Background Glass fiber-reinforced polymer (GFRP) is a commonly used material for insulating caps of electromagnetic pulse simulators owing to its favorable insulating and mechanical properties. In recent years, the increase in operating voltage of electromagnetic pulse simulators has imposed higher requirements on the surface insulation performance of GFRP. According to literature reports, doping is an effective approach to improve the surface insulation characteristics of materials. Nevertheless, there are few extensive studies on the doping-modified performance of GFRP.

Purpose This paper aims to investigate the mechanical and surface insulation properties of Al₂O₃-doped GFRP composites, and analyze the effects of nano-Al₂O₃ doping with different particle sizes and mass fractions on the composite performance, thereby providing valid references for the insulation design of electromagnetic pulse simulators.

Methods Five groups of glass fiber-reinforced composites were fabricated by the vacuum infusion molding process, including an undoped control group and four groups doped with alpha-Al₂O₃ nanoparticles of two particle sizes (20 nm and 50 nm) at two mass fractions (1% and 3%). Tensile and flexural properties were tested according to GB/T 1448—2005. Surface flashover voltages under positive and negative nanosecond pulses in SF₆ gas at 0.1-1.6 MPa were measured using a Marx generator with finger-type electrodes.

Results Doping significantly reduced the tensile and flexural properties, and the degradation became more pronounced with increasing particle size. The 50 nm-1% sample exhibited decreases of 74%, 54%, 53%, and 49% in tensile strength, tensile modulus, flexural strength, and flexural modulus, respectively, yet the doped composites still retained tensile and flexural strengths markedly higher than those of conventional insulating materials such as PMMA and nylon. The flashover voltage increased with gas pressure for all samples. The control group showed the highest flashover voltage at 0.1-0.4 MPa, whereas the doped samples performed better at 0.8-1.6 MPa, with the 50 nm-3% sample achieving an approximately 25% higher flashover voltage than the control. The polarity effect was pressure-dependent: the negative flashover voltage significantly exceeded the positive one at low pressure, and the difference nearly vanished at high pressure.

Conclusions Nano-Al₂O₃ doping degrades the mechanical properties of glass fiber-reinforced composites, but the doped materials remain far superior to conventional insulating materials such as PMMA and nylon, satisfying engineering requirements. The undoped material is preferred for devices operating at or below 0.4 MPa, whereas the 50 nm-3% formulation is optimal for high-voltage devices operating at 0.8 MPa or above, providing an approximately 25% improvement in surface flashover voltage.