Damage accumulation under multiaxial fatigue loading (original) (raw)

Modeling Damage, Fatigue and Failure of Composite Materials, 2016

Abstract

Abstract In this chapter, the fatigue behavior of composite laminates under multiaxial loading is analyzed and discussed. In the scientific literature it is widely shown that the multiaxial stress state as well as the load ratio (minimum to maximum load) are strong factors in determining the cycles spent for the final failure of laminates. Fewer studies report that also damage evolution, consisting of the initiation and propagation of multiple off-axis cracks, depends on the degree of multiaxiality. Understanding and predicting these phenomena, which are governed by matrix and interface properties, is of fundamental importance, mainly for a stiffness-based fatigue design. With the aim to provide a deeper insight into this area an extensive experimental study was carried out by the present authors using glass–epoxy tubular samples under combined tension and torsion. It was found that the life to crack initiation, the crack propagation rate, and the damage mechanisms at the microscopic scale are strongly dependent on the value of the shear stress relative to the transverse stress. In addition, the influence of the load ratio was investigated for three different multiaxial conditions. Finally, it will be shown that the characterization of multiaxial fatigue behavior, in terms of crack initiation and propagation, can be suitably conducted by means of properly designed flat laminates under uniaxial loading, exploiting the local multiaxial stress state arising from the material anisotropy.

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