The Characterization Of The Resistance ToLateral Impact Of The Insulating Parts Of TheP2 Rail Fastening

Abstract

A methodology is established for the laboratory simulation of the lateral impact process generated by the passing of trains on the insulating parts of the P2 rail fastening, which determines the relationship between the dynamic load applied on the insulating parts and their displacements. By comparing the types and forms of fracture obtained in the laboratory tests with those produced in situ on the line the validity of the similarities obtained is proven. To assist in the material selection and design for these parts the mechanical behaviour under impact of different materials (acetalic resin and polyamide reinforced with different grades of fibre glass) has also been performed. INTRODUCTION At the end of the 70's, RENFE (The Spanish National Railway Company) developed a new rail fastening system, called P2, as its predecesor, the RN system, presented two principal defects. Firstly it allowed relative movements between the rail and the sleeper, which produced variations in the width of the line, and secondly, it didn't guarantee the electrical insulation between the two rails which produced short-circuits. The P2 rail fastening system electrically insulates the line by including a non conductive polymeric part The rest of the elements that form the rail fastening (lockscrews, nuts, washers and steel plates) help to fix the rail in place. A neoprene plate is placed under the rail to absorb vibrations produced by the passing of the train. Figure 1 shows the P2 system. When the train circulates it produces a sudden lateral movement in the rail with respect to the sleeper, causing instantaneous forces on the fastening capable Transactions on the Built Environment vol 8, © 1994 WIT Press, www.witpress.com, ISSN 1743-3509 184 Structures under Shock and Impact of producing the fracture of the insulating parts which are the object of this study. The factors which influence this phenomena are the speed with which the trains circulate and their weight which is conveyed onto the exterior insulating parts of the fastening. This situation produces a transversal displacement in the track with respect to the sleeper following the longitudinal axis of the line. These movements occur on the straights because of the whiplash effect produced by the train as a consecuence of the variations in the width of the line. On the curves these transversal displacements are caused by the centrifugal force induced by the trains onto the track (eg. Beltran [1]). Figure 1: Sketch of the P2 rail fastening Service use of the P2 fastening on experimental lines shows up the existence of unexpected fractures, the frequency of which depends on the material, being greater in the parts made of more rigid and resistant polymeric material. The parts have been homologated as a function of their mechanical behaviour under static force, fatigue and creep, but the types of fracture observed at testing level don't correlate with those on the line (eg. RENFE [2]). The main objective of this work is to find a characterization test for the parts under applied loads at high speeds which can justify the cracks produced in service on the line. Also in this study, as a complement to previous work (eg. Valiente[3], Casado [4] and Polanco [5]), an analysis of insulating parts with different designs or materials has been carried out to assess their behaviour under impact phenomena.