Design of End Casting for Thin Composite Stiffened Panels Subjected to Axial Compression Load

Abstract

Compression testing of large, thin, stiffened composite panels is complex due to the susceptibility of such panels to premature buckling and failure. Such failures are due to the artefacts of testing, such as, offset at load introduction edges, non-uniform distribution of loads, nature of lateral supports, crushing of panel edges etc. In this paper, a novel approach for compression loading of thin stiffened composite panels is proposed and validated from finite element analysis supported by tests. Compression loading of such panels (less than 2mm thick) is challenging since the edges are susceptible to local crushing. To avoid this, loading edges of the panel were encased in mild steel casing blocks filled with finely grounded aluminium powder mixed with epoxy resin. Coupon level tests were conducted to measure mechanical properties of the interface between composite and casting mixture. Digital Image Correlation (DIC) technique was used in these tests to measure the full field strains and to validate numerical simulations. Further, finite element analysis of the actual composite test panel with end casting mixture was performed which indicated that interface shear stresses and compression stresses at maximum expected load are much lower than allowables obtained from specimen tests. Hence, the Aluminium-Epoxy cast mixture proposed in this study can be used safely to cast edges of large stiffened panels for axial compression tests.