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This paper uses a two-scale material modeling approach to investigate fatigue crack initiation and propagation of the material X10CrMoVNb9-1 (P91) under cyclic loading at room temperature. The Voronoi tessellation method was implemented to generate an artificial microstructure model at the microstructure level, and then, the finite element (FE) method was applied to identify different stress distributions. The stress distributions for multiple artificial microstructures was analyzed by using the physically based Tanaka–Mura model to estimate the number of cycles for crack initiation. Considering the prediction of macro-scale and long-term crack formation, the Paris law was utilized in this research. Experimental work on fatigue life with this material was performed, and good agreement was found with the results obtained in FE modeling. The number of cycles for fatigue crack propagation attains up to a maximum of 40% of the final fatigue lifetime with a typical value of 15% in many cases. This physically based two-scale technique significantly advances fatigue research, particularly in power plants, and paves the way for rapid and low-cost virtual material analysis and fatigue resistance analysis in the context of environmental fatigue applications. [ABSTRACT FROM AUTHOR]

Erosion of metallic surfaces due to the permanent impact of high-speed water droplets is a significant concern in diverse industrial applications like turbine blades, among others. In the initial stage of water droplet erosion, there is an incubation regime with negligible mass loss whose duration is strongly dependent on water droplet sizes and velocities, the initial state of the surface, and the material properties of the target. The prediction of the incubation period duration is one of the main topics of research in the field. In this work, the interaction of the water droplets with a metallic surface is simulated using a hybrid Smoothed-Particle Hydrodynamics/Finite Element Method modeling scheme. The effect of multiple random impacts on representative target areas for certain ranges of impact angles and velocities was studied using a combination of simple material and damage models for the target surface of Ti-6Al-4V titanium alloy. The simulation is able to reproduce the main dependencies of the incubation regime and the first stages of water droplet erosion on the impact angle and velocity as reported in the literature. This framework can be considered a foundation for more advanced models with the goal of a better understanding of the physical mechanisms behind the incubation regime in order to devise strategies to extend it in real applications. [ABSTRACT FROM AUTHOR]

Auxetic structures made of biodegradable polymers are favorable for industrial and daily life applications. In this work, poly(butylene adipate-co-terephthalate) (PBAT) is chosen for the study of the deformation behavior of an inverse-honeycomb auxetic structure manufactured using the fused filament fabrication. The study focus is on auxetic behavior. One characteristic of polymer deformation prediction using finite element (FE) simulation is that no sounded FE model exists, due to the significantly different behavior of polymers under loading. The deformation behavior prediction of auxetic structures made of polymers poses more challenges, due to the coupled influences of material and topology on the overall behavior. Our work presents a general process to simulate auxetic structural deformation behavior for various polymers, such as PBAT, PLA (polylactic acid), and their blends. The current report emphasizes the first one. Limited by the state of the art, there is no unified regulation for calculating the Poisson's ratio ν for auxetic structures. Here, three calculation ways of ν are presented based on measured data, one of which is found to be suitable to present the auxetic structural behavior. Still, the influence of the auxetic structural topology on the calculated Poisson's ratio value is also discussed, and a suggestion is presented. The numerically predicted force–displacement curve, Poisson's ratio evolution, and the deformed auxetic structural status match the testing results very well. Furthermore, FE simulation results can easily illustrate the stress distribution both statistically and local-topology particularized, which is very helpful in analyzing in-depth the auxetic behavior. [ABSTRACT FROM AUTHOR]

A comprehensive approach to understand the mechanical behavior of materials involves costly and time-consuming experiments. Recent advances in machine learning and in the field of computational material science could significantly reduce the need for experiments by enabling the prediction of a material's mechanical behavior. In this paper, a reliable data pipeline consisting of experimentally validated phase field simulations and finite element analysis was created to generate a dataset of dual-phase steel microstructures and mechanical behaviors under different heat treatment conditions. Afterwards, a deep learning-based method was presented, which was the hybridization of two well-known transfer-learning approaches, ResNet50 and VGG16. Hyper parameter optimization (HPO) and fine-tuning were also implemented to train and boost both methods for the hybrid network. By fusing the hybrid model and the feature extractor, the dual-phase steels' yield stress, ultimate stress, and fracture strain under new treatment conditions were predicted with an error of less than 1%. [ABSTRACT FROM AUTHOR]

An investigation on the White Etching Crack (WEC) phenomenon as a severe damage mode in bearing applications led to the observation that in a latent pre-damage state period, visible alterations appear on the surface of the raceway. A detailed inspection of the microstructure underneath the alterations reveals the existence of plenty of nano-sized pores in a depth range of 80 µm to 200 µm. The depth of the maximum Hertzian stress is calculated to be at 127 µm subsurface. The present study investigates the effect of these nanopores on the fatigue crack initiation in SAE 52100 martensitic hardened bearing steel. In this sense, two micro-models by means of the Finite Element Method (FEM) are developed for both a sample with and a sample without pores. The number of cycles required for the crack initiation for both samples is calculated, using the physical-based Tanaka–Mura model. It is shown that pores reduce the number of cycles in bearing application to come to an earlier transition from microstructural short cracks (MSC) to long crack (LC) propagation significantly. [ABSTRACT FROM AUTHOR]

The interface plays a critical role in the mechanical properties of composites. In the present work, a novel phase-field based cohesive zone model (CZM) is proposed for the cracking simulation. The competition and interaction between the bulk and interfacial cracking are taken into consideration directly in both displacement- and phase-field. A family of modified degradation functions is utilized to describe the traction-separation law in the CZM. Finite element implementation of the present CZM was carried out with a completely staggered algorithm. Several numerical examples, including a single bar tension test, a double cantilever beam test, a three-point bending test, and a single-fiber reinforced composite test, are carried out to verify the present model by comparison with existing numerical and experimental results. The present model shows its advantage on modeling interaction between bulk and interfacial cracking. [ABSTRACT FROM AUTHOR]

This paper presents a method for predicting fatigue crack propagation in welded stiffened panels accounting for the effects of residual stresses. Well known power law models were employed to simulate fatigue life for a welded stiffened panel specimen damaged with a central crack. Stress intensity factor values (SIF) were obtained in finite element (FE) analyses by a linear superposition of the SIF values due to the applied load and due to weld residual stresses. The FE models included idealized, rectangular or triangular, residual stress distribution profiles. The effect of welding residual stresses on the crack propagation rate is taken into account by replacing the nominal stress ratio R in the power laws by the effective stress intensity factor ratio R eff . The considered stiffened panel specimen, made of mild steel commonly used in ship structures and manufactured by electric arc welding process, was subjected to the fatigue test with constant amplitude loading until failure occurred. By using the presented method remaining fatigue life of welded stiffened panel specimen was analysed. The simulated crack growth rate was relatively higher in the region of tensile residual stresses and lower between the stiffeners where compressive residual stresses prevail, which is in good agreement with physical principles and experimentally obtained results. [ABSTRACT FROM AUTHOR]

In this study, a computational mechanics approach has been developed to evaluate fracture toughness of an Al-Si cast alloy. Within the framework of the finite element method (FEM) CT-test experiments have been simulated on macro- and micro-scale levels with application of a cohesive zone model. Experimental CT tests have been performed and the parameters necessary for the FEM simulations (fracture energy and cohesive strength) have been determined. The estimation of fracture toughness from FEM simulations has been proposed based on a combination of crack propagation simulations on two-length scales in one run. The proposed approach enables one to understand the effect of pores of different sizes and locations on the fracture toughness of an Al-Si cast alloy. [ABSTRACT FROM AUTHOR]

Deals with developments in modeling based on the finite element method. Deformation analysis of metal matrix composites (MMC) problem; Iterative modeling procedure; Strength of MMC.

Interfacial debonding affects the mechanical behaviors of composite structures. In the present work, we developed a new phase-field-based cohesive zone model for modeling debonding at interfaces. The traction-separation law and evolution of phase-field considering the mixed-mode scheme of fracture toughness are given in a variational form. Besides, the present interfacial model can work with the phase-field cohesive zone model for the bulk region, in which a common phase-field value ϕ is shared for both regions. The interaction between the bulk region and interfacial cracking in both displacement, as well as phase-field, are taken into account directly to avoid the over-estimation of the free surface energy. The framework is implemented with the finite element method and validated with several numerical examples. The present work provides a unified approach for modeling quasi-brittle fracture in the bulk region and interfaces and shows its advantage in describing interactions between bulk and interfacial cracking. • A phase-field-based cohesive element is proposed for interfacial failure. • Srength and fracture toughness can be defined independently in different directions. • Closure effect of the interfacial crack can be modeled with given penalty stiffness. • Governing equation is given in a variational form. • Mixed-mode behaviors of interfacial fracture is also considered. • The interaction between interface and matrix is considered by a driving force term. [ABSTRACT FROM AUTHOR]

[Display omitted] • Interfacial debonding of a porous TBC system is studied via SEM image-based FE analysis. • Microstructural pores of SEM image of TBC sample are imported into FE software via CMM. • Pores of TC force the stress to be concentrated adjacent to rough TC/TGO interface and develop TC/TGO interface damage. • Porosity within the BC diminishes stress and damage values along the TGO/BC interface. • Creep leads to stress relaxation of TC up to 24.82 % and lowers the damage level of TGO/BC interface. Numerical analysis of interfacial delamination and the effect of microstructural pores and rough interfaces on the field variables in thermal barrier coatings (TBCs) based on a real scanning electron microscope (SEM) image is performed. The interfacial delamination is modelled by the utilization of cohesive zone method (CZM) in finite element (FE) analysis. The empirical TBC sample considered in this study is constructed via air plasma spray (APS) method and comprises ZrO 2 7 - 8 wt. % Y 2 O 3 ceramic top coat (TC), thermally grown oxide (TGO) made of Al 2 O 3 and NiCrAlY metallic bond coat (BC). A compatible geometry is provided by applying image processing technique to SEM image of the sample's cross-section. SEM image-based geometry imported into FE software to scrutinize the interplay effects of porosity and rough interfaces on temperature fields, thermal stresses and interfacial debonding of TC/TGO and TGO/BC interfaces of the TBC structure. FE analysis reveal that porosity distribution has a prominent role on the stress concentration zones at the sharp corners of pores especially adjacent to undulations of the TC/TGO interface, which is responsible for possible internal cracks and interfacial fracture, respectively. The main findings demonstrate that the porosity near the TC/TGO interface has detrimental effect as leads to aggravation in the TC/TGO interface damage, which causes an increment in TC/TGO interfacial crack length. While, the porosity within the BC has the ability to reduce the stress and damage level along the TGO/BC interface. In addition, considering creep for all layers leads to lower stress levels up to 24.82 % and consequently alleviates the TC/TGO interface damage. [ABSTRACT FROM AUTHOR]

• The physically based TM formulation is a promising numerical method to predict the fatigue short crack initiation, specially for the stent components. • By implementing the current numerical method we can predict the time before the nucleation of the first micro-cracks within the stent components. Most of the micro-components, such as coronary stents, consist of an oligo-crystalline micro-structure. This means that the detection of the few coarse grains which are columnar and parallel to the longitudinal ingot axis is possible. The deformation behavior of such micro-structures is obviously different from polycrystalline materials, since the anisotropic properties of one grain, in relation to its nearest neighbors should be considered. The goal of this study is the simulation of the crack initiation process under a cyclic loading situation in the oligo-crystalline micro-structure of the stent component made of X2CrNiMo-18-15-3. The crack initiation process is simulated employing the physically-based Tanaka-Mura model implemented in Finite Element Method (FEM). The available experimental result data have also been used as the input parameters to the current modelling approach. In this regard the grain size and the grain orientation are changed, and their effect together with the influence of the surface roughness on the fatigue life of the stent components has been studied. [ABSTRACT FROM AUTHOR]

• The interface crack between two dissimilar quasicrystal materials. • The gradient theory of thermoelasticity for quasicrystals. • The gradient theory for heat conduction problem. • Decagonal quasicrystal properties. • The mixed FEM formulation with C0 continuous finite elements for independent approximations of displacements and strains. The interface crack problem between two dissimilar materials under a thermal load is analyzed by the gradient elasticity theory since the size effect is expected in the very thin quasicrystal layer. The uncoupled thermoelasticity is considered here, where the thermal fields are independent on mechanical ones. The thermal transport can't be well described by classical Fourier's law in nano-sized structures. Therefore, a novel gradient theory is developed in such structures, where the second derivatives of temperature in the constitutive equation for the high-order heat flux are considered. Moreover, the phonon strain gradients are incorporated into the higher-grade continuum model. Decagonal quasicrystal material properties are considered here. Governing equations and corresponding boundary conditions are derived from the principle of virtual work. The mixed finite element method (MFEM) is developed for a general 2D boundary value problem. Numerical examples are presented to illustrate the phonon, phason and thermal response to external thermal loading within the considered model. [ABSTRACT FROM AUTHOR]

The graphite phase of ferritic cast-iron was assumed to consist of randomly oriented, rotationally symmetric, ellipsoidal inclusions of same dimensions. Accordingly, a self-consistent one-particle 3D unit cell model was developed to simulate the effect of graphite aspect ratio on cast-iron elastic constants. The cube shaped unit cell is made up of an inner rotational ellipsoid of graphite surrounded by α Fe–2.5%Si matrix in a concentric outer ellipsoid of the same aspect ratio as the inner graphite ellipsoid in order to model the desired graphite content. The remainder of the unit cell is filled up by the cast-iron compound, the elastic behaviour of which is determined self-consistently. In order to obtain elastic properties, the unit cell was subjected to uniaxial loading. Calculations of stress and strain distributions, in dependence on the orientation of the graphite ellipsoid, were carried out by the finite element method using 3D elements. Finally, updated values of Young’s modulus and Poisson’s ratio were derived by employing Hooke’s law. This procedure was repeated, using the updated elastic constants as new input, to get a self-consistent convergent solution. The results are compared with finite element calculations using a conventional one-particle 3D unit cell model with multiphase elements, and an analytical solution given in the literature. Comparison with experimental data shows the relatively wide range of validity and the superiority of the self-consistent method. [Copyright &y& Elsevier]

• MD simulation on crosslinking and deformation of pure and graphene reinforced epoxy. • A new multiscale simulation framework for nanocomposites on the micro- and nanoscale. • Crack simulation in composites by using the phase-field method. A novel multiscale simulation framework was proposed to investigate the mechanical properties of single layer graphene platelets reinforced crosslinked epoxy. Crosslinking reactions in composites were simulated with the molecular dynamics (MD) method in the nanoscale, and the mechanical properties of bulk epoxy and interfaces between unfunctionalized graphene and epoxy were obtained. These mechanical properties from MD method were used in FEM simulation in the microscale. The crack propagation in composites was investigated with the finite element method (FEM) based phase-field method (PFM). The influence of several morphologic factors of graphene platelets on mechanical properties, including volume fractions, distributions of graphene orientations and waviness of graphene, was investigated. Results showed that the increasing graphene volume fraction would lead to the decrease of mechanical properties of composites due to the weak interfacial strength in the present model. Meanwhile, aligned graphene platelets improve all the mechanical properties simultaneously. In addition, the graphene platelets with higher curvatures provide improvement of the overall mechanical properties of the composites because they can block interfacial sliding. The present research suggested that the interfacial strength can be the bottleneck in the graphene reinforced epoxy. [ABSTRACT FROM AUTHOR]

• Analyses of thermoelectric nano-sized structures with cracks. • The size-effect phenomenon is considered by strain-gradients in constitutive equations. • The mixed FEM formulation is applied for numerical implementation. • The influence of the size effect on the crack-opening-displacements is investigated. General 2D boundary value problems with cracks in nano-sized structures of thermoelectric materials are analyzed by the finite element method (FEM). The size-effect phenomenon observed in nano-sized structures is considered by strain-gradients in the constitutive equation for the high-order stress tensor. The variational principle is applied for derivation of coupled thermo-electro-mechanical governing equations. The thermo-electrical fields are fully coupled and the mechanical fields are coupled with temperature only. The mixed FEM with the C0 continuous interpolation for displacements and strains is developed. A collocation approach for kinematic constraints between strains and displacements is applied. The influence of the size effect on variation of crack opening displacements is demonstrated by some numerical examples. [ABSTRACT FROM AUTHOR]

Constitutive equations in gradient theory of quasicrystals are written for phonon and phason stresses, and the higher-order stress tensor. They are expressed by the phonon and phason strains and the gradient of phonon strains. The higher-order elastic parameters are proportional to the conventional elastic stiffness coefficients by the internal length material parameter. Material parameters in constitutive equations correspond to the decagonal quasicrystals. The principle of virtual work is applied to derive governing equations and corresponding boundary conditions. The finite element method (FEM) is developed to solve general 2D boundary value problems in problems described by governing equations for strain-gradient theory of quasicrystals. The path-independent J -integral is also derived for fracture mechanics analysis of such solids. Numerical examples are presented to demonstrate the veracity of the formulations. • Constitutive equations in gradient theory of decagonal quasicrystals. • The mixed FEM with C0 approximation. • The higher-order J -integral formula. [ABSTRACT FROM AUTHOR]

• Performing fracture tests under different loading, temperature and geometry conditions. • Extracting the corresponding values of crack-tip constraint using FEA. • Extracting J-Q curves under mixed-mode loading conditions. • Modifying J-R curves using crack-tip constraints for mixed-mode loading conditions. • Considering temperature in the modified J-R curve to eliminate the need for experimental testing in future research. The main objective of this study is the precise estimation of the fracture parameters by applying crack-tip constraint under mixed-mode loading conditions. To this aim, an AM60 magnesium alloy with elastic-plastic behavior has been utilized. Fracture tests were conducted using a modified version of Arcan device in mode-I, 45° mixed-mode, and mode-II loading conditions. Different initial crack lengths were used to create a wide range of crack-tip constraints. In addition, experiments have been carried out at different temperatures to enhance the applicability and effectiveness of research in real applications. Using finite element analysis (FEA), the crack-tip constraint, Q , corresponding to the laboratory conditions was extracted. The results show a strong dependency of Q constraint on the loading angle so that by changing the loading angle from mode-I to mode-II, the crack-tip constraint experienced a significant increasing trend, while the dependency on the crack length and temperature is negligible. Finally, the J - Q curves are presented for different temperatures and the corresponding relations are used for predicting the critical values of the J -integral in a specific condition and the obtained results are compared with the experimental results. According to the results, the minimum and maximum differences between the obtained results from the relations and the experimental result are 0.01% and 19.49%, respectively. Moreover, the J-R resistance curve has been modified using the crack-tip constraint. Regarding the obtained results, the minimum and maximum differences between the extracted values and the experimental results were 15.76% and 17.66% respectively. It can be concluded that using the results of this research eliminates the need for conducting the corresponding experimental tests, and the critical values of the J -integral can be obtained with reasonable accuracy by calculating the crack-tip constraint through FEA. [ABSTRACT FROM AUTHOR]