Vibration fatigue

About: Vibration fatigue is a research topic. Over the lifetime, 3460 publications have been published within this topic receiving 46297 citations.

Energy dissipation: the leading factor of fatigue

Abstract: By dynamic four point bending tests under controlled strain with a non-sinusoidal, composite signal it is shown that the fatigue life of asphalt beams is not only determined by the height of the strain amplitudes, but that the average energy, dissipated per load cycle describes the fatigue test much better. With the dissipated energy, a predictive model for the fatigue life had been composed, enabling calculation of the fatigue damages for, in principle, all types of load signals.

Finite element approach for modelling fatigue damage in fibre-reinforced composite materials

Abstract: Today, a lot of research is dedicated to the fatigue behaviour of fibre-reinforced composite materials, due to their increasing use in all sorts of applications. These materials have a quite good rating as regards to life time in fatigue, but the same does not apply to the number of cycles to initial damage nor to the evolution of damage. Composite materials are inhomogeneous and anisotropic, and their behaviour is more complicated than that of homogeneous and isotropic materials such as metals. A new finite element approach is proposed in order to deal with two conflicting demands: (i) due to the gradual stiffness degradation of a fibre-reinforced composite material under fatigue, stresses are continuously redistributed across the structure and as a consequence the simulation should follow the complete path of successive damage states; (ii) the finite element simulation should be fast and computationally efficient to meet the economic needs. The authors have adopted a cycle jump approach which allows to calculate a set of fatigue loading cycles at deliberately chosen intervals and to account for the effect of the fatigue loading cycles in between in an accurate manner. The finite element simulations are compared against the results of fatigue experiments on plain woven glass/epoxy specimens with a [#45°]8 stacking sequence.

The Modified Wöhler Curve Method applied along with the Theory of Critical Distances to estimate finite life of notched components subjected to complex multiaxial loading paths

Abstract: This paper is concerned with the use of the Modified Wohler Curve Method (MWCM) applied in conjunction with the Theory of Critical Distances (TCD) to estimate fatigue lifetime of mechanical components subjected to multiaxial cyclic loading and experiencing stress concentration phenomena. In more detail, our engineering approach takes as its starting point the idea that accurate estimates can be obtained by simply assuming that the value of the critical length, LM, to be used to evaluate fatigue damage in the medium–cycle multiaxial fatigue regime is a function of the number of cycles to failure, Nf. In other words, the MWCM, which is a bi-parametrical critical plane approach, is suggested here to be applied by directly post-processing the linear-elastic stress state damaging a material point whose distance from the notch tip increases as Nf decreases. According to the main feature of the TCD, the above LM versus Nf relationship is assumed to be a material property to be determined experimentally: such an hypothesis results in a great simplification of the fatigue assessment problem because, for a given material, the same critical length can be used to estimate fatigue damage independent of the considered geometrical feature. The accuracy of the devised approach was checked by analysing about 150 experimental results we generated by testing V-notched cylindrical samples made of a commercial cold-rolled low-carbon steel. The above specimens were tested under in-phase and out-of-phase combined tension and torsion, considering the damaging effect of superimposed static stresses as well. Moreover, in order to better check its accuracy in assessing notched components subjected to complex loading paths, our method was also applied to several data sets taken from the literature. This extensive validation exercise allowed us to prove that the MWCM applied along with the TCD is successful in estimating medium-cycle multiaxial fatigue damage (Nf values in the range 104–106), resulting in predictions falling within the widest scatter band between the two used to calibrate the method itself. Such a high accuracy level is very promising, especially in light of the fact that the proposed approach predicts multiaxial fatigue lifetime by post-processing the linear elastic stress fields in the fatigue process zone: this makes our method suitable for being used to assess real components by performing the stress analysis through simple linear-elastic FE models.