The Preparation Of Cu/WCp Functional Gradient Materials And Fatigue Crack Growth Experiment

As a new type of composite material,functionally gradient material is designed to meet the new era of national defense and the people's livelihood and other high-tech areas of the stringent requirements of the material,it is considered to be one of the most promising composites under complex working conditions.Since the concept of functionally graded materials was put forward by Japanese scientist Shinno Masano in 1987,functionally graded materials have been widely used in the fields of nuclear energy,aerospace industry,microelectronics,high temperature structure and so on.Functionally graded materials are usually applied to complex working environment,which are quite different from traditional composites.Therefore,it is of great academic significance and engineering application to study the mechanical behavior of functionally graded materials,especially the behavior of fatigue crack propagation.Functionally graded materials originally intended to relax the thermal stress,used in high temperature environment,especially suitable for the material with the environmental temperature difference between the two sides.Subsequently,with the continuous development of functionally graded materials,the development of the functionally graded materials concept reached agreement,turned to the practical preparation methods and practical engineering applications.Copper based tungsten carbide(Cu/WCp)functionally graded material has good mechanical properties,which has attracted much attention from many researchers in the world.The combination of tungsten carbide(WCp)and copper(Cu)with good conductivity and thermal conductivity,according to the requirements of the actual application,out of hot pressing sintering with different WCp content gradient distribution of electrical contact materials.From the current collection of documents,there are few studies on the fatigue crack growth behavior of Cu/WCp functionally graded materials in domestic and abroad.Because of the Cu/WCp functionally gradient material has the characteristics of non-uniformity and design,it is necessary to study the mechanical behavior of Cu/WCp functionally graded materials,especially the behavior of fatigue crack propagation.In this paper,Cu/WCp compound material and volume fraction of laminated distribution(Vol=3%,9%and 15%)of functionally graded materials(FGM)were prepared by vacuum hot pressing sintering.The static mechanical properties of Cu/WCp particle reinforced composites was measured by strain gauge method and digital image correlation method(DIC).To provide the data support for the fatigue crack growth experiment and determine the maximum load Pmax.The fatigue crack growth of Cu/WCp homogeneous composites was studied:(1)The Cu/WCp composite material for fatigue crack propagation experiment was divided into two types,control stress ratio R=0.1 unchanged and control the content of WCp constant with R=0.1,0.3,0.5.(2)Experimental study on fatigue crack growth of Cu/WCp functionally gradient material and Cu/WCp multilayer functionally gradient material,analysis of fatigue crack growth mechanism of Cu/WCp functionally graded materials and interface on the fatigue crack growth rate of gradient materials was analyzed.(3)The Cu/WCp fatigue specimens were examined by scanning electron microscopy(SEM),in order to observe and analyze the Cu/WCp source of fatigue and fatigue crack of laminated FGM expansion zone from the fatigue fracture diagram,the effect of WCp particles and Cu/WCp interface on crack propagation in functionally graded materials is analyzed.(4)Finally,the fatigue crack growth of Cu/WCp composites and functionally graded materials were simulated by FRANC2D,compared fatigue crack growth curves obtained by numerical simulation with the experimental curves,verify the experimental data.The results of the study show that:(1)Cu/WCp composites with good properties and functional gradient materials can be prepared by vacuum hot pressing sintering process,with the increase of WCp particle content,The tensile strength of the Cu/WCp composite material(?b),yield strength(?y)and elastic modulus(E)has increased significantly.However,the Poisson's ratio(?)decreased with the increase of WCp content.(2)Under the condition of constant stress ratio(R=0.1),the fatigue crack growth rate of Cu/WCp composites decreases gradually with the increase of WCp content.Under the condition of the same WCp content,the fatigue life of Cu/WCp composites increases gradually with the increase of stress ratio(R=0.1,0.3 and 0.5),and the crack propagation rate decreases with the increase of stress ratio.(3)Under the same stress intensity factor range,the crack propagation rate of Cu/WCp bilayer functionally gradient material is lower than Cu/WCp homogeneous composites,the experimental results show that the Cu/WCp bilayer gradient composites have better resistance to fatigue crack propagation.(4)Under the same stress intensity factor range,the crack propagation rate of Cu/WCp multilayer functionally graded materials is lower than that of Cu/WCp homogeneous composites.When the crack tip is close to the interface,there is a significant deflection of the crack,the crack roughness increases and the crack propagation rate decreases.(5)FRANC2D was used to simulate the fatigue crack propagation of Cu/WCp composites and gradient materials.The calculated results are in good agreement with the experimental results that prove the experimental results are reliable.In this paper,the fatigue crack growth performance of Cu/WCp functionally gradient material has been studied.The results show that Cu/WCp functionally gradient material has better fatigue performance than traditional composite materials,and has high engineering application value.FRANC2D is used to simulate the fatigue crack propagation process of gradient material,which provides the experimental reference for the numerical simulation method to analyze the fatigue property of gradient material.