Peridynamics Analysis For Dynamic Crack In Functionally Gradient Materials Coating And Interface Layer

Functionally Graded Materials(FGM)is a new type of composite material,which can gradually change the gradient structure in the material components by a layer-by-layer manufacturing process to achieve the desired function.FGM has special mechanical properties compared to other composite materials through its gradual material properties.When FGM is used as a coating or interfacial layer,it fully reflects the superior performance of FGM.Because of the gradual material properties of FGM,the traditional finite element method has some limitations on the study of discontinuity in the dynamic failure process.Peridynamics(PD),based on non-linear theory,has advanced advantages in solving discontinuous problems.In this paper,the peridynamics theory based on "bond" theory is used to study the dynamic fracture problem of FGM as a coating material and an interface layer material.The following conclusions are drawn:(1)It briefly introduces the theoretical basis of peridynamics,put forward the parameter expression relationship of the bond-based peridynamics model near the connection of the gradient coating / the interface layer and the substrate material,and uses the modified method of "double bond" effect to further deal with the stress relationship near the connection between the gradient material and substrate material.Through the comparison and analysis of the simulation results,the correctness of the improved theory is proved.(2)Based on the improved peridynamics model with "double bond" effect between different materials,the dynamic fracture behavior of FGM coating components with cracks is analyzed.The effects of the different gradient form of the FGM coating(the elastic modulus function of linear,exponential and trigonometric),the ratio of elastic modulus of upper and lower surfaces,and the coating thickness on crack propagation behavior are investigated.It is fonud that the degree of the crack propagation is different in gradient form,but the general direction of deflection is uniform.The sample of exponential gradient form is most obvious for crack propagation of the coating.The ratio of elastic modulus and the coating thickness also have a great influence on the dynamic propagation of cracks.The material properties of FGM can be maximized by selecting the appropriate ratio of elastic modulus and the proper coating thickness.(3)The dynamic failure of crack specimens under four-point bending is analyzed when FGM is used as the interfacial layer materials of the structure.It is concluded that the change of pre-crack location can affect the failure behavior of the specimen.When the test piece contains a single crack,when the crack position moves along the FGM direction from the side of the small elastic modulus to the side of the large elastic modulus,the deflection angle of the crack becomes smaller and smaller until it is parallel to the stress direction.When the test piece contains double crack,the influence of crack spacing on its dynamic propagation is analyzed.It is concluded that the effect of crack spacing on dynamic propagation is limited.For the double-crack specimen,crack propagation behavior on the side with the smaller elastic modulus is similar to that of the single-crack specimen,but the crack on the side with the larger elastic modulus hardly extends.(4)The dynamic expansion behaviors of FGM with pre-crack as the interfacial layer under the tensile stress of the upper and lower surfaces and the impact load on the left side are observed.By analyzing the influence of cracks position,cracks spacing and thickness of FGM interfacial layer on the fracture behavior of the structure,it is found that the smaller the spacing between the cracks,the more likely the bending failure occurs,this is caused by the inhomogeneity of the gradient material.