Longitudinal Splitting in Epoxy and K-Polymer Composites: Shear Lag Analysis Including the Effect of Fiber Bridging

Abstract

The shear-lag model has previously been used to derive a fracture mechanics analysis of longitudinal splitting in finite-width double edge notched unidirectional composites (J. Comp. Mat., 22:561, 589 [1988]). In this paper we extend that analysis to account for the effect of fibers bridging across the longitudinal split. The new analysis has been used to measure the longitudinal splitting fracture toughness, G_lc, of composites of Hercules AS4/3501–6 and Avimid* K-polymer/Magnamite® IM-6 graphite. The effect of resin toughness was further investigated using laminates from a series of experimental resins based on the K-polymer chemistry. The 3501–6 epoxy laminates have a G_lc of 196 J/m1 and the Avimid® Klaminates have a G_lc of 414 J/m². The G_lc for the K-polymer based laminates was independent of laminate thickness but depended on the neat matrix toughness and on the processing conditions. The inclusion of fiber bridging in the fracture analysis has a significant effect on the reported fracture toughnesses. We claim that these new results give the correct fracture toughness and that previous results that ignored fiber bridging over estimated the laminate toughness.

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