Life prediction of expulsion bladders through fatigue test and fold strain analysis.

Consideration of the problem of reducing the probability of mechanical failure of bladder systems used for the expulsion of propellants into liquid rocket engines. It is shown that individual local folds in collapsing bladders can be classified into single and double folds, specifiable by nondimensional geometrical parameters which directly define the maximum strains at these folds. From these maximum strains the number of collapse/inflation cycles to failure can be obtained from low-cycle fatigue data experimentally determined for the bladder material of interest. Cycle life data are presented in terms of true maximum strain for four metals, two plastics, and two elastomers. It is found that double folds give rise to much more severe folding strains than do simple folds.