Spikes, together with tie plates and timber ties, are the dominant track components in North American freight railroads. For centuries, spikes, with marginal changes in terms of geometry and material, have consistently provided reliable restrictions to rails. With varying axle load and operational speed, spikes are being subjected to more demanding loading conditions, especially in the territories where tracks have high curvature and anchors are replaced with elastic fasteners. Recent inspections have identified frequent broken spikes in certain tracks. Traditional track inspection methods can hardly identify any broken spikes without manually pulling each spike out, which, of course, is impractical. This project first conducted numerical simulations to test the concept of using a laser to excite the spikes and estimate the reflection signals to distinguish between broken and good spikes. With the guidance of the numerical simulation results, laboratory experiments were also performed using laser pulses to excite the spike head and using a microphone and air coupled transducer to detect the reflection wave signals. Due to the high reflection rate of the spike’s head surface, a limited amount of laser energy penetrated into the spike. An ordinary microphone was not able to record distinguishable signals from the reflection waves from different spikes, even when the laser energy intensity was high enough to cause safety concerns. Fortunately, with guided wave and air-coupled transducer (ACT), the limited reflection wave could be detected and analyzed. Experiments with spikes oriented in both horizontal and vertical directions were performed.  With a carefully tuned setup in the laboratory, it was possible to distinguish broken spikes from good spikes.

The final report is available.