花岗岩动态轴向拉伸力学性能试验研究

在MTS试验机上对花岗岩进行不同应变率(10-6～10-2 s-1)、不同预静载下的冲击加载以及变幅三角波荷载下的动态轴向拉伸系列试验。试验结果表明:在10-6～10-2 s-1应变率范围内,岩石抗拉强度随应变率提高近线性增长;花岗岩的弹性模量随应变率变化无明显变化;峰值应变随应变率增大有增长的趋势,极限应变没有明显的率敏感性;不同应变率的名义应力–应变全曲线的上升段在约40%强度以前呈线性,之后出现明显非线性变形,但随着应变率的增加,非线性程度降低;下降段可简化为两段折线:从峰值卸载至25%强度时,出现拐点,此时应变为300～400με,此后应变增长速度加快,降至残余应力10%强度处时,应变为600～900με;50%以下预静载不会对花岗岩的动载强度产生不利,反而有所增强;更高的预静载则会降低动载强度;在往复加载的低周疲劳引起的损伤累积下,岩石的动强度低于单调加载;随着循环次数的增加,残余应变逐渐增加,且增加的幅度亦有所加大,出现损伤软化的特征。

EXPERIMENTAL STUDY OF DYNAMIC AXIAL TENSILE MECHANICAL PROPERTIES OF GRANITE

A series of dynamic axial tensile tests of granite are carried out by using MTS testing machine，considering the impact loads with different strain rates，different initial static loads and the variable amplitude triangular loads. The results indicate that：The tensile strength of granite increases linearly with the increase in strain rate ranging from 10－6 s－1 to 10－2 s－1. The elastic modulus of granite has no obvious change with the variation in strain rate. The peak strain has a increasing tendency with the increase in strain rate；and the ultimate strain is not sensitive to the strain rate. The ascending part of the nominal complete stress-strain curve before 40% of tensile strength under different strain rates is of linear；and then it goes into remarkable nonlinear stage，which the degree of linearity decreases with the increase in strain rate. The descending part can be divided into two segments，an inflexion point which strain is 300–400 me appears when the load decreases to 25% of tensile strength，then the deformation becomes aggravate；the strain is about 600–900 me  when the residual stress is about 10% of tensile strength. The initial static load less than 50% of tensile strength does not influence the dynamic tensile strength but be beneficial to it；the larger initial static load is harmful to the dynamic strength. The fatigue damage by the cyclic variable amplitude load leads to the descending of strength because of the cumulative damage. Residual strain increases gradually and the increase rate becomes larger and larger with the increase in cycle，which means that damage softening effect appears.