Notched strength analysis of tensile specimens taken from a thick, filament-wound graphite/epoxy pressure vessel

An experimental analysis of specimens taken from a thick, filament-wound composite material pressure vessel (cylinder) was performed by testing tensile coupons with various semi-elliptical surface notches. The strength of specimens with small notches was found to be notch insensitive. The strength of specimens with larger notches depended on the size of the notch.

The fracture toughness of the laminate was found by applying a general fracture-toughness parameter approach. Using this value, several approaches were employed to predict failure loads. The accuracy of the approaches depended on the size of the notches. In general, the linear-elastic fracture mechanics method overpredicted the failure strength of specimens with intermediate sized notches, but predicted failure strength accurately for specimens with large notches. A strength of materials approach accurately predicted notched strength only for specimens with small notches. Notched strength was more accurately predicted for all notch sizes using an empirical approach, with the notch area used to predict failure instead of the notch depth, which was used in the linear-elastic fracture mechanics and strength of materials approaches.