Abstract
AbstractThe continuous-time, high-cycle fatigue model of Ottosen et al. (2008) is modified by introducing a quadratic, instead of linear, endurance surface. This quadratic endurance surface induces an elliptical Haigh diagram, consistent with experimental fatigue data for ductile materials. With this modification we fit the model to uniaxial fatigue data, and predict the fatigue behavior for nonproportional, biaxial stress for AA7075-T6 in fully reversed shear with a superimposed, static tension/compression. However, the fatigue life is sometimes overestimated for a combination out-of-phase shear and tensile stress fluctuations.
Highlights
Fatigue failure is the result of a long process of mechanical deterioration due to a fluctuating stress during the life-time of the product
Ottosen et al [4] formulated a continuous-time fatigue (CTF) model, known as the continuum damage approach, for isotropic materials. This model is based on an endurance surface that depends on the first stress invariant and on the von Mises effective stress reduced by a backstress
We fit the CTF model to fatigue data from uniaxial experiments of AA7075-T6, and investigate the predictive capability of the model for this material subjected to nonproportional stress
Summary
Fatigue failure is the result of a long process of mechanical deterioration due to a fluctuating stress during the life-time of the product. Ottosen et al [4] formulated a CTF model, known as the continuum damage approach, for isotropic materials This model is based on an endurance surface that depends on the first stress invariant and on the von Mises effective stress reduced by a backstress. Brighenti et al [17] suggested a more elaborate variant of the endurance surface depending on several stress invariants modified by a backstress It was not possible, to use the model parameters fit for proportional stress data to predict the fatigue behavior for nonproportional stress [17]. The intention is to extend the range of faithful extrapolation across the HCF regime With this nonlinear formulation, we no longer find an analytical solution to the fatigue life for cyclic, proportional stress, as is the case for the preceding linear model [9]. The model, when fit only to uniaxial fatigue data of AA7075-T6, exhibits fair agreement with biaxial as well as nonproportional fatigue data
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