Compressive Char Strength of Thermoplastic Polyurethane Elastomer Nanocomposites

This research encompasses the study of testing protocols and the design of sensors for evaluating the compressive strength of the char layer of ablative material used in solid rocket motors (SRMs). The testing protocol that has been developed is the continuation of previous work for determining the compressive strengths between different SRM insulation materials. A crushing test method was further developed, and a sensor platform was assembled to perform the tests. The test procedure consists of measuring the amount of force required to crush a given area of the charred sample for a specified depth. The test was repeated for the industry standard Kevlar®-filled ethylene propylene diene monomer rubber and thermoplastic polyurethane elastomer nanocomposite with different weight loading of multi-walled carbon nanotubes, montmorillonite nanoclay, and carbon nanofibers. The energy of destruction or energy dissipated was quantified to determine which ablative exhibited the best performance. Maximum force was also recorded as a secondary quantity to determine char strength. The proposed test method is fully automated to ensure repeatability of each measurement and to remove the potential for human-induced error. Because char layer thickness varies depending on the material, a method of differentiating neat material from char was proposed and explored. The introduced procedure also represents a novel and unique approach to solve the problem of the determination of the char strength.