54 S.M. Kleinendorst et al. 8.5 Conclusions A novel method called Mechanical Shape Correlation has been developed. It is an integrated digital image correlation based method, which uses a finite element model for regularization of the displacement field. The goal of such a method is to obtain an adequate set of constitutive model parameters, such that the FE model describes the real, experimentally observed, behavior of the sample correctly. The novelty lies in the use of projections of the sample contour as input images for the algorithm, rather than grayscale speckle patterns. This approach makes it possible to apply the technique to experiments for which existing techniques are difficult to use, because of complex three-dimensional deformations that makes parts of the specimen move out of view or because of complications with pattern application. The MSC algorithm was explained along with some important changes with respect to the IDIC algorithm. The most important change is the type of images used and attention was paid as to how to create these projections from FE simulations and the important steps taken herein. Also masking of the structure itself in the created projections plays an important role. Two virtual experiments were executed to examine the method’s performance. The first virtual test case includes analysis of the difference in results in case the structure is masked in the images or not masked. It was concluded that the convergence behavior improves if masking is applied for all considered parameter variations, including the initial guess and perturbation factor P, but that the effect is strongest for small perturbation factors. In both virtual experiments a good accuracy in the objective model parameter, the Young’s modulus E, was obtained in a reasonably low amount of iterations. These results are promising for the method’s performance in other test cases. References 1. Neggers, J., Hoefnagels, J.P.M., Geers, M.G.D., Hild, F., Roux, S.: Time-resolved integrated digital image correlation. Int. J. Numer. Methods Eng. 103(3), 157–182 (2015). doi:10.1002/nme.4882 2. Ruybalid, A.P., Hoefnagels, J.P.M., van der Sluis O., Geers, M.G.D.: Comparison of the identification performance of conventional FEM updated and integrated DIC. Int. J. Numer. Methods Eng. 106(4), 298–320, (2016). doi:10.1002/nme.5127 3. Kleinendorst, S.M., Hoefnagels, J.P.M., Geers, M.G.D.: Mechanical shape correlation: a novel integrated digital image correlation approach. (2017, In preparation) 4. Han, K., Ciccotti, M., Roux, S.: Measuring nanoscale stress intensity factors with an atomic force microscope. EPL (Europhys. Lett.) 89(6), 66003 (2010). doi:10.1209/0295-5075/89/66003 5. Bergers, L.I.J.C., Hoefnagels, J.P.M., Geers, M.G.D.: Characterization of time-dependent anelastic microbeam bending mechanics. J. Phys. D. Appl. Phys. 47, 1–14 (2014). doi:10.1088/0022-3727/47/35/355306 6. Neggers, J., Hoefnagels, J.P.M., Hild, F., Roux, S., Geers, MG.D.: Direct stress-strain measurements from bulged membranes using topography image correlation. Exp. Mech. 54(5), 717–727 (2014). doi:10.1007/s11340-013-9832-4 7. Kleinendorst, S.M., Hoefnagels, J.P.M., Fleerakkers, R.C., van Maris, M.P.F.H.L., Cattarinuzzi, E., Verhoosel, C.V., Geers, M.G.D.: Adaptive isogeometric digital height correlation: application to stretchbale electronics. Strain 52(4), 336–354 (2016). doi:10.1111/str.12189 8. Luo, P.F., Chao, Y.J., Sutton, M.A., Peters, W.H.: Accurate measurement of three-dimensional deformations in deformable and rigid bodies using computer vision. Exp. Mech. 33(2), 123–132 (1993). doi:10.1007/BF02322488 9. Sutton, M.A., Orteu, J.J., Schreier, H.W.: Image Correlation for Shape, Motion and Deformation Measurement: Basis Concepts, Theory and Applications. Springer, Berlin (2009) S.M. Kleinendorst is a PhD-researcher in the Mechanics of Materials group at Eindhoven University of Technology. Her research is about stretchable electronics (SE) and in particular the development of algorithms that couple experimental observations to finite element simulations in order to obtain representative FE models, which can then be used to optimize the SE. J.P.M. Hoefnagels is associate professor in the field of experimental solid mechanics with a focus on thin films and interfaces. The research includes size effects, interface and damage mechanics, flexible/stretchable electronics, and MEMS. M.G.D. Geers is full professor in Mechanics of Materials at the Eindhoven University of Technology, Eindhoven, the Netherlands. His present interests are damage mechanics, micromechanics, multi-scale mechanics, generalized continua, crystal plasticity and metal forming, with a focus on numerical modeling.
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