This study examines the dielectric breakdown strength of unidirectional glass fibre-reinforced polymer composites under uniform in-plane alternating electric fields. A comprehensive experimental campaign was conducted on samples with varying fibre orientations relative to the electric field, cross-sectional areas, and electrode gap distances. Breakdown strength was found to increase with fibre angle while decreasing with larger sample cross-sectional area and electrode gap distance. Visual observations revealed that breakdown paths aligned with fibre directions (≤60°), indicating that the local tangential electric field component is the dominant contributor toing failure. Interestingly, numerical and analytical electric field analyses showed that this field component is not locally amplified, whereas the normal component experiences significant local amplification with increasing fibre angle. These findings suggest that fibre-aligned defects and breakdown propagation along fibres dominate breakdown behaviour. A modified two-parameter Weibull model was developed, incorporating an effective electric field based on the local tangential field component along fibres, and size effects expressed through theoretical failure path length and cross-sectional area, separately. The model showed good agreement with experimental data for composites with fibre-to-electric field angle up to 60°, confirming a) the significance of the tangential field component on failure, b) how electrode gap distance exerts a stronger influence than cross-sectional area, and c) that breakdown strength scales with theoretical path length rather than physical gap alone. These results provide a physics-based statistical framework for predicting in-plane dielectric performance in unidirectional glass fibre composites and offer critical insights useful in the design of advanced high-voltage insulating composite structures. • Breakdown behaviour in fibre composites studied in 150-specimen test campaign • Weibull model predicts breakdown for composites with varying fibre angles • The field component along fibres proposed as criterion for dielectric failure • Size effects quantified for glass fibre reinforced polymer composites • Introducing breakdown path length improves modelling, confirming its size effect
Arvidsson et al. (Fri,) studied this question.