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[Display omitted] • Atomistic simulation and modeling of free surface effect on nanocrack initiation. • Nanocrack initiation and intergranular fracture due to nanocrack growth are captured. • Theoretical description of nanocrack initiation induced by GB dislocation pileup. Free surfaces have significant effects on plastic deformation and fracture of nanocrystalline materials (NMs), especially for nano- or micro- scale specimens. To reveal the influence mechanism of free surfaces on crack initiation and growth, molecular dynamics (MD) simulations are carried out. The results show nanocrack initiation at triple junctions near free surfaces and the intergranular fracture due to nanocrack growth and coalescence. Based on the mechanism captured by MD, a theoretical model is established to describe the process of grain boundary (GB) dislocation evolution and nanocrack initiation. The critical stress for nanocrack initiation and the critical magnitude of GB sliding step are obtained for nanocrystalline nickel, aluminum and copper. Based on the proposed theoretical model, the fracture behaviors are discussed for the three nanomaterials. [ABSTRACT FROM AUTHOR]

In this work, an efficient and accurate meshfree method, named the two-level nesting smoothed extended meshless method (S-XMM-N), is developed for simulating the static and dynamic fracture behaviors of two-dimensional (2D) functionally graded materials (FGMs). To accurately capture the displacement discontinuity along the crack face and the stress singularities at the crack tips in FGMs, we improve the extended meshless approximation by adding the Heaviside function and four crack tip enrichment functions to the approximation of RPIM. This approximation not only inherits all the advantages of traditional extended meshless approximation but also has interpolation properties. Furthermore, to avoid the complex and expensive integration calculation when constructing the global stiffness matrix, we use the recently developed two-level nesting smoothing integration algorithm, which is based on the first and second level smoothed strains and Richardson extrapolation theory. The static and dynamic stress intensity factors (SIFs) are calculated by the interaction integral. Several static and dynamic problems of FGM thin plates with the elastic modulus varying with respect to the exponential or hyperbolic tangent functions are solved by S-XMM-N. By investigating the SIFs given by various methods, the feasibility and effectiveness of the proposed methods are validated. [ABSTRACT FROM AUTHOR]

• Theoretical solution of an elastic-plastic crack in a half plane is presented. • Theoretical modeling of crack-tip plasticity in a strain-hardening material. • Theoretical modeling of plasticity at the mixed-mode crack tip. • Crack plane displacement is predicted accurately by the theoretical modeling. The crack growth behavior is influenced greatly by the crack-tip plasticity. Most of the existing two-dimensional (2D) theoretical models of crack-tip plasticity are appropriate only for elastic perfectly-plastic materials under simple mode load, which limits the application range. This paper presents a theoretical model based on the distributed dislocation technique (DDT) that can be used at mixed loads with bilinear strain-hardening and perfectly-plastic materials. The problem of a half plane containing an edge crack under uniaxial tensile load or mixed loads is considered in both 2D limit cases: plane stress and plane strain. The theoretical modeling results are compared with finite element simulations. The results show the developed models are suitable for strain-hardening materials under mixed loads, which is a new progress in the theoretical modeling of crack-tip plasticity. [ABSTRACT FROM AUTHOR]

• A crack tip in the SEZ of another crack deflects the maximum von Mises stress gradient towards the latter tip. • The inclined angle of a smaller crack has a greater influence on the ESIF and plastic zone of other crack tips. • The influence of micro-cracks is concentrated around the tips of macro-cracks, whereas the influence of macro-cracks is dispersed around micro-cracks. • In the SEZ, a smaller crack inclined angle has a greater effect on promoting the mutual fusion between the plastic zones of other cracks. • The interaction range between kinked cracks with certain inclined angles can exceed the influence zone of a straight crack on a kinked crack. The influence range of crack interaction is studied using the distribution dislocation technique, and is defined as the influenced zone. For elastic materials with cracks, the equivalent stress intensity factor influenced zone is obtained, while for plastic materials with cracks, the plasticity influenced zone is determined. The interaction between multiple cracks can be analyzed by introducing the concept of the influenced zone, which simplifies the analysis. The results indicate that if a crack is located outside the influenced zone of another crack, the effect of the former on the latter can be ignored within an acceptable range of error. The influenced zone for elastic materials depends on the length and inclined angle of a crack, whereas for plastic materials, the plastic influenced zone is affected by the crack length, inclined angle, and material yield limit simultaneously. In the case of plastic materials with multiple cracks, fusion of plastic zones between two cracks may occur at certain positions under the influence of other cracks. These theoretical findings can simplify the analysis of the fatigue fracture behavior of materials with multiple cracks, whether they are elastic or plastic. [ABSTRACT FROM AUTHOR]

The detailed time-space distribution of acoustic emission (AE) events during the catastrophic fracture of rock samples containing a pre-existing joint or potential fracture plane is obtained under triaxial compression using a high-speed 32-channel waveform recording system, and the results are discussed with respect to the prediction and characterization of catastrophic fault failure. AE activity is modeled quantitatively in terms of the seismic b-value of the magnitude–frequency relation, the self-excitation strength of the AE time series, and the fractal dimension of AE hypocenters. Consistent with previous studies on rock samples containing a fracture plane with several asperities, the present analyses reveal three long-term phases of AE activity associated with damage creation on heterogeneous faults, each clearly identifiable based on the above parameters. A long-term decreasing trend and short-term fluctuation of the b-value in the phase immediately preceding dynamic fracture are identified as characteristic features of the failure of heterogeneous faults. Based on the experimental results it is suggested that precursory anomalies related to earthquakes and other events associated with rock failure are strongly dependent on the heterogeneity of the fault or rock mass. A homogeneous fault or rock mass appears to fracture unpredictably without a consistent trend in precursory statistics, while inhomogeneous faults fracture with clear precursors related to the nature of the heterogeneity. [Copyright &y& Elsevier]