The effect of fiber volume fraction on filament wound composite pressure vessel strength

This paper is a continuation of previous research reported in Ref. [1]. The previous paper discussed the relationship between fiber volume fraction in filament wound composite vessels and failure pressure. This research included a design of experiment investigation of manufacturing and design variables that affect composite vessel quality and strength. Statistical analysis of the data shows that composite vessel strength was affected by the manufacturing and design variables. In general, it was found that the laminate stacking sequence, winding tension, winding-tension gradient, winding time, and the interaction between winding-tension gradient and winding time significantly affected composite strength. The mechanism responsible for increases in composite strength was related to the strong correlation between fiber volume fraction in the composite and vessel strength. Cylinders with high-fiber volume in the hoop layers tended to deliver high-fiber strength. This paper further examines the relationship between fiber volume fraction and fiber strain to failure. Data from unidirectional strand tests and additional vessel tests are presented. A computer program that is based on the thermokinetics of the resin and processing conditions is used to calculate the fiber volume fraction distribution in the filament wound vessel. The strand's strength-versus-fiber volume data together with the computer program are used to predict composite vessel burst pressure. In general, good agreement with experimental data is observed.