花岗岩动态劈裂拉伸实验及动力作用机制

Experimental and Mechanism of Granite on Its Dynamic Splitting Tensile Property

岩石作为一种常见的工程材料,其动态拉伸力学性能的准确核定及其破坏机理至关重要。借助霍普金森压杆(split Hopkinson pressure bar,SHPB)实验装置,对75块花岗岩试样进行了不同冲击速度下的动态劈裂拉伸实验,分析其动态强度与变形的应变率效应,以及冲击劈裂后的破坏形态,进而得到花岗岩试样的应变率、应力峰值、弹性模量等相关力学参数之间的关系。研究表明,在动态劈裂实验中,应变率约在100 s^(-1)左右,花岗岩试样开始出现裂纹;应变率在100~150 s^(-1)内,花岗岩试样在冲击后为破碎状态;当应变率超过150 s^(-1)后花岗岩在冲击加载后试样为粉碎的状态。随着应变率的逐渐增大,动态拉伸弹性模量逐渐增加,但峰值应变却随着应变率的增大而逐渐减小,表明随着应变率的提高,花岗岩的变形能力变差,更易破坏。同时提出了动态拉伸敏感性指标,该指标物理意义明确,能够准确反映岩石类准脆性介质在动态拉伸受力情况下的率效应。进而通过数值模拟,分析验证了冲击劈裂实验的应力波传播三阶段、试样破坏特性及裂纹衍生规律。进一步地,基于Hopkinson效应和冲击劈裂现象相结合的动态拉伸强度,其本质上是受岩石的不均匀性、应力速率、相邻微裂纹处释放的应力引起的裂纹止裂以及裂纹扩展速度等众多因素的共同影响。

As a common engineering material,the accurate verification of dynamic tensile mechanical properties and failure mechanism of rock are much more important.By using the experimental device of split Hopkinson pressure bar(SHPB),the dynamic splitting tensile testing of 75 granite samples under different impact velocities were carried out.The strain rate effect of dynamic strength and deformation,as well as the failure mode after impact splitting were analyzed,and then the relationship among the relevant mechanical parameters such as strain rate,peak stress and elastic modulus of granite samples were obtained.The results show that for the dynamic splitting tensile testing,when the strain rate is about 100 s^(-1),the granite sample starts to crack.While when the strain rate is in the range of 100~150 s^(-1),the granite sample could be broken after impact.For the strain rate exceeds 150 s^(-1),the granite sample would be crushed.Furthermore,with the increase of strain rate,the dynamic tensile elastic modulus increases gradually,but the peak strain decreases,which indicates that with the increase of strain rate,the deformation ability of granite becomes worse and it is prefer to be failed.At the same time,the dynamic tensile sensitivity index is proposed,which has a clear physical meaning and can accurately reflect the rate effect of rock under dynamic tensile stress.Moreover,the three stages of stress wave propagation,the failure characteristics of the specimen and the law of crack propagation have been verified by numerical simulation.In advance,based on the combination of Hopkinson effect and impact splitting theory,the dynamic tensile strength is essentially affected by many factors,such as rock heterogeneity,stress rate,crack arrest caused by stress released from adjacent micro-cracks and crack growth rate and so on.