A Re-Examination of Failure Analysis and Root Cause Determination

28Visual ExaminationThe two as-received pins are shown in figure 1 where an arrow shows the location offailure. The failure occurred in a 1.230-inch-diameter cylindrical part of the pin whichwas corroded on the outer surface. One side of the fracture surface is shown in figure2, below.Convergent chevron patterns identified the fracture initiation site on the outside surface.The fracture initiation site is marked by a red arrow in figure 2. Most of the fracturesurface had been darkened by corrosion. A series of coarse low cycle fatigue crackarrest marks was identified at the ends of the two discolored crack-propagation fronts.The exterior surface of the 1.230 inch diameter cylindrical part of the pin containedcorrosion pits. Corrosion pitting was also visible at the fracture initiation site. Thefracture surface profile is shown in figure 3.A circumferential ridge and depression were found in the cylindrical surface. A similarridge and depression were seen in the unbroken pin. By comparing the cylindrical partsof the two pins it was found that the fracture of the broken pin had initiated at thecircumferential depression.The part of the fracture surface containing the fracture initiation site was macroetchedfor 30 seconds in a hot aqueous 50 percent hydrochloric acid solution to remove thecorrosion products. The clean surface showed the fracture initiation site, as seen infigure 3.