Experimental investigation of joint stiffness and composite pressure vessel performance for pyramid and inverted pyramid joints

The focus of this study is on the application of classical laminate theory analysis tools directed toward filament wound pressure vessel wall performance, laminated joint stiffness and burst failure prediction. Two 18-inch diameter 12-ply filament wound pressure vessels were fabricated for this study. One vessel was fabricated with a 24-ply pyramid laminated adhesive double strap butt joint. The second vessel was fabricated with an inverted pyramid joint. The experimental results from hydrostatic tests are presented. Experimental results were used as input to the computer programs GENLAM and Laminate, and the output compared to test.; By using the axial stress resultant, the classical laminate theory results show a correlation within 1% to the experimental results in predicting the pressure vessel wall pressure performance. The prediction of joint stiffness for the two adhesive joints in the axial direction is within 1% of the experimental results. The calculated hoop direction joint stress resultant is 25% less than the measured resultant for both joint configurations. A correction factor is derived and used in the joint analysis. The correction factor is derived from the hoop stress resultant from the tank wall performance investigation. The pyramid joint vessel is determined to have failed in the joint area. The hydrostatic pressure at failure was 33% below the predicted failure pressure. The inverted pyramid joint vessel is determined to have failed in the wall acreage. The hydrostatic pressure at failure was 10% below the predicted failure pressure.