Effects of notch length, specimen thickness, ply thickness and type of defect on the fracture behaviour of angle-ply graphite-epoxy composites

Abstract

An experimental study was carried out on the effects of notch length, specimen thickness, ply thickness and type of defect (centre-notch or hole) on the fracture toughness of graphite-epoxy composites with lay-up sequences of 0/±45°/0 and 0/90°. Three fracture-mechanical concepts were applied: the Waddoups-Eisenmann-Kaminski (WEK) model, the Whitney-Nuismer model (point and average stress cirteria) and the KR-curve method. An increase of notch length as well as an increase of ply thickness led to a higher toughness, whereas a change in specimen thickness did not noticeably affect the toughness. Furthermore, the hole caused a smaller strength reduction than a notch. The applicability of the above-mentioned concepts is probably restricted mainly because of the fact that they do not, or do only insufficiently, regard the damage zone near the border of the defect, if a large damage zone usually leads to larger material parameters of the investigated concepts, namely the inherent flaw size, the characteristic lengths of the point and average stress criterions and the KR -value at fracture.