Case Histories

Manufacturing

Cavitation Damage

Cavitation damage of injection piston
Region of cavitation damage on a cast iron injection housing
SEM of cavitation damage of injection piston
Scanning electron microscopy image of a typical “cavity” caused by cavitation damage

Specimen: Cast iron injection housing

Material: ASTM A 536 Grade 65-45-12 ductile iron

Background: The cast iron injection piston housing had been subject to approximately 1 million cycles in a plastic injection moulding system. Seven identical failures of localized damage to the ring seal on identical cast iron injection piston housings had occurred.

Service Life: Approximately 1.5 years, or 1 million cycles

Findings: Visual examination of the region of localized damage revealed areas of large “craters” surrounded by smaller craters or micro-pits. Such damage is typical of cavitation damage. Cavitation damage is defined as the wearing away of metal through the formation and collapse of cavities in a liquid, subject to rapid and intense pressure changes. In this situation, the liquid was the oil used to lubricate the piston and housing. The very rapid movement of the piston through the housing caused the rapid and intense pressure changes in the oil, thus causing cavitation damage.


 

Failure of Wire Rope

Failure Analysis of a Wire Rope - Multiple strand failure
Failure Analysis of a Wire Rope – Multiple strand failure
Failure Analysis of a Wire Rope
Failure Analysis of a Wire Rope

Specimen: 9/16-inch diameter; 8 x 26 Cushion Pac 8 High Performance Wire Rope

Material: Improved Plowed Steel

Background: The wire rope was used on a hoist cable from a 110-foot crane in the shipping area of a manufacturing plant. The wire rope fractured while lifting bundles which weighed only approx. 28% of the maximum recommended load capacity of the crane.

Service Life: 6 Months

Findings: The majority of the breaks in the wire rope occurred in a similar region of the strand’s helix. This would indicate that the fracture had initiated by bending fatigue which would load the wires repeatedly in one plane. Multiple fatigue breaks eventually lead to the ultimate catastrophic failure of the wire rope.