Material and component validation by speckle interferometry and correlation methods

Challenging the limits of modern material and component designs requires a deep understanding of the product performance with respect to stress distribution, fatigue and lifetime. With the help of modern simulation tools such as FEA this process has significantly been improved and simplified. However, for experimental validation in the test, modern and efficient test methods have to be provided. Here, the speckle technique offers an excellent potential. Electronic speckle pattern interferometry (ESPI) has been proven to be a flexible and efficient tool for characterisation of material properties of complex materials. Inversing the measuring principle by moving the illumination instead of the object, the ESPI technique also enables contour measurement functions, which have been integrated into the ESPI technique. This enlarged the application range to the inspection of components under load and for direct comparison of the measured contour and strain data with the FEA simulation. In order to meet the increasing need for the analysis of a larger range of deformations, for example informing processes or for inspection of polymers, the development of a new digital 3D image correlation technique was initiated. Two cameras observe the object under investigation and calculate the 3D surface of the component using a photogrammetric algorithm. The correlation of images, taken at different load levels leads to the complete information about the deformations and strains at each point of the surface. In this paper, both techniques are compared and examples of successful applications are presented.