Improvement of crack detection on rough materials by digital holographic interferometry in combination with non-uniform thermal loads

The aim of this work is to present an experimental procedure to improve crack detection in rough surfaces by means of lensless Fourier digital holographic interferometry (DHI). To overcome the problem of analyzing high speckle interferograms that blurs phase maps and hinders, or even prevents, crack detection, it is proposed the application of a non-uniform thermal load to the object under study, as excitation source, instead of the most common uniform heating. Different tests with mock ups of cracks of controlled width allowed us to demonstrate the effect of a non-uniform thermal load, and confirmed the enhancement in DHI information, especially in unwrapping phase maps. Finally, DHI was applied to the detection of a crack in a cast iron sample and the results obtained with both uniform and non-uniform heating procedures were compared and the improvement attained by means of non-uniform heating was confirmed.