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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]

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: 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]

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]

[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]

• 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]

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]