Evaluation of nondestructive evaluation techniques for determination of flawed conditions and the effects of flaws on the burst pressure in Kevlar-epoxy filament-wound spherical test specimens

A study of nondestructive evaluation techniques on spherical filament-wound Kevlar-epoxy test specimens has been performed, and the results are presented. The objectives of the study were (1) to determine the sensitivity of several NDE techniques for the detection of a series of flaw conditions in an enclosed geometry and (2) to determine which flaw conditions affected the mechanical strength of the composite specimens. Seventy spherical specimens were made. Ten of the specimens contained one of seven defect conditions which simulated manufacturing or handling defects. Defect conditions involving delaminations, voids, inclusions, loss of fiber, loss of matrix, reduced fiber modulus, or matrix cracking were readily detectable with one or more inspection techniques. Specimens with fiber tension variation could not be distinguished from standard no-defect specimens with the inspection techniques used in this study. It was found that nominal defects introduced during the manufacturing or handling process do not significantly reduce the ultimate burst strength of the composite material in this geometry; however, impact damage was found to significantly affect burst pressure and location. Acousto-ultrasonic and acoustic emission techniques were found to be predictive of burst pressure for specimens with a normal matrix. Low-epoxy matrix specimens were found to sustain more damage more » for a given impact energy than specimens containing a normal matrix. 23 refs., 3 tabs. « less