三维动静加载下不同长径比煤样力学特性及能量耗散规律

Mechanical properties and energy dissipation laws of coal samples with different length-to-diameter ratios under 3D coupled static and dynamic loads

为研究三维动静加载下不同长径比煤样力学特性及能量耗散规律,利用改进的分离式霍普金森压杆(SHPB)装置,对直径50 mm,长径比分别为0.5,0.6,0.8和1.0的4组圆柱体试样开展三维动静加载试验,从动态应力和动态应变等方面研究不同长径比煤样的力学特性,并对破碎后煤样进行能量分析。研究结果表明:当试样长径比在0.5~1.0范围内时,动态峰值应力和组合峰值应力均随应变率增大呈乘幂函数关系增长,长径比越大,试样的应变率敏感性越强;相同应变率下,动态峰值应力和组合峰值应力随试样长径比增加而增大,且应变率越大,二者长径比效应越显著。试样动态峰值应变和动态最大应变均随应变率增大呈线性关系增长,不同长径比试样动态峰值应变及动态最大应变的应变率敏感性相差不大,相同应变率下动态峰值应变随试样长径比增加而减小,动态最大应变受预加静载及试样允许的最大变形量双重因素影响,随长径比增加表现为先减小再增大。试样长径比越大,煤的破碎耗能密度越小,破碎程度越高,破坏模式由张拉破坏向剪切破坏转变。研究成果有利于探究动静载叠加作用下冲击失稳破坏机制,为冲击地压防治提供理论支持。

In order to study the mechanical properties and energy dissipation laws of coal samples with different length-to-diameter ratios under three-dimensional(3D)coupled static and dynamic loads,four groups of cylinder specimens with a diameter of 50 mm and length-to-diameter ratios of 0.5,0.6,0.8 and 1.0 were respectively used to carry out 3D coupled static and dynamic loading experiment by using the improved split Hopkinson pressure bar(SHPB).The mechanical properties of coal samples with different length-to-diameter ratios were studied from the aspects of dynamic stress and dynamic strain,and the energy of the coal samples after crushed was analyzed.The results show that the dynamic peak stress and the combined peak stress increase as a power function of the strain rate,and the specimens with large length-to-diameter ratio are more sensitive to the strain rate when the length-to-diameter ratio of the samples is in the range of 0.5–1.0.At the same strain rate,the dynamic peak stress and the combined peak stress increase with increasing the length-to-diameter ratio,and the greater the strain rate,the more significant the length-to-diameter ratio effect.The dynamic peak strain and the dynamic maximum strain increase linearly with increasing the strain rate.There is little difference between the strain rate sensitivities of the dynamic peak strain and the dynamic maximum strain with different length-to-diameter ratios.Under the same strain rate,the dynamic peak strain decreases with increasing the length-to-diameter ratio.The dynamic maximum strain,affected by the double factors of the preload and the maximum allowable deformation of the specimens,decreases first and then increases with increasing the length-to-diameter ratio.The larger the length-to-diameter ratio of the samples,the lower the dissipated energy density and the higher the degree of crushing.The failure mode changes from tensile failure to shear failure with increasing the length-to-diameter ratio.The research results are helpful to explore the failure mechanism under the coupled static and dynamic loads,and provide theoretical support for the prevention and control of rockburst.