Newsletter - February 2017

Upcoming meeting

The 663rd SASRE General Meeting will be held at the Fhata Lushaka Boardroom, Koedoespoort Workshops, on Thursday, 23rd February 2017 at 17h00. Sizwe Nkosi, Mechanical Engineer at Transnet Freight Rail will present a paper entitled: ‘Laboratory Based Accelerated Fatigue Testing of F-type Couplers.’

Synopsis

To meet increasing demand, Transnet Freight Rail increased its throughput of iron ore from 29mtpa to 60mtpa. To achieve this on a single line, train lengths were increased from 216 wagon Head-End powered trains to 342 wagon Radio-Distributed Power trains. Due to the high trailing masses, couplers on these trains are operated at stresses beyond their fatigue limit. As a result the couplers have a specific fatigue life. The current coupler service life, and maintenance and inspection intervals are based on this fatigue life. From experience the failure mode of couplers is well known. Fatigue cracks initiate and grow behind the pulling lugs, a region of particularly high stress. After the fatigue crack has grown beyond a certain limit, the rest of the cross-section of the coupler fails catastrophically. If the service life is not accurately determined, or adequate nondestructive inspection is not done, in-service failure results, causing delays. The current service life of 12 years thus needs to be re-evaluated to accommodate the change in the train length. Hence a practical, scientific fatigue study was commissioned. This paper will describe the methodology implemented and results obtained. The steps taken included: analysing and summarising the load data for the heavy haul trains involved, subjecting selected couplers to accelerated fatigue testing to determine the cycles to failure, and analysis of the failure to determine the number of cycles to crack initiation, and the mode of failure.