RESIDUAL STRESS MEASUREMENT BY ELECTRONIC SPECKLE PATTERN INTERFEROMETRY: A STUDY OF THE INFLUENCE OF GEOMETRICAL PARAMETERS

Hole drilling (HDM) is the most widespread method for measuring residual stress profile. HDM is based on the principle that a hole in the material causes a stress relaxation; stress field around the hole changes so that the released strain can be measured in order to calculate initial residual stress. Recently the use of optical methods as measurements tool of the strain field generated around the drilled hole has been investigated in place of the traditional strain gauge rosette technique. Optical methods have the advantage to guarantee very high sensitivity, to provide a much more significant statistic, to eliminate error due to hole eccentricity and to reduce the cost of the single test. The accuracy of the final result depends, among other factors, on the exact knowledge of the geometrical parameters of the measuring system. The exact knowledge of the illumination and detection angles influences, in fact, the accuracy in the determination of pixel size and sensitivity vector. The effect of an error in the measurement of geometrical parameters on final residual stress results is presented in this paper aside to some considerations about the accuracy in the zero position detection.