Experimental Study On High Temperature Fracture Toughness Of Cu/WC Laminated Functionally Graded Materials

Cu/WC functionally graded material is a new material with high conductivity,high thermal conductivity of copper matrix and high hardness,high melting point,low thermal expansion coefficient of tungsten carbide(WC).The advantages of this material can exibit the good performance of Cu and WC respectively,also can make the material in the overall performance of metal heat conduction,conductive properties,good mechanical properties,but also has high strength,high temperature resistance,wear resistance.The main feature of Cu/WC functionally graded materials is control the interface components and the continuous changes of the organization,so the thermal stress of the material is greatly reduced.Cu/WC layered functionally graded materials is a new type of composite materials,in order to adapt to the new materials in the field of high-tech,meet in extreme temperature environment(high temperature,high temperature drop)under repeated work.In this paper,the digital image correlation method(Digital Image Correlation-DIC)was used to study the fracture toughness of Cu/WC functionally graded materials.In order to verify the correctness and feasibility of the DIC method,the fracture toughness of high strength Cr12MoV steel specimens was tested.The experimental results show that the DIC method can accurately test the fracture toughness of the metal materials.Then the three point bending experiments of Cu/WC composite and Cu/WC laminated functionally graded materials were carried out under room temperature and at different temperatures,and the digital image of the specimen surface was collected by CMOS camera during the experiment.Digital image acquired by each specimen based on application of digital image DIC method of Vic-2D software is calculated,the specimen near the crack tip strain field and displacement field is obtained,Strain field and displacement field of crack tip is obtained,and the test piece near the crack tip strain field and displacement field data into the corresponding programs are written in MATLAB to calculate stress crack opening mouth(crack mouth opening displacement-COD(P-V))displacement curve and force displacement curve(P-delta).The critical load and critical COD were determined by P-V,combining with digital image acquisition.The deformation work is obtained by curve of P-delta,according to the relationship between J integral and J integral deformation work,and calculating the critical value for JIC of J integral.In this paper,the DIC method was used to study the high temperature fracture toughness of Cu/WC functionally graded materials,the results show:(1)Cu/WC composites increase with the content of WC,when the WC content reaches 9%,the maximum value of fracture toughness,the content of WC was higher than 9%,the fracture toughness decreases;the specimen with the same content of WC,the fracture toughness decreased with the increase of temperature;.(2)Cu/WC layered functionally graded materials in the same direction of opening conditions,fracture toughness decreases with temperature increase;under the same content of WC and the same temperature,the crack opening direction of the specimen fracture toughness value is larger in the content of WC is lower than in the high WC content,indicating a high side WC the content of Cu/WC laminated functionally graded materials has a protective effect on the content of WC in the lower side.(3)In the high temperature environment,the DIC method can be used to test the fracture toughness value of Cu/WC functionally graded material conveniently and effectively,and provide a reference for the test of the fracture properties of heterogeneous materials.