Monitoring of debonding or cracking in bending tests by virtual image correlation

Abstract

Three or four point bending tests are able to initiate controlled mixed mode cracking between two layers of different materials (Hun in Influence de l’eau sur le décollement d’une chaussée urbaine, 2012). The monitoring of such phenomena is a difficult challenge as if global force-displacement measurements are able to detect from the apparition of a non linearity the existence of a defect, they cannot determine its nature or location. More recent Digital Image Correlation (DIC) techniques can help however their application is limited because they require an image of a speckled side of the beam. Due to the form factor of the plate or beam, this image cannot cover all the side of the test except if one owns a ultra-high definition camera and lens. On the contrary the Virtual Image Correlation (VIC) method (François et al. in Eur Phys J App Phys 56:1-10, 2011) allows the measurement of the plate shape without any speckle thus does not require ultra high definition imaging. This global image is correlated to a virtual image whose parameterized shape is simply issued from the beam or plate theory. The delamination or the cracking is respectively introduced in the computation from simple reduction of the beam stiffness or a plastic joint. It will be shown that both their magnitude and location can be measured by using the VIC.