不同孔隙率规则多孔钛的变形失效特征

Deformation Failure of Regular Porous Titanium with Diffe-rent Porosities

摘要:

设计和制备了孔隙率不同的3组规则多孔钛试样，采用分离式霍普金森压杆实验装置，开展了应变率范围在600~2100 s^-1的单轴压缩实验，研究了加载过程中整个试样和局部孔洞的变形失效特征。结果表明，试样展示出2种典型的变形模式：压缩变形模式和连通断裂模式。压缩变形模式主要发生在低孔隙率的试样，试样的外表面胞壁出现局部塌陷，而连通断裂模式易发生在高孔隙率的试样中，常在试样的一个或多个孔层出现连通的断裂。另外，2种变形模式下的局部孔洞也呈现出不同的形状变化特征，且在孔洞最小曲率的位置都形成明显的应力集中，相应的应力集中因子随试样孔隙率的增大而增大。微结构分析显示：剪切带是试样失效的主要机制，试样的断口容易产生韧窝和韧性条纹。

Abstract:

Regular porous titanium specimens with different porosities was fabricated to investigate the overall and local failure characteristics of porous metals. Dynamic compression tests were implemented using the split Hopkinson pressure bar system at the strain rates from 600 s^-1 to 2100 s^-1. Results show that the specimens with different porosities exhibit two typical deformation modes: compression deformation mode and connected fracture mode. The compression deformation mode mainly occurs in the specimens with low porosity, and the characteristic is that the cell walls of outer surface of the specimen exhibit local collapse. However, the connected fracture mode mostly occurs in the specimens with high porosity, and usually shows connected fracture in one or more pore layers. Moreover, the local pores of two deformation modes present different characteristics during compression, and the stress concentration occurs at the position with the minimum curvature of the pores. Microstructural analysis indicates that shear band appearing in the intercellular walls is the main failure mechanism of the specimens. Dimples and ductile stripes of fracture surface reveal that the collapse of the intercellular wall is a process of ductile fracture. Meanwhile, the softening failure of the cell walls and the strain hardening of the matrix material can affect the mechanical response of porous titanium. Additionally, with the increase of porosity, the greater the stress concentration factor, the easier the failure of porous metals.