A New Fatigue Testing Machine for Investigating the Behavior of Small Shear-Mode Fatigue Cracks

The investigation of the behavior of small shear-mode fatigue cracks in the high-cycle fatigue regime is essential to understand the mechanism of rolling-contact fatigue failures, such as flaking in bearings and shelling in rails, from the fracture mechanics point of view. The stable growth of a shear-mode fatigue crack was achieved by applying static compression to a specimen in a cyclic torsion fatigue test. This loading condition is usually obtained by a combined tension-torsion testing machine with a servo-hydraulic control system. In this study, a new testing machine was developed and found to be superior to the servo-hydraulic testing machine in terms of price, operation/maintenance costs, operating speed, and installation volume. For substantiation and demonstration purposes, a shear-mode fatigue crack growth test with a bearing steel was also carried out using both the new and the conventional servo-hydraulic testing machines. The experiments revealed that under the same loading conditions, nonpropagating shear-mode cracks of similar size and geometry could be obtained by the respective testing machines. Thus, it was concluded that the new testing machine has equivalent capabilities to the servo-hydraulic testing machine in performing shear-mode fatigue crack growth tests.