This thesis presents a flexible graphene/polyvinylidene difluoride (PVDF)/graphene sandwich for three-dimensional touch interactivity. Here, an x-y plane touch is sensed using graphene capacitive elements, while force sensing in the z-direction is by a piezoelectric PVDF/graphene sandwich. By employing different frequency bands for the capacitive- and force-induced electrical signals, the two stimuli are detected simultaneously, achieving three-dimensional touch sensing. Static force sensing and elimination of propagated stress are achieved by augmenting the transient piezo output with the capacitive touch, thus overcoming the intrinsic inability of the piezoelectric material in detecting non-transient force signals and avoiding force touch mis-registration by propagated stress. As a capacitive signal is important for force touch interpretation, optimization algorithms have been developed and implemented. With correlated double sampling (CDS) and spatial low-pass filtering (SLPF) based techniques, the signal-to-noise ratio (SNR) of the capacitive touch signal is boosted by 15.6 dB, indicating improved detection accuracy. In terms of the readout speed, fixed pattern and random pattern related down-sampling techniques are applied, giving rise to reductions in both readout time (11.3 ms) and power consumption (8.79 mW).

Although the topic of international mediation has been debated frequently amongst academic scholars, most literature has failed to address the notion of threat perception. This thesis examines the impact of threat perceptions from ideational and material force on the prospects for successful international mediation. In this comparative case study, I argue that threat perception is an influential factor conditioning the road towards peace agreements, by examining one case of failure and one case of success in international mediation of interstate conflicts. The first case in the comparison consists of the conflict between Armenia-Azerbaijan in the disputed region of Nagorno-Karabakh, where the OSCE Minsk Group has conducted mediation efforts. The second case examined is the conflict between Israel-Egypt which predominately have been mediated by the US. A conflict which ending was marked by the Camp David Accords in 1978 and resulted in a peace treaty the year after. The analysis shows that threat perception is indeed a factor of importance for outcome in relation to international mediation. Compared to previous research largely focused on material factors, the result shows that ideational factors should be considered to the same extent and are influential in both cases. This contribution to the field of war studies and international mediation literature also reflects the interconnectivity between threat perceptions from ideational and material force. An insight which I argue is pivotal for the comprehension of why some interstate conflicts appear to be resistant to resolution.

<div>As physical testing does not always yield insight into the mechanistic cause of failures, computational modeling is often used to develop an understanding of the goodness of a design and to shorten the product development time. One common, and widely used analysis technique is the Finite Element Method. A significant difficulty with the finite element method is the effort required to generate an analysis-suitable mesh due to the difference in the mathematical representation of geometry CAD and CAE systems. CAD systems commonly use Non-Uniform Rational B-Splines (NURBS) while the CAE tools rely on the finite element mesh. Efforts to unify CAD and CAE by carrying out analysis directly using NURBS models termed Isogeometric Analysis reduces the gap between CAD and CAE phases of product development. However, several challenges still remain in the field of isogeometric analysis. A critical challenge relates to the output of commercial CAD systems. B-rep CAD models generated by commercial CAD systems contain uncoupled NURBS patches and are therefore not suitable for analysis directly. Existing literature is largely missing methods to smoothly couple NURBS patches. This is the first topic of research in this thesis. Fracture-caused failures are a critical concern for the reliability of engineered structures in general and semiconductor chips in particular. The back-end of the line structures in modern semiconductor chips contain multi-material junctions that are sites of singular stress, and locations where cracks originate during fabrication or testing. Techniques to accurately model the singular stress fields at interfacial corners are relatively limited. This is the second topic addressed in this thesis. Thus, the overall objective of this dissertation is to develop an isogeometric framework for parametric domain decomposition and analysis of singular stresses using enriched isogeometric analysis.</div><div><br></div><div>Geometrically speaking, multi-material junctions, sub-domain interfaces and crack surfaces are lower-dimensional features relative to the two- or three-dimensional domain. The enriched isogeometric analysis described in this research builds enriching approximations directly on the lower-dimensional geometric features that then couple sub-domains or describe cracks. Since the interface or crack geometry is explicitly represented, it is easy to apply boundary conditions in a strong sense and to directly calculate geometric quantities such as normals or curvatures at any point on the geometry. These advantages contrast against those of implicit geometry methods including level set or phase-field methods. In the enriched isogeometric analysis, the base approximations in the domain/subdomains are enriched by the interfacial fields constructed as a function of distance from the interfaces. To circumvent the challenges of measuring distance and point of influence from the interface using iterative operations, algebraic level sets and algebraic point projection are utilized. The developed techniques are implemented as a program in the MATLAB environment named as <i>Hierarchical Design and Analysis Code</i>. The code is carefully designed to ensure simplicity and maintainability, to facilitate geometry creation, pre-processing, analysis and post-processing with optimal efficiency. </div><div><br></div><div>To couple NURBS patches, a parametric stitching strategy that assures arbitrary smoothness across subdomains with non-matching discretization is developed. The key concept used to accomplish the coupling is the insertion of a “parametric stitching” or p-stitching interface between the incompatible patches. In the present work, NURBS is chosen for discretizing the parametric subdomains. The developed procedure though is valid for other representations of subdomains whose basis functions obey partition of unity. The proposed method is validated through patch tests from which near-optimal rate of convergence is demonstrated. Several two- and three-dimensional elastostatic as well as heat conduction numerical examples are presented.</div><div><br></div><div>An enriched field approximation is then developed for characterizing stress singularities at junctions of general multi-material corners including crack tips. Using enriched isogeometric analysis, the developed method explicitly tracks the singular points and interfaces embedded in a non-conforming mesh. Solution convergence to those of linear elastic fracture mechanics is verified through several examples. More importantly, the proposed method enables direct extraction of generalized stress intensity factors upon solution of the problems without the need to use <i>a posteriori</i> path-independent integral such as the J-integral. Next, the analysis of crack initiation and propagation is carried out using the alternative concept of configurational force. The configurational force is first shown to result from a configurational optimization problem, which yields a configurational derivative as a necessary condition. For specific velocities imposed on the heterogeneities corresponding to translation, rotation or scaling, the configurational derivative is shown to yield the configurational force. The use of configurational force to analyze crack propagation is demonstrated through examples.</div><div><br></div><div>The developed methods are lastly applied to investigate the risk of ratcheting-induced fracture in the back end of line structure during thermal cycle test of a epoxy molded microelectronic package. The first principal stress and the opening mode stress intensity factor are proposed as the failure descriptors. A finite element analysis sub-modeling and load decomposition procedure is proposed to study the accumulation of plastic deformation in the metal line and to identify the critical loading mode. Enriched isogeometric analysis with singular stress enrichment is carried out to identify the interfacial corners most vulnerable to stress concentration and crack initiation. Correlation is made between the failure descriptors and the design parameters of the structure. Crack path from the identified critical corner is predicted using both linear elastic fracture mechanics criterion and configurational force criterion. </div>

The study at hand introduces a newapproach to characterize fatigue crack growth in small strain linear viscoelastic solids by configurational mechanics. In this study, Prony series with n-Maxwell elements are used to describe the viscoelastic behavior. As a starting point in this work, the local balance of energy momentum is derived using the free energy density. Moreover, at cyclic loading, the cyclic free energy substitutes the free energy. Using the cyclic free energy, the balance of cyclic energy momentum is obtained. The newly derived balance law at cyclic loading is appropriate for each cycle. In the finite element framework, nodal material forces and cyclic nodal material forces are obtained using the weak and discretized forms of the balance of energy momentum and cyclic energy momentum, respectively. The crack driving force and the cyclic crack driving force are determined by the nodal material forces and the cyclic nodal material forces, respectively. Finally, numerical examples are shown to illustrate path-independence of the domain integrals using material forces and cyclic material forces. The existence of the balance of energy momentum and cyclic energy momentum are also illustrated by numerical examples.