(A) study on the cure process design for the carbon phenolic thick composite cylinders with reduced residual stresses

Abstract

The nozzle parts of solid rocket motors must endure both the internal pressure generated by high temperature exhaust gas and the mechanical load generated by the steering operation of a rocket. Therefore, the nozzle parts of solid rocket motors are fabricated with thick carbon fiber phenolic resin composites due to their heat-resisting, ablative, and high strength characteristics. When the thick-walled phenolic composite cylinder is cooled down from the curing temperature of about 155 ℃ to the room temperature, thermal residual stresses are created due to the anisotropic thermal deformation of the composite structure. As the thickness of the composite cylinder increases, fabricational residual stresses due to the anisotropic thermal expansion or shrinkage of fabric composites also increase, which induces interlaminar failures. In this study, in order to reduce the through-thickness coefficient of thermal expansion (CTE) and the void content, a compression in the thickness direction was applied to the composite prepreg by a compressive jig during manufacturing of composite to supplement the low autoclave pressure. The through-thickness CTE of the fabric composite was calculated by a compaction model and compared with the measured one by thermo-mechanical analysis. The through-thickness CTE changed drastically with respect to the compaction amount, and the void content of the carbon phenolic fabric composite laminate showed different characteristics from the ordinary fabric laminates with respect to the autoclave pressure and the jig pressure. The residual stresses in thick cylinders made of carbon phenolic fabric composites were measured by a new radial-cut-cylinder-bending method. To obtain the residual stresses from the measured relative strains during the radial-cut operation, a bending test of the cylinder with the radial-cut was performed instead of measuring the material properties with respect to radial positions. The thermal residual stresses were...