Fiducial marker and blob detection-based motion compensation algorithm for Thermoelastic Stress Analysis measurements

Non-contact techniques for measuring stress and strain on structures offer advantages including preservation of structural integrity, remote and continuous monitoring, full-field measurement capability, non-destructive testing, and adaptability to various materials. Among them, thermoelastic stress analysis is one of the most established non-contact techniques to measures stress distributions in structures by analysing temperature-induced deformations. This research proposes a methodology for the compensation of the edge effect, a undesirable phenomenon resulting from rigid displacements in the analysed structure when using thermoelasticity approach. These displacements give rise to virtual stress distributions along the sample's edges. For this purpose, a fiducial marker was used to track rigid displacements in thermal images, that were then processed using a blob detection algorithm, for compensating for edge effects under different loading conditions. The algorithm was capable of measuring the displacement of a sample at different frequencies (5-25Hz) and distances from the target (300-600 mm), with the lowest uncertainty of 0.2 mm. The impact of compensation was found The impact of the compensation was found to be significant, especially at frequencies lower than 10 Hz, where the displacement was the highest.