Structural Integrity Assessment of Filament-Wound Components

This paper summarizes the results of a structural integrity assessment of filament-wound glass-epoxy cylinders and rocket motor cases under conditions of dynamic fracture due to internal pressure loadings of the order of 10-ms duration. Experiments were completed on four types of fiber glass configurations; straight cylinders of various angle ply orientations, tapered cylinders, and two bonded rocket motor case designs were evaluated. A brief review is provided of techniques to assess failure rates, and these elementary reliability techniques are used to establish the relative effects of variability in design pressure and burst pressure capacity. Type II and Type III extreme value and normal distributions are utilized. Polynominal approximations for normal distribution and graphical estimates as well as a transform method are used effectively in determining failure rates for nonnormal functional representation. Furthermore, the merit of several different design concepts, as well as the reliability growth achieved with improved manufacturing techniques, is quantified in terms of the estimated probability of component failure. Failure rates are shown to be more sensitive to design pressure variations than the conventional safety-factor approach. Finally, while the reliability methodology described in the paper is sufficient for preliminary design purposes, failure mode assessment via posttest examination and high-speed photographic observations suggests the necessity for further improvements in composite analysis procedures.