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Abstract: In this paper, the ductile fracture of Al-alloy 5052 is studied by experiments and simulations using a modified Rousselier model. Although tension failure has been successfully predicted by the classical Rousselier model, its predictive capability on shear failure was seldom discussed. A modified Rousselier model was proposed by incorporating the recent extended damage evolution model by Nahshon and Hutchinson. The modified Rousselier model can capture both tension and shear failure. A stress integration algorithm based on the general backward-Euler return algorithm for this constitutive model was developed and implemented into finite element model by the user defined material subroutine VUMAT in the ABAQUS/Explicit. The tensile tests of smooth round bar and notched round bars with different sizes were carried out to investigate the mechanical behavior of Al-alloy 5052. Consequently, the material parameters of the classical Rousselier model were identified by an inverse method using these experimental data. A shear test was also performed to calibrate the new shear damage coefficient in the modified Rousselier model. For the shear test, the simulations show that although shear failure can be predicted by the Rousselier model, the ductility was over-estimated. However, the modified Rousselier model can give more accurate results. The simulations on uniaxial tension of the round bars also confirm that the modified Rousselier model can well predict the cup-cone fracture mode. The results indicate that the Lode parameter in the new damage evolution model is important to capture the cup-cone fracture mode transition. [Copyright &y& Elsevier]

Abstract: The numerical investigations were carried out to determine the ballistic resistance of the carbon nanotube (CNT) fibres reinforced composites. In this paper, the fundamental studies of the reinforcement characteristics are presented. It includes the single fibre mechanical and geometric properties as well as fibres distribution and volume (mass) concentration. The continuum matrix material includes a certain amount of fibres made of CNTs. An impact of the projectile with the sharp nose on the metal matrix composite plate was analysed. The computer simulations were performed with the finite element method implemented in LS-DYNA code. The plane formulation allows analysing extremely dense meshes. The obtained results presented the significant role of the carbon nanotube fibres. [ABSTRACT FROM AUTHOR]

Abstract: Mechanical behavior for crystals at submicron-to-nanometer scales shows many atypical plastic phenomena. In this paper, a new hybrid multiscale simulation method named DD-FEM is developed by coupling the 3D discrete dislocation dynamics (DDD) simulation with the finite element method (FEM) under elasto-viscoplasticity continuum model. In this methodology, the discrete dislocation plasticity in a finite crystal is solved under a completed continuum mechanics framework. Our approach is competent at dealing with the large and non-linear deformation by communicating deformation information between DDD and FEM. As an application, the deformation of micropillar under uniaxial compression has been predicted. Our results show that the source-truncation hardening and mobile dislocation exhaustion hardening are the main mechanisms for flow intermittency, and stress heterogeneity plays a key role in the observed strain hardening. The effects of contact boundary condition between the indenter and the upper surface of the specimen, as well as the taper of the pillar are also investigated. [Copyright &y& Elsevier]