Failure behavior of power transmission engineering lap structures under dynamic impacts

• Impact resistance of transformer lap welds tested using a custom drop-weight fixture. • Increasing weld toe height significantly improved impact resistance and fracture energy. • Strain-rate-modified Kamtekar model predicted failure loads with <0.1 % deviation. • Microstructure revealed shear–ductile–brittle transition under high-rate impact. • FE simulation confirmed velocity-driven failure mode shift and energy absorption trend. Unpredictable deflagration accidents in ultra-high-voltage transmission systems pose a serious threat to the stability of power networks. In this study, a drop-weight impact testing apparatus and custom-designed fixture were employed to systematically investigate the impact resistance of critical S355 lap-welded joints in transformer oil tanks under dynamic loading. The experimental results demonstrate that increasing the weld toe height significantly enhances the impact resistance of the joints, accompanied by improved load-bearing capacity, energy absorption, and plastic deformation. Building upon this, the strain rate strengthening term from the Johnson–Cook constitutive model was incorporated to modify existing empirical formulas for predicting the ultimate load of lap joints. The revised Kamtekar-based model exhibited a deviation of less than 0.1 % from experimental results, confirming its high accuracy and applicability for failure prediction under high strain rate conditions. Microstructural characterization revealed a distinct brittle–ductile–brittle fracture evolution during impact failure. Furthermore, finite element simulations accurately reproduced the complete failure process and confirmed a strong correlation between failure modes and impact velocity. The findings provide theoretical and technical support for the explosion-resistant design of UHV transformer oil tank structures.