A failure analysis of two damaged crankshafts are presented: one obtained from a diesel engine of a mini backhoe, and another one from an automobile vehicle. The diesel motor suffered a serious mechanical damage after 3 years and 5000 hours in service: the connecting rod n° 3 broke and, in consequence, the crankcase and motor block suffered damage. The motor was repaired by a non-authorized workshop, but maintaining the same crankshaft without being properly inspected. After 1100 hours working the crankshaft failed on the 3 rd crankpin. The second crankshaft failed after 105 000 km in service. In both crankshafts a crack grew from the crankpin-web fillet, and their symmetric semi-elliptical crack front profiles confirms the effect of a pure mode I (reversed bending). Fractographic analyses show the semi-elliptical beach marks and results indicate that fatigue fracture was the dominant failure mechanism of these two crankshafts.
Fonte, M., Infante, V., Freitas, M., & Reis, L. (2016). Failure mode analysis of two diesel engine crankshafts. In Procedia Structural Integrity (Vol. 1, pp. 313–318). Elsevier B.V. https://doi.org/10.1016/j.prostr.2016.02.042