Abstract
The paper discusses the lifetime prediction of structures in high-cycle fatigue based on the two-scale fatigue criteria of Dang Van type and several of its extensions in finite lifetime regime. The main assumptions for this criteria are (i) the material is polycrystalline and undergoes localised plasticity in one of the misoriented grains and (ii) crack initiation arises as a consequence of cumulated plasticity in this grain.The novelty of the presented approach is twofold. On the one hand a generalisation of mesoscopic plasticity model is presented, on the other a fast time scale average is introduced for tracking the cyclic material behaviour and the subsequent evolution of damage. The tracking method is based on the split between a quick quasi-periodic response of the system to the cyclic load and a slow evolution of the internal hardening and damage parameters of the material at the mesoscopic scale. The proposed method can be extended to a large class of local material behaviours involving not only plasticity, but also crack and damage evolution.The paper proposes a simplified plasticity-based model for the mesoscopic material behaviour and presents a comparison between predicted and experimental lifetimes. The results are discussed in terms of prediction capabilities and also in terms of the identification procedure of parameters of the mesoscopic model.
Highlights
A series of fatigue prediction models for the cyclic behaviour of structures is based on multiscale analysis
This paper addresses the question of finite lifetime in the high cycle fatigue (HCF) regime for metallic polycristalline materials
Within HCF, it is common to assume that the structure is in elastic shakedown at the macroscospic scale but undergoes elastic or plastic shakedown at the mesoscale for infinite or finite lifetime respectively
Summary
A series of fatigue prediction models for the cyclic behaviour of structures is based on multiscale analysis. DT 0 amplitude of the macroscopic resolved shear stress on sy the critical plane for limit loading saxy amplitude of the mesoscopic resolved shear stress fatigue limit under fully reversed torsion mesoscopic strain mesoscopic plastic strain deviatoric part of the mesoscopic plastic strain cumulated mesoscopic plastic strain cumulated plastic mesostrain mesoscopic shear plastic strain macroscopic Lamè parameters macroscopic stress mesoscopic stress mean normal stress in the x direction amplitude of the normal stress in the x direction mesoscopic resolved shear stress shear yield limit of a crystal amplitude of xy shear component of stress tensor material behaviour and the subsequent evolution of damage This separation of time scales is justified by the great number of cycles usually considered in HCF experiments (104–107 cycles). An appendix completes the presentation with an extended computation of the lifetime using the saddle-node ghost estimates
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