Bolted structures that are widely used in power transformers are prone to failure under internal arcing faults. This study aims to investigate the influence of flange cover thickness and impact energy on the failure behavior of bolted structures on a chimney

and to establish a rapid structural failure assessment method. Accordingly

equivalent drop hammer impact tests and simulations are carried out on the bolted structure of the chimney. The maximum relative error of the structural failure characteristic parameters is only 8.71%

verifying the accuracy of the developed simulation model. Results indicate that the flange cover thickness affects the impact energy transmission path. As the thickness increases from 7.6 mm to 15.2 mm

the proportion of bolts deformation energy to the total impact energy rises from 4.2% to 8.1%

while four failure modes are observed in the bolted structure. Furthermore

dimensionless parameters including the maximum deformation of the flange cover

the bending angle at the bolt head

bolt elongation

and the earing height of the flange cover are selected to construct a failure mode space. The critical plate thickness for failure mode transition is identified as h1=13 mm

and boundary equations for each mode are established. Based on experimental and simulation data

a cubic polynomial function is developed to estimate the failure characteristic parameters

thereby constructing a failure mode prediction model. The maximum relative error between the predicted results and simulation values is only 7.9%

demonstrating good accuracy. This study provides valuable reference for the structural design of explosion-proof transformer tanks.