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.
Highlights
IntroductionA constant force amplitude is used in most tests: weights are suspended from the specimen to exert the bending moment
The basic principle of rotating-bending fatigue (RBF) tests is that a bending moment is exerted on a specimen at a critical location as the specimen is rotated about its longitudinal axis, resulting in a single fully reversed stress cycle for each rotation (R = −1)
Applied load the beginning test remained constantinthen continued to The decrease until theatspecimen failed of at each a certain remained constant decreased and continued to decrease until the specimen failed at a certain load
Summary
A constant force amplitude is used in most tests: weights are suspended from the specimen to exert the bending moment. In many instruments designed for such testing, the bending moment is applied as a constant deflection amplitude [1,6,7,8]. In both cases, the stress conditions during the fatigue test differ from the initial stress conditions due to cyclic changes in the specimen such as softening, hardening, or cracking. An increase in the ultimate strength after cyclic loading prior to crack nucleation is reported in [9]
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