Probabilistic fatigue life of balsa cored sandwich composites subjected to transverse shear

Abstract

A probabilistic fatigue life model for end-grain balsa cored sandwich composites subjected to transverse shear is proposed. The model is calibrated to measured three-point bending constant-amplitude fatigue test data using the maximum likelihood method. Some possible applications of the probabilistic model are obtaining characteristic S–N curves corresponding to a given survival probability, and calibrating partial safety factors for material fatigue. The latter is demonstrated by a calibration performed using reliability analysis with the first-order reliability method. The measured variance in balsa shear properties, for both static strength and fatigue failure, is higher than the variance normally observed in the properties for fiber-reinforced polymer composite laminates. This could be attributed to the fact that end-grain balsa wood is the product of a naturally occurring growth process, which cannot be controlled to the same extent as an industrial manufacturing processes. The large variance in the probabilistic model for fatigue life is reflected in the corresponding calibrated partial safety factors, which are higher than the factors usually associated with synthetic materials such as fiber-reinforced laminates.