Determining Residual Stress Using Indentation and Surface Displacement Measurement

Background

Residual stresses exist in many manufactured materials and must be measured and taken into account for safe structural design. Established residual stress measurement methods are either destructive or require substantial material-dependent calibration.

Objective

The present work is aimed at developing an indentation-based method for measuring residual stress that causes minimal specimen damage, does not require a stress-free reference specimen, and has the capability to identify both the size and direction of the surface residual stresses. In this initial study, the simpler case of equi-biaxial stresses is addressed in preparation for subsequent general stress evaluations.

Methods

The surface displacements around an indentation made by a conical indenter are measured using digital image correlation. The residual stresses are then identified by comparison to the results of a finite model of the indentation process.

Results

The proposed method is shown to 2–5 times more sensitive to the presence of residual stresses than other commonly used indentation methods, particularly for materials with low Hollomon exponent n. In example measurements, axi-symmetric residual stresses were determined within 8% of the material yield stress.

Conclusions

The initial study presented here successfully considered the equal-biaxial stress case. The proposed method is attractive for future development because it gives directional information and therefore can be extended to the general non-equal-biaxial case.