Development of Fatigue Monitoring System for a Hydraulic Excavator

The booms of two barge-mounted hydraulic excavators experienced substantial fatigue cracking during normal operation. Fatigue cracking of the smaller excavator, a Liebherr 994 known as the Hercules, occurred at a slower rate than the larger excavator, a Liebherr 996 known as the Antone. However, one crack on the Hercules boom went undetected so long that it grew to a critical length and the boom fractured. Because of the Hercules failure, the prior occurrence of several cracks on the Antone, and the anticipated difficult dredging in the coralline material at the Port of Miami, in Miami, Florida, the owner of the excavators sought assistance in mitigating the risk of damage to the Antone. To control the risk of fatigue cracking, the investigators decided to repair any existing cracks so the structure complied with ANSI/AWS requirements for a cyclically loaded structure; install strain gauges on the structure and perform static and dynamic load tests to determine the strain characteristics of the structure; and develop a structural maintenance program.