基于硬化-损伤机制的贫煤蠕变本构模型研究

岩石蠕变是其内部硬化效应和损伤效应共同作用演化的结果。通过分级加载下贫煤单轴压缩蠕变试验，基于试验中瞬时弹性模量增大和黏滞系数减小的现象，分析贫煤蠕变中的硬化-损伤机制。结果表明，较低应力下煤样的变形仅为瞬时应变，煤样仅有硬化效应；当应力达到蠕变起始应力阈值时煤样逐渐出现损伤，次生裂纹出现并扩展，硬化效应与损伤效应共同作用下煤样表现出衰减蠕变和稳定蠕变特征。长期蠕变过程中煤样强度经历先硬化再弱化的过程，最终因累计损伤过大而失稳破坏，依据各级应力下煤样的变形特征，构建了符合其变形规律的黏弹塑性组合模型，并引入了硬化函数和损伤函数，推导得到其蠕变本构方程。采用该模型描述分级加载下贫煤单轴压缩蠕变变形曲线，试验曲线和模型曲线吻合良好。该模型元件简单，物理意义明确，能很好地反映贫煤单轴压缩下的硬化–损伤蠕变特性。

A creep model for lean coal based on hardening-damage mechanism

Rock creep is the evolution result of the interaction of hardening effect and damage effect inside it. A series of uniaxial compression creep experiments of raw lean coals are conducted by stepwise loading in this work, and the increasing instantaneous elasticity modulus and decreasing viscosity coefficient are taken to analyze the hardening-damage mechanism of lean coal. The results show that at low stress load, coal strain is just instantaneous, and only hardening effect exists. When the stress reaches or exceeds the creep start stress threshold, damage effect emerges, and interacts with hardening effect, resulting in transient creep and steady creep. In long term creep, coals are first hardened and then weakened and finally fail due to large accumulative damage. On basis of the strain characteristics of lean colas at different stress loads, a combined viscous-elastic plastic model is established; and then the hardening function and damage function are both introduced into the model; thus the creep constitutive equation is obtained. This model is used to depict lean coal’s creep curves and the results show the model curves fit the experimental data very well. This model is simple with clear physical meaning, and it can reflect the hardening-damage creep characteristics of lean coal in uniaxial compression very well.