Dynamic Fracture And Transient Heat Transfer Analysis Of Rock Materials Based On Peridynamics

As a natural material,rock materials contain a large number of primary cracks in different directions.It is very important for rock mass engineering to study the accumulation,expansion,and bifurcation of these primary cracks,which leads to the failure and instability of rock mass.At the same time,with the rapid development of China's economy and the demand for environmentally friendly energy,shale gas has become a "new darling" in the field of unconventional oil and gas resources exploration and development in the world.With the success of the “shale gas revolution” in North America in the early 21 st century,the strategic position of shale gas has gradually received more attention,and China is still in its infancy for the exploitation of shale gas,so it also has good development prospects.However,in recent years,some numerical calculation methods based on continuous hypothesis such as finite element,boundary element,finite difference method and meshless method as well as discrete element and discontinuous deformation analysis method based on discontinuous hypothesis,have certain limitations in the face of the rock material.The reason is rock material has the characteristics of continuous and discontinuous.The Peridynaimcs(PD)used in this paper can avoid the singularity problems encountered in dealing with step continuity problems.In this paper,the method of peridynaimcs is used to study the dynamic fracture and instantaneous heat transfer behavior of rock material,and the following conclusion are drawn:(1)In order to obtain the crack propagation path and the extended state of the pre-notch rock material more accurately,this paper refines the "bond" between the material points on the basis of the existing theory,and proposes the "inner-layer bond" and the “inter-layer bond” calculation model to deals with the influence of material performance parameters on crack propagation in different material layers in a more reasonable way.By comparing the numerical calculation results with the results obtained from the existing experiments and the results obtained from thetraditional numerical method,the validity of the "single and double bond" model in studying the dynamic fracture and instantaneous heat conduction of layered rock materials is verified.(2)Based on the "single and double bond" model proposed in this paper,the convergence of layered rock materials is analyzed to obtain a reasonable lattice constant value(m(28)4).At the same time,the analysis of the crack propagation path containing prefabricated two vertical cracks is analyzed.It is found that under the impact load,the crack propagation path and the pre-notch show an angle of about 70°.(3)Based on the "single and double bond" model proposed in this paper,the dynamic fracture problem of layered rock materials under uniaxial compressive stress and biaxial tensile stress is analyzed.The relationship between crack inclination and stress ratio for extended path and extended state is studied.Influence,it is found that different crack inclination angles and stress ratios will affect the crack propagation path and state.Through the analysis of the crack propagation path and the extended state of the three-layered stratified rock,it is found that the primary crack along the bedding direction in the layered rock is the main cracking site,and the crack coalescence is mainly concentrated in the central rock layer regions and propagating toward the end and sides of the specimen.Finally,by changing the loading mode,the crack initiation time of the rock material containing a single pre-crack and the load required for the crack initiation are 10 ?s and 7 MPa,respectively.(4)Based on the "single and double bond" model proposed in this paper,the effects of Young's modulus,thermal diffusivity,the number of cracks and the boundary temperature on the instantaneous thermal conduction behavior of layered rock materials are studied.It is considered that the number of cracks and the boundary temperature will be the transient thermal conduction of layered rock materials has a certain influence.At the same time,the thermal conduction behavior of layered rock materials under thermal-mechanical coupling conditions is preliminarily studied.The factors affecting the displacement of material nodes under thermo-mechanical coupling conditions are obtained.