Development of a shear char strength sensing technique to study thermoplastic polyurethane elastomer nanocomposites

Abstract

Ablative materials, such as thermoplastic elastomer nanocomposites (TPUNs) are used as internal insulation materials for solid rocket motors. These TPUNs are thermoplastic elastomer reinforced by montmorillonite nanoclays, carbon nanofibers, and multi‐walled carbon nanotubes. When these TPUN materials are exposed to an extreme heat flux, a char layer forms along the surface as it ablates. This research aims to use the newly developed shear strength sensor to evaluate the shear strength of this char layer, a characteristic that is important to evaluate ablative materials. This device consists of a method to apply a transverse loading on a test specimen, while measuring the reaction force and the induced strain. This device was used on several types of TPUN test specimens to demonstrate its effectiveness. As a means to determine which ablative exhibited the best performance, the energy of destruction or the energy of dissipation was developed. The maximum force was also accounted for as a secondary quantity for determining the char shear strength. This new shear char strength sensor is fully automated to ensure that each test is repeatable. This guaranteed reliability when collecting the data and eliminated the potential for human error. Copyright © 2017 John Wiley & Sons, Ltd.