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Highlights • Strain fields on the surface of a transverse flat specimen are obtained with a DIC system (ARAMIS). • Experimental strain fields obtained from ARAMIS are compared to the Rousselier simulation results. • The Rousselier model is used to predict stress-strain curve and crack propagation of different specimens from welded joints. Abstract In this paper, the fracture behavior of an aluminum laser welded butt joint was studied numerically and experimentally. With the assistance of a digital image correlation (DIC) system, the strain variation of the flat specimen under deformation is obtained. Void sheeting mechanism and shear bands are found on the surface of the specimen to precede rupture. Although initial pores are found in the fusion zone, good predictions are obtained with respect to stress-strain, F-COD as well as fracture resistance J R curves for flat and compact tension (C(T)) specimens, confirming the Rousselier model can predict the fracture behavior of aluminum laser welded joint well, with the Rousselier parameters calibrated from simulation of fracture behavior of notched round specimens. [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]

Fracture criteria for prediction of extension of the interface crack and of the crack growth direction in a bimaterial consisting of a homogeneous and a functionally graded material (FGM) with systems of internal defects are studied. The bimaterial is subjected to a heat flux and a tensile load applied at infinity. It is assumed that the thermal properties of the FGM have exponential form. The Young’s modulus and Poisson’s ratio are assumed to be constant. In the previous papers (Petrova and Schmauder, 2011a,b, 2012a,b) asymptotic analytical formulas for the stress intensity factors (SIFs) at the interface crack tips were obtained as a series of a small parameter (the ratio between sizes of the internal and interface cracks). These SIFs are used in fracture criteria to obtain the possible direction of crack propagation and critical loads. The maximum circumferential stress criterion is used and some results for the fracture angles is obtained by the minimum strain energy density in order to compare the predictions for the fracture angles by two fracture criteria. The influence of geometry of the problem (location and orientation of cracks) and the parameters of non-homogeneity of FGMs on the main fracture characteristics is investigated. [ABSTRACT FROM AUTHOR]

Abstract: The work is devoted to the investigation of fracture processes in the vicinity of an interface crack in functionally graded/homogeneous bimaterials with internal defects subjected to tensile loading and a heat flux. A previously obtained solution () for the case of thermal loading on the same geometry is used as a part of the present solution. The solution is based on the integral equation method and it is assumed that thermal properties of the functionally graded material (FGM) possess exponential form. An asymptotic analytical solution is derived for a special case where an interface crack is larger than internal cracks in the FGM. The stress intensity factors are presented as asymptotic analytical functions of geometry of the problem and material properties. Analyses of the effects of the location and orientation of the cracks and the material non-homogeneity parameters on the stress intensity factors in FGM/homogeneous bimaterials is performed in the presence of thermal and mechanical loading. Examples of some FGM/homogeneous bimaterial are discussed. [Copyright &y& Elsevier]

Abstract: The work is devoted to mathematical modeling of the fracture processes in the vicinity of an interface crack in functionally graded/homogeneous bimaterials with internal defects subjected to a thermal flux. A previously obtained solution (Petrova and Schmauder, 2009, 2011) is used and supplemented with the additional possibility to take into account the crack closure. The solution is based on the integral equation method and it is assumed that thermal properties of the functionally graded material (FGM) have exponential form. For a special case where an interface crack length is much larger than the internal cracks in the FGM an asymptotic analytical solution of the problem is obtained as series of a small parameter (the ratio between sizes of the internal and interface cracks). Analyses of the effects of the location and orientation of the cracks, the material non-homogeneity parameters and the crack closure effects on the thermal stress intensity factors of the interface crack in FGM/homogeneous bimaterials are performed. Examples of some FGM/homogeneous bimaterial combinations (i.e., metal/metal, ceramic/metal) are discussed. [Copyright &y& Elsevier]

Abstract: In this study the elastoplastic behaviour of nanodispersed elastomeric copolymer particle-modified PA6 is investigated. Micromechanical modelling is proposed to predict the elastoplastic response of the PA6/elastomer composite under uniaxial tensile loading. A 3D self-consistent embedded unit cell model is chosen in this work which has been successfully applied for simulating the mechanical behaviour of metal matrix composites (MMCs). This model is applied for the first time to evaluate the elastoplastic behaviour of PA6 matrix composites with varying volume fractions of elastomer. The elastomer particles are idealistically assumed to be spherical. In the model a circular inclusion is surrounded by the PA6 polymer matrix, which is again embedded in the PA6/elastomer composite. This cell was subjected to uniaxial loading. The mechanical behaviour is determined iteratively in a self-consistent manner using updated elastic–plastic data as new input. A detailed experimental procedure (uniaxial tensile tests in combination with the ARAMIS high speed camera systems) for determining the true stress–strain curves of the matrix and the elastomer as input data for the simulation is reported. In addition, a numerical surface model based on the real structure of the elastomer particles is studied numerically for comparison. Two analytical micromechanical composite models are chosen for evaluating the elastic performance of the composite. The predictions from the 3D self-consistent embedded unit cell model are in good agreement with the experimental results. [Copyright &y& Elsevier]

Abstract: The thermal fracture of a bimaterial consisting of a homogeneous material and a functionally graded material (FGM) with a system of internal cracks and an interface crack is investigated. The bimaterial is subjected to a heat flux. The thermal properties of FGM are assumed to be continues functions of the thickness coordinate, while the elastic properties are constants. The method of the solution is based on the singular integral equations. For a special case where the interface crack is much larger than the internal cracks in the FGM the asymptotic analytical solution of the problem is obtained as series in a small parameter (the ratio between sizes of the internal and interface crack) and the thermal stress intensity factors (TSIFs) are derived as functions of geometry of the problem and material characteristics. A parametric analysis of the effects of the location and orientation of the cracks and of the inhomogeneity parameter of FGM’s thermal conductivity on the TSIFs is performed. The results are applicable to such kinds FGMs as ceramic/ceramic FGMs, e.g., TiC/SiC, MoSi2/Al2O3 and MoSi2/SiC, and also some ceramic/metal FGMs. [Copyright &y& Elsevier]

• Thermal fracture of functionally graded coatings (FGCs) on a homogeneous substrate is studied. • The effect of residual stresses caused by temperature changes on ΔT (cooling) is investigated. • The mathematical description of the model is based on singular integral equations. • The stress intensity factors and fracture angles were derived. • Combinations of PSZ and mullite as FGCs and Ni superalloy and steel as substrates are used. • Illustrative examples are presented to study the interaction of edge cracks with internal cracks at a weak zone. The problem of fracture of functionally graded coatings (FGCs) on a homogeneous substrate (a semi-infinite medium) is investigated under the influence of thermal and/or mechanical loads (e.g. a heat flux, residual thermal stresses caused by cooling-heating, tension). These loads reflect the most important cases, which arise during the exploitation of FGC structures. The FGC contains pre-existing systems of cracks, such as edge, internal and interface cracks. The mathematical description of the model is based on singular integral equations. The properties of the FGC are continuous functions of the thickness coordinate. Furthermore, the non-homogeneity of the functionally graded material is revealed in the form of corresponding inhomogeneous traction distributions on the surfaces of cracks. This method is approximate and used with the assumption, that the gradation of material properties of the FGC with the depth of the layer is not abrupt. The influence of residual stresses caused by temperature changes on ΔT (e.g. cooling from operating temperatures) is investigated in detail. Different crack patterns (which are reported in experiments and available in the literature) are studied by carrying out numerical experiments with respect to stress intensity factors and fracture angles (a deviation of cracks from the initial direction of propagation). The proposed model in combination with a detailed parametric analysis can help to optimize FGCs in order to improve the fracture resistance of FGC/homogeneous structures. [ABSTRACT FROM AUTHOR]

The microstructure of composite plays a critical role in its mechanical performance. In present work, a series of finite element models are developed to simulate the strength and damage evolution of nanoplatelets reinforced polymer. In order to overcome the mesh issue that occurs in many works due to the extreme high aspect ratios of the nanoplatelets, a novel strategy is proposed to add membrane/shell elements representing nanofillers in a representative volume element. In addition, interfacial debonding can also be simulated within this framework. Furthermore, a modified phase-field method is proposed to model brittle fracture in the polymer matrix. Numerical results show that a quite low volume of nanoplatelets can improve the macroscopic Young's modulus and strength of nanocomposites simultaneously. Interfacial debonding would affect both strength and toughness properties of nanoplatelets reinforced polymer through changing the morphology of cracks. The new modeling strategy in the present work can improve both efficiency and accuracy of finite element modeling nanoplatelets, especially with extremely high aspect ratio reinforced polymers. [ABSTRACT FROM AUTHOR]

• Overview of the available results for Mode III interface crack problems is presented. • Mode III interface crack problem is posed using analytic functions of complex variable. • Closed form analytical solution for interface crack- microcrack interaction is presented. • Solutions for SIFs are discussed with respect to their dependency on bimaterial constants. An overview of the results for Mode III interface crack problems available in the literature, as well as those obtained by the authors, is presented in the paper. The analytical and semi-analytical solutions for the main fracture characteristics (i.e. stress intensity factors and energy release rates) are discussed with respect to their dependency on bimaterial constants. Detailed formulation for the antiplane shear problem for an interface crack interacting with internal cracks is presented using the methods of complex potentials and singular integral equations. Some particular solutions (e.g. for the problem of a singularity interacting with an interface and for the Mode III interface crack) are obtained, and these can serve as benchmark solutions or as parts of other similar problems. The approximate closed-form solution is derived for a special case of the interaction between the interface crack and internal micro-cracks. The resulting form of the solution for the stress intensity factors is rather simple and its structure is easily analyzed. A theoretical analysis of the explicit form of expressions for the stress intensity factors shows the conditions under which the solution for the interface crack depends on the bimaterial mismatch, and those under which it does not depend. This formula also allows to define the condition, when a small internal crack does not influence the stress intensity factor of the interface crack (i.e. invisible for the interface crack). [ABSTRACT FROM AUTHOR]

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]

Abstract Copper alloys show a structural variability leading to a range of diverse electronic, transport, and mechanical properties. Here, we investigate the influence of the type and amount of alloying on the electronic transport properties across copper alloys. Specifically, we investigate the electronic transmission along copper in its fcc crystal structure. The characteristic change when adding impurities, such as nickel, aluminum, and silicon in the structure and transport properties is assessed through density functional theory calculations together with the non-equilibrium Greens functions approach. The results are analyzed with respect to the structural characteristics, the electronic and transport properties in these alloys for different concentrations of the impurities. A clear trend in the electronic transmission, thus the conductance, along these materials was found with the addition of certain impurities and their clusters. Coherent with experimental observations, we conclude that the higher the concentration of the impurities, the lower the electronic transmission along the alloys as compared to a pure copper crystal. Furthermore, we show that the bonding environment in the impurity clusters can be associated to additional valence states and significantly influences the conductance. In the end, we discuss the relevance of our results for practical applications. Highlights • Impurities enhance valence band of alloy. • Conductance decrease of Cu alloy pronounced for Si. • Impurity clusters enhance Cu alloy conductance. • High impurity concentration decreases the conductance of Co alloys. [ABSTRACT FROM AUTHOR]

Abstract Erosion caused by repeated impact of solid particles entrained in a moving fluid is relevant for many technical applications like resulting wear and reduced service life of turbine blades, propellers and valves. In this work, a lattice Monte Carlo model for erosion of a class of glass submitted to impact of alumina particles reproduces and enhances experimental and simulation results described in Jafar et al., Wear 303, no. 1 (2013): 302–312. The lattice Monte Carlo model of solid particle erosion (LMC-SPE model) is based on a three dimensional representation of the target surface by a cubic lattice, where each cell embodies a small portion of the material susceptible of damage accumulation (in this case, brittle fracture) and subsequent removal. The simulation is driven by a kinetic Monte Carlo method where individual impacts can be generated according to probability distributions of experimental parameters (for example, size, velocity and spatial distributions of particles). In addition, a phenomenological model of the interaction of impacting particles with an already eroded and rough surface is introduced in order to correct unrealistic large final surface roughness and erosion rates obtained otherwise. In spite of its simplicity, the LMC-SPE model can simulate the main topographic features of individual impacts and reproduce correctly dependencies of the erosion rate on velocity, size, and impact angle of the particles. Consequently roughening regimes due to the accumulative effect of thousands of individual impacts acting on relatively large areas are simulated within reasonable computational times. Due to its three dimensional character, LMC-SPE simulations can be compared directly with channels obtained with abrasive jet micro-machining techniques (AJM) described in literature. Highlights • The LMC-SPE model simulates millions of particle impacts on a brittle surface. • Monte Carlo algorithms reproduce statistical distributions of experimental parameters. • Local roughness and accumulated damage are taken into account to reproduce experiments. • Topography and roughness of simulations can be compared with micro-machined surfaces. [ABSTRACT FROM AUTHOR]

Interfacial bonding of three different semi-coherent bcc-Fe(110)/graphene interfaces is investigated using the plane-wave pseudopotential method within density functional theory. The analysis of bond lengths, charge densities, charge transfer, magnetic moments and densities of states shows that interfacial adhesion can be understood from the electronic structure. Graphene is considered on Fe(110) surfaces as well as embedded in (110) planes of bulk Fe. Moreover, the influence of single vacancies in graphene is studied in case of graphene on the Fe(110) surfaces. It is found that a single vacancy in graphene leads to a strong increase of interfacial adhesion. The most important contribution to the adhesion is covalent bonding with hybridization of Fe states and C states which is most pronounced for neighboring atoms of the vacancy. [Display omitted] • bcc-Fe(110)/graphene interfaces exhibit strong adhesion due to covalent Fe–C bonds. • Single vacancies in graphene lead to a strong increase of adhesion. • Large magnetic moments are induced at C atoms neighboring a single vacancy. [ABSTRACT FROM AUTHOR]

This paper develops an approach to model the deformation and fracture of heterogeneous materials at different scales (including multiscale modeling) within a discrete representation of the medium. Within this approach, molecular dynamics is used for the atomic-scale simulation. The simply deformable distinct element method is applied for simulating at higher length scales. This approach is proposed to be implemented using a general way to derive relations for interaction forces between distinct elements in a many-body approximation similar to that of the embedded atom method. This makes it possible to overcome limitations of the distinct element method which are related to difficulties in implementing complex rheological and fracture models of solids at different length scales. For an adequate description of the mechanical behavior features of materials at the micro- and mesoscales, two kinds of models that consider grain and phase boundaries within the discrete element framework are proposed. Examples are given to illustrate the application of the developed formalism to the study of the mechanical response (including fracture) of materials with multiscale internal structure. The examples show that the simply deformable distinct element method is a correct and efficient tool for analyzing complex problems in solid mechanics (including mechanics of discontinua) at different scales. [ABSTRACT FROM AUTHOR]

In the present study, Taguchi approach is coupled with fuzzy-multiple attribute decision making methods for achieving better surface quality in constant cutting speed face turning of EN 1.4404 austenitic, EN 1.4462 standard duplex and EN 1.4410 super duplex stainless steels. Two typical multiple attribute decision making techniques were simultaneously adopted to determine multi-surface quality characteristics indices. The differences in rankings among derived indices are solved through converting each crisp values into trapezoidal fuzzy number and unifying them using fuzzy simple additive weight method. The fuzzy numbers are then deffuzified into crisp values employing techniques like; the spread, mode and area between centroid of centroids. Through this procedure, the decision maker is provided with necessary decision tools to optimize the cutting conditions with less sensitivity to the change of weights and no difference in ranking among the deffuzification techniques. Additionally, results of analyses of means and the validation experiments confirm that the optimum cutting conditions derived by this method produce far better surface finish than the best finish obtained during the course of experimentation. Analyses of variance results have shown the predominant effect of feed rate on surface quality. Finally, the collected chip at constant cutting speed and varying feed rates and depth of cuts has shown that friendlier-to-machine chips are obtained when machining austenitic stainless steels than duplex stainless steel grades. [ABSTRACT FROM AUTHOR]

In rock-like materials, mode I and II fracture toughness are distinctive while the compressive strength is much greater than the tensile strength. Besides, mixed-mode fractures instead of pure mode I or II fractures occur under complicated load cases in those materials. Therefore, to capture the mixed-mode cracking process, we developed a mixed-mode phase-field cohesive zone model based on the unified phase-field theory proposed by Wu. The model was built based on a strain energy decomposition scheme and the softening behavior of each mode is controlled by an independent degradation function. Thus, independent values of strength and toughness can be given for different failure modes simultaneously. A simple mixture rule of fracture toughness was introduced to describe the transition between different failure modes. The model can keep variational consistency perfectly and governing equations for displacement- and phase-field, which was never reported in other works. Several numerical examples verified the effectiveness and flexibility of this work. The present work showed a simple but effective way to simulate mixed-mode fracture. • A modified phase-field cohesive zone model is developed for mixed-mode fracture. • A simple mixture rule is utilized to describe the transition between each fracture mode. • The present model can keep the variational consistency perfectly. • Several numerical cases verify the present model. [ABSTRACT FROM AUTHOR]

• B substitution of a C atom increases the work of separation on the Fe(110) surface. • There is almost no effect of N on the graphene/Fe(110) interface. • B and N impurities affect the charge states of the nearest C atoms. • Impurities influence on the magnetic state of the nearest Fe atoms. Influence of B and N substitutional impurities on the adhesion properties, electronic and magnetic characteristics of the external and internal graphene/Fe(110) semi-coherent interface was investigated by the projector augmented-wave method within the density functional theory. The analysis of interatomic distances, charge densities, charge transfer and magnetic states of atoms was performed. It was shown that B-doped graphene has a higher adhesion energy on the Fe(110) surface and in the iron bulk in comparison with the undoped systems; whereas, N-doped graphene in the Fe bulk demonstrates the opposite trend and on the surface it has no effect. Boron acts as electron donor that increases charges of the nearest C atoms by 0.5–0.6 e. Nitrogen due to its high electronegativity is an acceptor and as a result the nearest C atoms lose 0.2–0.3 e. Both impurities, depending on the position, influence differently on the magnetic moment of the nearest iron atoms. [Display omitted] [ABSTRACT FROM AUTHOR]

To gain a deeper insight into the anomalous yield behavior of Ni 3 Al, it is essential to obtain temperature-dependent formation Gibbs energies of the relevant planar defects. Here, the Gibbs energy of the complex stacking fault (CSF) is evaluated using a recently proposed ab initio framework [Acta Materialia, 255 (2023) 118986], accounting for all thermal contributions—including anharmonicity and paramagnetism—up to the melting point. The CSF energy shows a moderate decrease from 300 K to about 1200 K, followed by a stronger drop. We demonstrate the necessity to carefully consider the individual thermal excitations. We also propose a way to analyze the origin of the significant anharmonic contribution to the CSF energy through atomic pair distributions at the CSF plane. With the newly available high-temperature CSF data, an increasing contribution to the energy barrier for the cross-slip process in Ni 3 Al with increasing temperature is unveiled, necessitating the refinement of existing analytical models. [ABSTRACT FROM AUTHOR]

Abstract: A three-dimensional numerical analysis of the mesoscale deformation behavior of welded low-carbon steel specimens is performed. A weld-affected polycrystalline microstructure is designed to reproduce gradual changes of the grain size throughout the base metal and heat-affected zone regions. A mathematical model based on a double-limit yield criterion is used to describe Lüders band propagation characteristic of this type of steel. The effects of the free surface, grain boundaries and interfaces between the fusion zone and the heat-affected zone, and between the heat-affected zone and the base metal are discussed. [Copyright &y& Elsevier]

Abstract: In this study semi-crystalline polyamide 6 (PA 6) and its composites consisting of a semi-crystalline PA 6 matrix filled with up to 32.9vol.% submicron elastomeric copolymer particles are investigated. The aim of this paper is to show how micro-mechanical modelling can predict the elastic behaviour of these composites from the experimentally observed morphology and determined parameters. Semi-crystalline PA 6 possesses a spherulitic morphology, consisting of a radial assembly of amorphous layers and nano-sized crystalline lamellae. In the continuum mechanical representation of semi-crystalline PA 6, nano-sized crystallite lamellae are considered as a phase which is additionally embedded into the amorphous matrix. The 2D self-consistent embedded cell model was chosen to predict the Young’s modulus of the semi-crystalline PA 6 material. In this model a rectangular lamella is surrounded by an amorphous matrix, which is again embedded in the semi-crystalline PA 6 material with the mechanical behaviour to be determined iteratively in a self-consistent manner. The Young’s modulus of PA 6 has been calculated by an appropriate integration of results of all orientations of the crystalline lamellae. The Young’s modulus of PA 6/elastomer composite is also predicted by a 3D self-consistent embedded cell model. In this model a circular inclusion is surrounded by the PA 6 polymer matrix, which is again embedded in the PA 6/elastomer composite. Good agreement is obtained between experiments and the prediction with the self-consistent embedded cell models. [ABSTRACT FROM AUTHOR]

Abstract: Functionally graded materials (FGMs) have great potential as energy absorbing devices, electrical transducers, thermal barriers, etc. Study of the propagation of elastic waves is imperative for a number of such applications. In this paper, a simple one-dimensional model is proposed to study the stress waves in discretely graded media. The model uses spectral approach to determine the stresses due to the incident and reflected waves in FGMs. It has been observed that FGMs attenuate and delay the peak stresses considerably as compared to composites with sharp interfaces. Performance of different number of inner layers on the reflected wave characteristics has been discussed. Stress time history profiles are also presented for Alumina–Aluminum FGMs that are used in armor applications. [Copyright &y& Elsevier]

Abstract: Classical molecular dynamics simulations of the interaction of edge dislocations in Ni with chains of spherical Ni3Al precipitates are performed using EAM potentials. The order hardening is investigated at temperature  K by determining the critical resolved shear stresses (CRSSs) for a superdislocation that is dissociated into four partial dislocations. The CRSS is computed as a function of the radius and the distance of the precipitates. It is found that for precipitates with a diameter smaller than the dissociation width of perfect edge dislocation in Ni, the CRSS of the trailing dislocation of the superdislocation is a fraction of about 0.4 of the CRSS of the leading dislocation. [Copyright &y& Elsevier]

The present paper deals with a class of functionally graded materials (FGM), called active FGM that has electro-elastically graded material phases. An active FGM system leads to minimization of stress concentration that arises due to mismatch in the electrical and elastic properties of the constituent phases. This work focuses on the characterization of the through thickness stresses of an active FGM subjected to electrical excitation. The structure is comprised of a substrate, an electro-elastically graded layer and an active layer. A formulation for exact solutions of the system based on Euler–Bernoulli theory is presented. Power-law variation of the composition of the two phases in the graded layer is considered. Performance of linearly gradient FGM for a range of stiffness and electrical property ratios of the active and substrate materials have been studied. It is observed that the electrical strain component and the compositional gradation significantly influence the stress characteristics of the active FGM. [Copyright &y& Elsevier]

Co(0001)/TaC(01 2 ¯) interfaces with Re impurities are investigated using the plane-wave pseudopotential method within density functional theory. Two interface configurations and several interfacial sites for Re impurities are considered. The calculations reveal that Re doping can lead to more favourable interfaces with lower interface energies. It is shown that the decrease of interface energy can be understood from the electronic structure. Analyses of bond lengths, overlap populations, charge density distributions and densities of state demonstrate the importance of C-Co and C-Re bonds across the interface. Image 1 • Interfacial Re impurities increase interface strength. • Increased interface strength is mainly caused by strong C-Re covalent bonds. • Most favourable configuration of Co/TaC interface is changed by Re doping. [ABSTRACT FROM AUTHOR]

Low cycle fatigue tests for P92 heat-resistant steels (P92 HRS) were conducted at room temperature (RT) and elevated temperature (873 K). The fatigue test results showed that P92 steel showed softening characteristics during fatigue at RT and 873 K, and the increase of temperature and strain amplitude was the main reason for the decrease of uniaxial fatigue life. The specimens before and after fatigue test at two temperatures were observed and analyzed by transmission electron microscope (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS) and selected area electron diffraction (SAED). Microstructure observations revealed that the cyclic softening was caused by the annihilation of dislocations, as well as the fragmentation and polygonization of lath structure. High temperature promoted the formation of subgrains by accelerating the motion of dislocations and migration of low-angle grain boundaries (LABs). With the continuously decreasing of dislocation density, the growth of equiaxed subgrains and the weakening of the precipitation strengthening, the softening rate of the material was further increased until the final fracture occurs. Therefore, the evolution of microstructure of 9Cr martensitic steel during the low cycle fatigue process was deduced and described. • The initial lath structure is changed into equiaxed subgrains with reduced dislocation density. • High temperature promotes the formation and growth of subgrains by accelerating dislocation movement and boundary migration. • The cyclic softening is suppressed by the interactions between dislocations and the precipitates. • At high temperature, this interactions effect is weakened. [ABSTRACT FROM AUTHOR]

Binary complexes that can be found in copper alloys are investigated in this work through a combination of computer simulations and machine learning. Copper alloys are made of a copper matrix and a combination of single alloying elements in n -ary forms. Due to the coexistence of different types of phases in this matrix, complex regions exist for which information on their precise atomistic structure is missing. In order to uncover such information, we apply active learning and generate moment tensor potentials. This development is based on quantum-mechanical calculations. This approach allows the on-the-fly relaxation of many thousands of potentially novel candidates and check their stability. The ground-state energy of these structures is used to build active learning-generated convex hulls, which are in turn being compared to those from the simulations and the AFLOW database. This procedure provides an insight to additional new stable copper alloy relevant binary complexes. Here, in view of Cu–Ni–Si–Cr alloys, the binary complexes Cu–Si, Ni–Si, Cr–Si, Cr–Ni, Cu–Ni, and Cu–Cr have been investigated. Their stability and the identification of novel stable candidates are discussed based on energetic arguments and the analysis of the respective phonon dispersion. The pipeline followed in this work is able to successfully predict binary phases in Cu–Ni–Si–Cr alloys, specifically for the Cu-Si, Ni–Si, Cr–Ni and Cu–Ni complexes, and to extend the already reported structures in the AFLOW library. In the end, we show the applicability of a predicted Cu–Si stable phase and the developed machine learned potentials at the larger scale of atomistic simulations for the calculation of their mechanical properties and melting behavior. This work provides a computationally efficient framework for material structure prediction and calculation of their properties at a quantum-mechanical accuracy. • Efficient discovery of new binary phases of Cu-Ni-Si-Cr alloys. • Active learning training of moment tensor potentials. • Generation of machine-learned potentials with quantum-mechanical accuracy. [ABSTRACT FROM AUTHOR]

Antiphase boundaries (APBs) are crucial to understand the anomalous temperature dependence of the yield stress of Ni 3 Al. However, the required, accurate prediction of temperature-dependent APB energies has been missing. In particular, the impact of magnetism at elevated temperatures has been mostly neglected, based on the argument that Ni 3 Al is a weak ferromagnet. Here, we show that this is an inappropriate assumption and that – in addition to anharmonic and electronic excitations – thermally-induced magnetic spin fluctuations strongly affect the APB energies, especially for the (100)APB with an increase of nearly up to 40% over the nonmagnetic data. We utilize an ab initio framework that incorporates explicit lattice vibrations, electronic excitations, and the impact of magnetic excitations up to the melting temperature. Our results prompt to take full account of thermally-induced spin fluctuations even for weak itinerant ferromagnetic materials. Consequences for large-scale modeling in Ni-based superalloys, e.g., of dislocations or the elastic–plastic behavior, can be expected. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract A Mo alloyed Oxide Dispersion Strengthened (ODS) austenitic alloy with a design composition of Fe-25Cr-20Ni-2Mo-0.35Y 2 O 3 -0.5Ti was fabricated by the process of mechanical alloying and the hot isostatic press. The ODS alloy shows very fine grains with an average size of 300 nm and homogeneously dispersed ultrafine Y 2 Ti 2 O 7 particles with sizes between several nm to tens nm. The effects of plastic deformation combined with annealing on the tensile property were investigated. The treatments of forging, rolling and annealing can balance the strength and plasticity of the alloy effectively. The microstructure and the mechanical property of the Mo alloyed ODS austenitic alloy were compared with a similar ODS austenitic steel without Mo. The addition of Mo shows almost no influence on the microstructure, while can improve the tensile strength obviously, especially at the high temperature of 700 °C. [ABSTRACT FROM AUTHOR]

In order to contribute to the understanding of advanced materials with improved mechanical properties we investigate strengthening and failure processes in iron-graphene composites using molecular dynamics simulations. Graphene sheets are embedded in {110} planes of bulk iron. Tensile tests and shear tests are conducted and evaluated with regard to the orientation of the graphene sheet. It is found that two different failure mechanisms involving interfacial fracture and dislocation nucleation can occur due to tensile load. The shear tests revealed three mechanisms of dislocation-obstacle interaction. The highest strengthening was found for graphene sheet orientations which normal vectors are not orthogonal to the Burgers vector of the interacting dislocation. [Display omitted] • Graphene sheet orientation significantly affects failure and strengthening • High CRSS and low UTS with non zero components in tensile and shear direction • Dislocation interaction with graphene is mostly cutting of the matrix • Cutting results in folding, straining and rotation of the sheet. [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]

[Display omitted] • Strategy for bridging microscopic and macroscopic crack-growth simulation proposed. • The multiscale model and the concept of the bridging method are integrated. • Reduction of more than 90% in the numerical costs compared to multiscale model. • Accurate and efficient prediction of fatigue life/limit and crack-growth processes. • Can evaluate fatigue failure behaviour of thick components/structures. A strategy for bridging microscopic and macroscopic crack-growth simulations is proposed for efficiently and accurately predicting the fatigue strength of steels by integrating the multiscale model and the concept of the bridging method. Validation by comparing the experimental results of macro-crack specimens and the numerical results of the multiscale model shows a reduction of more than 90% in the numerical costs with the proposed strategy compared to the multiscale model. Only 4.2% and 2.7% errors in fatigue life for the two macro-crack specimens under the maximum loading cases are achieved, whereas no errors in fatigue limits are observed using the proposed strategy, compared to the multiscale model. The accuracy and efficiency of predicted results indicate that the proposed strategy can serve as a robust foundation for evaluating the fatigue failure behaviour of thick components/structures in engineering applications. [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 creep behavior of HR3C austenitic steels was investigated at 650 °C and over the stress range from 150 to 250 MPa for up to 13,730 h. The corresponding microstructure evolution was characterized by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In the initial stage of the creep process, the creep-resistance of HR3C steel is enhanced by the precipitation of second-phases particles in the grain and at the grain boundary. Compared with the precipitates inside the grain, the higher nucleation and growth rate of precipitates at the grain boundary is related to the higher interfacial energy and diffusion rate of atoms. The high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) results show that the precipitates inside the grain may initially nucleate at dislocation pile-up sites, and the interface coherency between the precipitate and the matrix can be destroyed after a long-term creep process. The TEM morphology indicates that the agglomerated tiny particles interact with the dislocations, contributing mostly to the precipitation strengthening inside the grain during the long-term creep process at 650 °C, while the growth of chain-like M 23 C 6 precipitates at the grain boundary increases the tendency of intergranular cracking as the creep time increased. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations are used to investigate tensile strengths and failure mechanisms of aluminium nanopolycrystals with an average grain diameter of 8 nm containing dissolved Ni, Cu, Mg or Ti atoms. It is shown that tensile strengths are influenced by several factors such as stacking fault energies as well as types, concentrations and positions of the dissolved atoms. A strong strengthening was found in case of Cu whereas Ni or Ti lead to a moderate increase of strength, while Mg even lowers the tensile strength. It was found that both dislocation processes as well as grain boundary dominated effects contribute to plastic failure mechanisms. Type and concentration of dissolved atoms possess a significant influence on these failure mechanisms. Whereas alloying with Ni, Cu or Mg supports grain boundary dominated failure processes, dissolved Ti atoms lead to a significant increase of stacking faults and dislocations. [ABSTRACT FROM AUTHOR]

Highlights: [•] We present results from virtual nano-mechanical testing on Cu alloyed α-Fe using Molecular Dynamics (MD) simulations. [•] We investigate the coarsening behaviour of Cu-rich precipitates during thermal ageing and its effect on the material strength. [•] Samples are obtained from a multiscale approach coupling kinetic Monte-Carlo (KMC) and Phase-field Method (PFM) simulations. [•] MD results show the correctness of the multiscale approach, predicting a continuous trend in structure–property correlation. [Copyright &y& Elsevier]

Abstract: The coarsening kinetics of Cu-rich precipitates in an α-Fe matrix for thermally aged Fe–Cu alloys at temperatures above 700°C is studied using a kinetic Monte Carlo (KMC) simulation and a phase-field method (PFM). In this work, the KMC approach adequately captures the early stage of the system evolution which involves nucleation, growth and coarsening, while the PFM provides a suitable framework for studying late-stage coarsening at large precipitate volume fraction regimes. Hence, both models complement each other by transferring the results of KMC along with precipitate–matrix interface energies from a broken-bond model to a quantitative PFM based on a grand chemical potential formulation and the CALPHAD database. Furthermore, molecular dynamics simulations provide information on the structural coherency of the precipitates and hence justify the sequential parameter transfer. We show that our PFM can be validated quantitatively for the Gibbs–Thomson effect and that it also predicts the coarsening kinetics correctly. It is found that the kinetics closely follow the LSW (Lifshitz–Slyozov–Wagner) law, whereas the coarsening rate constant increases with an increase in volume fraction of precipitates. [Copyright &y& Elsevier]

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]

• Damage mechanism is investigated using in-situ tensile testing. • 3D Micromechanical FEM is used for modeling DP steels under different stress states. • The MMC damage model was calibrated for the ferrite phase in DP steels using RSM. • The FE model predicted stress–strain curve and fracture strain for different BCs. • The proposed FE model predicted damage mechanisms in the in-situ tensile test. In this paper, the fracture behavior and micro-damage evolution in DP600 and DP980 steels were studied using experimental and numerical methods. First, four specimens with different loading conditions were tested to investigate the influence of the stress state on the fracture behavior and in-situ tensile tests were carried out in order to evaluate damage evolution in the two steels. Afterwards, 3D RVEs based on random martensite phase distribution were generated for both materials and a VUMAT subroutine was utilized to include the Modified Mohr-Coulomb (MMC) damage model in the ferrite phase and predict the macroscopic fracture strain under complex loading conditions. Finally, damage mechanism in the RVE was compared to the in-situ test. It was observed that damage initiation mechanism in DP steels is dependent on the size of ferrite phases. In DP steels with large ferrite phases, strain localization in the middle of the phase caused damage initiation, whereas for steels with smaller ferrite grains, such as DP980, strain localization in the boundary of two phases is the dominant damage initiation mechanism. Furthermore, damage occurred by formation of voids, initiation of micro-cracks near the voids, and propagation and coalescence of these micro-cracks. Also, the response surface methodology can be used to calibrate parameters of the MMC damage model and the resulting FE model can accurately predict the stress–strain curve and fracture strain for all considered loading conditions, except for the shear loading condition. Finally, the proposed micromechanical FE model can be used to predict the same damage mechanisms as the in-situ tensile test. [ABSTRACT FROM AUTHOR]