Observation of Bending Fatigue Testing of Metal Plate at Ultrasonic Frequency

Introduction

Fatigue failure refers to the fracture of a component due to repeated load cycles, which can occur using a force much smaller than the static fracture strength. Also, because fatigue-related failure occurs suddenly, there are cases where this has led to serious accidents involving ships and aircraft. Therefore, knowledge of the fatigue properties of materials used in products is very important. However, determination of fatigue characteristics typically requires time-consuming testing using 107 repetitions (as per JIS Z2273, General Rules for Fatigue Testing of Metals), which at 10 Hz, takes about 12 days to complete. Also, due to enhancements in equipment efficiency and speed, there are now requests for fatigue evaluation with more than 107 repetitions. In response to this, an ultrasonic testing machine capable of 20 kHz ultrasonic fatigue testing is now in use. However, due to the very rapid vibration that is generated during measurement with this instrument, visual confirmation of the movement and deformation of the specimen is not possible. Therefore, a high-speed video camera was used to observe the movement of a metal plate vibrating while conducting a 20 kHz bending fatigue test. Previously, gaining an understanding of the overall movement of the test specimen required incremental repositioning of a displacement gauge, but with the high-speed video camera, it is possible to evaluate the movement of the specimen in a single observation process. Further, the possibility of determining the amount of movement of the specimen from captured images was also demonstrated.

August 26, 2015 GMT