盐岩应变硬化自弱化现象研究

STUDY ON PHENOMENON OF SELF-WEAKENING OF STRAIN HARDENING OF SALT ROCK

为探究盐岩的应变硬化自弱化现象及机制,拟通过单轴压缩卸载、静置、二次加载试验来研究盐岩自弱化后强度指标和变形指标的变化规律。并基于位错理论,对自弱化的微观机制进行阐述。研究结果表明:(1)盐岩自弱化后的强度和弹性模量随静置时间(弱化时间)的变长而呈现弱化趋势;且4 h之前弱化趋势明显,之后趋势特征不明显。(2)盐岩弱化后的泊松比和等容变形率在4 h前后有台阶特征。泊松比的前台阶值小于后台阶值,等容变形率的前台阶值大于后台阶值。(3)盐岩自弱化现象是应变硬化后位错在内部残余应力(摩擦力和位错弹性力)的作用下逐渐远离集中区,均匀化的结果。

In order to explore the mechanisms that govern the self-weakening of strain hardening of salt rock,the tests under uniaxial compression unloading,standing still and second time loading were performed with the variation of indices of strength and strain obtained in this study. The micro-mechanism of the phenomenon of self-weakening of strain hardening was explained with the dislocation theory. After self-weakening,the peak strength and elastic modulus of rock salt in the second loading period exhibited a weakening trend with the interval time between two times loading tests. When the interval time was less than 4 h,the strength indices decreased sharply. While for the case of more than 4 h,no evident decrease was observed. When the interval time was approximately 4 h,Poisson?s ratio and isometric deformation rate of salt rock jumped upward and downward. The self-weakening effect was resulted from the behavior of crystal dislocations that was removed away from original dislocation accumulation zone due to the drive of residual stress(mainly friction and unevenly elastic dislocation force).