Failure Analysis on Fractured Diesel Engine Camshafts
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The diesel engine injection pump camshafts used in a truck failed after only 13,000 km of service. The failed camshafts were made from a 20Cr steel. The failure occurred at the keyway region of the camshafts. Fractographic studies indicate that fatigue fracture was the main failure mechanism, and the circumferential tangent stress resulting from insufficient static friction force between the cone of the camshaft and the timer acting on the edges of the keyway caused the initiation of the fatigue cracks at the root of the keyway. An abnormal Widmannstätten structure ferrite microstructure was found at the cone position of the camshafts, and initiation and growth of the cracks was facilitated by the microstructure.