Study On Anti - Ablative Modified Phenolic Resin System For RTM And Its Application

At present, ablative thermal protection materials of solid rocket engine nozzle are based on high silica / phenolic and carbon / phenolic carbonized ablative materials,but these composites have many disadvantages, such as low normal strength,high brittleness, and layer-stripping is caused by poor anti-erosion ability of ablation surface. Using RTM technology with three-dimensional woven preform forming ablative composites is one of the ways to solve this problem, but resin systems commonly used for the RTM process can not be used as ablative resin matrix.So the key to solve this problem is the research on ablative resin system suitable for RTM process.RTM251 resin, B-80 resin and low-viscosity resin were studied in this paper. Curing characteristics were tested by Differential Scanning Calorimetry(DSC) and Thermogravimetric Analysis(TG).Properties of resin casting,such as thermal properties, mechanical properties and micro-morphologies,were studied,dynamic viscosity and isothermal viscosity of resins were also investigated.Based on the isothermal viscosity, a chemorheology model was built to predict RTM process window. Results show that both RTM251 resin and B-80 resin have good mechanical properties and ablative performance,they also have the ideal platform of low viscosity and long low-viscosity holding time.Therefore, RTM251 resin and B-80 resin are suitable for RTM process as the matrix of ablation resistant composites.Flat samples of B-80/punch composite and RTM251/acupuncture composite were made by RTM process.Influences on the properties of composites by different resin matrix were investigated. Results show that RTM251/acupuncture composite is more outstanding in overall performance with good mechanical properties, density, ablative properties and so on.But in terms of the thermal physical properties, B-80/acupuncture composite is better.B-80/acupuncture has high heat capacity and small thermal conductivity,which can meet the requirements of ablative materials. The main reason of RTM251/acupuncture composite’s better comprehensive performance is largely due to the good performance of resin matrix.Experimental results show that good comprehensive properties of the resin matrix is more advantageous to improve the performance of the composite materials.Flat sample of RTM251/2.5D braided composite was fabricated by RTM process. Comparing with RTM251/acupuncture composite,effects on the properties of composites caused by different structure prefabricated body were investigated.Results show that RTM251/2.5D braided composite has high density,exhibit excellent ablation performance and anti-erosion ability,oxygen-acetylene line ablation rate and mass ablation rate are 0.024mm?s-1 and 0.0569 g ? s-1, its preform structure is hardly destroyed by heat-scouring.And its linear expansion coefficient is very small, close to zero expansion,so it has good dimensional stability under heat conditions. RTM251/2.5D braided composite shows the potential as ablation resistant materials.A typical heat component was made by RTM process with RTM251 resin and 2.5 D braided prefabricated body. The product exhibits high dimension accuracy, smooth inner and outer surface,and good apparent quality.Its normal decibel is in the range of 78 ~ 84 d B by using ultrasonic testing, the decibel difference is only 6 d B.The results show the internal material of the typical heat component is dense homogeneous.