Mark B. Gruber

Performance of a Filament Wound Graphite/Thermoplastic Composite Ring-Stiffened Pressure Hull Model

The design, analysis, manufacture, and hydrostatic testing results of a 24- inchdiameter ringstiffened pressurehull model are presented. The AS-4 graphite/PEEK cylinder is manufactured using a nonautoclave insitu filament winding and tape laydown process. The cylinder incorporates 5 hoopwound rings and a shell (hoop/axial construction) that are integrally wound during manufacture. Ultrasonic inspection in conjunction with optical microscopy of end rings indicates that high quality is achieved with a void content of less than 1%. Translation of coupon data into the structure is quantified by subcomponent tests that measure insitu properties (A and Bbasis allowables) including shell axial compressive stiffness and strength and interlaminar shear strength. Analysis of the structure indicates that high interlaminar shear stress exists in the ring fillet areas. Subcomponent tests with supporting analysis to design the test method indicated that this failure mode was not critical. Design and analysis efforts focused on midbay and endbay performance. Axial compressive stress concentrations in the endbay were reduced by incorporating local increases in shell thickness and a steel insert ring that provided radial constraint of the shell to reduce the probability of an endbrooming failure mode. Steel hemispherical heads were designed and manufactured to further reduce axial compressive stress concentrations in the endbay. The test model was instrumented with strain gages and acoustic emission sensors and tested at Carderock Division, Naval Surface Warfare Center (CD-NSWC). Increments in pressure were followed by a 5-minute dwell time. Acoustic emission ceased for all pressures except the last two increments at 5250 and 5500 psi. The collapse pressure of 5500 psi was within 3% of our Bbasis prediction. The cylinder weight-to-displacement ratio, W/D, was 0.212 (unitless). Axial compression failure occurred in the cylinder midbay in agreement with our analysis.

Buckling Performance of Hydrostatic Compression-Loaded 7-Inch Diameter Thermoplastic Composite Monocoque Cylinders

The general instability, or buckling performance, of thick compression loaded composite cylinders is not well understood. Few cylinders have been hydrostatically tested that exhibit a well-controlled buckling failure. This work includes the design, fabrication, and test results for two monocoque cylinders tested in hydrostatic compression to measure buckling performance. The design focused on assuring that buckling failure would occur before a strength failure. The analysis accounted for the effects of end cap design and boundary conditions. The two cylinders were insitu thermoplastic filament wound using AS4 Graphite/PEKK and S-2 Glass/PEKK. Quality was excellent, with 1% void volume fraction and negligible waviness. Both cylinders buckled elastically in their respective tests. The test results include acoustic emissions (AE) and measured strains versus pressure. Experimental results show excellent correlation with analytical predictions.