Fracture and Reliability of Filament-Wound Chambers

A comprehensive literature survey showed that the reliability of a filament-wound chamber depends on four primary factors: Materials, environment, fabrication, and time. A detailed investigation was made of the material factor which has as chief parameters the glass filament, the matrix resin, and the resin-glass bond. It was concluded that motor reliability increases as the resin shear modulus and ductility increases, and as the lower fiber strengths increase. Also, the Poisson's ratio of the glass fiber and resin should be kept as small as feasible for any particular Young's modulus and should be compatible to reduce the resin strain concentrations. An analytical study of the influence of the material parameters on chamber reliability was also conducted. The resin was treated as a bilinear elastic material and the fibers were assumed to possess a modified Weibull flaw distribution. The reliability load was calculated for the cases of bonded and unbonded resin. The predicted bonded reliability was substantially higher than the predicted unbonded reliability. The difference between the two cases (15% to 47%) depended on the distribution of ultimate fiber strengths within the element. Hence, achievement of this increase in reliability requires a resin-curative system that will prevent debonding.