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.

Effect of Specimen Shape on Fatigue Behavior in Thin Pure Copper Sheet for Smart Stress-memory Patch

“…[6][7][8][9][10][11] Sensor in smart patch consists of a thin metal sheet with a pre-crack, and number of fatigue cycles and stress amplitude on structure can be estimated from fatigue crack growth in the sensor. Since the accumulation of the fatigue damage is memorized in the sensor itself, it requires no power supply, wiring, continuous monitoring or high-speed communication.…”

“…However, the measurement range of stress amplitude is limited from 100 MPa to 200 MPa when the smart patch is attached to steel materials. 8) To apply various stress conditions, the measurement range of stress should be further extended.…”

Fatigue Crack Length Measurement of Sputtered Metal Film for RFID-based Smart Stress Memory Patch

“…Our proposed sensor called smart stress memory patch (hereinafter called "smart patch") which consists of a thin copper specimen with a pre-crack can estimate fatigue damage parameters such as number of cycles, stress amplitude, and maximum stress of structures. [17][18][19][20][21] The stress amplitude and the cyclic numbers can be estimated from the fatigue crack growth of smart patch fixed on the structure, and maximum stress can be obtained by the AE onset stress. Since this smart patch needs neither the continuous power supply nor wiring, it is potentially applicable to RFID sensor network.…”

Effects of Fabrication Method, Shape, Strain and Temperature on Conductive Properties of Smart Stress-Memory Patch

“…First, a typical rectangle shape was set as Shape 0, which is similar to an previous study. 6) Then, the area near the crack was enlarged to increase influence of crack development (Shape 1). Furthermore, the path around the crack tip was narrowed in attend to control the route of the electric current (Shape 2).…”