Novel Techniques for Investigating Shear of PMCs

Abstract

Composite materials continue to see increasing usage in a variety of industries due to their high strength to weight ratio. To incorporate composites in aerospace and marine applications, certification and damage tolerance assessment must be performed. Damage evolution, specifically under shear stresses, can be particularly challenging to predict. Shear failure in composite structures is difficult to characterize experimentally. Developing physics-based theories for computational modeling composites is crucial and must be substantiated with experimental evidence. Local tri-axial stress states must be considered for a valid shear experiment. For a near pure shear test, the hydrostatic pressure must be significantly less than the equivalent stress at the fracture location [1]. A novel technique to investigate the shear failure of PMCs, inspired by the isotropic butterfly notch specimen, is proposed. The novel technique uses uniaxial loading in compression or tension; however, a specific region of interest locally fails under shear load conditions. Several panels of IM7/977-3 with various stacking sequences were manufactured using traditional autoclave processing of prepreg. Specimens were fabricated using a waterjet. Tests were conducted in tension and compression while non-contact surface strain measurements were recorded utilizing digital image correlation (DIC). Post failure, specimens were characterized using micro computed X-ray tomography (μCT) to analyze the failure mechanisms. Additional work used discrete damage modeling techniques to simulate the load configurations help validate a newly implemented shear failure criteria. Additional comparisons to existing failure criterions, such as LARCO4, were made. While the geometry shows promise for assessing the shear performance of composite materials, further experimental characterization must be completed to fully vet this novel approach as a standardized shear test method.