Continuous Estimation of the Crack Growth Rate during Rotating‒Bending Fatigue Testing

Abstract

A method for estimating the crack growth rate in steel during rotating‒bending fatigue testing is presented. Constant deflection tests were conducted in which the initial load remained constant prior to crack nucleation, when it decreased as the crack grew. In the proposed approach, steel samples were sharp-notched to produce a characteristic circular fracture upon loading and the final fracture area was correlated with a ratio of the load prior to fracture and the initial load. In this method, the deflection imposed is a function of a material’s elastic modulus rather than its yield strength and the correlation obtained to estimate the average crack length as a function of the instantaneous load is independent of the applied stress or steel grade.

Study of the Rotary Bending Fatigue Resistance of 30MnB5, 41CrS4 and 30MnVS6 Steels

“…In this way, the specimen, at a given moment, has an induced tensile stress on the upper surface, while the lower surface is subjected to compression (Figure 2). This situation is reversed when the specimen is rotated, establishing a complete cycle in each rotation [35,36]. Under these alternating stress conditions, the load ratio is R = −1.…”

Influence of Boron Additions and Heat Treatments on the Fatigue Resistance of CoCrMo Alloys

“…Fatigue samples were machined at the dimensions required for evaluation in the rotating bending fatigue equipment described in a previous work [23]. The loading was applied by constant deflection, implying that the load decreased as the crack grew.…”