Fire Performance of Short and Long Glass Fiber Polypropylene Composites for Electric Vehicle Battery Enclosures

Abstract

In response to the significant need to identify damage and failure modes occurring in lithium-ion (LI) electric vehicle (EV) battery packs under mechanical loading and external fire exposure, this research is designed to evaluate the fire performance of new injection-molded, flame-retarded polypropylenes (PP) with 30% long and short glass fiber, STAMAX30YH570 and PPc-H1030, respectively, for battery pack enclosures. This effort includes a series of experiments to quantify the mechanically loaded composite material plates' thermal, physical, and structural behavior under a one-sided fire exposure. A non-contact thermal digital image correlation (TDIC) method was implemented to measure full-field, transient 3D deformations and temperature distribution over the unexposed surface of the composite plates. The effect of plate thickness, fire exposure size, and glass fiber-reinforcement length were studied experimentally. It was found that the occurrence of intumescence slowed down the spread of heat through the plastic plate thickness, as it created a thermal shield. No significant intumescence was observed in thin plates before failure, and it was found that increasing the plate thickness delayed the failure time by a factor of approximately six, while having no significant impact on the unexposed surface failure temperatures. The fire performance of the composite plates under extremely large fire exposure was characterized, and the coupled impacts of thermal expansion and intumescence on the failure of long- and short-fiber composites was studied. Some perspectives and outlooks on the enhancement of the complex interaction of the composite plate and the simulated mechanical loading are proposed for future development.