Abstract
In March 2023, a tower of a 1.5MW wind turbine was cut off and the upper part of the wind turbine
fell to the ground. This paper presents the mechanism of the fracture. Detailed investigations of the fractured
part of the tower were carried out by visual and macroscopic inspection and mechanical testing of specimens.
The wind and operating conditions of the turbine were also investigated. It was found that there was
misalignment of the center of thickness of two adjacent plates at the weld, and this caused an increase in
stress at the weld. Furthermore, there is a dominant wind direction at the site and the direction was matched
to the part where the misalignment of center lines was large. It is concluded that the misalignment and the
dominant wind direction cause unexpected fatigue failure. The ultimate strength of the tower with fatigue
fracture was analyzed by numerical simulation. When the circumferential length of the fatigue fracture is 3
m or more, the tower is cut off by ductile fracture and buckling of the tower. Preventive measures have
already been implemented for the same type of tower and wind turbine.
