Often when engineers consider mechanical fatigue they envision cyclic, reversing stresses in a spinning shaft or possibly the up and down flex of aircraft wings. Rolling contact fatigue (RCF) or the associated mechanical wear is an important, closely related process to the traditional mechanism of fatigue but with distinct differences. RCF is also often known as spalling.
Adenosine triphosphate (ATP) assays have been used to quantify bioburdens (biomass) in low-organic-compoundcontent fluids (freshwater, seawater, cooling tower water, and similar fluids) since the early 1950s. The original methodology was labor intensive and required considerable laboratory skill. Over the past half-century, the protocol has been simplified substantially, but until recently, chemical interferences made it impractical to use the ATP test in metalworking fluids (MWF).
Two cores from a marine diesel engine oil cooler were received for analysis to investigate the cause of failure via leaking. Results indicate that the cooler core failed due to pitting corrosion initiated on the interior (oil side) at the edge of the fins.
The four seized bearings submitted for metallurgical analysis were determined to have suffered deterioration of their grease to the point that it was inhibiting motion rather than enabling. The grease had turned to a thick (viscous) black sludge that was full of particulate. Electrical pitting was found in the seized bearings, especially the inner races. Signs of axial (thrust) loads were noted, mainly in the outer raceways. Larger arc strike regions were found on the balls.
A welded left front spindle/steering arm assembly that had fractured at the fillet weld joint between the steering arm and inner brake boss was received for analysis to determine the mode of failure.
Several concentrating still condenser tubes exhibiting pitting were received to determine the cause of pitting. Results indicate the tubes pitted initially from the inner diameter (ID) surface due to microbiological corrosion (MIC). MIC pitting initiated preferentially at the tube seam weld. Additional ID surface pits and significant pit enlargement of MIC pits due to chloride pitting were also observed. The chlorine is likely remains from the hydrochloric cleaning process
Creep of a metal or alloy is defined as its time-dependent deformation under constant stress at a given temperature, and is associated with elevated temperatures, usually defined as any temperature above 1/2 the melting point (in absolute degrees).