不同冻融条件下砂岩损伤力学特性

Damage mechanical properties of sandstone under different freeze⁃thaw conditions

为探究不同冻融条件下砂岩冻融损伤规律及其力学特性,对不同冻融周期和不同循环次数的冻融砂岩进行单轴压缩破坏性试验,监测其声发射信号,并基于试验结果和统计损伤理论建立了损伤演化方程。结果表明:冻融循环时,冻融周期和循环次数的增加均会造成砂岩冻融损伤的增加,砂岩单轴抗压强度和弹性模量随冻融周期的增长呈指数型衰减,随循环次数的增加呈线性降低;声发射累计振铃计数变化趋势与应力⁃应变曲线表现出较好的一致性,压密阶段和线弹性阶段累计振铃计数很小,塑性变形阶段累计振铃计数逐渐增加,且增速不断上升,峰后破坏阶段累计振铃计数剧增,冻融周期越长、循环次数越多,砂岩破坏时累计振铃计数越小;冻融损伤变量决定冻融载荷作用下总损伤变量的初始值,冻融周期越长、循环次数越多,砂岩初始总损伤变量越大,损伤演化曲线分为3个阶段,初始阶段损伤几乎不增加,发育阶段损伤逐渐增加,且增速越来越大,加速阶段损伤剧增并造成砂岩宏观破坏。

In order to explore the freeze⁃thaw damage and mechanical properties of sandstone under dif⁃ferent freeze⁃thaw conditions,sandstone undergone different freeze⁃thaw cycles and cycle times is selected for uniaxial compression tests and acoustic emission monitoring tests.The damage evolution equations of sandstone are established,with the test results and the statistical damage theory.The results show that:Both freeze⁃thaw cycle and cycle times affect the freeze⁃thaw damage of sandstone.The strength and elastic modulus of sandstone decrease exponentially and linearly with the increase of freeze⁃thaw cycle and cycle times respectively.The cumulative ringing counts are consistent with the stress⁃strain curves.The cu⁃mulative ringing count in the compaction stage and linear elastic stage is very small.The cumulative rin⁃ging count in the plastic deformation stage gradually increases,and the growth rate keeps rising.The cu⁃mulative ringing count in the post peak damage stage increases dramatically.The longer the freeze⁃thaw cycle and the more cycle times,the smaller the cumulative ringing count of sandstone.The freeze⁃thaw damage variable determines the initial value of the total damage variable under freeze⁃thaw and load.The damage evolution curve can be divided into three stages:in the initial stage damage rarely increase,in the development stage damage increases gradually,and the growth rate is getting higher,and in the accelerated stage damage increases dramatically and causes macro damage of sandstone.