RESEARCH ON CHARACTERISTIC PARAMETERS OF SANDSTONE THREE-POINT BENDING FAILURE UNDER DIFFERENT TEMPERATURES
ZUO Jianping1，2，ZHOU Hongwei1，2，LIU Yujie2
(1. State Key Laboratory of Coal Resources and Safe Mining，China University of Mining and Technology，Beijing 100083，China； 2. School of Mechanics and Civil Engineering，China University of Mining and Technology，Beijing 100083，China)
Abstract：Based on three-point bending tests，the characteristic parameters of Pingdingshan sandstone under different temperatures have been investigated. The variation of three characteristic parameters with thermal effects is focused on，namely，elastic modulus，damage parameter and ductility ratio. Based on numerical statistical method，a new parameter has been put forward to characterize rock material property，namely，numerical elastic modulus. The method is convenient for experimental methods to determinate elastic modulus for brittle materials. Thermal damage has been defined according to the variation of elastic modulus at different temperatures with Lemaitre¢s damage theory. A piecewise four-order polynomial has been used to fit the nonlinear relationship between the thermal damage and temperatures. And the fitting results agree well with experimental results. The thermal damage under different temperatures can be divided into four stages，namely，instable stage of thermal damage，initial thermal damage stage，stable thermal damage stage and fast thermal damage stage. At last，based on concrete structure theory，ductility ratio to characterize the ductility property of sandstone at different temperatures is employed；and the ductility ratio value of two may be approximately as the point of brittle-ductile transition.
