The widespread use of the concrete sleeper has led to substantial changes in railway fastening systems, since these require an elastic element to be placed between the rail and the sleeper itself in order to avoid, as far as possible, impact loads between the two components and to counteract the excessive stiffness of the concrete (3- 5 times suffer than wooden sleepers). This element is called the 'elastic setting pad'. Thermoplastic elastomer railway pads, placed between the base of the steel rails and the prestressed concrete sleepers, play a major role in the general maintenance of the state of the overall structure of a railway line. These rail setting pads provide the elasticity of the line and damp the vibrations which the rail transmits to the sleeper, thus avoiding the cracking of the concrete sleepers and preventing the wear and tear of the ballast. They also provide electrical insulation between the rails. This paper describes a test methodology for determining the dynamic behaviour of railway fastening setting pads in working conditions, which may involve a wide range of temperatures associated to the wear and the hardening they undergo during the cyclical load process applied on them caused by the passing of the trains. To this end, measurements of the evolution of the stiffness of the pads have been made, both static and dynamic. Also associated energy parameters have been measured, establishing an index of the degree of deterioration undergone by these pads. The deterioration in the railway setting pad produced by its use in normal working conditions can be evaluated using the value of dissipated energy, Ed, per cycle in both dynamic and static conditions. This energetic parameter varies linearly with temperature, allowing a direct correlation to be established with the stiffness and hardness of the pad. Hardness correlates linearly with stiffness and so an index of the degree of degradation in the pad can be established. This parameter is very useful as it can be easily measured by a non destructive test on the own track. Extreme temperature values on the railway track (-20 and 80 deg C) establish threshold working values for setting pads. Under normal working conditions, the environmental ageing of the setting pads does not generate a great decrease in the mechanical performance characteristics. In the worst case, for pads with an excessive degree of humidity, condition H, a stiffness increase of 12% after the fatigue process, can be obtained.
Dynamic behaviour of railway fastening setting pads
Dynamisches Verhalten von Eisenbahn Fixierungs- und Befestigungselementen
2007
10 Seiten, 17 Bilder, 2 Tabellen, 8 Quellen
Conference paper
English
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