| Summary: | This study investigated the fatigue fracture of bilateral drive drum shafts in casting bridge cranes including its fracture morphology and factors, such as materials, manufacturing processes, and loads. Seven conditions were designed to test the effects of changes in the speed and torque of the drum shafts during startup, commissioning and braking under different loads. A dynamic model was developed for the structure and control system of the hoisting mechanism. Changes in the speed and torque of the motor and drum shafts were simulated under common operating conditions such as speed and load changes of the motor, control asynchrony and single-motor towing. The results showed that asynchronous motor starting and braking, motor dragging and other behaviors led the left and right drum shafts undergo oscillated torque with a value reached 2 × 10<sup>5</sup> N∙m in a period of approximately 13 s, and a residual torque about 3 × 10<sup>4</sup> N∙m was retained after braking. The torques on the drum shafts changed suddenly during the processes of starting, shifting and braking. Dynamic loading was the root cause of fatigue fracture of the drum shafts.
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