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Now showing items 1 - 6 of 6

  • Comprehensive Mechanical and Tribological Characterization of Ultra-Thin-Films

    Gitis, Norm   Vinogradov, Michael   Hermann, Ilja   Kuiry, Suresh  

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  • METHOD AND DEVICE FOR MEASURING FORCES

    The device of the invention is intended for measuring a loading force and a friction force in a tribological system. The device includes an assembly of two deformation sensitive sensors (200, 300) for simultaneous equal deformation in two opposite directions for eliminating misbalance created in the measurement system (100) when a single sensor is used. Each sensor (200, 300) comprises a deformable beam (212, 312) having through longitudinal slots (218, 220) extending in different and non-parallel directions and overlapped within the body of the beam (212, 312). Each sensor (200, 300) deforms in one direction under the effect of a loading force beam in another direction under the effect of a friction force measured by another two pairs of strain gauges (R1-2 and R3-2) located on opposite sides of the beam (212, 312) near the other end of the beam (212, 312). Two aforementioned sensors (200, 300) are sandwiched between two plates (102, 104) in diagonally symmetrical positions, so as to transmit forces between both plates (102, 104) and at the same time to ensure limited freedom of movement between both plates (102, 104) to allow deformations caused by the applied forces. One plate (102) is attached to the loading unit of the tribological system and another (104) supports an upper sample for engagement with the lower sample of the system.
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  • Tribometrology of Skin

    Gitis, Norm   Sivamani, Raja  

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  • [ASME ASME/STLE 2007 International Joint Tribology Conference - San Diego, California, USA (October 22–24, 2007)] ASME/STLE 2007 International Joint Tribology Conference, Parts A and B - Comprehensive Nano-Mechanical and Tribological Characterization of Hair

    Gitis, Norm   Hermann, Ilja   Kuiry, Suresh   Khosla, Vishal  

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  • Phenomenological nanoindentation technique in quality control of optoelectronics devices

    Daugela, Antanas   Gitis, Norm   Gelfeindbein, Vladimir  

    Multiphase and porous ceramic materials are being used as passive semiconductors for building modern optoelectronics devices. Prescreening of the critical parts for subsurface defects before assembly can prevent device failures in the field. A new nanoindentation based non-destructive method has been proposed where shapes of loading-unloading curves can fingerprint subsurface cracking and material porosity induced inelastic behavior in defected multiphase, rough and porous ceramic parts. In addition to the differences in nanoindentation loading-unloading curve shapes, nanohardness values associated with the cracked contact surfaces were 40% lower. The non-destructive nanoindentation results agree well with the destructive Knoop's microhardness results. A commercially available nanoindentation instrument integrated into the tribometer together with high-resolution optical microscope was utilized for automated and qualitative/quantitative surface materials properties characterization of optoelectronics parts. The proposed instrument and nondestructive testing method can be used for quality control of optoelectronics parts before assembly, significantly improving the yields.
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  • Wear behavior and wear debris distribution of UHMWPE against Si3N4 ball in bi-directional sliding

    Ge, Shirong   Wang, Shibo   Gitis, Norm   Vinogradov, Michael   Xiao, Jun  

    Four kinds of wear tracks possibly occurred in the wear of artificial hip joints, including uni-directional sliding, oval curvilinear sliding, double-elliptical sliding, triple-elliptical sliding, were simulated on the UNIT wear tester by using of a Si3N4 ball sliding on the UHMWPE disc under bi-directional sliding motion. The wear behavior and wear particle distribution of UHMWPE in plasma solution lubrication were studied for these sliding motions. The experimental results indicate that the wear mass loss in uni-directional reciprocating sliding is much smaller than those in bi-directional sliding modes. The wear rates of UHMWPE in bi-directional sliding modes are linearly inverse proportional to the defined frequency factor, as agreed with the cross-shear theory. This result suggests that cross-shear movement with larger intersection angles is a significant factor influencing the wear rate of UHMWPE, and the bi-directional sliding path at direction reversals will play an important role on the increasing of UHMWPE wear compared to uni-directional sliding motion. In bi-directional sliding modes, the wear particle distribution range decreases when direction reversal path increases in the sliding motions. So, the complex wear tracks are harmful to the implant joint due to the higher wear and more active wear particles. The particles sizes follow a lognormal distribution. The central size and the peak accumulation of UHMWPE particles decreases and increases against the frequency ratio, respectively, besides the uni-directional reciprocating sliding. These suggest that the intersection angle increasing on sliding path will contribute to the size decreasing of UHMWPE wear particle. Also, cross-points on sliding track will produce wear particles in smaller size. The radius of curvature of the curvilinear paths may be dictating the size reducing of UHMWPE wear particles. The main wear mechanisms are ploughing in uni-directional reciprocation, while plastic deformation, adhesion and fatigue in the bi-directional sliding modes. (c) 2007 Elsevier B.V. All rights reserved.
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