Tool for Analysis to Predict Strength and Durability of Curved and Tapered Composite Structures under Multiaxial Loading

The Navy currently has a need to accurately measure the durability of rotorcraft flexbeams since testing on the flexbeam shows actual life well below required service life and what was analytically predicted. However, existing analysis tools cannot accurately resolve the out-of-plane shear stresses necessary to predict delamination and inadequate to represent complicated composite structures with hundreds of plies and curved and tapered geometry. The objective of the proposed effort is to develop an analysis tool to predict the strength and fatigue life of curved and tapered composite rotorcraft flexbeams with emphasis on accurately modeling transverse shear and ply drop-offs. TDA’s approach is consist of: 1) develop a simplified FE modeling approach for accurate determination of interlaminar stresses with fewer number of elements, 2) develop an analysis tool to predict delamination of the tapered composite structure with multiaxial failure model for crack initiation and two-parameter fracture mechanics model for crack propagation, 3) extend two-parameter fracture mechanics model to fatigue crack growth which can reliably predict fatigue life. To provide an easy-to-use analysis tool with computational efficiency, conventional FE method will be utilized with combination of some simplified and innovative ideas without using advanced FE methods nor microscale approach.