准静态应变率下的煤岩非线性力学特性

为研究开挖扰动下煤岩的非线性力学特征,利用MTS815伺服刚性试验机对芙蓉白皎煤矿煤岩进行10-5~10-2s-1准静态应变率下的单轴压缩试验,分析准静态应变率下煤岩的应力-应变曲线、抗压强度、弹性模量、泊松比等力学特性的变化规律,基于煤岩显著的非线性力学特征,修正并验证黏弹性损伤本构模型的合理性。研究表明:①煤岩单轴压缩荷载作用下具有明显的压密、线弹性、塑性屈服、峰后破坏4个阶段;煤岩力学特性应变率相关性突出,随着应变率的增加,压密阶段缩短,线弹性阶段增长,屈服阶段应力强化特征及峰后破坏阶段应力软化特征趋于明显;②由于原生裂隙的闭合和扩展,煤岩受载作用下,各阶段均呈现显著的非线性力学特征,随着应变率的增加,压密阶段和线弹性阶段表现出的明显非线性特征呈减弱趋势;③准静态应变率10-5~10-2s-1范围内,抗压强度随应变率增加由8.83MPa增加至12.57MPa,增长率42.35%;弹性模量随应变率增加总体呈现先增加后减小的变化趋势,在10-5~10-4s-1应变率区间,弹性模量由1644MPa增加至1825MPa,随后在10-4~10-2s-1应变率区间内减小,变化趋势发生明显转折;泊松比在准静态应变率下随应变率增加而呈现逐渐减小的变化趋势,从1.53下降到0.71,减小53.59%;整个准静态应变率范畴下,煤岩的力学特征参数(抗压强度、弹性模量、泊松比)均表现出显著的非线性变化趋势,均在临界应变率10-3s-1附近发生转折。④利用一个损伤体和一个Maxwell模型并联方式,综合考虑准静态应变率下煤岩的非线性变化特征后,引入材料常数a对胡克定律进行修正,推导得出准静态应变率下煤岩的非线性损伤演化本构方程,并结合煤岩单轴压缩试验对其合理性进行验证。

Nonlinear mechanical properties of coal rock under quasi-static strain rate

In order to study the nonlinear mechanical characteristics of coal rock under excavation disturbance,the uniaxial compression test of quasi-static strain rate of 10-5-10-2 s-1 was carried out by MTS815 servo rigidity testing machine on the coal rock of Fu Rong,Bai Jiao Coal Mine,China.The variation of mechanical properties such as stress-strain curve,compressive strength,elastic modulus and Poisson’s ratio of coal rock under quasi-static strain rate were analyzed.Based on the significant nonlinear mechanical characteristics of coal rock,the viscoelastic damage constitutive model was modified and verified.The research shows that ① Under uniaxial compression loading,the coal rock has four stages,such as compaction,linear elasticity,plastic yield and post-peak damage.The strain rate correlation of coal rock mechanical properties is outstanding.With the increase of strain rate,the compaction phase is shortened,the linear elastic phase is increased,and the stress strengthening characteristics in the yielding stage and the stress softening characteristics in the post-peak failure stage tend to be obvious.② Due to the closure and expansion of the primary fissures,each stage of the loading coal rock presents remarkable nonlinear mechanical characteristics.With the increase of strain rate,the obvious nonlinear characteristics of the compaction stage and the linear elastic stage show a weakening trend.③ In the range of quasi-static strain rate 10-5-10-2 s-1,the compressive strength increases with the strain rate from 8.83 MPa to 12.57 MPa,the growth rate is 42.35%.The modulus of elasticity generally increases first and then decreases with the increase of strain rate.In the range of 10-5-10-4 s-1 strain rate,the elastic modulus increases from 1 644 MPa to 1 825 MPa,followed by 10-4-10-2 s-1 is reduced within the strain rate interval,and the trend of change is obviously turning.The Poisson’s ratio shows a decreasing trend with the increase of strain rate under the quasi-static strain rate,which decreases from 1.53 to 0.71,and decreases value by 53.59%.The mechanical characteristics parameters (compressive strength,elastic modulus,Poisson’s ratio) of coal rock under the whole quasi-static strain rate category all shows significant nonlinear changes,and all of them turn around the critical strain rate of 10-3 s-1.④ Using a damage body and a Maxwell model in parallel,considering the nonlinear variation characteristics of coal rock under quasi-static strain rate,the material constant a is used to modify the Hooke’s law,and the constitutive equation of nonlinear damage evolution of coal rock under quasi-static strain rate is derived.The constitutive equation’ rationality is verified with the combination of the uniaxial compression test of coal rock.