Gyu-ho Kim

Oklahoma State University - Stillwater, Stillwater, OK, United States

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Publications (5)2.78 Total impact

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    ABSTRACT: We report an jet rollable nanoimprint lithography tool as a low cost method to produce micro- and nano-structures rapidly over large areas. We integrated a piezoelectric nozzle to deposit resist in-line in a low-waste, high-precision manner. We demonstrate the capabilities of this system by creating a variety of microstructures in SU8 resist with high pattern transfer fidelity.
    2013 IEEE 13th International Conference on Nanotechnology (IEEE-NANO); 08/2013
  • Gyu-Ho Kim, Hongbing Lu
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    ABSTRACT: An accelerated life testing (ALT) method has been developed to determine the long-term fatigue strength over millions of cycles for glassy polymers. Dumbbell shaped specimens made of carbon particle filled polycarbonate (PC) were tested under tension–tension fatigue, based on the strength–lifetime approach (S–N curve). Fatigue-induced localized irreversible deformation is considered to be the defect leading to fatigue failure; its evolution behavior is characterized by a modified energy activation model in which temperature and stress are considered as fatigue acceleration factors. This model allows the reduced time concept to account for the effects of different temperatures and stresses in the short-term fatigue data. The long-term fatigue life is determined through the use of time–temperature and time–stress superpositions that are applicable under low frequency and isothermal conditions. The experimental results provide assurance for the proposed accelerated fatigue life testing technique for polymers.
    Polymer Testing 02/2008; 27(1):114-121. · 1.65 Impact Factor
  • Gyu-Ho Kim, Hongbing Lu
    [Show abstract] [Hide abstract]
    ABSTRACT: An accelerated lifetime testing (ALT) technique has been developed to determine the long-term fatigue life over millions of cycles for glassy polymers. Dumbbell shaped specimens made of carbon-filled polycarbonate (PC) were tested under fatigue based on the stress–lifetime approach (S–N curve). Fatigue-induced localized yield-like deformation is considered as the defect leading to fatigue, and its evolution behavior is characterized by a modified energy activation model in which temperature and frequency are considered as fatigue acceleration factors. This model allows the reduced time concept to account for effects of different temperatures and frequencies in short-term fatigue data to determine long-term fatigue life through the use of time–temperature and time–frequency superpositions that are applicable under high frequency and athermal conditions. The experimental results show that the application of the reduced time model can be a possible method for ALT of time-dependent polymeric materials.
    Polymer Testing. 01/2007;
  • Bo Wang, Hongbing Lu, Gyu-ho Kim
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    ABSTRACT: A continuum damage model is proposed to investigate the fatigue damage behavior for elastomers. The elastic strain energy of a damaged material is expressed based on the Ogden model, and the damage strain energy release rate is derived in the context of continuum damage mechanics. The damage evolution equation is established to develop a formula to describe the fatigue life as a function of the nominal strain amplitude under cyclic loading. Experiments on the fatigue of a carbon-filled natural rubber were conducted to determine the relation between the fatigue life and the nominal strain amplitude. The results indicate that the theoretical formula for the fatigue life as a function of the nominal strain amplitude, derived from the proposed damage model, can describe experimental data for carbon-filled natural rubbers very well.
    Mechanics of Materials. 01/2002; 34(8):475-483.
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    ABSTRACT: Considerable crack-like-defects were observed in an auxiliary power unit (APU) exhaust duct flange area in a jet aircraft with 900 cumulative flying hours. A detailed investigation of crack-induced fracture surface was conducted using Scanning Electron Microscopy (SEM) and computer aided thermal-stress analysis. The results showed that failure of the flange occurred due to the combined effects of the flange constraint and the cyclic thermal stress of the duct. The failure analysis in this study calls for the need for improvement in structure design and installation method of the APU duct system in order to reduce the damage resulting from the creep and fatigue crack during the early stages of service.
    Engineering Failure Analysis 20:97–104. · 1.13 Impact Factor

Publication Stats

25 Citations
2.78 Total Impact Points

Institutions

  • 2002–2007
    • Oklahoma State University - Stillwater
      • School of Mechanical and Aerospace Engineering
      Stillwater, OK, United States