Fracture Characteristics of Torsion-Bending Fatigue and Impact Fatigue Failure of Two Steel Pins in a Crawler Excavator

摘要

The arms of crawler excavators used in diverse quarries work under extremely harsh conditions. A common failure during their operation is the fracture of the steel pin joints that permit free movement of the two adjacent booms closer to the machine housing, as well as the motion of the backhoe bucket against its nearest boom. This work presents examples of two steel pin joint failures. The pins had a diameter of 90 mm, and the failures resulted in high stand-by time for repairs. The first failure was caused by the combination of bending and torsion fatigue, and the second fracture occurred because of impact fatigue. Optical metallography and scanning electron microscopy/electron dispersive x-ray analysis (SEM/EDS) analysis provided a better understanding of the failure mechanism of the two steel pins, since these particular components exhibited excellent fatigue characteristics in both mating fracture surfaces.