Pressure-assisted RTM Molding Technology Of Ablative And Heat-resistant Composite Materials

The ablative polymer matrix composites for thermal protection are indispensable advanced materials in high-tech fields such as aerospace,they are mature and widely used materials with low thermal conductivity,good thermal insulation performance,high strength,high temperature resistance,fatigue resistance and so on.At present,the resin matrix ablative compsites are usually made by the processing of die molding,tape wrapping and layups et al.Barium phenolic and aminonia phenolic are the most widely used matrix,and the reinforcements are mostly one-dimensional or two-dimensional fibers or fabrics.High porosity may be existed in the products because phenolics release volatiles when curing,low strength and slag easily in one-dimensional stucture,and low interlaminar strength in two-dimensional composites,which will affect ablative performance.In view of above problems,needling carbon clothes reinforced RTM phenolic ablative composites proessed by the pressure-assisted RTM processing were studied in this paper,which takes solid rocket motor nozzle as application background.The performance of the ablative composites is excellent and can be applied in the fields of aerospace.The properties of RTM phenolic were studied first in this paper.The curing reaction mechanism was inferred by the infrared spectroscopy and molecular weight distribution.The rheological properties and curing kinetics were investigated,and the injection temperature and curing system of RTM phenolic were determined.The heat resistance,thermal stability,mechanical properties and ablation performance of RTM phenolic casting were tested.The characteristics of preform were studied and resin filling process was simulated by RTM-worx software.Then the pressure-assisted RTM processing was used to prepare the orthogonal experimental composite flats,and the porosity,ablative performance and mechanical properties were tested.The optimization flats were prepared and the properties were analyzed.Finally,processability and properties of carbon/phenolic divergent section were studied and the pressure-assisted RTM processing was applied to the tube composites.The results show that molecular weight distribution of RTM phenolic is narrow and the viscosity is low,volatiles release when curing.DSC tests show that the initial,peak and terminational curing temperature are 128.2?,164?and 194?respectively.The density,tensile strength,T_g,char yield at 800?,line ablation rate and mass ablation rate of phenolic casting are 1.214 g·cm^-3,20.2 MPa,235?,60%,0.167 mm·s^-1 and 0.0654 g·s^-1respectively.Above data indicates that RTM phenolic is suitable for the matrix of ablative materials and applied in RTM processing.The superiority and feasibility of pressure-assisted RTM processing were proved by resin filling process simulation.Optimized parameters by orthogonal experiment as follows:fiber volume fraction is 42%,curing pressure is 3 MPa,and temperature of pressing is 85?.The density,porosity,interlaminar shear strength,compression strength,line ablation rate and mass ablation rate of optimization flats are 1.361 g·cm^-3,4.61%,34.9 MPa,194 MPa,0.017 mm·s^-1 and0.0557 g·s^-1 respectively,and the thermophysical properties are excellent.Above data indicates that the comprehensive properties of optimization flats are high,and the pressure-assisted RTM processing is suitable for preparation of ablative composites;The apparent quality of divergent section is good,the porosity,tensile strength,compression strength,flexural strength,line ablation rate and mass ablation rate are 3.29%,73.2 MPa,189 MPa,152 MPa,0.016 mm·s^-1 and 0.0708 g·s^-1,which demonstrate that the ablative composites prepared by the pressure-assisted RTM processing have excellent ablative and mechanical properties.