Feasibility of digital image correlation for railroad tie inspection and ballast support assessment

Structural Health Monitoring (SHM) of aging railway tracks is important for safety, to prevent catastrophic failure, and to reduce maintenance costs. The tracks and foundations are complex systems that may contain defects or damage including internal rail cracks, pitting or surface erosion, degradation of ballast support, or railway crosstie-ballast failures. In recent years, interest has grown in performing SHM by measuring structural deformation, full-field strain, and geometry profiles using three-dimensional (3D) Digital Image Correlation (DIC) systems. In this study, a novel approach to use DIC and pattern projection to assess the deformation of railway tracks is proposed. The proposed sensing approach should allow a railcar mounted sensing system to perform interrogation while moving at typical operating speeds (e.g. 60 mph). The feasibility of the proposed 3D DIC system is evaluated through extensive laboratory testing. The approach's ability to measure the crosstie's full-field displacement and shape (i.e. at levels similar to what is found in the field) as different loading conditions are applied is demonstrated. The influence of motion similar to what might be found in a railroad service environment on the accuracy of the measurements is also quantified.