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干湿循环石灰岩动态压缩能量演化及变形破坏特征

Dynamic compression energy evolution and deformation and failure characteristics of limestone under dry-wet cycles

  • 摘要: 为研究干湿循环石灰岩在动态压缩破坏过程中的能量耗散规律,采用直径50 mm分离式霍普金森压杆试验系统,对不同干湿循环等级的石灰岩试样进行动态压缩试验,结合超高速摄像机探究干湿循环作用及应变率对石灰岩样动力学参数、应变场演化规律、能量耗散特征以及破碎分形维数的影响,并借助扫描电子显微镜观测干湿循环过程中石灰岩微观结构的演变过程,揭示其宏观物理力学劣化行为的微观机制。结果表明:随着干湿循环次数的增加,石灰岩试样内部胶体溶解、颗粒受损,导致其结构骨架承载能力下降,进而表现为试样纵波波速、抗压强度和弹性模量的逐渐降低及孔隙率的增加;在冲击荷载的持续作用下,试样经历动态平衡后,其薄弱环节率先形成最大主应变集中域,应变集中域随加载时间延伸、聚集并伴随微裂纹产生、扩展、交错,最终形成破裂面,直至试件破坏;随着应力率的提升,试样内部微裂纹生成与活化显著增强,进而促进了抗压强度的提高,同时动态压缩破坏过程中试样最大主应变增大,耗散能增加,分形维数也相应提高;随着干湿循环次数的增加,试样内部孔隙和微裂隙等结构缺陷逐渐显著,进而在动载压缩破坏过程中引起试样最大主应变的上升,耗散能的减少,并伴随分形维数的增大。研究结果可为干湿循环岩体动力灾害控制提供重要的理论支撑和参考依据。

     

    Abstract: To investigate the energy dissipation pattern of limestone during dynamic compression deformation and failure under wet-dry cycles, a 50 mm diameter Split Hopkinson Pressure Bar testing system was employed to conduct dynamic compression tests on limestone samples under various wet-dry cycles conditions. Utilizing an ultra-high-speed camera, the influence of wet-dry cycling and strain rate on limestone's dynamic parameters, strain field evolution, energy dissipation characteristics, and fractal dimension of fragmentation was examined. Furthermore, the evolution of limestone's microstructure during wet-dry cycles was observed using a scanning electron microscope to reveal the microscopic mechanisms underlying its macroscopic physical and mechanical degradation. The results indicate that as the number of wet-dry cycles increases, the internal colloid dissolution and particle damage of limestone samples deteriorate their structural framework's load-bearing capacity, leading to a gradual decrease in longitudinal wave velocity, compressive strength, and elastic modulus, along with an increase in porosity. Under continuous impact loading, limestone samples reach a dynamic equilibrium state, with the weakest sections first forming concentrated regions of maximum principal strain. These strain concentration zones expand and coalesce with the progression of loading time, accompanied by the generation, propagation, and intersection of microcracks, ultimately culminating in fracture surfaces and specimen failure. As the stress rate increases, the generation and activation of microcracks within the samples become significantly enhanced, contributing to an increase in compressive strength. Concurrently, the maximum principal strain and dissipated energy increase during dynamic compression failure, leading to a corresponding rise in the fractal dimension. As the number of wet-dry cycles increases, structural defects such as pores and microcracks within the samples become more prominent, causing an increase in the maximum principal strain, a decrease in dissipated energy, and an augmentation of the fractal dimension during dynamic compression failure. The research results can provide important theoretical support and reference for the dynamic disaster control of dry-wet cycle rock mass.

     

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