2‐D crack growth measurement using circular grating moiré fringes and pattern matching: Fid-Bau Portal

2‐D crack growth measurement using circular grating moiré fringes and pattern matching

Yen, K. S. / Ratnam, M. M.

A two‐dimensional (2‐D) crack growth measurement method that uses moiré fringes generated by circular gratings and pattern matching was developed in this work for application in structural health monitoring. The moiré fringe patterns were extracted by transforming the circular gratings into linear gratings using polar‐radius transformation and applying a one‐dimensional average filter. The filtered image was inversely transformed to recover the moiré fringes. Pattern matching was performed by comparing the absolute difference between an input fringe pattern caused by an unknown displacement and a series of reference fringe patterns of known displacements in one direction. The matching of the moiré fringes caused by displacement at 90° to that in the reference patterns and combination of the two orthogonal directions was carried out after applying a rotational angle search algorithm. Demonstration using a crack model showed the applicability of the proposed system for the measurement of relative displacement of crack development along two directions with a sensitivity of 0.02 mm. The measured displacements were found to have high correlation with the actual displacements with a R² value of 0.9985. Copyright © 2010 John Wiley & Sons, Ltd.