for the transition to fiber-avoiding crack mode, we should understand the damage mode transition appropriately with the analysis on the cluster growth of fiber-end damage. [ABSTRACT FROM AUTHOR]

This paper addresses mixed-mode crack growth in two-dimensional functionally graded materials, and assesses the predictive capability of some fracture criteria on both crack growth direction and crack initiation condition. Automatic simulation of mixed-mode crack propagation in homogeneous and functionally graded materials is performed by means of the finite element method in conjunction with a remeshing algorithm. Crack growth simulation consists of iterative procedures for the calculation of mixed-mode stress intensity factors by means of the interaction integral method, determination of crack growth direction and crack initiation, and local automatic remeshing along the crack path. The present approach requires a user-defined crack increment at the beginning of the simulation. Crack trajectories obtained by the present simulation are compared with available experimental results. [ABSTRACT FROM AUTHOR]

This paper investigates the effectiveness of theoretical failure criteria in the estimation of workability limits in cold forging through Finite Element Analysis (FEA), by incorporating them into the commercial software ABAQUS 6.3.1. Universal applicability of the threshold values of these criteria functions, at the location and instant of fracture, represents their overall performance. FEA of various cold working processes involving typical materials was carried out up to the experimentally observed limit for fracture. Threshold values of all failure criteria depended on the stress-state resulting from geometry and loading conditions of the process. Poor scalability of the failure criteria across stress-states is attributed to the transition in modes of fracture, from global ductile - local brittle to shear depending upon the level of hydrostatic stress at fracture sites. There exists a race between the types of fracture in the deformation zone and failure occurs by the mechanism reaching the threshold first. Among the existing failure models, Kuhn's fracture locus successfully delineates the safe and unsafe regions in plastic strain-space, irrespective of the mode of fracture. [ABSTRACT FROM AUTHOR]

This paper presents an application of the k -version finite element method to the numerical simulation of boundary value problems that contain singularity of the solution derivatives at certain point(s) in the domain. The theoretical solutions of such problems contain extremely isolated high solution gradients that approach infinity at the singular point(s); i.e., the solutions are not analytic at the singular point(s) but are analytic everywhere else. It is demonstrated that when numerical solutions of such problems are simulated in progressively increasing order scalar product spaces k , p ( e ), they approach the same characteristics in terms of differentiability as the theoretical solution as k is increased and in the limit k ? 8 , the numerical solutions have exactly the same global differentiability characteristics as the theoretical solutions. A two-dimensional linear elastic fracture mechanics problem is used as a model problem to illustrate the salient features of the k -version finite element method. [ABSTRACT FROM AUTHOR]

This paper presents the formulation and finite element implementation of the equivalent domain integral (EDI) for fracture analysis of functionally graded materials (FGMs) under thermal stresses. By carrying out the neccesary modifications resulting from material nonhomogeneity and thermal strains, the generalized J-integral is converted to an equivalent domain integral around the crack tip for both plane stress and plane strain problems of thermoelasticity. The developed procedure is integrated in a fracture analysis code FRAC2D using graded and cubic finite elements in order to calculate the stress intensity factor under mode I steady-state and transient thermal loading conditions. Temperature distribution profiles in FGMs are calculated using the finite elements based heat transfer analysis code HEAT2D. Comparisons of the computed thermal stress intensity factors to the results available in the literature and to those calculated by an enriched finite element method show that developed EDI approach produces highly accurate results and possesses the required domain independence. Detailed parametric analyses are performed in order to examine the influences of material property variation profiles and geometrical parameters on the mode I stress intensity factors. It is shown that variation profiles of the thermomechanical parameters such as Poisson's ratio, thermal expansion coefficient and thermal conductivity significantly influence both the amplitude of the stress intensity factors and the transient crack closure behavior. [ABSTRACT FROM AUTHOR]

In this study, a model hot mix asphalt (HMA) pavement was constructed in the laboratory and tested under repeated wheel load applications using Model Mobile Load Simulator 3 (MMLS3). This study presents a discussion on the background of MMLS3, production of test slabs, use of various strain gauges, loading, data acquisition using strain gauges in various directions and analysis of test results. Analysis of data showed the effect of wheel load on fatigue performance of the pavement in terms of strain history and cracking. Different phases of strain history have been identified and their role on fatigue performance discussed. A rational approach of calculation of strain corresponding to failure load applications has also been presented. A finite element model of MMLS3 pavement showed the usefulness of numerical solutions over closed form solutions with respect to effects of boundary conditions. The finite element model presented in this paper successfully described the behavior of the pavement loaded with the MMLS3 in terms of effect of variation of pavement thickness and relative magnitude of strains in different directions. Based on the observations from several trials involving preparation of test pavement slabs and, loading and testing, it is concluded that the MMLS3 can be used for evaluation of HMA for fatigue characterization. A proper protocol for preparation of slabs, loading and testing with the MMLS3 is being developed. Once developed, the protocol will be used for more rigorous HMA material characterization in the laboratory. [ABSTRACT FROM AUTHOR]

Several methods for damage detection based on identifying changes in strain energy mode shapes (SEMS) have been recently described in the literature. Most of these methods require knowing strain energy distribution for the undamaged structure (baseline SEMS). This is especially true for detection of small damages, where changes in the SEMS cannot be observed otherwise. Usually, the mode shapes from the structure under test should be compared to the baseline mode shapes to provide sufficient data for damage detection. However, these methods do not cover damage detection on structures where baseline mode shapes cannot be readily obtained, for example, structures with preexisting damage. Conventional methods, like building a finite element (FE) model of a structure to be used as a baseline might be an expensive and time-consuming task that can be impossible for complex structures. This paper suggests a method for extraction of localized changes (damage peaks) from SEMS based on Fourier analysis of the strain energy distribution. A detailed analytical proof is given for the case of a pinned–pinned beam and a numerical proof for the free–free beam. The analytical predictions have been confirmed both by the FE model and impact testing experiments on a free–free aluminum beam, including single and multiple damage scenarios. [ABSTRACT FROM AUTHOR]

The effect of a rectangular convex/concave shape formed on adherend surfaces in terms of preventing the crack growth of adhesively bonded joints was analytically investigated. The finite element method was used to evaluate crack growth resistance along the crack path by simulating a double cantilever beam test in which a single convex/concave shape was formed on the adherend material. The obtained crack growth resistance clearly demonstrated that both concave and convex shapes improved the apparent fracture toughness; i.e., the convex/concave shape functioned as a crack arrester. We identified the cause of the improvement as the dispersion of energy allocated to crack propagation due to the accumulation of the strain energy or the reduction of the stress concentration at the crack tip. It is noteworthy that the crack growth was arrested even when the convex shape did not interrupt the crack path. [ABSTRACT FROM AUTHOR]

Enamel possesses ingenious hierarchical structure that gives rise to superior fracture resistance. Despite considerable efforts devoted to characterization of fracture behavior of enamel, the role of rod decussation in fracture of enamel is largely unknown. In this study, the features of rod decussation in the inner enamel are experimentally identified, and analyses of crack growth in enamel are carried out using a micromechanical model of enamel, in which the structural features of the outer enamel and rod decussation of the inner enamel are incorporated. We carry out calculations within a framework based on the extended finite element method, and the crack growth and crack path selection are natural outcomes of imposed loading. We show that crack deflection in enamel is controlled by rod decussation. For crack growth in the parazone, the crack path is oriented along the axis of enamel rods, leading to gross crack deflection. The microstructure of inner enamel with intermediate inclination angle enables multiple crack deflections, giving rise to enhanced toughness. For crack growth in the diazone, the transition in orientation of crack deflection occurs as inclination angle increases. The relatively straight crack path emerges in the case of the microstructure of enamel with intermediate inclination angle, leading to weak fracture resistance. It is further found that compared with the diazone, the gross crack deflection in the parazone provides greater contribution to fracture resistance of enamel. The findings of this study provide a good mechanistic understanding of the role of rod decussation in enamel. [ABSTRACT FROM AUTHOR]

The hanger-to-girder connection is a vital load-bearing component of suspension bridges. However, two types of premature cracking (types A and B) in hanger-to-girder connections of the Runyang Suspension Bridge have been observed only several years after the bridge was open to traffic. This paper presents the field inspections on the pattern, location and propagation of cracks. To further investigate the mechanism of cracking, a multi-scale finite element (FE) model of the bridge is developed. It is observed from FE analysis results that under vehicle loads, large stress range and significant stress concentration exist. The type A cracks are mainly due to the discontinuity of hanger-to-girder connections and in-plane shear/bending deformation, and out-of-plane bending deformation of the welded connections accelerated type B cracking. To this end, probabilistic FE analyses are performed, and the predicted fatigue lives of the hanger-to-girder connections are obtained and compared with those in the field, where good agreement is observed. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrated stable nanoscale fracture in single-crystal silicon using an in-situ wedge-loaded double cantilever beam (DCB) specimen. The fracture toughness KIC was calculated directly from instrumented measurement of force and displacement via finite element analysis with frictional corrections. Measurements on multiple test specimens were used to show KIC = 0.72 ± 0.07 MPa m1/2 on {111} planes and observe the crack-growth resistance curve in <500 nm increments. The exquisite stability of crack growth, instrumented measurement of material response, and direct visual access to observe nanoscale fracture processes in an ideally brittle material differentiate this approach from prior DCB methods. In-situ fracture toughness experiments on single-crystal silicon revealed stable nanoscale fracture and identified the shape of the crack-growth resistance curve, role of fabrication-induced artifacts, and origin of fracture surface features. [ABSTRACT FROM AUTHOR]

For efficient use of adhesive joints, reliable prediction techniques should be made available to the designer. Simulation of these joints' behaviour is usually performed using the Finite Element Method (FEM). However, it is known that, in adhesive joints, the adhesive thickness (tA) is much smaller than the adherend thickness (tP), thus requiring a highly refined mesh to produce good results. Linked to this, the adhesive has to withstand high strains, causing mesh distortion and hindering the resolution. In these cases, meshless methods can be a good alternative. This work aims to implement the von Mises (vM) and Exponent Drucker-Prager (EDP) criteria combined with a meshless formulation based on the Radial Point Interpolation Method (RPIM), for the strength prediction of adhesively-bonded single-lap joints (SLJ). Validation with experiments is undertaken for joints with brittle to ductile adhesives, with varying overlap lengths (LO). Stress and strain distributions were plotted in the adhesive layer, and the failure load (Pm) was assessed by strength of materials failure criteria. Significant adhesive and LO effects were found on Pm. The RPIM proved to be a promising tool to predict the behaviour of bonded joints, although some limitations were found by using strength of materials criteria. [ABSTRACT FROM AUTHOR]

This paper reports the results of elastic-creep finite element (FE) analyses of a P91 steel pipe weld with two external 'type IV' circumferential cracks, subjected to internal pressure and end (system) load using creep properties obtained at 650°C. Numerical contour integral calculations have been performed to obtain both transient and stationary high temperature fracture mechanics parameters. A mesh sensitivity analysis was performed in order to ensure the accuracy of FE analyses in the transient creep stage. The effects of load magnitude, the material mismatch near the crack surfaces and the crack depth on the stationary creep C* contour integrals have been investigated, and corresponding analytical correlations are presented. [ABSTRACT FROM AUTHOR]

Simulations of delamination propagation and the initiation and crushing of composite laminates are made using a finite-element crash code, LS-DYNA. Delamination growth is modelled using cohesive failure models native to LS-DYNA, and in-plane failures are made using a laminated composite failure model. Results show that it is possible to accurately simulate simple dynamic delamination propagation events. Response during laminate crushing initiation is significantly more complex. Qualitative similarity between experimental data and crushing simulations is found, though quantitative correlation remains elusive. [ABSTRACT FROM AUTHOR]

Lifetime prediction of adhesively bonded joints under constant amplitude fatigue has been carried out using two finite element-based, progressive damage modelling methods. The first method used a fracture mechanics (FM)-based crack growth law in which the relationship between strain energy release rate and crack growth rate under fatigue was determined from experiments using compound double cantilever beam specimens. It was found that the FM approach predicted the fatigue life well at higher fatigue loads but under-predicted the fatigue life at lower fatigue loads. This was attributed to the increasing importance of crack initiation at lower fatigue loads. This problem was solved in the second predictive method, which was based on a continuum damage mechanics approach. A power law relationship to plastic strain was used to define the damage rate. The damage law was able to simulate damage evolution prior to crack growth and excellent predictions of fatigue life were found at all fatigue loads. [ABSTRACT FROM AUTHOR]

The increased incidence of fractures in aging tramway rails has motivated the development of a new, efficient numerical tool for studying structural mechanics problems related to such rails. We introduce virtual velocity fields reflecting axial, bending, shear, and torsional deformations, which are then translated, via the principle of virtual power, into corresponding equilibrium conditions. The resulting equations are numerically solved by means of sequential 1D and 2D Finite Element analyses, providing displacement quantities and stress resultants along the beam axis, as well as cross-sectional stress distributions. Finally, the key advantages of this modeling approach, including excellent efficiency and reliability, as well as straightforward applicability to a wide range of cross-sectional shapes and structural settings, are demonstrated via numerical examples. [ABSTRACT FROM AUTHOR]

The present study reports on the evaluation of residual stress field formation and distribution in Central Cut Plies (CCP) specimens. Real-time measurements were performed using a distributed sensing fiber optic system based on Rayleigh Backscattering, which was successfully able to capture strain distribution inside the adhesive layer at every 0.65 mm during the entire curing cycle, for both unidirectional and cross ply laminate configurations. A finite element analysis was also performed to cross-correlate with the experimental residual strain distributions in the proximity of the severed central cut plies. The results outlined in this study demonstrate the presences of tensile residual stresses within the adhesive layer for both configurations. A full field strain distribution and the significance of these findings in relation to the use of the CCP test for fracture mechanics testing will be discussed. Results of this study have shown that residual stresses arise after the curing process for which the amount of longitudinal and transverse residual stresses for the unidirectional CCP laminate are 61% and 19% of the total strength of the adhesive, respectively, while for the cross-ply CCP laminate are 72% and 71%, respectively. [ABSTRACT FROM AUTHOR]

We established an effective finite element model of knee joint for observation of stress and displacement of meniscus related changes after medial meniscus injury. Different types of medial meniscus injury can lead to varied meniscus stress and displacement changes. Stress and displacement concentration were found in fissure tip of meniscus tear compared to normal meniscus. The posterior horn injury of medial meniscus may initiate combined injury of medial meniscus posterior horn (MMPH) and that of medial meniscus body, and combined injury of MMPH and that of lateral meniscus anterior horn; fissure expansions regarding horizontal fissure, longitudinal fissure and grip-shaped fissure of MMPH were spotted. [ABSTRACT FROM AUTHOR]

Aiming to investigate the propagation behaviour of distortion-induced fatigue cracks in steel bridge web gaps, multi-scale numerical analysis models were built based on fracture mechanics theory and extended finite element method (XFEM), combining with the full-scale fatigue tests data. Propagation behaviours of representative fatigue cracks in vertical stiffener web gaps and horizontal gusset plate web gaps were analysed. Finite element models of welds connecting web, vertical stiffener and horizontal gusset plate were built, and the welding residual stresses of such details were analysed. Significant transverse welding residual tensile stresses exist at stiffener web weld toes for web gap details. Residual stress measurements were conducted, and the crack shape and the propagation direction path were basically the same with that in the numerical simulation, indicating that the numerical simulation results were relatively reliable. Furthermore, the welding residual stress fields were considered in the crack propagation analysis models. Representative fatigue cracks at web gaps are Mode I leading mixed-mode cracks of Modes I, II and III. Crack propagation considering welding residual stress has faster propagation rate and is more consistent with fatigue test results. The welding residual stress cannot be ignored for analysis and assessment of distortion-induced fatigue cracks in steel bridges. [ABSTRACT FROM AUTHOR]

To predict lifetime and damage tolerance of adhesively bonded joints, crack growth behavior need to be understood, as it oftentimes serves as a basis or proof of, e.g., numerical models. Within this work, a method is presented to measure crack length in dynamically loaded adhesively bonded CFRP-joints by means of 2D digital image correlation. Automated picture acquisition at the maximum force level within a cycle allows measurements during the fatigue testing. The strain level in front of the crack tip was defined as maximum possible strain within the bond line. Higher strains were denoted as crack. Marking the crack path automatically led to the associated crack length and could afterward be derived to a crack propagation rate. Different destructive tests were carried out on composite single, double and crack lap shear specimens. [ABSTRACT FROM AUTHOR]

Hybrid adhesive bonding is widely applied in industry nowadays. Whereas combinations of mechanical fastening and structural adhesive bonding are being used for a long time, hybrid bonds, which combine (resistance spot) welding and adhesive bonding, are a quite recent development. Although this technique of hybrid joining yields structures with excellent mechanical characteristics concerning static and dynamic stiffness and strength, it is hard to numerically predict these characteristics accurately. This originates from the fact that usually only some data is known on the stiffness and strength of the adhesive and spot welds but very few accurate and relevant information is available on the fracture toughness of both joining types. The presented research work consists of three main parts. - Main theoretical background on stiffness, strength and fracture characteristics of the considered joint types. - Mode I and II testing of hybrid adhesive bonded/spot welded specimen to retrieve force-displacement data and virtual testing based on finite element (FE) modelling. - Uncertainty quantification between experimental and virtual work. In general, the mode II tests correspond well with real test data. This cannot be concluded for the mode I tests. The flexibility of the double U–type samples (KS2) is difficult to simulate accurately, particularly from the point when first damage occurs. For both, the experimental and virtual data, the hybrid adhesive/spot welded joints showed the highest maximum force. [ABSTRACT FROM AUTHOR]

Bonding with adhesives is increasingly being used in the design of mechanical structures, because of the significant advantages of this technique compared to traditional joints. Different joint configurations are available, depending on the desired bond strength to be achieved and geometry of the parent structures. Tubular joints find applications in the piping industry, vehicle frames or thin-walled tubes, for instance, but they are seldom studied in the literature. This work numerically compares the performance of three structural adhesives on the tensile strength of aluminium tubular joints, after validation of the numerical tool with experiments. The numerical analysis consisted of using the Finite Element (FE) method to analyse peel (σy) and shear stresses (τxy) in the adhesive layer and cohesive zone models (CZM) to predict the maximum load (Pm). Numerically, the effect of the overlap length (LO) and the thickness of the inner and outer tubes (tSI and tSE, respectively) is addressed. Additionally, outer and inner chamfering of the tubes was tested to reduce peak stresses and increase Pm. The CZM technique was positively validated for the strength analysis of tubular joints. It was also shown that the joints' geometry and type of adhesive highly influence the joints' behaviour. [ABSTRACT FROM AUTHOR]