Life Prediction of Composite Pressure Vessels

Stress-rupture life is a significant design issue for fiber reinforced composite pressure vessels subjected to long term pressurization. The considerable scatter in stress-rupture life exhibited by fiber reinforced composites, coupled with the lack of reliable life prediction methods, have led to the requirement for low operating pressures in relation to the design burst pressure. This leads to overly conservative designs and limited service life. Without a more reliable methodology for predicting stress-rupture life and proven accelerated test methods, a large number of tests over long periods of time are required. An improved approach for predicting the stress-rupture life of composite pressure vessels, based on actual fiber stress history, is needed. Under the proposed Phase II SBIR program, an improved methodology for predicting the stress-rupture life of filament wound composite pressure vessels based on actual fiber and matrix stress history is developed. The methodology includes an analytical model for predicting life based on the time-dependent behavior and failure mechanisms associated with fiber reinforced composites. The analytical model is supported by short-term and long-term testing of fiber properties, accelerated testing using time-temperature-stress superposition (TTSSP) as applied to dynamic mechanical analysis (DMA), and stress-rupture testing of composite pressure vessels.