Reliability Based Design of Composite Over-Wrapped Tanks

Filament wound composite over-wrapped tanks are considered for applications in solid rockets motor cases. An analytical procedure is developed, in form of a computer code (GENOA), to assess the durability and damage tolerance of pressurized tanks. The winding simulation calculates thickness and ply angle distributions and residual stresses resulting from the wrapping of the tanks. The durability evaluation predicts micro-crack formation, delamination initiation and progression, failure modes and burst (fracture) loads. Deterministic simulation resulted in burst pressures that are within 8.8% of the test. The pressurized tanks are also evaluated in presence of uncertainties in constituent stiffness and strength and manufacturing variables. Based on assumed scatter, the probability that the tank burst pressure lies within the test range is 27.5%. The sensitivity analysis indicated that fiber misalignment and ply thickness are the most influential variables that affect the burst pressure.