Abstract
Abstract A 2-D cohesive micromechanic fatigue model is proposed. The material is represented by uniaxial elements equally spread in all directions and having a statistical strength distribution. The model is based on two simple microscale assumptions: (a) an interference between a broken element and its vicinity exists, such that the neighbor element may lose some of its strength for the rest of the material's life, and (b) the material microstructure leads to a specific probability function for the neighbor direction. These microscale concepts inherently lead to the basic fatigue behaviors seen from experiments: the s-N power law and the endurance limit. Further properties of the model that are analyzed and discussed are: (a) an inherent directional damage evolution (loading dependent anisotropy), (b) fatigue failure envelopes for biaxial loading, (c) the appearance of cracks parallel to the loading direction under uniaxial compression, and (d) the effect of initial damage on fatigue life. By representing folded macromolecules in polymers as bundles of parallel elements, a relation between the directional probability parameter (and therefore, the macro fatigue response) and the molecular weight is found and discussed.
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