岩样直剪应力-应变全程曲线研究

基于直剪试验机–岩样系统加载过程中各组成部件不同受力特点,运用功能原理,建立联合作用下的一维剪切实测应力–应变曲线全过程的参数方程,推导岩样失稳破坏判据和系统回跳条件,指出试验机–岩样系统弹性区段的存在是造成实测剪应力–剪应变曲线与岩样真实直剪本构曲线不一致和产生岩样失稳破坏、系统回跳现象的主要原因。通过算例分析剪切带宽度和试件高度对实测直剪应力–应变全程曲线的影响关系。分析结果表明,加载系统弹性受力区段越长,局部化剪切带宽度越小,实测软化段曲线就越陡,加载系统就越不稳定,越容易出现系统回跳现象,且在加载过程中岩样就会越早发生脆性破坏。

STUDY ON COMPLETE STRESS-STRAIN CURVE OF ROCK SPECIMEN UNDER DIRECT SHEAR TEST

Based on mechanical behavior of the different parts of testing machine-specimen system and using the energy conservation principle,a parametric equation of the complete stress-strain curve in direct shear is deduced.A criterion of instability and a critical condition of snap-back of testing machine-specimen system are put forward.The research work shows that the elastic parts of testing machine-specimen system are the origin of the failure or the snap-back of testing machine-specimen system.It leads to the discretional results of complete stress-strain curve in direct shear,which differ from shear stress-strain constitutive relation.The analysis of the relationship between the shear stress-strain curve and the shear band thickness shows that the thicker the shear band thickness ist,he less brittle the material becomes and the earlier failure the specimen happens during loading.The analysis of the relationship between the shear stress-strain curve and the elastic parts length shows that the longer the elastic parts length is,the more brittle the material becomes and the earlier failure the specimen happens during loading.