Long glass fiber reinforced thermoplastic composites have been increasingly used in automotive parts due to their excellent mechanical properties and recyclability. However, the effects of strain rates on the mechanical properties and failure mechanisms of long glass fiber reinforced polypropylene composites (LGFRPPs) have not been studied systematically. In this study, the effects of strain rates (from 0.001 s⁻¹ to 400 s⁻¹) on the mechanical properties and failure mechanism of LGFRPPs were investigated. The results showed that ultimate strength and fracture strain of the LGFRPPs increased obviously, whereas the stiffness remained essentially unchanged with the strain rates from low to high. The micro-failure modes mainly consisted of fibers pulled out, fiber breakage, interfacial debonding, matrix cracking, and ductile to brittle (ductile pulling of fibrils/micro-fibrils) fracture behavior of the matrix. As the strain rates increased, the interfacial bonding properties of LGFRPPs increased, resulting in a gradual increase of fiber breakage at the fracture surface of the specimen and the gradual decrease of pull-out. In this process, more failure energy was absorbed, thus, the ultimate strength and fracture strain of LGFRPPs were improved.

In this paper, the corrosion mechanism and tensile properties of basalt fibers in sodium hydroxide (NaOH) solution with various concentrations and temperatures were studied. The hydroxyl ions disrupt the –Si–O–Si– and –Si–O–Al– bonds leading to the formation of insoluble hydroxides. With the continuation of the hydration reaction, a hydration layer (corrosion shell) with high content of calcium, iron, manganese and titanium ions was formed on the fiber surface. The corrosion shell enabled an increase in the strength and elongation at break of basalt fibers, significantly. Results showed that the tensile strength of fibers was strongly dependent on temperature and concentration. After the basalt fibers were immersed in 1 mol/L NaOH solution at 50 °C for 1 h, 3 h, 6 h, 1 day and 3 days, their retention ratios of strength were 67.6%, 57.8%, 52.5%, 49.0%, 58.2%, respectively. Higher temperature accelerated the corrosion rate of basalt fibers, shortened the formation time of the corrosion shell and increased mass loss. From 25 to 70 °C, the mass loss of fibers increased from 2.4% to 33.8% for fibers immersed in 1 mol/L NaOH for 3 days. The experimental results from quantitative x-ray fluorescence (XRF) showed that the mass loss of basalt fibers was mainly due to the leaching of silicon, aluminum and potassium ions.