Estimating Residual Strength in Filament Wound Casings from Nondestructive Evaluation of Impact Damage

Abstract

The purpose of this study is to improve the ability to detect hidden damage in thick composites caused by low velocity impact and to predict the remaining strength of those materials. An impact study has been undertaken NASA's on filament graphite/epoxy casings, such as those proposed for space shuttle solid fuel rocket boosters. In thick wound composite materials, low-velocity impact may not be visually evident, depending on the impacter shape; yet the damage may the site's ultimate strength. one A model of a damage filament wound compromise casing was compo- fabri- cated with fifth of the diameter (30 inches) but with the full'thickness (1.4inches) of the full rocket motor (12 feet was and and 1.4 inches, respectively). It impacted with various masses energy levels using inch diameter ball as the indenter. This casing was subsequently cut into a one coupons of 2 in. width by 12 in. length. These samples were nondestruc- tively examined for the degree of Next, these samples were loaded with dye in tension until failure. Efforts to accurately detect the damage. penetrants that displayed and x-ray no visible this material, ultrasonic phase velocity methods damage. have proven unsatisfactory in the samples damage In spite of the high attenuation of promise in predicting the residual strength of the coupons. Predictions and attenuation images show of the profile, therefore the cross-section of the in the direction of loading, damage and obtained by assuming an "effective" damage value for the attenuation of the were part of the filament casing material "effective" value for the velocity of the damaged part. of the filament wound damaged casing material estimates were based partially on measurements impact 2250 m/ wound s). These thin composite material. The remaining strength predictions from damaged these ultrasonic data significant over the x-ray predictions of remaining strength OS dB/MHz-cm) and an the may be usable for predictions of remaining strength of full scale rocket motors that may have suffered damage.