Microvoid multistage nucleation model and its application in analysis of micro damage and fracture

In this paper, the microvoid multistage nucleation model [14,15] suggested by the authors of this paper has been studied on the micro ductile damage and fracture of metallic material under large elastic-plastic deformation.Using this model, the analyses of micro damage and fracture for various axisymmetric tensile specimens and for TPB and CCP cracked specimens have been carried out. And the results from these analyses on damage development and fracture are in good agreement with the experimental ones for axisymmetric specimens and reasonable for cracked specimens from the microscopic point of view.The project surported by National Science Foundations of China.     

Modelling of dynamic ductile fracture and application to the simulation of plate impact tests on tantalum

A model of dynamic damage by void nucleation and growth is proposed for elastic-viscoplastic materials sustaining intense loading. The model is dedicated to ductile materials for which fracture is caused by microvoiding. The material contains potential nucleation sites where microvoids are generated when the local pressure overcomes the nucleation pressure. A probability density function is adopted to describe the fluctuation of the nucleation pressure within the material. The void growth is described by using a hollow sphere model where micro-inertia effects are accounted for. The matrix weakening due to void growth is also included.The model has been first tested under uniaxial deformation. When the strain rate is assumed constant, the pressure inside the material has nearly a linear response up to a maximum. An analytical expression for the maximum pressure is proposed.Finite element simulations of plate impact tests have been carried out and compared to experiments on tantalum. From simulations based on the proposed model, an increase of the spall strength is observed with higher shock intensities. Therefore, the relationship between the velocity pullback and spall strength usually assumed in the literature (based on the acoustic approach) seems to be inadequate. Velocity profiles are simulated for different flyer thicknesses and different impact velocities with close agreement with experiments.