Application of the fracture mechanics methodologies in aeronautics to improve the safety of railway transport

On June 29, 2009 a train, transporting liquid gas, derailed at the Central Station in Viareggio; the derailment was caused by the fatigue failure of an axle. The impact of the first tank on the ground caused a cut, the flammable gas flourished out and fired, causing the death of 32 people. This paper describes a research activity to determine the mechanism of crack propagation in the cracked section of the axle and, in particular, the "initial crack", i.e. the extension of the crack present at the last inspection before the failure. Both numerical and experimental analyses have been performed; the first are based on Linear-Elastic fracture mechanics and the experimental studies include crack propagation tests on standard specimens as well as full-scale tests on railway axles. The tests were conducted at the Fatigue laboratory of the (former) Department of Aerospace Engineering in Pisa. The experiments allowed us to understand the limits of the classical crack propagation laws usually (and, sometimes, improperly) adopted. The decisive aspect of the research was the possibility to interpret the markings which are present on the cracked section of the axle.