Development of a Vacuum Bagging Technique for Autoclave Curing of Filament Wound Thin-Walled Tubes

The investigation of techniques for the manufacture of hoop wound composite tubes for use as in-plane shear specimens was undertaken. The principle concerns were achieving a smooth surface finish, uniform wall thickness, acceptable laminate consolidation and minimal defects. Filament winding of Hercules AS4/3501-6 12K pre-preg tow was used to manufacture 19 hoop wound thin-walled tubes. Four main vacuum bagging techniques were evaluated. The most successful of these utilized a thin external mild steel sheet together with shrink tape prior to autoclave curing. Ultrasonic C-scan results indicated that the tubes were free of detectable voids and defects. Microscopic analysis showed excellent laminate consolidation and very good geometric tolerances (tube thickness, roundness, concentricity and straightness). Of particular note was the exceptional surface finish and thin axial seam for the final specimens. It was found during torsion testing of the tubes that a thin axial seam was associated with a higher ultimate shear strength. The vacuum bagging techniques are described and discussed in detail.