Research On Failure Behavior Of Kinked Crack Under Chemical Corrosion

The natural rock mass contains a lot of joints and cracks,sometimes in the complicated natural environment with corrosion for a long time.The mechanical properties of rock masses and the mechanism of crack propagation have long been a subject of concern in the field of rock mechanics.At present,related research at home and abroad has mainly focused on two aspects: one is the study of mechanical properties and failure mechanisms of rock masses with straight fractures;the other is to consider the effect of chemical corrosion on rock physical and mechanical behavior.A small number of scholars have considered the effects of cracks and chemical corrosion on the mechanical properties and failure mechanisms of rock masses at the same time.However,due to the majority of fractures in natural rock mass are non straight fractures,at present,the research on the failure mechanism of non straight fractures is relatively small,and there is no relevant research on the impact of chemical corrosion on the non straight fractures.The failure mechanism of the common non straight fractures in nature under the corrosive environment is not clear.Kinked fracture is a typical non straight fracture.It has important theoretical and practical significance to study the failure behavior of kinked fracture considering chemical corrosion.This paper completed the following work:(1)In order to investigate the effects of chemical corrosion and the shape of the kinked crack on the mechanical properties and failure behavior of limestone specimens,the p H,the salt ion concentration,and the branch fissure inclinations were used as variables to carry out a large number of uniaxial compression test on the limestone samples containing kinked crack.The chemical corrosion mechanism was analyzed through chemical reaction equations at the microscopic level and the failure modes of crack coalescence were summarized at the macro level.The influence of the branch fissure inclination and chemical corrosion effects on the failure modes was analyzed.During uniaxial compression,a high-speed camera was used to capture the entire surface crack growth process of the samples.At the same time,the acoustic emission system was used to record the internal crack activity of the specimens,and the kinked crack growth law was comprehensively analyzed in combination with the stressstrain curve.(2)This paper summarized the previous research on the stress intensity factor at the tip of kinked crack under compression load,and on the basis of previous research on kinked crack under tensile load,the formula for calculating the stress intensity factor of kinked crack under uniaxial tensile load was derived.The accuracy and scope of the derived formula are verified by finite element analysis,and the model is improved based on the finite element results and the equivalent force.Following the process of establishing crack fracture criteria under chemical corrosion by Ding and Feng,a stress intensity factor calculation model for the kinked crack under chemical corrosion was established,and the change of cracking angle after chemical corrosion was analyzed based on the model.It was found that based on this model,the crack initiation angle of straight fracture will not change,but that of kinked fracture will change.(3)The basic theory of the extended finite element method(XFEM)is introduced.The XFEM is used to simulate the test of the prefabricated kinked crack specimens under uniaxial compressive load.By comparing the crack initiation position,cracking initiation direction and expansion path.The validity of the XFEM simulation of rock-like materials is verified.The cloud of Mises stress and maximum principal stress before failure are compared,and the whole processes of crack initiation,propagation and coalescence in the numerical simulation were analyzed.The results show that the maximum principal stress cloud before failure can reflect the crack initiation position of rock-like material.