THE HYDROSTATIC COLLAPSE PRESSURE TEST AND FAILURE ANALYSIS OF A 610 MM I.D. AS-4/APC-2 THERMOPLASTIC COMPOSITE RING-STIFFENED CYLINDER

摘要

A 610 mm (24-inch) I.D. ring-stiffened cylinder was fabricated from AS-4/APC-2 to demonstrate its hydrostatic pressure load-carrying capability. The fabrication process was in situ thermoplastic filament winding/tape placement. Excellent laminate quality was identified by the 0.9% Vf, minimal ply undulation, uniform C-scans, and high mechanical properties measured from cylinder building blocks. The cylinder enclosed with hemispherical steel end domes was designed to exhibit a strength failure, and had a 0.212 weight-to-displacement ratio. Before testing, the team documented the expected axial collapse pressure at 39.2 MPa (5680 psi). In the test, the cylinder collapsed at 37.9 MPa (5500 psi), within 3% of prediction. Axial strains exceeded -14,000 μstrain and the shell laminate failed axially away from the hemispherical ends. The finite element model was updated with dimensions, properties, and the pre-test geometric shape resulting from process-induced residual stresses. A novel technique accounted for non-linear shear in the material constitutive law. The predicted strains matched the test strains within 15% and were often closer. Four failure criteria were evaluated using the finite element model.