Executive Summary : | The current research work is aimed at developing fatigue life calculation methodology and computational tool suite for composite laminates and structures under multi-axial variable amplitude loads. Attributed to the classical laminate theory (CLT) combined with cumbersome calculation procedure, historically, the fatigue life of composite laminates and structures is mainly estimated under in-plane loads. However, as the size of the composite structures is increasing such as large scale off-shore and on-shore wind turbine rotor blades, the out-of-plane fatigue loads are becoming more important for design considerations. Hence, the following three goals are set for the current research work: i) the primary objective is to estimate the fatigue life of composite structures under combined effects of in-plane and out-of-plane variable amplitude fatigue loads; ii) the second objective is to estimate the fatigue run-out stress/strain limits for composite laminates under multi-axial in-plane stress state; iii) the final objective of the current research work is to develop a combined analytical and numerical (plug-in) tool suite for estimating the life of composite laminates and structures under variable amplitude fatigue loads. In order to achieve the above mentioned objectives, initially, the selected composite laminate with specific stacking sequence will be subjected to experimental quasi-static tension, compression and in-plane shear loads using the Acoustic Emission (AE) as a damage monitoring technique. With the aforementioned test procedure, precise static damage initiation threshold such as the fiber/matrix interface crack initiation stress levels can be obtained. Later, experimental testing will be extended to Tension-Tension (T-T), Tension-Compression (T-C), and Compression-Compression (C-C) fatigue loads at a specific load ratio’s (R-values of 0.1, -1 and 10) in the fiber, transverse and off-axis directions. |