Sinclair Knight Merz and Hamersley Iron
Hamersley Iron operates a fleet of approximately 4000 ore wagons of which approximately 2400 of the wagons are of 1966 to 1978 vintage. These older M-Series wagons are a fabricated mild steel box car on cast steel bogies. Given the age of the fleet there is concerns over the serviceable life of all wagon components, including the fatigue life of the bogies, as the consequences of a mainline derailment caused by bogie fatigue would be far reaching.
To provide Hamersley Iron with information to assist in making decisions regarding the retention, refurbishment, capacity upgrade or replacement of the M-Series wagons, SKM was commissioned to undertake a remaining fatigue life assessment of the M-Series bogies.
In-Service Strain Gauge Testing to correlate with Finite Element Simulation
A combined Finite Element (FE) modelling and in-service strain gauge testing approach was adopted to generate load cycling statistics the bogies have experienced at fatigue sensitive locations. Based on the FE and strain gauge test results, fatigue life estimates have been made based on fatigue test S/N data obtained for AAR Grade C casting material. Fatigue crack critical crack size and crack growth rate evaluations have been undertaken to determine how fast cracks may grow in service and to what size before fracture.
Fatigue Life and Crack Growth calculations
The study has found relatively long fatigue design lives and long crack growth periods and extended future operation is possible with a relatively low risk of fatigue cracking. A one off NDT inspection and routine future inspections at critical identified locations would safeguard against crack growth from casting defects that may exist.
Substantial Cost Savings
Extending the service life of the bogies has the potential of substantial cost savings to Hamersley Iron compared to fleet replacement at this point in time.