An Analysis of Curvature and Layup Effects on Delamination in Notched Composite Beams

Two-dimensional finite element modeling has been used to determine strain energy release rates for delamination cracks in straight and curved notched tensile beams. The notched tensile beam (NTB) is a low-order analog of a cylindrical pressure vessel with an external part-through hole. The material was an S-glass/epoxy fiber rein forced composite material. Specimens were 8 plies thick with notches 2 and 4 plies deep. Uni-directional [0°]8 and multi-directional [0°,0°, +77°, -77°]2 layups have been in vestigated. Strain energy release rates were calculated using the virtual crack closure tech nique. The finite element results reveal a mode II dominance similar to the cracked lap shear (CLS) specimen. The effect of curvature was to lower the strain energy release rates slightly (5-13%). Total strain energy release rates were generally higher for the multi- directional layup (by 1½ to 3 times), but the GII/G I ratio may increase or decrease depend ing on the notch depth and the orientation of the plies bounding the delamination.