Spherical Indentation Method for Measuring Biaxial Residual Stresses Without Using Stress-Free Sample

Since residual stresses can affect the mechanical performance of in-service engineering structures, accurate evaluation of biaxial residual stresses is of great significance to service safety. Previous indentation methods for evaluating biaxial residual stresses usually require a stress-free sample as a reference, which is difficult to obtain in engineering.

In present work, a spherical indentation method for evaluating biaxial residual stresses without using stress-free sample was established.

To avoid using stress-free sample, a method for deriving the loading work in unstressed state from the load-depth curve in stressed state, was established. Through dimensional analysis and finite simulations, biaxial residual stresses were quantitatively correlated to the fractional change in loading work between stressed and unstressed states, and the flattening factor of residual imprint. Based on such correlations, biaxial residual stresses can be evaluated without using stress-free sample. A biaxial stress-generating jig was used to validate the method experimentally.

Finite element analyses and experimental results demonstrate that the proposed method could evaluate biaxial residual stresses with reasonable accuracy.

Combined with portable micro-indentation device, the proposed method has broad application prospects in evaluating biaxial residual stress of in-service engineering structures.