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.