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This work deals with fracture mechanisms in quasi-brittle materials, focusing on the characterization of the Fracture Process Zone (FPZ) of specimens under tensile load. Particularly, paper was used as model material. Experiments were conducted on notched and unnotched specimens. Based on an image analysis of these observations, a stochastic finite element model was developed, using both a nonlocal stress-based approach and a discretized random field modeling of the Young's modulus. The proposed methodology allowed characterizing the damage zone and the size of the FPZ, analyzing the influence of the mesostructure, composed of flocs (fiber aggregates where the basis weight is larger than the average one) and antiflocs (complement of flocs). The area of the active FPZ and the normalized stress drop were linked using a surface energy dissipated in the active FPZ. The stress drop, until limiting value, increased with the width of the active FPZ. Finally, a relationship between the surface energy and the nonlocal internal length was established. [ABSTRACT FROM AUTHOR]

In this paper, the absolute nodal coordinate formulation (ANCF) is applied to simulate the magnetic shape memory effect. Using the absolute nodal coordinate formulation makes it possible to describe complicated or large deformation cases. The nonlinear bidirectional coupling terms between the mechanical and magnetic field are taken into account in the analysis of the single-crystalline Ni-Mn-Ga sample. A two-loop iteration procedure with variable steps is implemented to predict the magnetic-field-induced strain (MFIS) in the specimen under a changing external magnetic field and a constant auxiliary compression. In addition, the proposed approach is used to track the superelastic behavior of the magnetic shape memory alloy when subjected to a constant magnetic field. The approach effectively describes the hysteresis and superelastic phenomenon of the shape memory effect. The solution is compared here with solutions obtained using classical linear and quadratic quadrilateral elements. The deviation observed in the solution is discussed, and its cause is further clarified from a two-domain pure magnetostatic analysis of a permanent magnet. It is found that the accurate solution of such problems is associated with discontinuity of the normal component of the magnetic potential gradient across the domain interface. Special measures must be taken to make the absolute nodal coordinate formulation element compatible with the discontinuity. A mixed FEs strategy, which adopts ANCF FE in the displacement field solver and classical FE in the magnetic field solver, is proposed as an alternative option to rectify the problem, which is verified by predicting the MFIS and the dynamic mechanical response of a sample under cyclic compression. [ABSTRACT FROM AUTHOR]

In this paper, a theoretical model is established to describe the effect of nanoscale amorphization in nanocrystalline bimaterials on the dislocation emission from the tip of a collinear crack at the interface. In the description, nanoscale amorphization is formed by the splitting transition of the Grain Boundary (GB, the disclination of GBs caused by the movement of GBs). The analytical solution of the model is obtained by the elasticity complex potential solution method. In addition, the effects of nanoscale amorphization, dislocation emission angle, interfacial crack length and material constants of nanocrystalline bimaterials on the critical stress intensity factor of interfacial crack tip corresponding to dislocation emission are discussed through numerical analysis. The analysis shows that the influence of nanoscale amorphization in nanocrystalline bimaterials on the critical stress intensity factor (SIF) corresponding to dislocation emission depends on the dislocation emission angle, the position and size of the nanoscale amorphization, interface crack length and relative shear modulus. With the increase in relative shear modulus and dislocation emission angle, the normalized critical SIF decreases at first and increases afterwards. When the nanoscale amorphization size is small, the critical SIF of the dislocation is less affected, but when the size is larger, the impact becomes great. The influence of nanoscale amorphization on the dislocation emission from collinear interface crack tip is related to nanoscale amorphization and relative shear modulus. There is a critical relative shear modulus that the increase in dislocation intensity has little effect on dislocation emission. Appropriate selection of materials for the upper and lower planes can reduce the critical stress intensity factor corresponding to dislocation emission, thereby promoting the dislocation emission from interface cracks and improving the toughness of the nanocrystalline bimaterials. [ABSTRACT FROM AUTHOR]

This paper is concerned with free vibration analyses of a circular transversely isotropic elastic plate based on Reddy plate theory and modified higher-order shear deformation plate theory (MHSDT). Hamilton's principle is used to derive the equations of motion and boundary conditions of the circular plate. Natural frequencies are determined from the solution of the governing equations and boundary conditions along the circular edge. Comparisons of natural frequencies and mode shapes arising from the Mindlin plate theory, the Reddy plate theory, MHSDT, and finite element method are made for fully free and clamped circular plates. The comparison results show that MHSDT has better accuracy than the other analytical plate theories in terms of the natural frequencies and corresponding mode shapes. [ABSTRACT FROM AUTHOR]