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Title: Ablatives Based on Multiple Reinforced Elastomeric Composites for Aerospace Applications
Authors: Iqbal, Nadeem
Keywords: Applied Sciences
Chemical engineering
Issue Date: 2013
Publisher: National University of Sciences & Technology (NUST)
Abstract: Ablatives are materials used to protect the inner hardware of aerospace structures from the inimical temperature and shear environments. Fifty six diverse compositions have been used with numerous incorporations (MWCNTs, nanokaolinite, nanomontmorillonite, fine natural cork, phenolic resin, carbon fiber, Kevlar fiber, glass fiber, Spectra fiber, and ceramic fiber) and elastomeric matrices ( ethylene propylene monomer, styrene butadiene, silicon, and nitrile butadiene rubber) to fabricate polymer ablative composites for hyperthermal/hypersonic environment encountered during the space vehicle and ballistic missiles re-entry missions. The reinforcements have been impregnated into the elastomeric matrices using internal dispersion kneader and two-roller mixing mill. Three types of mold geometries have been used according to ASTM standards to fabricate the composites on the hot isostatic press to evaluate in-situ back-face temperature elevation, linear/radial ablation resistance, and mechanical properties. High temperature ( ≈ 3000 o C) oxy–acetylene torch coupled with the temperature data logging system was used to execute the ablation measurements of the ablative composites. Thermal stability and heat absorbing capability investigations have been carried out on the TG/DTA equipment. Mechanical properties have been executed using Universal Testing Machine (UTM) and rubber hardness tester. Scanning electron microscopy coupled with the energy dispersive spectroscopy was performed to demonstrate the reinforcement’s dispersion, interface quality, char morphology, char–reinforcement interaction, and compositional analysis of the composites. The ablation, thermal, and mechanical properties of the fabricated composites have been positively influenced with increasing the concentration of the nanoclays/synthetic fibers/nanotubes in the host rubber matrices. The least backface temperature evolution under 200s flame exposure, best linear/radial/mass ablation resistance, and the utmost improvement in tensile strength and elongation at break have been observed for 30 wt% nanokaolinite and 7 wt% chopped Kevlar fiber impregnated ablative composites. High thermal stability, heat quenching capability, low thermal conductivity, mechanical strength, and remarkable reinforcement–matrix adhesion are identified as the most viiprominent factors for enhanced ablation performance. The novelty of this research work is the fabrication of new ablative formulations with augmented ablation resistance (linear ablation rate of ~ 0.002mm/s) and back-face temperatures in the vicinity of 55 o C. This compares with the ablation rates of 0.01mm/s and back-face temperatures 130 o C for contemporary work using elastomeric composites under similar conditions. A host of ablators have been ranked in terms of linear and radial ablation rate, backface temperature, and mechanical strength following head-on impingement, or radial flow conditions of oxy- acetylene flame. The designer can choose the appropriate combination of ablators for the situation at hand using the ablation data provided in consolidated form towards the end of the thesis.
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