Crack initiation studies using a speckle technique

Abstract

This paper presents a laser-based method for fatigue crack detection. The proposed parameter, integrated peak spectral intensity coefficient Hi, which can be rapidly computed using a personal computer, shows a drastic change when a 0.1 mm crack appears. A definition for fatigue crack initiation based on the intersection of two straight lines on the Hi versus fatigue cycle plot is also proposed. Using this method, surface crack initiation can be detected at a crack length of less than 0.1 mm, within a circle of 1.0 mm diameter near a notch root. Tension-tension fatigue tests are conducted on 2024-T351 aluminum alloy notched specimens and the results are compared with a mechanical model. © 1994.