Research On Residual Stress Simulation And Experiments Based On The Indentation-strain Method

In the practical engineering,the residual stress will have a great influence on the mechanical properties of the material,so that it can't reach the design requirements.The indentation strain-gage method has the characteristics of high measuring precision and micro-damage,but the method needs to be calibrated and the measurement of residual stress under the condition of unknown direction of principal stress is complicated.Therefore,the residual stress is quantitatively analyzed from two aspects of simulation and experiment based on the indentation strain-gage method,the quantitative relationship between residual stress of metal material and the strain increment after unloading is obtained,and the measurement method is improved correspondingly.Firstly,this paper simulates the whole process of the spherical indenter with a diameter of 1 mm pressing into the specimen and unloading by using ABAQUS software,and the stress-strain relationship of the specimen surface after unloading is obtained.Through the analysis of a large number of simulation data,the position of the strain increment was selected at 3 mm from the center of the indentation center,and the load force on the spherical indenter was 960 N.The strain increment of the specified position under different residual stress is obtained,and the strain increment is linearly correlated with uniaxial and biaxial residual stresses,which verifies the feasibility of the indentation strain-gage method.In order to enhance the universality of the simulation results,the influence of material parameters on the change of strain increment is analyzed,and it is found that the elastic modulus,yield strength and hardening exponent are linear,inversely proportional and logarithmic in relation to the change of strain increment.Secondly,the prestressing with different size is applied to the specimen by selfdesigned prestressed device,and the loading and unloading process is completed by using the electronic universal testing machine and the Brinell indenter with diameter of 1 mm in this paper.The strain increment measured by strain gage at 3 mm from the center of indentation center was found to be linear with uniaxial and biaxial residual stresses,and the experimental results verify the accuracy of simulation results.Finally,the relationship between strain increment and residual stress is directly established based on indentation,and a relatively complete method of measuring residual stress is formed.In addition,the calibration experiment and the measurement of residual stress under the condition of unknown direction of principal stress are improved in this paper.By introducing the influence of elastic modulus,yield strength and hardening exponent into the relationship between strain increment and residual stress,the empirical formula is proposed,which replaces the time-consuming and laborious calibration experiment.Under the condition of unknown direction of principal stress,the empirical formula between strain increment and biaxial residual stress is proposed,and the direction of residual stress is determined according to the size of pile-up and strain increment to achieve the objective of measuring residual stress.The sensitivity of measurement method and the source of experimental error are also analyzed.Based on the indentation strain-gage method and its improved method,this paper realizes the measurement of the residual stress of the component,its measurement precision has reached the standard of engineering measurement,and provides a new idea for the measurement of residual stress.