Abstract
The objective of this study was to characterize the thermal insulation efficiency of the silicone rubber reinforced composites by oxyacetylene torch. These composites reinforced by glass, carbon, ceramics and silica fibers were intended to be used as ablators in a low-thrust hybrid propulsion motor. The back-face temperature measurements were used as a criterion for insulation efficiency of the specimens, whose frontal face is subjected to the oxyacetylene flame for 40 s. The paper includes the results of the ablation rate measurements and the influence of orientation of glass and carbon fibers relatively to the flame direction on the back-face temperature of the specimens.
Highlights
The presented study was motivated by the necessity of a prolonged fire testing of the low thrust hybrid propulsion motor developed at the University of Brasilia (Andrianov et al 2015)
The reinforcement of silicone rubber composites with fiberglass fabric or carbon tape in parallel-to-flame direction is impractical due to low insulating effectiveness
For carbon-reinforced composites, this difference is even greater due to high thermal conductivity of carbon: the back-face temperature of perpendicular specimens is in the range 67.5–74.4 °C after 40 s of burning, whereas in parallel specimens the temperature is greater than 350 °C after 30 s of burning
Summary
The presented study was motivated by the necessity of a prolonged fire testing of the low thrust hybrid propulsion motor developed at the University of Brasilia (Andrianov et al 2015). The required operation time of the motor should be at least 40 s, which requires special measures to ensure thermal protection of the motor casing. Thermal protection for hybrids can be adopted from solid propellant rocket motors. Insulators for solid rocket motors are identified by filler (reinforcement) and matrix (binder); the latter identifies the class of insulation material, which can be thermosetting or elastomeric plastic. The most common thermosetting matrix is phenolic resin, a char-yielding material with good temperature resistance, but with relatively low elasticity (Ahmed 2009), which limits its application for heat insulation of motor casings experiencing high deformations. Body insulations are usually elastomeric composites providing strain tolerance (Youren 1971)
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