A Study of Ply Thickness and Angle Designs for Preventing Permeability of the IM7/977-2 Polymer Composite Cryogenic Tank

Abstract

Ply angle and thickness designs for preventing micro crack development in an IM7/977-2 pressurized disk were investigated through a numerical procedure. The composite disk was employed to represent a cryogenic tank dome under both fuel pressure and assembly loads. A micro mechanics model, the equivalent constraint model (ECM), was incorporated in the progressive failure finite element analyzer (GENOA) to address the initiation and evolution of micro cracks in the disk during the loading process. Two laminate configurations, [45/90/-45/0]4s (Lay-up 1) and [0/0/16/-16/21/-21/26/-26/36/-36/45/45/55/-55/75/-75/90]s (Lay-up 2), were adopted in the ply angle effect study. The simulated micro crack density development in the disk made from Lay-up 1 shows better leakage resistance than the disk fabricated from Lay-up 2. To investigate the ply thickness design in preventing permeability, certain layers in the 32-layer quasi-isotropic laminate with per ply thickness 0.0052 inches (layup 1) were replaced with 0.0026-inch thick, highly cracking resistant plies in the disk. Simulation results show the 0.0026-inch thick layers in the pressurized disk play an importance role in stopping the leakage path formation through the disk thickness.