The two as-received pins are shown above. An arrow shows the location of failure. The failure occurred in a 1.230-inch-diameter cylindrical part of the pin which was corroded on the outer surface. One side of the fracture surface is shown in the image below. Convergent chevron patterns identified the fracture initiation site on the outside surface. The fracture initiation site is marked by a red arrow in the figure below Most of the fracture surface had been darkened by corrosion. A series of coarse low cycle fatigue crack arrest 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 contained corrosion pits. Corrosion pitting was also visible at the fracture initiation site. The fracture surface profile is shown below.
A circumferential ridge and depression were found in the cylindrical surface. A similar ridge and depression were seen in the unbroken pin. By comparing the cylindrical parts of the two pins it was found that the fracture of the broken pin had initiated at the circumferential depression.The part of the fracture surface containing the fracture initiation site was macroetched for 30 seconds in a hot aqueous 50 percent hydrochloric acid solution to remove the corrosion products. The clean surface showed the fracture initiation site, as seen in the image below.