Compressive response of notched glass-fiber epoxy/honeycomb sandwich panels

The quasi-static uniaxial compressive response of E-glass/epoxy-Nomex (TM) sandwich panels containing circular through-holes was studied experimentall y. Specimens with four and eight-harness satin weave fabric face-sheets wer e tested. In both materials the principal failure mechanism consisted of li near damage zones (LDZs) emanating from the hole edge. LDZs are macroscopic ally similar to fiber-bridged cracks in tension, and propagated in a stable manner. Cross-sectioning indicated that the LDZ wake was characterized by fiber-kinking in all warp tows, and weft tow cracking. Strain gauges were u sed to measure local deformation as the LDZ propagated across the width of the specimen; a strain-softening behavior was observed in the LDZ wake. A d amage zone model (DZM) was applied in order to determine its validity and m echanistic basis. This was assessed by examining its ability to predict thr ee experimentally observed phenomena: the notched strength, local strain di stribution, and LDZ growth characteristics. Two models were created in orde r to interrogate the DZM. The damage growth model was used to determine the ability of the DZM to predict the LDZ growth behavior and notched strength . A finite element model was implemented to predict the local strain distri bution. In both cases discrete nonlinear springs acting in the wake of an e quivalent crack were used to model the LDZ. This approach provided a good c orrelation with whichever set of measurements was used to calibrate it. Ext ension of the model to the other phenomena resulted in weaker correlations with the data, suggesting that further work is required to develop a true m echanism-based model. (C) 2001 Elsevier Science Ltd. All rights reserved.