JEC COMPOSITES MAGAZINE - Issue #39 - March/April 2008 - 110

KNOW-HOW Process RTM and 3D reinforcements: a technological breakthrough in solid-fuel propulsion To reduce costs and improve the mechanical properties of 2D bidirectional phenolic materials, a new process combining 3D high-strength carbon reinforcement with an RTM-injected phenolic resin has been developed. Other advantages of the process are fewer steps and better health, safety and environment (HSE) conditions. the thickness to interlock them with the fibres in the plies below it. This reinforcement was adapted to the requirements of carbon/phenolic heat shield parts for nozzles (see Figure1). 1- MARTINE DAUCHIER, R&T PHENOLIC ABLATIVE MATERIALS MANAGER 2- JEAN-LOUIS LIMOUSIN, METHODS AND PROCESS MANAGER 3- JEAN-CLAUDE TRICOT, R&T PROGRAMME MANAGER SNECMA PROPULSION SOLIDE T he heat shields for solid rocket nozzle consist mostly of laminate or bidirectional phenolic-resin materials. The shields are usually made by tape wrapping 2D carbon or silica fabric tapes that have been pre-impregnated with phenolic resin, then curing them under high temperature and pressure in an autoclave. Because the process requires many steps, it is relatively expensive and produces materials with rather low mechanical properties, in particular for interlaminar strength. Fig. 1: Subscale motor preform Resin impregnation An RTM process was designed and developed, taking into consideration the constraints dictated by geometry and thickness of the parts to be manufactured. The first two production parts developed were the P80 nozzle’s exit cone section and cowl, for the first stage of the Vega launcher vehicle. Tab. 1: Part dimensions Designing a phenolic material with 3D reinforcement The concept that was developed had three goals, which were: - increasing the mechanical properties to eliminate all or part of the structural reinforcements, - simplifying the process to make it more HSE friendly, - reducing costs. The material design involved the use of an RTM-impregnated 3D reinforcement made from industrial carbon fibres. Cowl (mm) Internal diameter Height Thickness φ1 φ2 h e 1,120 1,240 430 80 Exit cone (mm) 1,470 2,010 970 45 - 55 Reinforcement Snecma Propulsion Solide (SPS) had already developed Naxeco, a 3D reinforcement for thermostructural applications. The reinforcement is manufactured by winding and needlepunching carbon plies on a mandrel. The needle-punching step involves transferring some of the ply fibres through The reinforcement in each of the two parts is oriented differently as a function of the part’s position in the nozzle and the heat erosion it is subject to during firing. As a result, the RTM process used had to be adapted for both configurations. The choice of resin was guided by the experience acquired from fabric-based carbon/phenolic part manufacturing and by the application type, which required a resin with high coke content. Several different types of resin were assessed; the same phenolic resin used to make impregnated 2D ablative fabrics was chosen as the only one that met the overall JEC Composites Magazine / No39 March - April 2008

JEC COMPOSITES MAGAZINE - Issue #39 - March/April 2008

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #39 - March/April 2008