Flexural Response of Phenolic Composites Reinforced With Discontinuous Glass Fibers Under Varying Temperatures and Loading Rates

ABSTRACT The time–temperature superposition principle (TTSP) is generally applicable to long‐term mechanical behavior within the linear viscoelastic region. However, its validity for predicting long‐term durability of polymer deformations in the nonlinear viscoelastic region remains scarcely reported. Due to this limitation in application, this paper investigates the application of TTSP for long‐term mechanical performance in the nonlinear viscoelastic region. In this study, discontinuous glass fiber‐reinforced phenolic composites were prepared via injection molding. The composites were subsequently characterized through three‐point bending experiments, dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM) to investigate flexural response for materials at varying temperatures and loading rates (time), as well as the influence on dynamic mechanical properties. The TTSP was applied to construct storage modulus master curves for predicting the material's long‐term performance. Finally, the application of TTSP to static flexural modulus was discussed. The experimental data showed that loading rates and temperatures significantly affect the dynamic mechanical properties and static flexural properties for phenolic resin and glass fiber (GF)/phenolic composites. Specimens exhibited increased flexural strength and flexural modulus with increasing flexural strain rate but decreased with increasing temperature. The storage modulus versus temperature and frequency exhibited a similar trend, all conforming to the TTSP. Moreover, the storage modulus master curves indicated that the durability of GF/phenolic composites was fundamentally determined by the phenolic resin matrix, but the addition of GF enhanced the durability. Even after aging for 190.3 years, the durability was still improved by 2.6%.