Failure Analysis of Composite C-Spars Under Inter-Laminar Tensile (ILT) Configurations: An Experimental & Numerical Evaluation

Abstract

In designing composite structures, it is fundamental to understand critical areas of structural deficiencies that lead to failures. One such critical design element is the failure caused by out-of-plane loads propagating through the bending of a composite laminate. In such cases, load offsets and element heights are generally the primary contributors to moments and forces leading to the degree of bending. In curved beams, these load conditions result in inter-laminar tension (ILT) type failures between plies, resulting in delamination and eventual failure. This work investigates such an ILT failure mechanism on composite C-Spars. The C-Spar specimen was constructed entirely of a quasi-isotropic [45/0/-45/90]4S layup and consisted of two 90-degree radii along with straight web sections defining the height of the element. To examine the contribution of the bending moment, resultant force, and rotation on the unfolding radii, varying loading arm configurations were investigated with a pinned load applicator. High-fidelity finite element (FE) analysis using B-Spline Analysis Method (BSAM), developed under the Air Force Research Laboratories (AFRL), was also utilized to predict failure of the C-Spars. The FE models showed good agreement with that of the experimental data and predicted failure loads within 10% on multiple configurations while also mimicking the geometric nonlinearity under larger deformation. Having successfully modeled the rotation and failure of the C-Spar configuration, this enables further investigation into the critical inter-laminar stresses induced within the design of such structures.