Driveline analysis of cardan shaft fractures

Challenge
ESR Technology was asked to investigate an increasing number of in service fractured cardan shafts on Class 15x vehicles which occurred after 200,000 – 350,000 miles.

Solution
Component examination by ESR Technology’s consultants identified the failure mode as bending fatigue of the shaft at the spline-tube weld. To understand why the failure was occurring a series of on track vehicle tests was undertaken with a fully instrumented driveline.

The results of the testing showed that the rubber elements of the torsional damper had a secondary effect of damping out lateral shaft vibration. On failed cardan shafts the torsional damper was found to be faulty and locked up which resulted in an increase in lateral shaft vibration. On two occasions this resulted in severe engine damage and in one case in partial derailment of a vehicle while in passenger service.

A practical on depot vehicle inspection procedure was developed by ESR Technology to identify the faulty dampers and mitigate the risk of in service failures. A design solution was also developed as a long term remedy. Finite element analysis was carried out to understand why the weld had a lower strength than expected and with this knowledge the weld procedure was modified to increase its strength. Fatigue testing on full size sample shafts was carried out to demonstrate the substantial improvement in weld fatigue strength.

Benefits
Since ESR Technology’s solution was implemented there has been no reoccurrence of cardan shaft fractures on Class 15x vehicles. The service interval for cardan shaft replacement is now set at 500,000 miles.