Determination of principal residual stresses’ directions by incremental strain method

Abstract

The ring-core method is the semi-destructive experimental method used for evaluation of the homogeneous and non-homogeneous residual stresses, acting over depth of drilled core. By using incremental strain method (ISM) for the residual state of stress determination, this article describes procedure how unknown directions and magnitudes of principal residual stresses can be determined. Finite element method (FEM) is used for the numerical simulation of homogenous residual state of stress and for subsequent strain determination. Relieved strains on the top of the model’s core are measured by simulated three-element strain gauge, turned by the axis of strain gauge “a” from the direction of the principal stress σ1 about unknown angle α. Depth dependent magnitudes of relieved strains, their differences and set of known values of calibration coefficients K1 and K2 or relaxation coefficients A and B are used together for determination of the angle α and for re-calculation of principal stresses.