Experimental Research On Deformation Characteristics Of Rock Under Tension-compression Cyclic Loading Based On Digital Image Correlation

The mechanical properties of rock are very important for evaluating and maintaining the stability of rock mass.In the process of geotechnical engineering excavation,the redistribution of in-situ stress in rock mass will often occur,and the rock mass will be in a complex in-situ stress environment.Taking the tuff in Tianxia as the research object,this paper carries out the experimental study on rock deformation characteristics under five different test conditions,namely,different strain amplitude,different tension amplitude,different compression amplitude,different strain rate and compression-tension cycle,under the loading and unloading conditions of tension-compression cycle,and analyses the tension-compression(compression-tension)cycle load under different test conditions combined with the non-contact full-field deformation measurement cloud chart.These results have important theoretical and practical significance for understanding the failure mechanism of rock under complex stress conditions and evaluating the stability and safety of rock mass correctly.To sum up,the main research work and achievements of this paper are as follows:(1)The transition between tension and compression is continuous and smooth in rock tension-compression cyclic loading test.With the cyclic compression,the specimen is shortened in the axial direction and expanded in the radial direction.Under tension-compression cyclic loading and unloading conditions,the specimen is more likely to be damaged in the tension stage,and the tensile strength of the undamaged specimen increases slightly after tension-compression cyclic testing.(2)At the end of the first cycle of tension-compression cyclic load,more residual deformation and more dissipated energy are produced.There may be a threshold value for failure of specimens under tension-compression cyclic loading and unloading conditions,which is affected by both tension and compression amplitudes.(3)In the tension-compression cyclic loading test,the phenomenon of deformation localization is also mainly concentrated in the deformation localization zone,which is also the location where the failure occurs in the later stage.In addition to the fracture location of the specimen,strain rebound occurs in other localized deformation areas in the early stage,where the specimen still has the ability to withstand tensile elastic deformation.(4)The variation trend of tangent modulus,secant modulus,upper limit stress,dissipated energy and strain nephogram during tension-compression cyclic loading can better reflect the process that the localized deformation area of the specimen expands gradually from generation to failure,and the propagation process of microcracks in the process of failure,so they can be used to infer the damage of the specimen.