岩石直接拉伸与压缩变形的循环加载实验与双模量本构模型

Cycle loading tests of rock samples under direct tension and compression and bi-modular constitutive model

采用一种可对同一岩石试样进行单轴压缩和直接拉伸试验的岩石试样试验装置,对5种岩石进行了压缩和拉伸循环加载试验。结果表明,对于其中压缩平均变形模量ECA较拉伸平均模量ETA大得多的3种岩石(ECA/ETA分别等于2,2.5和6),拉伸下的卸载平均模量ETAUN远大于ETA,且ETAUN约等于ECA。因此,虽然这几种岩石压缩下的变形可近似视为弹性的,拉伸下的变形却是非弹性或塑性的。一些研究者对ET<<EC的岩石引用了压缩和拉伸下均为线弹性但ET≠EC的双线弹性本构模型。本文的结果则表明,已知一种岩石的ET≠EC,不等于双线弹性模型能适用于该种岩石。对于这类拉伸变形为塑性的岩石,必须发展更复杂的本构模型。

Cycle loading tests under direct tension and compression were conducted for five rock types with a new testing frame that could carry out both of these tests on a same rock sample. The results showed that for three rock types of which the average Young＇s moduli in tension, ETA, were much smaller than those in compression, ECA, （ECA/ETA ratio equals 2, 2.5 and 6） the average deformation modulus of unloading in tension, ETAUN, was much greater than ETA, and the values of ETAUN were approximately equal to ECA. Therefore, for these rocks, the relationship between stress and strain was no longer elastic even though their deformation in compression was approximately elastic, Some researchers had developed a constitutive model named “double elasticity” and applied it in the rocks with ET≠EC. The present test results showed that a rock with ET≠EC did not mean that the double elasticity model was applicable to this rock, because its deformation in tension might be plastic. For the rocks having plastic behaviour in tension as those presented in this paper, a more complicated constitutive model had to be developed.