Exploration of failure mechanisms in a novel basalt fiber-reinforced phthalonitrile composite under extreme temperature conditions

As composites become increasingly prevalent in aerospace structures, their resistance to high temperatures in extreme environments has captured the attention of numerous scholars. This paper discussed the development of a new basalt fiber-reinforced phthalonitrile matrix (BFRPN) composite, examining its mechanical performance across a spectrum of temperatures, including −55 °C low-temperature dry state (CTD), 23 °C room-temperature dry state (RTD), 250 °C, 350 °C, and 450 °C. The reliability of the mechanical properties was assessed by calculating the B-basis value. Additionally, optical and scanning electron microscope (SEM) photos were employed to analyze the damage morphology and elucidate the failure mechanisms at both high and low temperatures. The study revealed that the BFRPN composites maintained functional integrity from −55 °C to 350 °C. For representative unnotched plate tensile (UPT) and unnotched plate compression (UPC) specimens, the retention of UPT strength and UPC strength stayed above 100 % and 83 % respectively. At 450 °C, the retention rate of UPT strength consistently exceeds 78 %, while the matrix undergoes significant oxidative decomposition, with delamination being the main observed damage mode.