Evaluation Methods of Mechanical Properties of Micro-Sized Specimens

Micro-sized components have been widely used to microelectromechanical systems (MEMSs) and medical apparatus in recent years. Measurement methodologies of the mechanical property of small materials need to be improved for structural designing of these devices because of their component size reduced to micro- or nano-regime where sample size effects emerge. Mechanical properties and deformation behavior could be very different with their dimensions and geometries especially for small materials. Our experiments on the micro-specimen tested in different dimensions and loading directions are suitable for the evaluations of materials for MEMS components. In this chapter, recent studies on micro-testing of bending, compression, and tension with micro-sized samples will be presented including fabrication methods of non-tapered micro-sized specimens

Mechanical Property Evaluation of Electrodeposited Nanocrystalline Metals by Micro-testing

Electrodeposition is a very important technology in the fabrication of micro-components for micro-electro-mechanical systems (MEMS) or integrated circuits. Evaluations of the materials used in these devices as 3D components should be conducted using micro-sized specimens due to the sample size effect on the practical use of the components. Nanocrystalline metals could be deposited using an electrodeposition method with supercritical CO2 emulsion. Our experiment on the micro-specimens provides information on micro-mechanical testing of electrodeposited metals including the effect of sample size, grain size, and anisotropic structures on mechanical properties. In this chapter, recent studies on crystal growth in electrodeposition of metals and its evaluation using micron-sized testing will be presented

Electrodeposition of Gold Alloys and the Mechanical Properties

Strengthening of electrodeposited gold-based materials is achieved by alloying with copper according to the solid solution strengthening mechanism. Composition of the Au–Cu alloys is affected by the applied current density. The mechanical properties are evaluated by micro-compression tests to evaluate the mechanical properties in microscale to take consideration of the sample size effect for applications as microcomponents in MEMS devices. The yield strength reaches 1.15 GPa for the micropillar fabricated from constant current electrodeposited Au–Cu film, and the film is composed of 30.3 at% Cu with an average grain size of 5.3 nm. The yield strength further increases to 1.50 GPa when pulse current electrodeposition method is applied, and the Cu concentration is 36.9 at% with the average grain size at 4.4 nm

Pulse-Current Electrodeposition of Gold

Pulse-current electrodeposition and a sulfite-based electrolyte were used in fabrication of pure gold films. Surface of the pulse-electrodeposited gold film possessed less defect, lower roughness, smaller grain size, and denser texture when compared with the gold film prepared by constant-current electrodeposition. Microstructures and compressive yield strength of the electrodeposited gold could be controlled by regulating the pulse on-time and off-time intervals in pulse-current electrodeposition. The gold film prepared under the optimum conditions showed an average grain size at 10.4 nm, and the compressive yield strength reached 800 MPa for a pillar-type micro-specimen having dimensions of 10 μm × 10 μm × 20 μm fabricated from the pulse-electrodeposited gold film. Average grain size of the pulse-electrodeposited gold film was much smaller, and the compressive yield strength was much higher than the values reported in other studies. The high strength is due to the grain boundary strengthening mechanism known as the Hall-Petch relationship. In general, the pulse-electrodeposited gold films showed yield strength ranging from 400 to 673 MPa when the average grain size varied by adjusting the pulse-electrodeposition parameters

Phenotypic Spectrum Caused by Transgenic Overexpression of Activated Akt in the Heart

The serine-threonine kinase, Akt, inhibits cardiomyocyte apoptosis acutely both in vitro and in vivo. However, the effects of chronic Akt activation in the heart are unknown. To address this issue, we generated transgenic mice (TG ) with cardiac-specific expression of a constitutively active mutant of Akt (myr-Akt) driven by the myosin heavy chain- promoter. Three TG founders (9–19 weeks) died suddenly with massive cardiac dilatation. Two viable TG lines (TG564 and TG20) derived from independent founders demonstrated cardiac-specific transgene expression as well as activation of Akt and p70S6 kinase. TG564 (n 19) showed cardiac hypertrophy with a heart/body weight ratio 2.3-fold greater than littermates (n 17, p < 0.005). TG20 (n 18) had less marked cardiac hypertrophy with a heart/body weight ratio 1.6-fold greater than littermates (n 17, p < 0.005). Isolated TG564 myocytes were also hypertrophic with surface areas 1.7-fold greater than littermates (p < 0.000001). Echocardiograms in both lines demonstrated concentric hypertrophy and preserved systolic function. After ischemia-reperfusion, TG had a 50% reduction in infarct size versus TG (17 3% versus 34 4%, p < 0.001). Thus, chronic Akt activation is sufficient to cause a spectrum of phenotypes from moderate cardiac hypertrophy with preserved systolic function and cardioprotection to massive cardiac dilatation and sudden death

Isolation and function of mouse tissue resident vascular precursors marked by myelin protein zero

Newly identified tissue-resident vascular precursor cells are recruited into growing vessels and contribute to vasculogenesis in adult mice