Experimental Study On Time-Dependency Of Mechanical Properties On Tage Tuff Under Tensile Conditions

As everyone knows, Rock burst, foundation cracking, landslide and other engineering disasters caused by rock deformation damage have obvious timeliness. In other words, the geotechnical engineering disaster does not necessarily occur in the process of engineering construction or during a short time after project completion and operation, but often occurs through varied time. Therefore, the research of time effect of rock mechanical properties is very important for reducing and preventing the related engineering disasters. In the present, the research of the rock time effect is mainly concentrated on the compression, and the tensile is quite absent. However, the rocks in many engineering conditions are under tensile stress, so the study of time effect of rock under tensile stress has prominent guiding significance.In this article, Japanese tage tuff is chose as the research object, on the basis of studying and summarizing previous studies, A uniaxial tensile test system is developed for direct tensile test of rock. It can help to achieve the linear combination of stress and strain on the basis of the traditional stress control and strain control and it is also called as the control of the stress return method. This study is made up of five experiments, including the direct tensile test of constant strain rate at different loading rates, the direct tensile test at alternating loading rate, the generalized stress relaxation test based on the control of the stress return method(the stress and strain are changed simultaneously, but the linear combination of stress and strain is unchanged), the creep test and the relaxation test. According to the direct tensile test and the properties of generalized stress relaxation of tage tuff, a suitable constitutive model called nonlinear visco elastic constitutive model with variable modulus has been chosen. And the parameters of the constitutive model have been determined by the direct tensile tests and the generalized stress relaxation experiments. The final work is the verification of the model calculation results and the main conclusions are as follows:1) The loading rate dependency of basic mechanical parameter of the direct tension test was studied and the index b of the loading rate dependency which show the size of the loading rate dependency was defined. In the tests, the indexes of the loading rate dependency of the strength of tension?Young modulus and failure strain were 0.0214?0.0087 and 0.0129 respectively. The inelastic strain ?2 was analyzed to find that when ?2 runs up to 0.4×10-3, the specimen would be damaged and it had nothing to do with the loading rate. Comparing with the results of alternating loading test and constant loading rate test, the similarity of the two tests was high.2) The rheological properties including creep?relaxation and generalized relaxation of tage tuff were studied. The relationship between creep strain and time, creep rate and time under different stress levels were obtained. Also the relationship between stress drops and time, the relaxation rate and time under different strain levels were gained. Finally, the generalized relaxation property of different direction in the same actuation point was analyzed and the isochrone of generalized relaxation were gained.3) The appropriate constitutive model in the tensile condition was selected and the constitutive equations was got. In this model, six parameters were confirmed, a1=1, a2=0.0001, m1=43, m2=20, n1=n2=46, and using this constitutive model, the complete stress and strain test of different rate of tage tuff in the direct tensile condition and creep test under different stress levels were simulated successfully. The consistency of results of calculation and tests is good.