Low cost digital image correlation (DIC) for monitoring components undergoing fatigue loading

Abstract

An alternative approach to dealing with noise in digital image correlated data. The target application is for non-destructive inspection of components outside of laboratory conditions, where oscillatory loading (either as part of the normal service or especially excited) is used to produce the strain changes required to determine the strain field. The approach is to use a lock-in amplifier, obtaining the reference signal from an accelerometer on the structure under scrutiny. The challenge of low sampling rates relative to the loading excitation is considered, and it is demonstrated that by careful selection of sampling and loading frequency combinations, standard low speed, low cost digital cameras can be used to obtain high fidelity strain measurements with a fine spatial resolution.