Fatigue failure of short glass fibre reinforced PA 6.6 structural pieces for railway track fasteners

The optimal viscosity for railway fastening parts, injected with a thermoplastic polymeric matrix of PA 6.6 (Nylon 6.6) reinforced with a 35% weight of short glass fibre, guarantees that they work properly during the mechanical actions applied on them in relation with the forces transmitted by the rails. Under the previous optimum material injection criteria, verified in this work, a fatigue characterization for the polymeric parts using the Locati method has been developed in this paper. A model is proposed for the identification of the critical conditions through a study of the evolution of various parameters during the fatigue process: the stored and dissipated energy and the phase lag between the load and strain signals These parameters will indicate the situation for which the material temperature reaches the glass transition value, as a consequence of the internal heat generated by the fatigue. From this point the material increases its deformation continuously due to the material damage leading to the fatigue failure.