不同应变率单轴加载条件下页岩的各向异性力学行为

摘要

基于静载条件下的常规力学试验可以证明,页岩层理面的存在是导致其力学行为各向异性的主要原因,而应变率的变化势必也影响着页岩各向异性特征的变化.为探究应变率对页岩各向异性力学行为的影响,分别在10-4s-1、5×10-4 s-1、10-3 s-1和10-2 s-14种应变率条件下对不同层理角度的页岩进行单轴压缩力学试验.研究表明:(1)页岩弹性模量的各向异性程度随应变率升高而减弱,泊松比的各向异性程度受应变率的影响不明显;(2)页岩峰值强度随应变率升高而增加,其中45°～ 60°试样应变率敏感性最强,页岩的强度各向异性度随应变率升高而降低;(3)随着应变率升高,层理面对页岩破坏模式的控制作用得到削弱,破坏模式的各向异性程度减弱.总体而言,页岩的各向异性力学特征随应变率升高而减弱,研究结论有助于页岩力学行为的深入理解.%Shale is a kind of sedimentary rock with well-developed bedding planes.It is proved by conventional mechanical tests under static loading that bedding planes is the main influence factor on the anisotropic behavior of shale.However,as an experimental factor,strain rate is supposed to have a nonnegligible influence on the anisotropic behavior of shale as well.To investigate the effects of strain rates on the anisotropic mechanical properties of shale and the corresponding failure modes,the experiment on the shale samples with varied bedding plane angleβ from 0°to 90°at the interval of 15°is conducted under strain rates of 10-4 s-1,5×10-4 s-1,10-3 s-1 and 10-2 s-1,respectively.The tests give the following results.(1) The anisotropic behavior of elastic modulus of shale samples becomes less obvious under high strain rates,while the Poisson's ratio of shale samples is rarely affected by strain rate.(2)The increase of compressive strength of shale samples forβ=45° ～60°is the most obvious one if compared with the rest shale samples.The anisotropic behavior of peak strength of shale samples is weakened by high strain rate.(3) The failure modes of shale samples are relatively less affected by bedding planes under high strain rates and the anisotropic behavior of shale samples becomes less obvious under high strain rates.In conclusion,the anisotropic behavior of shale is weakened by high strain rate.The results can provide references for a deeper understanding of the mechanical properties of shale.