Towards the Development of a Global Cn-Continuous DIC Procedure?

In this work, a novel yet easy to use Global Digital Image Correlation algorithm is presented. The proposed method is developed to counter one of the important drawbacks of the most frequently adopted DIC techniques, namely the non-continuity of the strain field. In both the local subset method (no continuity) as in the widely known global Q4-DIC method (C0-continuity) this problem arises. The proposed method is developed to obtain a C1-continuous displacement field, and thus obtain a continuous strain field. In this way, strains can be derived directly from the algorithm without any post processing or filtering of the displacement, this in contrast to the previously mentioned DIC techniques. In these, the strain calculation is mostly done by using polynomial smoothing (e.g. strain window) of the displacement field. The extent of smoothing is controlled by user settings, making the measurement results significantly influenced by the user. The proposed algorithm uses well known principles both from the standard global DIC method as well as principles from finite element analysis to obtain a continuous strain field. Here an algorithm is presented using rather simple, specifically developed element shape functions, making the algorithm extremely easy to be implemented in a standard global approach.