Failure mode analysis of torsion beam rear suspension under service conditions

• Fatigue failure location and failure critical load of torsion beam rear suspension under service conditions was investigated.
• Service loads were measured on a test track of proving ground.
• Fatigue crack occurs on the torsion beam near the welding seam.
• Vertical force FZ is primarily responsible for the failure of rear suspension.

The failure mode of torsion beam rear suspension under service conditions was investigated, which refers to the identification of the failure position and failure critical loads because the failure of automobile structures was mainly caused by fatigue. Service loading histories, in the form of wheel loads (forces and moments) and strains of critical regions were measured on a test track of a proving ground. Failure position was determined by comparing the damage values of the critical regions calculated with linear damage rule, while critical loads were determined by the correlation analysis between wheel loads and strain of failure position. The results of damage comparison and correlation analysis indicate that fatigue failure occurs on the torsion beam near the welding seam between it and reinforcing part and could be attributable to vertical forces on the wheel, especially the difference between left and right wheel which introduced an additional torque on the beam. The correctness of the deduced failure mode was demonstrated by conducting fatigue tests on MTS 6DOF road load simulator under all wheel loads and only vertical forces. The conclusion could be helpful for the design and developing load spectrum for accelerated durability test of this kind rear suspension.