Determination Of Residual Stress Of Metal Materials Based On Indentation Pile-up Morphology

In the process of mechanical manufacture,processing,and surface treatment of components,residual stress will inevitably be introduced.In the real service environment,the residual stress will also undergo further evolution and development,which will directly affect the properties of materials or components,and then threaten the safety of life and property.Therefore,it is of great practical value to study the rapid and accurate measurement method of residual stress.When the indentation method is used for residual stress testing,it has the advantages of convenient operation and small damage to the specimen.However,the traditional residual stress measurement method based on load-displacement curve is not accurate enough.This paper studies the measurement method based on indentation pile-up height to obtain the magnitude and direction of residual stress.Through the combination of finite element simulation and experiment,the key issues such as the non-uniform distribution of residual stress along with depth,how to determine the magnitude and direction of in-plane stress are studied.The main research contents and conclusions of this paper are as follows:1.Indicates the indenter type and applicable object of the residual stress measurement method based on indentation pile-up height and the simulation proves that the magnitude of residual stress can be obtained based on the pile-up height of indentation.The results show that the pile-up height has higher sensitivity as the response of indentation morphology,and the pile-up height of the spherical indenter is more obvious than that of the conical indenter.Besides,the pile-up height after indentation unloading is less affected by the yield strength of the material,while the hardening index and elastic modulus are more affected.Materials with a hardening index greater than 0.3 or an elastic modulus greater than 400 GPa are not recommended to use this method.2.The influence of the non-uniform distribution of residual stress along the depth on the measurement of residual stress based on spherical indentation is systematically analyzed.The results show that the residual stress on the surface layer is the main factor causing the height of the indentation pile-up.When the indentation depth exceeds 0.3 mm,the error caused by the form of residual stress distribution is within 3%.Besides,the residual stress beyond 0.6 mm depth below the surface has no effect on the pile-up height after indentation unloading.3.The loading device which can realize a two-direction stress state has been designed and the experimental test platform has been established.The indentation experiments of the two-direction stress state are carried out and compared with three-dimensional finite element model.The experimental results show that the maximum pile-up height of the indentation corresponds to the two surface principal stress directions under any two-direction stress state,thus the principal stress directions can be determined.The results of the two-direction stress state indentation experiments are consistent with the finite element simulation results,which prove the feasibility of using the indentation pile-up height experiment to realize the two-direction residual stress measurement.