Study On Residual Stress Test Method Of 304 Austenitic Stainless Steel Dased On Indentation Test

In the machining process of welding joint material 304 austenitic stainless steel,uneven deformation caused by external forces and temperature changes will cause residual stress.Because residual stress has a significant impact on the safety of mechanical structures.It is very important to find a convenient,safe and effective residual stress test method.The indentation method has the advantages of simple operation,quickness and slight damage,and has been widely used in the measurement of the mechanical properties of materials.In this thesis,the influence of residual stress on indentation response parameters is investigated by means of numerical simulation and experiment,and the relationship between residual stress and several indentation response parameters is established.Thereby establishing a new method for testing residual stress based on indentation experiments.The main work accomplished and the results achieved are as follows:(1)Based on the basic principles of indentation experiments and elastoplastic contact mechanics,a finite element model for indentation experiments is established.The indentation experiments under no residual stress verifies the correctness of the material model,geometric model,and mechanical model in the finite element.Derive the formula for calculating the material indentation hardness during numerical simulation.(2)The influence of material mechanical parameters and contact surface friction coefficient on the indentation experiment was analyzed.The effects of yield strength,hardening index,and offset coefficient on the mechanical field in the indentation zone were studied.It is concluded that the numerical simulation results are most in line with the actual situation when the contact friction coefficient is 0.2.(3)Based on the finite element model,explore the relationship between residual stress and mechanical parameters such as hardness,load-depth curve,indentation protrusion,and indentation load.It is concluded that the effects of residual stress on hardness,indentation protrusion,and maximum load all have non-linear effects.The effect of tensile residual stress on several indentation response parameters is about 11%.The effect of compressive residual stress on several indentation parameters is within 4%.(4)Based on the principle of thread self-locking,a set of unidirectional residual stress loading device was designed to simulate the residual stress by prestressing.The indentation hardness test of the sample under different tensile and compressive residual stress loading was achieved.It is concluded that tensile residual stress reduces the indentation hardness,and compressive residual stress increases the indentation hardness.Compared with the compressive residual stress,the hardness value is more sensitive to the change of tensile residual stress.The experimental results are basically consistent with the numerical simulation results.