基于亚临界裂纹扩展的岩石蠕变−冲击变形破裂特征研究

Deformation and fracture characteristics of rock under creep-impact loading based on subcritical crack growth

  • 摘要: 在深部资源开采过程中,深部岩石长期承受高应力及动载扰动,冲击地压、岩爆等动力灾害频发,严重制约了深部资源的安全高效生产。为研究深部岩石在蠕变和冲击载荷共同作用下的变形破坏机制,基于亚临界裂纹扩展理论及断裂力学理论建立了岩石蠕变模型,通过统一时间尺度的方式实现了蠕变和冲击2个不同应变率范围载荷的统一求解,并基于二维块体离散元软件UDEC开发了岩石在蠕变和冲击共同作用下的数值模型,在验证该模型的基础上,研究了不同蠕变应力水平和不同冲击载荷对岩石变形破裂特征的影响。研究表明:基于亚临界裂纹扩展理论的岩石蠕变−冲击模型能较好地描述岩石初始蠕变、稳态蠕变和加速蠕变3个阶段,且该数值模型可以准确地模拟冲击载荷后蠕变应变增加及蠕变破坏时间缩短的效应;随着亚临界裂纹常量B增大或应力腐蚀指数n减小,岩石稳态蠕变阶段应变率增大,岩石稳态蠕变阶段及蠕变破坏寿命缩短;随着蠕变应力水平的增加,岩石瞬时弹性应变及稳态蠕变阶段相同冲击载荷引起的瞬时应变随蠕变应力水平的增加而增加,且岩石在蠕变和冲击的作用下的破坏时间具有明显的非线性特征;随着冲击载荷增加,岩石的瞬时应变明显增大,在高冲击载荷下具有更快的增长率,且岩石失稳破坏时间随冲击载荷的变化差异明显,在高冲击载荷下,岩石试样失稳破坏时间明显缩短。

     

    Abstract: During deep resources extraction, deep rock is subjected to high stress and dynamic disturbances, leading to frequent dynamic disasters such as coal rock bursts that severely restrict the safe and efficient production of deep resources. To investigate the deformation and failure mechanisms of deep rock under the combined effects of creep and impact loadings, a rock creep model was established based on subcritical crack growth theory and fracture mechanics. The model provides unified solutions for creep and impact loadings across different strain rate ranges using a unified time scale approach. Additionally, the numerical model for rock under the combined effects of creep and impact was developed using the two-dimensional discrete element software UDEC. Based on the validation of this model, the influence of different creep stress levels and impact loadings on the deformation and fracture characteristics of rock was simulated and studied. The study reveals the following key findings: The rock creep-impact model based on subcritical crack growth theory can effectively describe the three stages of primary creep, steady creep and accelerated creep. The numerical model can accurately simulate the effects of increased creep strain and the shortened time-to-failure in creep after impact loading. As the subcritical crack constant B increases or the stress corrosion index n decreases, the strain rate during the steady creep stage increases, resulting in a shortening of the steady creep stage and the creep failure lifespan. Increasing creep stress levels leads to higher instantaneous elastic strain and the instantaneous strain caused by the same impact loading in the steady creep stage. And the failure time of rock under the action of creep and impact has obvious nonlinear characteristics. With an increase in impact loadings, the instantaneous strain of the rock increases significantly, showing a faster growth rate under high impact loadings. The time-to-failure of the rock varies significantly with changes in impact loading, with a notably shorter time-to-failure under high impact loadings.

     

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