Post‐Thermal Strength of Basalt and Kevlar Phenolic Composites: A Weibull Reliability Approach

ABSTRACT The focus of this study is to evaluate the performance and reliability of basalt fiber‐reinforced phenolic (BFRP) and Kevlar fiber‐reinforced phenolic (KFRP) after exposure to elevated temperatures up to 400°C. Results indicated that BFRP withstood higher temperatures and maintained greater tensile strength and modulus, preserving 95% and 100% of its tensile strength and modulus at 250°C, respectively, outperforming KFRP, which retained only 79% and 71%. Even at 400°C, BFRP maintained a measurable strength (26% retention), while KFRP underwent combustion. Thermogravimetric analysis (TGA) confirmed the superior thermal stability of BFRP, showing a higher degradation onset temperature and significantly lower mass loss at 1000°C. Furthermore, Weibull analysis confirmed that elevated temperatures increase data scatter, thereby reducing reliability. Nevertheless, BFRP consistently demonstrated lower variance and higher reliability than KFRP. The Weibull distribution was also used to create reliability‐based design strength for different levels of reliability (0.1–0.99). The two‐parameter Weibull distribution was evaluated and compared with the normal and lognormal distributions using the Kolmogorov–Smirnov (K–S) test, which showed superior performance, particularly at extreme temperatures. This work established a reliability assessment framework to quantify the post‐thermal uncertainty of BFRP and KFRP composites, enabling safer, more efficient designs and applications.