Stress Analysis and the Cause of the Fracture of a Clevis at the End of a Hydraulic Piston Rod
A hydraulic piston assembly fractured while in service. The fracture involved a clevis assembled to the end of the cylinder piston rod. In fact, there were two fractures: one where a threaded end on the clevis was assembled to the piston rod and a second involving a fracture through the wall of the clevis. Analysis by plant personnel suggested that the stresses involved were small and that fracture should not have been expected. As a more detailed stress analysis of the clevis ring demonstrated, the stresses associated with the clevis, treated as a closed ring, were more than sufficient to have resulted in the fracture through the clevis wall. The other fracture, the fracture at the point of assembly to the piston rod, was proved to be secondary. Stress analysis as well as fracture analysis proved the point and allowed appropriate recommendations to be made to avoid a reoccurrence.