Ablation modeling of state of the art EPDM based elastomeric heat shielding materials for solid rocket motors

Abstract

Elastomeric Heat Shielding Materials (EHSMs) are essential to manufacture Solid Rocket Motor (SRM) liners. Ethylene Propylene Diene Monomer (EPDM) represents the State Of The Art (SOTA) matrix for EHSMs and it is generally combined with aramid fibers and nanosilica to enable a sufficient ablation resistance. In addition to aramid, researches also tested other organic reinforcements such as Kynol® and Zylon®. Our team previously compared aramid (Twaron®) and phenolic filaments (Kynol®) and evidenced merits and deficiencies of both of fibers when embedded in EPDM based EHSMs. In this new step of this research we introduced a 1D model able to describe the insulation capability of the studied materials. The analytical considerations introduced in the theoretical section allowed to implement a numerical tool able to take into consideration the reversible and irreversible thermal expansion of the virgin and charred material. Furthermore, some efforts were effectively spent to introduce a model able to consider the coking process – char densification – due to the carbon deposition of the pyrolysis gases through porous carbonaceous skeleton. These considerations allowed to proper account for the in depth temperature profiles and also to produce the real char densities of the materials tested through oxy-acetylene tests.