基于畸变能的煤岩材料动态强度准则及本构关系研究

Dynamic strength criterion and constitutive relation of coal and rock materials based on distortion energy

  • 摘要: 在深部岩体工程中,经常面临在中高应变率扰动下的岩体稳定性问题,强度准则是解决工程问题的基础。从能量角度出发,以引起形状改变的畸变能作为煤岩材料破坏的判据,理论推导了材料的动态能量强度准则,揭示了岩石动力破坏机理。引入动态能量强度准则来描述材料的损伤,建立了材料的动态统计损伤本构关系,对强度准则和本构关系的适用性进行了分析和验证。研究结果表明:煤岩材料的塑性破坏由畸变能控制,加载速率一定时,单向应力状态下,材料破坏所需畸变能最小,强度最低。随着围压增大,材料破坏所需畸变能增大,强度增高。围压一定时,材料破坏所需畸变能随应变率的增高而增大;根据动态能量强度准则,静态加载时材料内部能量缓慢积聚,破坏时畸变能刚好达到所需能量阈值,材料表现为静态破坏。动态加载时材料内部能量迅速积聚,破坏时畸变能大于所需能量阈值,材料发生爆炸性动态破坏。发生卸荷扰动时,材料强度与破坏所需能量降低,原本不足以使其发生破坏的能量便有可能达到破坏能量阈值,工程岩体易发生卸荷破坏;煤样动态应力‒应变曲线的理论拟合度均值可达96%以上,表明所建立的动态本构关系适用于描述材料在动载荷下的应力‒应变关系。本构关系中各拟合参量之间具有较强的相关性关系,各拟合参数随应变率变化呈现出指数型变化,理论曲线的拟合度主要由参数mφb决定。研究结论可为煤岩材料动态力学特性的研究提供借鉴。

     

    Abstract: In deep rock mass engineering, the stability of rock mass under medium and high strain rate disturbance is often faced. The strength criterion is the basis for solving engineering problems. From the perspective of energy, the dynamic energy strength criterion of the material is derived theoretically by using the distortion energy that causes the shape change as the criterion for the failure of coal and rock materials, and the dynamic failure mechanism of rock is revealed. The dynamic energy strength criterion is introduced to describe the material damage, and the dynamic statistical damage constitutive relation of material is established. The applicability of strength criterion and constitutive relation is analyzed and verified. The results show that: The plastic failure of coal and rock materials is controlled by the distortion energy. When the loading rate is constant, the distortion energy required for material failure is the smallest and the strength is the lowest under the unidirectional stress state. With the increase of confining pressure, the distortion energy required for material failure increases and the strength increases. When the confining pressure is constant, the distortion energy required for material failure increases with the increase of strain rate. According to the dynamic energy strength criterion, the internal energy of the material is slowly accumulated during static loading, and the distortion energy just reaches the required energy threshold when the material is destroyed. During dynamic loading, the internal energy of the material accumulates rapidly, and the distortion energy is greater than the required energy threshold when the material is destroyed, and the explosive dynamic damage occurs. When the unloading disturbance occurs, the strength of the material and the energy required for failure are reduced. The energy that is not enough to cause failure may reach the failure energy threshold, and the engineering rock mass is prone to unloading failure. The average theoretical fitting degree of the dynamic stress-strain curve of coal specimens can reach more than 96%, indicating that the established dynamic constitutive relation is suitable for describing the stress-strain relation of materials under dynamic load. There is a strong correlation between the fitting parameters in the constitutive relation, and the fitting parameters change exponentially with the change of strain rate, and the fitting degree of the theoretical curve is mainly determined by the parameters m and φb. The research conclusions can provide reference for the study of dynamic mechanical properties of coal and rock materials.

     

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