Correlation between crack length and load drop for low-cycle fatigue crack growth in Ti-6242

Abstract

a b s t r a c tFor low-cycle fatigue tests with smooth bars the number of cycles to initiation is commonly defined from a measured relative drop in maximum load. This criterion cannot be directly related to the crack length, which is the actual measure of interest. In order to establish a relation between load drop and crack length for the high strength titanium alloy Ti-6242, this investigation compares data from controlled low-cycle fatigue crack growth tests and numerical simulations of these tests. To achieve sufficient accuracy in this relation, focus is given to modelling of mean stress relaxation. Three constitutive models, the Chaboche, the Ohno-Wang and the Chaboche with threshold, are evaluated with respect to experiments. Furthermore, a straightforward method with cycle-scaling of the material parameters are used to efficiently reduce calculation cost. It is shown that it is possible to determine the relationship between load drop and crack length from numerical simulations, provided that care is taken to relevant aspects of the materials stress-strain response. These results are also used to numerically evaluate the effect on load drop of the extensometer position relative to the crack.

Microstructure-based fatigue life model of metallic alloys with bilinear Coffin-Manson behavior

“…An estimation of the number of cycles to crack initiation is also included in Fig.1(b) together with the number of cycles to failure. Crack initiation was assumed when the maximum load during cyclic loading dropped by 5%, as suggested in many studies [25,21]. From this estimation of the number of cycles for crack initiation, it can be concluded that the fatigue life was controlled by crack nucleation in the whole range of cyclic strain ranges covered in the experimental campaign.…”

Fatigue life prediction of additively manufactured ductile nickel-based superalloys : Constitutive and crack initiation modelling

“…[69,70]. Another method has also been proposed, where the material parameters are calibrated based on a scaled amount of cycles, where only this number of cycles needs to be simulated, see [71]. Another approach is the discrete change of parameters, where the parameters are changed from a virgin state to parameters representing the preferred cycle, e.g.…”

Modeling of kinematic hardening at large biaxial deformations in pearlitic rail steel

“…This model has been shown to work well for uniaxial ratcheting (see e.g. Ohno and Wang, 1993b;Brommesson et al, 2015 ). Formulating the second Ohno-Wang model in terms of the Mandel stress, we extend the model to finite strains:…”