Ap Andre Ruybalid

On the Boundary Conditions and Optimization Methods in Integrated Digital Image Correlation

In integrated digital image correlation (IDIC) methods attention must be paid to the influence of using a correct geometric and material model, but also to make the boundary conditions in the FE simulation match the real experiment. Another issue is the robustness and convergence of the IDIC algorithm itself, especially in cases when (FEM) simulations are slow. These two issues have been explored in this proceeding. The basis of the algorithm is the minimization of the residual. Different approaches for this minimization exist, of which a Gauss-Newton method is used most often. In this paper several other methods are presented as well and their performance is compared in terms of number of FE simulations needed, since this is the most time-consuming step in the iterative procedure. Beside method-specific recommendations, the main finding of this work is that, in practical use of IDIC, it is recommended to start using a very robust, but slow, derivative-free optimization method (e.g. Nelder-Mead) to determine the search direction and increasing the initial guess accuracy, while after some iterations, it is recommended to switch to a faster gradient-based method, e.g. (update-limited) Gauss-Newton.

Advances in Delamination Modeling of Metal/Polymer Systems: Continuum Aspects

Adhesion and delamination have been pervasive problems hampering the performance and reliability of micro- and nano-electronic devices. In order to understand, predict, and ultimately prevent interface failure in electronic devices, development of accurate, robust, and efficient delamination testing and prediction methods is crucial. Adhesion is essentially a multi-scale phenomenon: at the smallest scale possible, it is defined by the thermodynamic work of adhesion. At larger scales, additional dissipative mechanisms may be active which results in enhanced adhesion at the macroscopic scale and are the main cause for the mode angle dependency of the interface toughness. Undoubtedly, the macroscopic adhesion properties are a complex function of all dissipation mechanisms across the scales. Thorough understanding of the significance of each of these dissipative mechanisms is of utmost importance in order to establish physically correct, unambiguous values of the adhesion properties, which can only be achieved by proper multi-scale techniques.

Full-Field Identification of Interfaces in Microelectronic Devices

To improve the integrity of densely stacked multilayers in microelectronic systems, e.g., Light Emitting Diodes (LED), and thereby overcome the currently experienced problems related to interface failure during manufacturing of such devices, accurate identification of interface properties is essential. The behavior of the interface is only measurable through kinematic information from adjacent materials.The goal of this research is to identify interface parameters by Integrated Digital Image Correlation (IDIC), in which experimental images of a deformation process are correlated by utilizing the mechanical response from finite element (FE) simulations. An interface is herein modeled by cohesive zone (CZ) elements exhibiting constitutive traction-separation laws. The versatility of FE simulations and the kinematic richness of the full-field measurements are thereby exploited.Comprising an elastic hinge system, a small-scale mechanical test-setup is designed from two 3-axes (XYZ) piezo stages, with which micrometer displacements and realistic interface loading conditions (shear, normal, and mixed-mode loading) can be applied to an LED specimen. This allows to, in a well-controlled manner, mechanically mimic interface delamination that is typically induced during fabrication steps by thermal expansion. This setup and the IDIC method are integrated to identify the CZ parameters of the critical interface of an LED specimen.

Self-adaptive isogeometric global digital image correlation and digital height correlation

This work explores the full potential of isogeometric shape functions for global digital image correlation. To this end, a novel DIC and DHC (digital height correlation) methodology have been developed based on adaptive refinement of isogeometric shape functions. Non-Uniform Rational B-Spline (NURBS) shape functions are used employed of their flexibility and versatility, which enables a wide range of kinematic descriptions. In the adaptive refinement algorithm, the shape functions are automatically adjusted to be able to describe the kinematics of the sought (2D or 3D) displacement field with an optimized number of degrees of freedom. Both methods show high accuracy as demonstrated by various virtual experiments with predefined, highly localized (2D and 3D) displacement field. For adaptive iso-GDIC, real tensile tests of complex sample geometries demonstrate its effectiveness in practice, showing local refinement at the areas of localization, without the need of making problem-specific choices regarding the structure of the shape functions. For adaptive iso-GDHC, the correlation of surface height profiles of deforming stretchable electronics structures shows successful autonomous refinement at two localized buckles, thereby strongly reducing the 3D residual, while also analytical differentiation of the C1-continuous 3D displacement field yields the curvature field of the deforming stretchable interconnect.

Full-field identification methods:comparison of FEM updating and integrated DIC

Full-field identification methods are increasingly used to adequately identify constitutive parameters to describe the mechanical behavior of materials. This research investigates the more recently introduced, one-step method of Integrated Digital Image Correlation (IDIC) with respect to the most commonly used, two-step method of Finite Element Model Updating (FEMU), which uses a subset-based digital image correlation algorithm.

Performance Assessment of Integrated Digital Image Correlation Versus FEM Updating

Full-field identification methods can adequately identify constitutive material parameters, by combining Digital Image Correlation (DIC) with Finite Element (FE) simulation. It is known that interpolation within the DIC procedure is an important error source for DIC-results. In this study, the influence of these errors on the eventual identification results is investigated.