Research on fatigue test of welded hollow spherical joints in grid structure based on infrared thermography

The grid structure with welded hollow spherical joints has been widely used in industrial buildings with suspending cranes. The alternating and reciprocating action of the suspending crane causes fatigue failure to welded hollow spherical joints. During the fatigue test, temperature of the surface of welded hollow spherical joint was detected by infrared thermal imager. The higher temperature rise area was located at the weld toe of the sphere in the welded parts. This area corresponded to the final fatigue failure position. During the test, the location of the temperature rise area at the weld toe was almost constant. When the fatigue crack penetrated the wall thickness of the sphere, the position of the temperature rise area changed. The experimental results show that the temperature rise of the surface of the joint can be recorded in real time by infrared thermal imager. By analyzing the temperature rise in those area, the location of fatigue fracture can be predicted without any visible cracks. The fatigue life of the joints when the crack penetrates the wall of the sphere corresponds to the change of the position of the temperature rise area at weld toe.