Damage Monitoring of Metal Materials by Laser Speckle Assisted by Image Processing Techniques. 3rd Report, Fatigue Monitoring of Steel.

Abstract

In this paper, we present a method for monitoring fatigue damage of steel specimens with no contact using the laser speckle method. This method is based on the phenomenon whereby the intensity distribution of the laser speckle changes depending on surface profile change invoked by fatigue damage. Analysis of the laser speckle distribution can be made quantitatively using an image processing system. Distribution of the speckle intensity was observed under cyclic tensile load with a constant stress amplitude. Surface roughness and surface profile were also investigated during the experiment. Intensity distribution of the laser speckle was found to be related to frequency distribution of the surface profile. This is the same as in the case of the static tensile test reported in the previous paper. The results showed that distribution of the laser speckle changes with the number of loading cycles. It was found that there is a possibility of estimating fatigue damage by observing the distribution of laser speckle intensity.