Study On The Fracture Characteristic Of Two Kinds Of Steel Under Large Range Stress Triaxiality

Steel is widely used in automobile,civil engineering,equipment,weapon manufacturing and other industries due to its good strength and rigidity,machinability,fatigue resistance,multiple impact resistance,light weight and recycling.Steel fracture will cause serious casualties and economic losses,so the problem of steel fractures has attracted widespread attention in the engineering community.In order to study the fracture characteristics of 10B21 steel and 42CrMo steel under different stress triaxiality.The quasi-static failure tests of the specimens under various stress states,such as notch tension,pure torsion,tension torsion combination,uniaxial compression,and dynamic Hopkinson pull rod failure test are carried out.The stress triaxiality involved ranges from-0.33 to 1.11.The fracture of the specimen was observed by SEM and the fracture mechanism was analyzed.Combine with the finite element software.Simulate the experiments in this article.The parameters of principal stress,shear stress and stress triaxiality are extracted.Calculate and determine all parameters in the stress triaxial fracture criterion.The main work and innovation achievements of this paper are as follows:1、After completing the tests under various stress states,the fracture surfaces of 10B21 steel and 42CrMo were observed by SEM.By analyzing its fracture mechanism,it is found that the four fracture forms proposed in the stress triaxial fracture criterion all appear.The crack initiation position and crack direction of the specimen are consistent with the prediction results in the stress triaxial fracture criterion.This shows that the stress triaxiality fracture criterion can explain the fracture problem of metal materials well.2、In this paper,through the comparison of experiments and finite element simulation to study the fracture of steel.The test and finite element comparison results are consistent.The finite element can reflect the real test situation.The effective principal stress and shear stress are extracted.Substitute into the stress triaxiality fracture criterion formula to get the parameter value in the criterion,and provide a reference basis for the application of stress triaxial fracture criterion in engineering.3、By using the Freudenthal fracture criterion and Cockcroft-Latham fracture criterion to simulate the fracture of steel.In the numerical simulation of metallic materials,the selection of ductile fracture criterion and threshold has a great influence on the accuracy of the simulation results.The DEFORM finite element software was used to simulate the tensile fracture test of 10B21 steel and 42CrMo steel.Get the fracture threshold of two commonly used ductile fracture criteria.Provide application for numerical simulation research of 10B21 steel and 42CrMo steel.4、In this paper,the dynamic fracture behavior of 10B21 steel was studied by Hopkinson pull rod test.The results show that the mechanical properties of 10B21 steel in dynamic state are quite different from those in quasi-static state.10B21 steel is strain rate sensitive material.However,the change trend of 10B21 steel failure stress and strain with stress triaxiality under dynamics are consistent with the quasi-static triaxiality.The initial location of the steel cracking and the direction of cracking are also consistent with the predicted results in the stress triaxial fracture criterion.This shows that the stress triaxiality fracture criterion can qualitatively explain the fracture problem of metal materials under dynamic conditions.