Development of a Novel Ablative Composite Tape Layup Technology for Solid Rocket Motor Nozzle and Liquid Engine Liners

Solid rocket motor nozzles and liquid engine throats use ablative composite materials to protect the structures from the extremely severe operating conditions of high temperature, pressure and particle impingement. These ablative nozzle liners are processed from carbon phenolic/silica phenolic prepregs using a complex processing cycle. The process starts from impregnating the fibres with phenolic resin followed by either moulding or wrapping/winding prepreg tapes over metallic mandrels followed by polymerization under pressure. Traditionally, prepreg is cut into straight tapes and wound on mandrels to form the divergents. For throats and convergents, prepreg patterns are cut and stacked for curing. Plies of shape conforming to the development of base cone are cut from the prepreg and wound on the mandrel. After polymerization, the final required configuration is machined from this cylindrical blank after the liners are cured. The new method, described in this paper, replaces the straight-cut prepreg tapes by bias-cut prepreg tapes. These can be used for ablative liners in which the plies are at an angle to the direction of the flow. Bias tapes are cut at 45° to the warp and weft directions of the fabric to the required width and formed to the required frustum of cone. Since the cone is formed from straight cut bias tape, the fibre construction will be uniform around the circumference unlike the pattern cut tape. The efficiency of this process depends on the wrapping ratio which is in turn a function of the diameter, ply angle and tape width. To get the best wrapping ratio, shaped mandrels are used which brings down the material wastage and machining allowances. This paper describes the attempts to develop the Bias wrapping technology for angle wound liners. The details of process trials, challenges faced and how they were overcome, advantages of the process over conventional process etc are explained. Exhaustive material characterization of the material was done. Property comparison and validation of performance in subscale tests and a full scale static test are also discussed. The analysis indicates that this new technology has good potential in replacing the traditional tape-winding technology for rocket motor nozzle liners.