Host: The Japan Society of Mechanical Engineers
Name : [in Japanese]
Date : September 03, 2023 - September 06, 2023
The gondola of the building maintenance unit (BMU) installed on the roof of a building for window cleaning suddenly fell during work after about a year owing to fracture of the main shaft of the wind-up drum in the BMU. The cause was investigated by fractographic observation of the fracture surface using scanning electron microscope (SEM) and stress analyses caluculated by the finite element method (FEM). Striations as the characteristic of fatigue fracture are observed by SEM on the fracture surface of the main shaft. FEM alalyses show that the tensile stress equivalent to the yield stress of JIS S45C is applied to the surface of the main shaft in case of 1 mm misalignment between the main shaft and driven shaft. Owing to the misalignment between the main shaft and driven shaft, the main shaft of the wind-up drum was subjected to a tensile stress equivalent to the yield stress of the material of it with each rotation, and then fatigue failure of the main shaft occurred in a very short period of time.
