The upper limit extension of loading frequency in the rotating bending fatigue test

Abstract

Fatigue property in gigacycle regime is focused as an important subject in recent years. In such a long-life region, a tremendous long period is required to perform the fatigue tests. In order to overcome this difficulty, special types of fatigue testing machines in rotating bending whose loading type is cantilever bending has been developed. It is known that this type of fatigue machine can be performed much quickly comparing with the tension and compression fatigue testing machines. And these experimental results are consistent with much data obtained by using traditional testing machines like tension and compression fatigue testing machines and the rotating bending fatigue test machines whose loading type is uniform bending named as Ono type, though it is unclear that much data of an ultrasonic fatigue testing machine are consistent with them. Although it prefers to perform the fatigue tests as fast as possible, but the maximum frequency of a rotating bending fatigue test are limited because of the possibility of temperature rise in specimen caused by the cyclic plastic work and the heat transfer from fatigue testing machine. Such local temperature rise might affect the fatigue property. However, the appropriate loading frequency limit is unclear because of the difficulty of the temperature measurement in the fracture portion of a specimen precisely during the rotating bending fatigue test. An in-situ temperature measuring technique is proposed to measure the temperature at the fracture portion of the specimen in real time during the fatigue testing, and the validity to determine the loading frequency of a rotating bending fatigue testing machine is discussed in this study.

Keywords

• maximum speed
• loading frequency
• rotating bending fatigue testing machine
• temperature measuring
• fracture portion
• specimen
• cantilever type
• heat generation