End Notched Flexure (ENF) specimen containing a teflon insert (0.05mm) at one end is used to measure interlaminar shear fracture toughness of unidirectional graphite/epoxy composite laminate. The loading condition is three point bending which produces bending-induced shear deformation at notch tip. Linear beam theory included shear deformation is applied to calculate the toughness. In order to verify indirectly validity of the data reduction for the toughness, theoretical compliance is compared with experimental compliance.
In this study the effect of notch tip and span length(2L) of beam on the toughness is investigated in the range of normalized crack length(a/L) 0.4-0.7. Test results show that $G_{II}c$ of specimen having pre-crack at the notch tip is smaller than that of specimen without pre-crack, $G_{II}c$measured on 100mm span beam is generally larger than one with 70mm.