Speaker
Description
In the field of experimental mechanics, strain is a very frequently measured variable. Furthermore, the experimental determination of inhomogeneous strains is often necessary. This requires powerful field measurement methods which, due to their characteristic, have a high information density. One measurement method that is becoming increasingly important in this context is digital image correlation (DIC), which is highly developed with increasingly powerful hardware and software. For small deformations, however, this method has system-related limitations due to its limited sensitivity. In contrast, for large deformations, this method is very well suited.
In this contribution, a method is presented that enables an extension of the measuring range of DIC to smaller deformations. For this purpose, a B-spline approximation of the displacements (DIC raw data) with optimized smoothing is carried out. To assess the method, it was analyzed regarding precision and accuracy in a four-point bending test with an aluminum beam in the elastic strain range of the metal. A 3D DIC strain analysis was performed at the front side between the load application sections. The very precise and accurate strain measurement using electrical strain gages, which were applied to the top and bottom of the bending beam between the load application sections, served as a reference measurement method. The results show good agreement of the strains, which proves the high precision and accuracy of the strain determination with the approximation-based method. In addition, the results are compared with strain distributions obtained using the standard evaluation method.
Furthermore, an application example for the method, which has been extended with regard to circular boundaries, is shown. Therein, the deformation analysis of a borehole environment at a loaded plastic specimen based on 2D DIC data is presented, which is potentially to be used in the context of residual stress analyses. The strain fields obtained in this way show high precision likewise.
