基于剪切修正GTN模型的金属弹性退化机理研究

许多金属材料在进行显微或宏观压入测试时,测得的弹性模量会随着压入深度的增大而不断降低.考虑到在压痕测试过程中金属材料并不产生明显的裂纹,这种性能退化应是由材料的损伤引起.然而,经典损伤理论认为以受压和受剪为主的压入变形不会引起材料软化和损伤.本文结合剪切变形下材料损伤的萌生和演化机理,对经典的GTN(Gurson-Tvergaard-Needleman)模型进行了修正,对压入测试进行了有限元模拟.模拟结果显示,材料在压入过程中的损伤是由现有空洞的扭曲变形和次级空洞的萌生共同引起,如果只考虑现有空洞变形则会低估材料在压入变形过程中的损伤演变.

THE DEGRADATION OF THE ELASTIC PROPERTIES OF METALLIC MATERIALS EVALUATED BASED ON AN EXTENDED GTN MODEL

Although an indentation does not induce apparent cracking in ductile materials, the degradation of the elastic stiffness of ductile metals does occur in micro-/macro-indentation tests. After comparing the degradation predicted based on extended damaged-plasticity models with that measured by experimental testing, it is found that the softening due to the distortion of the existing voids is not enough to cause a notable degradation of elasticity. It is suggested that an independent damage-nucleation mechanism due to the shear deformation may be in operation. Although attractive in practical applications for its nondestructive nature, the damage-based indentation technique for estimating the fracture properties of ductile materials needs further investigations.