PSI - Issue 13

Zheng Miao et al. / Procedia Structural Integrity 13 (2018) 1043–1046 M. Zheng, X. Yu and J. Yin/ StructuralIntegrity Procedia 00 (2018) 000–000

1044

2

1. Introduction Material damage research is a classic topic. It has a long history for its complicated, but its application demand is strong. With the development of science and technology, the demand for material with better performance is more intense. More stringent and strict requirements for materials have promoted systematic and meticulous research on the damage evolution behavior of material, with a view to revealing the mechanism of damage. The spallation under plane impact is the interaction of two rarefaction waves in the experimental sample. When the tensile stress pulse exceeds the material limit, the heterogeneous microstructure inside the material is activated. The multi-scale and strongly coupled physical and mechanical processed of damage, growth and aggregation occur. Under the condition of strong loading, the metal will undergo a complex physical process such as loading, unloading reverse stretching and reloading, in which the material damage and spallation are easily induced in the reverse stretching stage. In order to study the fracture phenomenon in depth, a VG-Spall model is developed, which is based on cavity growth, polymerization and collapse. The VG-Spall model take into account the process of growing a large number of ting cavities in the material under tensile stress during the tensile stage, and determines whether the continuously expanding cavities reach continuous through state by the presupposition of the limit porosity. For the damaged or cracked materials being loaded and compressed again, the VG-Spall model is used to establish the corresponding collapse model. 2. Theoretical scheme and verification of spallation model 2.1. Basic idea of physical of spallation Considering the fracture behavior of the material under complex loading conditions, combined with the relevant theoretical and experimental research, the physical modeling of spallation is mainly based on the following considerations. a) In the physical modeling of the spallation, porosity is used as the damage variable. Porosity refers to the volume fraction of cavities in the material unit. The initial porosity distribution parameter is initial porosity and the influence of nucleation process on porosity evolution is not considered. b) After the material enters the tensile stage, it becomes porous material containing cavities. The equation of stage is to calculate the pressure and specific internal energy of the solid component first. The pressure and internal energy of the solid component are averaged, then the pressure and internal energy of the whole porous material unit are obtained. c) If the porosity of the unit reaches the limited porosity, it is considered that the cavity in the material has grows up to each other to form a macro crack, and the unit is invalid as a whole and can not continue to bear the shear deformation, but the unit will continue to expand to simulate the expansion effect of crack, at this time the average press and stress of unit are zero, and internal energy and temperature remains uncharged. d) If the material is fractured and compressed again, it is considered that the material is again compressed into a porous material with cavities or dense material. 2.2. Hole growth and collapse model The cavity growth is described by VG-Spall model. The model is based on the elastoplastic stress field around cavity. The stress field in the representative cell containing spherical cavity is in equilibrium state, and its expansion degree is:

P  

0,

0

    

(1)

1    

2

1



  3

 1 ,    3 P





1

0



0



where α is the expansion degree of material unit, α 0 the initial expansion degree of material unit; η material stickiness, 100GPaꞏμs, P  driving force of hole growth: