Semi-Automatic Deflection Measurement Using Digital Image Correlation

Abstract

The aim of this thesis was to develop an easy-to-use method for providing initial guesses for DIC grid point locations and rotations on objects where major deflection occurs. Study of literature revealed that special approach is required to be able to perform DIC on subsets that are rotated, although such methods exist they are difficult to implement. A method was proposed that employs manual input for creating a curve across image width that describes the specimen deformation. Deflection curve could then be used to provide initial guesses and rotations prior DIC. The approach was implemented using MATLAB and several tests were made to evaluate the algorithm. The results showed that curve based grid transformation can provide sufficient estimation to be able to carry out DIC measurements and converge to sub-pixel accurate solution. The magnitude of displacement error caused by transformation was shown to be irrelevant when search windows are big enough for the correct location to be included. However rotational errors were proven to be significant for sub-pixel accuracy, additional method was proposed and shown to work for compensating errors in rotation estimations. In conclusion the results have shown that the described method can be used for providing initial guesses for grid point locations on deflected objects. Therefore DIC can be used with this approach to carry out deflection measurements.