含裂隙软煤试样破坏过程中的变形局部化特征

Localized deformation characteristics of soft coal with fractures at different dip angles

为探究含裂隙软煤的局部化演化特征,将石膏与水以质量比7:3混合制成类软煤含裂隙试样,进行单轴压缩试验并采用数字散斑相关测量方法采集加载全程试样表面应变、位移信息,分析其变形位移和变形能密度演化特征。结果表明:不同倾角试样局部化带开始出现位置和扩展方向不同,倾角为0°时局部化带沿预制裂隙中央向试样上端和下端部扩展,60°时局部化带沿预制裂隙端部向试样对角方向扩展,随倾角增大,局部化带稳定时所对应的应力水平接近1。试样破坏由局部化带的张开和错动共同作用导致,局部化带张开与错动速率存在缓慢演化和加速演化阶段,应力峰值前后,局部化带之间扩展交汇引起速率加速演化。局部化带的能量演化经历累积(A)、累积与释放交替(A-R)、释放(R)3个阶段。在加载初始阶段,总体表现出A过程,加载至应力峰值前后,能量发生A-R波动式演化过程,加载至应力峰值后期,表现为R过程,A-R阶段随裂隙倾角增大发生相对后移现象。

In order to explore the localized evolution characteristics of soft coal with fissures,uniaxial compression tests on soft coal samples with single fissures at different inclination angles were carried out.The digital speckle correlation measurement method was used to collect the surface strain and displacement information of the sample during the entire loading process,with its localized displacement and evolution characteristics of deformation energy density analyzed.The results show that:The localization zone of the sample with different dip angles began to appear different positions and expansion directions.When the dip Angle was 0,the localization zone expanded step by step along the center of the prefabricated crack to the upper and lower ends of the sample.When the dip Angle was 60,the localization zone expanded along the end of the prefabricated crack to the diagonal direction of the sample.The failure of the specimen is caused by the joint action of the opening and dislocation of the localized zone,and there is a slow evolution of the localized zone opening and dislocation rate.And the accelerated evolution stage,before and after the stress peak,the expansion and intersection between the localized zones cause the rate to accelerate.The energy evolution of the localized zone of the soft coal samples with different fracture angles undergoes accumulation(A),alternating accumulation and release(A-R),release(R)Three stages.In the initial stage of loading,the overall A process is shown.Before and after loading to the peak stress,the energy undergoes an A-R fluctuating evolution process.When the load reaches the late stress peak,it appears as an R process.The A-R phase occurs relative to the increase of the crack inclination angle showing backward movement phenomenon.