転がリ軸受用鋼のせん断疲労特性を迅速評価するための超音波ねじリ疲労試験機の開発

摘要

In rolling bearings, subsurface flaking failures occur under pure rolling contact fatigue conditions. In such failures, one of the crack initiation factors is believed to be the results of repetitive orthogonal shear stresses. Accordingly, we have deemed that it is of critical importance to evaluate the shear fatigue properties, which can be obtained by torsional fatigue testing. However, up until now, it has been all but impossible to establish the shear fatigue properties of giga-cycle regimes because of conventional low loading frequency torsional fatigue testers. This is due primarily to time constraints. Ultrasonic fatigue axial loading testing has been employed for rapid evaluation of tension-compression fatigue properties. We have developed an ultrasonic torsional fatigue tester which enables for the rapid evaluation of shear fatigue properties. A loading frequency of 20,000 Hz is quite high, and as such results in a radical reduction of testing duration. It is possible to produce maximum shear stress amplitudes of about 950 MPa at the surface of specimen's minimum diameter. This is sufficient for the evaluation of high strength rolling bearing steels over wide ranges of loading cycles.%転がり軸受の内部起点型はく離に先立つ初期き裂の発生とその初期進展を支配する応力の一つとして，表層に繰返し作用する交番せん断応力（ほぼ両振り）が挙げられる.そのため，転がり軸受の内部起点型はく離による寿命を把握する上で,せん断疲労特性を評価すること重要である.