Evaluation of fatigue crack growth and repair effect of steel bridge members by infrared stress measurement

Abstract

In order to maintain the safety of infrastructures such as steel bridges, it is important to detect fatigue cracks by nondestructive evaluation, to evaluate crack propagation rate, and to verify the effectiveness of crack repair.One of the effective non-destructive evaluation methods for these purposes is thermoelastic stress measurement by infrared thermography.In this method, stress distribution is measured based on the temperature fluctuation due to the thermoelastic effect. It enables us to conduct remote nondestructive and noncontact measurement of stress distribution.In this study, a plate bending fatigue test was carried out using specimens simulating steel members with fatigue cracks in actual bridges. The relationship between crack propagation rate and stress intensity factor range were obtained from measured stress data. It is found that obtained relation agrees well with the Paris law. Based on the experimental result, the reduction of crack propagation rate by the repair works in the actual bridge is estimated.