Prediction of Pressure Cycle Induced Microcrack Damage in Linerless Composite Tanks

摘要

Linerless composite tanks made from continuous carbon fiber reinforced polymers will enable significant mass and cost savings over lined, composite overwrapped tanks. The key technical challenge in developing these linerless tanks will be to choose and/or design the material to resist microcracks that may lead to leakage. Microcracks are known to form in the matrix of a composite due to mechanical stresses transverse to the reinforcing fiber direction. This paper presents an approach for characterizing the accumulation of microcracks in linerless composite tank materials under cyclic mechanical loading associated with multiple fill-and-drain pressure cycles. The model assumes that the rate of microcrack-damage accumulation is related to the microcracking fracture toughness of the material through a modified Paris-law formulation. A key artifact of this model is that microcrack-damage accumulation under cyclic load can be predicted from only two material constants. This damage accumulation model is validated through a series of coupon tests, and an illustrative example is presented to demonstrate how the model can be used to predict the microcracking performance of a linerless composite tank subjected to fatigue cycles.