The effect of circular delaminations on the buckling and postbuckling behaviour of glare laminates under compression

A series of Glare 4B specimens with and without artificial circular delaminations to represent manufacturing defects or damage after impact (bird strike, tool drop) were tested under compression to examine their buckling and postbuckling behaviour and hence the effect of such defects on performance. Tests were monitored using Digital Image Correlation (DIC) for visualisation of full-field displacements whilst Acoustic Emission (AE) monitoring enabled the detection and location of damage propagation. Results for specimens incorporating delaminations inserted in the first Aluminium/GFRP interface and pristine specimens are presented here. Tests have been modelled using a bi-linear cohesive zone model (CZM) implemented in ABAQUS/Explicit to perform dynamic nonlinear analyses incorporating load eccentricity and geometrical initial imperfection. Good correlation is observed between test results and model predictions. Introduction FML’s including Glare are manufactured from alternating metallic sheets and fibre reinforced composite layers. Glare offers a 10% reduction in specific weight compared with aluminium and has advantages over CFRP’s including improved impact, fire and corrosion resistance; and increased damage tolerance leading to its increased commercial use, with applications including the A380 fuselage, the ECOS3 blast-resistant Unit Load Device (a freight container designed to contain explosion and fire), the Learjet 45, the cargo floors of the Boeing 737, and the cargo doors of the latest models of the C-17 Globemaster III [1, 2]. Despite its advantages however, the use of Glare brings additional challenges in terms of understanding damage mechanisms. This paper examines the effects of potential damage arising from the manufacturing process or impact, specifically from artificial circular delaminations.