Fatigue failure analysis of holding U-bolts of a cooling fan blade

Fatigue failure of holding U-bolt of a cooling fan blade is analyzed. Fractography of the fracture surface reveals the characteristics of a fatigue fracture. Finite element modeling is used for stress analyzing. Analysis of the loading conditions indicates that the bolts are under multiaxial fatigue. Effective alternating and mean stresses are obtained based on the multiaxial fatigue criteria. By using the modified Goodman approach and considering the notch effect, effective stress amplitude, is obtained for all nodes. The highest stress amplitude is obtained at six critical nodes. Fatigue life for the most critical node is determined as 3.63 million cycles.

► Fractography of the fracture surface indicates that fatigue is the most probable cause of failure.
► Analysis of the loading conditions indicates that the bolts are under multiaxial fatigue.
► Fatigue analysis by finite element modeling demonstrates that six critical nodes have the highest stress amplitude.
► Fatigue life for the most critical node is obtained as 3.63 million cycles or 593 h.