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Nanocompression of oriented pillars from Al thin film
Kuběna, Ivo ; Kruml, Tomáš
In this paper, a new method of measurement of mechanical properties of thin films is presented. This method combines specimen preparation by focused ion beam (FIB) and compression test using nanoindentation device. Compression specimens were prepared from thin film, Al-1.5%Cu, which is commonly used in integrated circuit. Cylindrical specimens were prepared by FIB milling. The height of specimens (pillars) was about 2 mircrometers (equal to the film thickness) and their diameter was about 1.3 micrometers. The pillars are single crystalline, therefore the results depend on crystallographic orientation of pillar, which was specified by EBSD (electron backscatter diffraction). Stress-strain curves of the thin film were obtained in two representations.
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Kinetics of fatigue crack growth in Eurofer 97 steel
Kruml, Tomáš ; Hutař, Pavel ; Náhlík, Luboš ; Seitl, Stanislav ; Polák, Jaroslav
The fatigue crack growth rate in the Eurofer 97 steel was measured by two different methodologies. Small crack growth data were obtained using cylindrical specimens with a shallow notch. No artificial crack starters were used. The growth of semicircular cracks of length between 10 – 2000 m were measured in symmetrical tension-compression cycling with constant strain amplitude (R = -1). Long crack data were measured using standard CT specimen and ASTM methodology in stress control with R = 0.1. The growth of fatigue cracks with length in the range of 10 – 30 mm was determined. It is shown that the crack growth rate of both types of cracks are in a very good agreement if J-integral rep-resentation is used and reasonable assumptions of the crack closure effects are taken into account.
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High-Quality Vector Field and Direct Vorticity Estimation Uusing the Affine Correlation Method
Gronát, Petr
We present a correlation method for direct vorticity computation of the fluid velocity field. The correlation method allows the affine transformation of a correlation window. It is shown that Lagrangian field of displacements is locally affine considering linear terms only. Using the Normalized-Cross-Correlation (NCC) combined with affine transformation and Newton-Raphson iterative method, six parameters defining this transformation are estimated. Subsequently, using these parameters, both displacement and vorticity can be computed, hence, these properties are being obtained for every single pixel directly during the correlation procedure.
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A New Method for Vector Fields Dynamic Analysis
Uruba, Václav
A method for analysis of spatio-temporal data is proposed. This is based on combination of Proper Orthogonal Decomposition and Principal Oscil-lation Patterns methods. The method provides dynamical characteristics of spatial modes evaluated either on both energetic or stability basis. Example on TR-PIV results on unsteady separation is shown.
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FE model of the human vocal folds considering fluid-structure interaction
Švancara, P. ; Horáček, Jaromír ; Hrůza, V.
The study presents three-dimensional finite element (FE) model of flow induced oscillations of the human vocal folds in interaction with acoustic processes in the simplified vocal tract model. The FE model includes vocal folds pretension before phonation, large deformations of the vocal fold tissue, vocal folds contact, fluid-structure interaction, morphing the fluid mesh according the vocal folds motion, unsteady viscous compressible airflow and airflow separation during the glottis closure. Fluid-structure interaction is solved using partitioned approach, where the results of solution for the flow are transferred as loads on the vocal folds surface, then the vocal folds motion is computed and then again the equations for the flow are solved. Numerical results confirmed that the developed model can be used for simulation of the vocal folds self-oscillations, and especially for numerical simulations of quantities that are difficult to measure in clinical research.
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Preliminary interferometry measurements of flow field around a fluttering NACA0015 profile
Vlček, Václav ; Kozánek, Jan
The paper presents experimental results of the optical measurements of flow field around a fluttering NACA0015 profile elastically supported with two degrees of freedom in subsonic wind flow. The high-speed camera was used for the interferometry visualization of the airflow in different phases of the profile motion. Special care was devoted to the plotting of the fringes near the surface of the profile, which was blurry due to the fast vibration. Examples of the interferograms, pressure and velocity development around the surface of the vibrating body and the phase shift between rotation and translation cycles are presented.
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Vibration and stability of electro-mechanical system with limited source of energy
Půst, Ladislav ; Radolfová, Alena
The paper presents an analysis of vibration of electromechanics system consisting of a 1DOF vibrating mechanical subsystem connected by means of spring and crank mechanisms with an electric driving motor with limited power and inertia. After transformation of motion equations and using averaging method, the approximate expressions for stationary and transient vibrations are derived. Owing to the non-ideal excitation, the unstable section of stationary response curve originates and causes jumps at transient processes. Influence of slope of moment characteristics and driving motor inertia on the range and level of instability domain is shown and discussed as well.
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