Failure analysis of composite cylinders subject to internal blast

The response of advanced composite and 6061-T6 monocoque cylinders of the same length, radius and weight to a point internal blast detonation at the geometric center was computer analyzed. Composite skins were composed of uniaxial plies stacked in the axial, diagonal and hoop directions. The ratio of critical-charge mass to fail high-strength graphite/epoxy (25 plies each in the 0, 45, -45, 90 degree directions) to that to fail a 6061-T6 cylinder was 0.33, or for 15, 15, 15, 55 plies, 0.41. Respective ratios of bending stiffness (composite/6061-T6) were 1.4; unity. Further increase of hoop plies would have reduced the bending stiffness below that of the 6061-T6. For B/epoxy and 11, 11, 11, 67 respective plies the critical-charge mass ratio was 0.36 and the bending stiffness ratio unity. Design recommendations for blast- tolerant composite helicopter tailcones and plans for more detailed analytic and experimental study were discussed.-- EPAA /AF.