PSI - Issue 39

Giovanni Pio Pucillo et al. / Procedia Structural Integrity 39 (2022) 700–710 Author name / Structural Integrity Procedia 00 (2019) 000–000

702

3

Table 1 – High-Speed lines in different countries (UIC Passenger Department, April 2018).

Country

In service [km]

Under construction [km]

Total [km]

China Japan Spain France

26869

10738

37607

3041 2852 2814 1658

402 904

3443 3756 2814 1843 1095

0

Germany

185 200

Italy

895 887 724 354 268 209 200 144 120 113

South Korea

0

887

Turkey Taiwan Austria Belgium Morocco

1395

2119

0

354 549 209 200 159 120 343 453 193

281

0 0

Swiss

15

Netherlands

0

United Kingdom

230 453 193

Saudi Arabia United States

0 0 0

Denmark

56

56

All these kilometers of track are periodically checked by ad-hoc trains, mainly during the night. Instrumented trains equipped with ultrasonic controls are adopted to detect possible point of the track where fatigue crack may exist (Jeong, Tang, and Orringer 1997; Zerbst et al. 2009); successively, if a crack is believed to be present, a check is done with more sensible devices. Among rail failure modes, fatigue fracture originating from bolt-holes of insulated or non insulated rail joints is one of the most common (Zerbst, Schödel, and Heyder 2009; Cannon et al. 2003; Milo et al. 2018). While non-insulated rail joints are mainly used for temporary repairs (Carolan, Jeong, and Perlman 2014; Talamini, Jeong, and Gordon 2007), insulated rail joints (IRJs) are fundamental components for railway safety, because they provide a tool to detect broken rails (Jeong, Bruzek, and Tajaddini 2014) and guarantee electrical insulation of two adjacent track sections for signaling purposes (Himebaugh, Plaut, and Dillard 2008), and gives economic advantages for substitution of track segments submitted to accelerated wear, for example in curves. However, severe high wheel/track impact forces and reduced flexural stiffness than conventional rails make IRJs prone to fatigue cracking at the hole surface (Dick 2001). Furthermore, the same holes of IRJs dramatically reduces the fatigue resistance, because of the stress concentration effect (Carpinteri 1993; Carpinteri, Brighenti, and Vantadori 2006; Aglan and Fateh 2007; Carpinteri and Vantadori 2009; De_Iorio, Grasso, Kotsikos, et al. 2012; De_Iorio, Grasso, Penta, et al. 2012; Carpinteri, Ronchei, and Vantadori 2013; Grasso et al. 2013; Pucillo, Esposito, and Leonetti 2019) A useful strategy for improving the fatigue strength of structural parts is the induction of compressive residual stresses in correspondence of the most stressed points. Pad coining, interference-fit fasteners, split-sleeve cold expansion, e.g., are widely used in the aeronautical field (Fu et al. 2015). Between them, cold expansion has the advantage to be effective throughout the entire thickness of a drilled component, and for this reason is the only one that can be considered as a possible solution to improve the fatigue strength of IRJs. Indeed, thanks to its adaptability it was possible to apply this technique to rail joints (Cannon, Sinclair, and Sharpe 1986; Reid 1993). During the split-sleeve cold expansion, an oversized tapered mandrel is forced to pass through the hole, whose effect is the plasticization of the material surrounding the hole and the induction of a residual stress field in this zone.