Influence of Residual Stress on Indentation Hardness

The hardness was tested for the materials with residual stress.The elastic-plastic constitutive relation affected by residual stress was analyzed and hardness was calculated by finite element method(FEM).The FEM calculated hardness agrees well with measured hardness from the hardness testing.So the FEM result is reliable.Based on the finite element simulation,the influence of residual stress on hardness was studied to establish the quadratic polynomial fitting expression to describe the relationship between hardness and residual stress.The result shows that hardness is seriously affected by tensile stress,and lightly affected by compression stress.The pile-up or sink-in emerged around indentation depends on both magnitude of load and degree of compression/tensile residual stress because of the different elastic-plastic deformation,which affect the indentation depth and contact area and have an influence on the hardness testing values.