Evaluation of Fatigue Properties of Steel Bar by Smart Stress-memory Patch

Abstract

A fatigue sensor called “smart stress-memory patch” has been presented to evaluate the fatigue damage of infrastructures as bridges and ship. In this study, the smart stress-memory patch was applied to the steel bar to estimate the stress amplitude and the cyclic number. Firstly, the fatigue test of the steel bar with attached sensor was carried out and the fatigue crack growth behavior of the sensor was investigated. Secondly, the stress distribution of the sensor was calculated by using the finite element method to evaluate a complex strain transfer from the steel bar. Finally, the possibility of measurement for the stress amplitude and the cyclic number by using smart patch was evaluated. The fatigue crack growth rate of the attached sensor was decreasing with the crack growth. Especially when the stress amplitude was large, the crack growth rate decreased dramatically with the crack growth. The analysis of stress distribution shows that the size of plastic zone around crack tip decreases with the crack length and the load subjected to the sensor is similar to that of the uniform displacement testing. In addition, the modified stress intensity factor based on the uniform displacement testing is proposed to correct the shape effect of the attached sensor on crack growth behavior. Appling the modified stress intensity factor to the principle of smart patch, it was demonstrated that the stress amplitude and the cyclic number of the steel bar could be estimated from the crack lengths of two sensors.