Wonsuk Kim

University of Michigan-Dearborn, Dearborn, Michigan, United States

Are you Wonsuk Kim?

Claim your profile

Publications (8)11.17 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The damping characteristics of an Ni–Ti shape memory alloy (SMA) beam are theoretically and experimentally studied with interest in identifying an appropriate damping model for the material. The SMA beam is manufactured by a spray deposition method followed by heat treatment and found to have nanocrystalline structure in which damping capacity is high. The beam is then tested to obtain an impulse response and the frequency response function (FRF). By using the Hilbert transform technique it is shown that damping of the beam is almost amplitude independent in the tested range of displacement. It is also shown from the FRF that the damping of the spray-deposited shape memory alloy beam is well represented by a model including both linear viscous and hysteretic dampings.
    Journal of Sound and Vibration 07/2014; 333(15):3356–3366. · 1.61 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ocular tissue properties have been widely studied in tension and compression for humans and a variety of animals. However, direct shear testing of the tissues of the corneo-scleral shell appears to be absent from the literature even though modeling, analyses and anatomical studies have indicated that shear may play a role in the etiology of primary open angle glaucoma. In this work, the mechanical behavior of bovine scleral tissue in shear has been studied in both out-of plane and in-plane modes of deformation. Stress-strain and relaxation tests were conducted on tissue specimens at controlled temperature and hydration focusing on trends related to specimen location and orientation. There was generally found to be no significant effect of specimen orientation and angular location in the globe on shear stiffness in both modes. The in-plane response, which is the primary load carrying mode, was found to be substantially stiffer than the out-of-plane mode. Also, within the in-plane studies, tissue further from the optic nerve was stiffer than the near tissue. The viscosity coefficient of the tissue varied insignificantly with distance from the optic nerve, but overall was much higher in-plane than out-of-plane.
    Journal of Biomechanical Engineering 05/2014; · 1.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The mechanical properties of polypropylene (PP) composites with short, wheat straw natural-fiber reinforcements are studied in tension at various temperatures and rates of loading. Specimens of two fiber lengths have been considered with both closed-form, microcellular voids and in solid form. Results of mechanical stress-strain tests are given at static to moderate rates of strain, specifically 0.0005/s, 0.025/s and 14/s. Testing at these strain rates is conducted up to specimen failure at low, room and high temperatures of -30° C, 22° C, and 107° C, respectively. Primary findings suggest that fibers increase the tangent modulus and ultimate stress, while reducing the failure strain, compared to pure polymer. The presence of microcellular voids generally reduces ultimate strength, but does not reduce failure strain. In many cases, the microcellular composites display reduced rate sensitivity that would result in the development of lower stress than solid counterparts during high rate and/or high strain events. The performance difference between the two fiber cases studied here is largest at room temperature and quasi-static strain rates, and in most cases becomes insignificant with increasing or decreasing temperature and increasing strain rates.
    Polymer Testing 01/2014; · 1.65 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The constitutive behavior of bovine scleral and corneal tissues is measured in tension and compression, at quasi-static and moderate strain rates. Experiments are conducted at strain rates up to about 50 strain per second by a pneumatic testing system developed to overcome noise and measurement difficulties associated with the time dependent test of low impedance materials. Results for the tissues at room and the natural bovine body temperatures are similar and indicate that ocular tissue exhibits nonlinear stiffening for increasing strain rates, a phenomena termed rate hardening. For example, at a tensile strain rate of 29/s, corneal tissue is found to develop 10 times the stress that it does quasi-statically at the same strain. Thus, conventional constitutive models will grossly underpredict stresses occurring in the corneo-scleral shell due to moderate dynamic events. This has implication to the accuracy of ocular injury models, the study of the stress field in the corneo-scleral shell for glaucoma research and tonometry measure-ments. The measured data at various strain rates is represented using the general frame-work of a constitutive model that has been used to represent biological tissue mechanical data. Here it is extended to represent the measured data of the ocular tissues over the range of tested strain rates. Its form allows for straightforward incorporation in various numerical codes. The experimental and analytical methods developed here are felt to be applicable to the test of human ocular tissue. [
    Journal of Biomechanical Engineering 06/2012; 134(6):061002-1. · 1.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The constitutive behavior of bovine scleral and corneal tissues is measured in tension and compression, at quasi-static and moderate strain rates. Experiments are conducted at strain rates up to about 50 strain per second by a pneumatic testing system developed to overcome noise and measurement difficulties associated with the time dependent test of low impedance materials. Results for the tissues at room and the natural bovine body temperatures are similar and indicate that ocular tissue exhibits nonlinear stiffening for increasing strain rates, a phenomena termed rate hardening. For example, at a tensile strain rate of 29/s, corneal tissue is found to develop 10 times the stress that it does quasi-statically at the same strain. Thus, conventional constitutive models will grossly underpredict stresses occurring in the corneo-scleral shell due to moderate dynamic events. This has implication to the accuracy of ocular injury models, the study of the stress field in the corneo-scleral shell for glaucoma research and tonometry measurements. The measured data at various strain rates is represented using the general framework of a constitutive model that has been used to represent biological tissue mechanical data. Here it is extended to represent the measured data of the ocular tissues over the range of tested strain rates. Its form allows for straightforward incorporation in various numerical codes. The experimental and analytical methods developed here are felt to be applicable to the test of human ocular tissue.
    Journal of Biomechanical Engineering 06/2012; 134(6):061002. · 1.52 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The high strain-rate constitutive behavior of polymer composites with various natural fibers is studied. Hemp, hemp/glass hybrid, cellulose, and wheat straw-reinforced polymeric composites have been manufactured, and a split-Hopkinson pressure bar apparatus has been designed to measure the dynamic stress–strain response of the materials. Using the apparatus, compressive stress–strain curves have been obtained that reveal the materials’ constitutive characteristics at strain rates between 600 and 2400 strain/s. Primary findings indicate that natural fibers in thermoset composites dissipate energy at lower levels of stress and higher strain than glass-reinforced composites. In the case of thermoplastic matrices, the effect on energy dissipation of natural fibers vs. conventional talc reinforcements is highly dependent on resin properties. Natural fibers in polypropylene homopolymer show improved reinforcement but have degraded energy dissipation compared to talc. Whereas in polypropylene copolymer, natural fibers result in improved energy dissipation compared to talc. These data are useful for proper design, analysis, and simulation of lightweight biocomposites.
    Journal of Composite Materials 01/2012; 46(9):1051-1065. · 0.94 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The effects of loading rate on bio-, nano-, and microcellular composite systems have been studied. Fiber–resin systems have been manufactured and dynamically tested at various speeds to assess their strain-rate dependencies (rate hardening) and energy-dissipation characteristics compared to conventional materials. The following composite systems have been fabricated and studied: polypropylene/sisal fiber biocomposite, hemp/vinyl ester biocomposite, thermoplastic olefin/nanoclay composite, microcellular polypropylene/sisal fiber biocomposite, and microcellular thermoplastic olefin/nanoclay composite. It has been determined that the biocomposite systems studied possess unique energy dissipation characteristics and muted rate dependence, while the nanocomposite system did not. In addition, microcellular foaming of these materials further enhanced the effects. Though the exact mechanisms at play are not fully understood at this point, it has been found that in addition to the microcellular voids, the anatomical vasculature of the natural fibers may play a role in energy dissipation processes in these hybrid materials. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers
    Polymer Composites 08/2011; 32(9):1423 - 1429. · 1.48 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: It was theoretically shown by the authors in a previous article that by adding a layer of metal on the outside of a carbon fiber-reinforced composite shaft, the bending natural frequencies of the shaft could be increased in some cases due to reduction of the effects of shear deformation by the metal layer. In the present study, composite shafts having a metal casing have been manufactured by spray deposition process over filament wound, fiber reinforced polymeric shafts. The natural frequencies of the spray deposited composite shafts have been measured and found to compare well to theoretically calculated values. The experiments also confirm the shear deformation effect described above. Some manufacturing issues on the spray deposition of metals over carbon fiber-reinforced plastics are addressed.
    Journal of Composite Materials 01/2009; 43(3):277-287. · 0.94 Impact Factor