Experimental Verification of Spline Stress Analysis Method for a Structural Composite Laminate Containing a Hole

Abstract

Moire interferometry surface strain measurements for a uniaxially loaded composite laminate with an open hole were compared to predictions from threedimensional spline variational theory, from two-dimensional finite element analysis, and from two-dimensional elasticity theory. Strain measurements and a progressive damage investigation were accomplished using twenty-eight ply fiber dominated, IM7/5250-4, laminates. At low load levels, prior to matrix cracking, phase shifting moire interferometry was used to measure in-plane displacements. Experimental surface strains were calculated based on digital analysis of the displacement fields. Direct comparisons between theory and experiment were made using contour plots of ex,, Eyy, and yxy. For all in-plane surface strains, the spline variational theory results showed good agreement with experiment in close proximity to the hole. A separate group of specimens were loaded incrementally until failure, and the initiation and progression of damage was documented using x-ray images. Regions where the stress exceeded the ultimate transverse strength are compared to the actual damage images using contour plotting schemes. Overall, the location of initial failure as predicted by the spline variational theory corresponded well with damage observations for early stages of damage.