Dalton Junction Rail Crash - Investigation

Investigation

The tender axle was eventually found in four separate pieces, having fractured across the shaft, and the rails were severely damaged as well.

The axle was made of best Lowmoor wrought iron, and had run about 220,000 miles during its 7 years service (normal life was 10 years or 300,000 miles). The fracture surface of the principal break showed what is now called a slow growth region on the outer part of the diameter, with a fast growth section at the centre. Although Captain Tyler of the Railway Inspectorate did not recognize the problem as fatigue, he had seen many similar fracture surfaces in his career, attributing the break to the two key holes machined into the outer surface of the axle. He was quite right. The fatigue cracks probably grew from one or more of the sharp corners of the keyways, extending slowly around the circumference until the axle could no longer support its load, and the crack (or cracks) grew catastrophically. The load on an axle is complex, but involves both bending from the load in the vehicle above, and torsion from the rotation of the axle. He suggested that the four keyways rather than two be used, effectively spreading the load. Nowadays, the sharpness of the corners would also be reduced, so lessening the stress concentration. Thickening the shaft was done after this accident, and would also have helped to lower net stresses in the axle.