Development of a small-punch-fatigue test method to evaluate fatigue strength and fatigue crack propagation

Herein, fatigue and crack propagation tests were conducted using the small-punch-fatigue (SPF) test to verify its applicability to assess fatigue strength and fatigue crack propagation behavior. During the SPF test, a fatigue crack first initiated at the specimen center and then propagated in the radial direction. In most cases, three fatigue cracks propagated from the specimen center to the radial direction in point symmetry. X-ray computed tomography revealed that the crack initiated by the SPF test had a quarter ellipse shape. Elastic finite element (FE) analysis was conducted to estimate the stress state and stress intensity factor (SIF) of the specimen, and an approximate equation was obtained as a function of the applied load. The experimental results comprising fatigue lives and crack growth rates obtained the SPF test were compared with the conventional uniaxial test data as functions of the stress amplitude and SIF determined elastic FE analysis, respectively. This comparison showed that the SPF test can be applied to the fatigue test and fatigue crack propagation test.