We have developed a new digital image correlation (DIC) algorithm for non-contact, two-dimensional, whole-field displacement and strain measurement. Relative to existing algorithms, our algorithm substantially reduces the calculation expense by using neighborhood information while processing the data to determine the displacement field in a sub-region of interest. The new algorithm also uses higher-order interpolations of the displacement field, allowing for better accuracy in estimating strain distributions when the deformation field is non-homogeneous. Numerically-generated digital images are used to show that the new algorithm accurately reproduces the imposed displacement fields. The algorithm is also tested on actual images from deformed specimens from a variety of experiments, and shown to perform satisfactorily. / Singapore-MIT Alliance (SMA)

The aim of this thesis is to design and build a torsional Kolsky bar apparatus for testing cylindrical specimens in torsion at high strain-rates. In addition to well-established designs, this testing apparatus will include a conical mirror combined with a high speed camera that allows time-resolved optical observation of the shear deformation on the surface of the specimen. The basic design of a Kolsky bar consists of a loading bar, input bar, specimen, and output bar. The experiment is conducted by storing torque in the loading bar and then releasing the torque by breaking the clamp and sending a shear wave pulse through the apparatus into the specimen. This shear wave pulse is monitored by strain gages mounted on the input and output bars. Analysis of the strain waves in the input and output bar is used to extract the shear stress - shear strain profile of the specimen. Several experiments were conducted on 6061-O and 1100-O aluminum with wall thicknesses ranging from 0.3 to 1.5 mm. / text

In this thesis, vibration analyses of electronic assemblies that consist of an electronic box, printed circuit board and electronic components are presented. A detailed vibration analysis of a real electronic assembly is performed by finite element methods and vibration tests. Effects of component addition and component modeling are investigated by finite element analysis in detail. Results are compared in order to identify the most efficient, reliable and suitable method depending on the type of problem. Experimental results for the vibration of an electronic box, PCB and components are presented and discussed. Furthermore, an analytical model that represents a printed circuit board and electronic component is suggested for fixed and simply supported boundary conditions of the PCB. Different types of electronic components are modeled analytically to observe different dynamic characteristics. The validity of the analytical model is computationally checked by comparing results with those of finite element solution.

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No description available.

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Structural optimization is achieving the best objective function from a predefined medium, well bounded by constraints. Optimization methods have been utilized on different engineering applications to minimize the conceptual design effort that creates the necessity of new optimization techniques. Evolutionary Structural Optimization (ESO) is a topological optimization algorithm, which is defined as removing of inefficient elements from a design domain. ESO stress based method is applied to linear elastic, isotropic aircraft components for multiple load case. The bulk structure is modeled and discretized into three dimensional solid hexahedron or tetrahedron mesh, afterwards constraints, load and boundary conditions are defined in MSC.PATRAN. MSC.NASTRAN is utilized as finite element solver. The stress results are collected and evaluated by program developed in MICROSOFT VISUAL BASIC. The elements which are below the stress limit are eliminated. The remaining elements are operated after increasing the stress limit. The iteration process continued until prescribed rejection ratio is reached. Well known examples in literature are solved using program code and similar results are obtained which is a check for the code developed. Four generic aircraft components, the clevis, the lug, the main landing fitting and power control unit fitting were structurally optimized. The stress distribution in optimized results and existing aircraft designs are compared.

The application of polymers in robust engineering designs is on the rise due to their excellent mechanical properties such as high fracture toughness, specific strength, durability, as well as, thermal and chemical resistances. Implementation of some advanced polymeric solids is limited due to the lack of available mechanical properties. In order for these materials to endure strenuous engineering designs it is vital to investigate their response in multiple loading rates and conditions. In this thesis, the mechanical response of polyethermide (PEI) is characterized under quasi-static, high strain rate, and multiple impact conditions. Standard tension, torsion, and compression experiments are performed in order to distinguish the multi-regime response of PEI. The effects of physical ageing and rejuvenation on the quasi-static mechanical response are investigated. The strain softening regime resulting from strain localization is eliminated by thermal and mechanical rejuvenation, and the advantages of these processes are discussed. The dynamic fracture toughness of the material in response to notched impact via Charpy impact test is evaluated. The high strain-rate response of PEI to uniaxial compression is evaluated at rates exceeding 104/s via miniaturized Split Hopkinson Pressure Bar (MSHPB), and compared to the quasi-static case to determine strain-rate sensitivity. The elastic response of the aged material to multiple loading conditions are correlated using the Ramberg-Osgood equation, while the elastoplastic response of rejuvenated PEI is correlated using a both the Ramberg-Osgood equation and a novel model. The strain-rate sensitivity of the strength is found to be nominally bilinear and transition strains are modeled using the Ree-Erying formulation. Finally, multiple impact experiments are performed on PEI using the MSHPB and a model is proposed to quantify damage as a result of collision.

With the rapid development in today&rsquo / s technology, reliability and performance requirements on components of various mechanical systems, which tend to be much lighter and work under much more severe working conditions, dramatically increased. In general, analysis techniques based on simplified model of structural components with linearity assumption may provide time saving for solutions with reasonable accuracy. However, since most engineering structures are often very complex and intrinsically nonlinear, in some cases they may behave in a different manner which cannot be fully described by linear mathematical models, or linear treatments may not be applicable at all. In fact, some studies revealed that deviations in the modal properties of dynamic structures gathered from measured data are due to nonlinearities in the structure. Hence, in problems where accuracy is the primary concern, taking the nonlinear effects into account becomes inevitable. In this thesis, it is aimed to analyze the harmonic response characteristics of multi degree of freedom nonlinear structures having different type of nonlinearities. The amplitude dependencies of nonlinearities are modelled by using describing function method. To increase the accuracy of the results, effect of the higher order harmonic terms will be considered by using multi harmonic describing function theory. Mathematical formulations are embedded in a computer program developed in MATLAB&reg / with graphical user interface. The program gets the system matricies from the file which is obtained by using substructuring analysis in ANSYS&reg / , and nonlinearities in the system can easily be defined through the graphical user interface of the MATLAB&reg / program.

Der Tagungsband wurde im Rahmen des 10th Youth Symposium on Experimental Solid Mechanics vom 25. bis 28. Mai 2011 an der Technischen Universität Chemnitz publiziert. Es werden aktuelle Arbeiten von jungen Wissenschaftlern aus 11 Nationen auf dem Gebiet der experimentellen Festkörpermechanik vorgestellt. Dabei reichen die Beiträge von Material- über Bauteilprüfung bis zur Biomechanik und beleuchten eine Reihe unterschiedlicher Messmethoden und Anwendungen. / This proceedings were published on the occasion of the 10th Youth Symposium on Experimental Solid Mechanics from 25th to 28th May 2011 at the Chemnitz University of Technology. It presents the current work from young researchers from 11 nations in the field of experimental solid mechanics. The contributions have a range from materials testing over components testing to biomechanics and examine a number of different measurement methods and applications.