Life Prediction of Composite Pressure Vessels

Stress-rupture is a significant design issue for 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 predictionmethods, has led to the requirement for low operating pressures in relation to the design burst pressure, resulting in overly conservative designs and/or limited service life. An improved methodology for predicting the stress-rupture life of compositepressure vessels, based on actual fiber and matrix stress history, is proposed. The methodology includes: (1) an analytical model for predicting the time-dependent behavior of viscoelastic polymer matrix composites; (2) accelerated testing using atime-temperature-stress superposition (TTSSP) principle; (3) statistical analysis to address data scatter and allow extrapolation of the model and test data; and (4) acoustic emission (AE) monitoring to provide a possible NDE tool for extending the life ofexisting pressure vessels and an improved understanding of the effect of damage. The focus of the proposed Phase I research will be on the analytical model development and feasibility demonstration. Dynamic mechanical analysis (DMA) and limitedstress-rupture testing and AE monitoring of pressure vessels are also proposed to provide a preliminary assessment of the merits of the proposed approach. The proposed research has significant potential benefits for both military and commercialapplications.The development and validation of an improved methodology and accelerated test procedure would result in reduced costs, extended service life and improved (i.e., lighter weight) pressure vessel designs for defense, aerospace, aircraft, marine and numerouscommercial applications (e.g., spacecraft propellant tanks, natural gas vehicle tanks, compressed gas tanks for breathing apparatus, inflation systems on aircraft).