Using Solitary Waves to Monitor/Measure Axial Stress

Abstract

This article presents a numerical formulation about the dynamic interaction between highly nonlinear solitary waves generated along a mono-periodic array of spherical particles and rails in a point contact with the array. A general finite element model of stress-free and axially stressed rails was developed and coupled to a discrete particle model able to predict the propagation of the solitary waves along an L-shaped granular medium located perpendicular and in a point contact with the web of the rail. The models were validated experimentally by testing a 0.9 m long rail segment subjected to compressive load. The scope of the study was the development of a new nondestructive evaluation technique able to estimate the stress in continuous welded rails and eventually to infer the track neutral temperature, i.e. the temperature at which the longitudinal stress in rails is zero. The numerical findings presented in this article demonstrate that certain features, such as amplitude and time of flight, of the solitary waves are affected by the axial stress. The experimental results confirmed the numerical prediction although laboratory constraints limited the ability to extend the stress range to significant levels of compression or to test longer rail segments in the operating rail system.