• Journal of Mechanical Science and Technology
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• v.17 no.9
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• pp.1332-1338
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• 2003

To estimate the true wear rate of polyethylene acetabular cups used in total hip arthroplasty, the dynamic compressive creep deformation of ultra-high molecular weight polyethylene (UHMWPE) was quantified as a function of time, load amplitude, and radial location of the specimen in the extruded rod stock. These data were also compared with the creep behavior of polyethylene observed under static loading. Total creep strains under dynamic loading were only 64％, 70％, and 61％ of the total creep strains under static loading at the same maximum pressures of 2 MPa,4 MPa, and 8 MPa, respectively. Specimens cut from the periphery of the rod stock demonstrated more creep than those cut from the center when they were compressed in a direction parallel to the extrusion direction (vertical loading) whereas the opposite was observed when specimens were compressed in a direction perpendicular to the extrusion direction (transverse loading). These findings show that creep deformation of UHMWPE depends upon the orientation of the crystalline lamellae.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.42-47
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• 2004

Metallic glasses are amorphous meta-stable solids and are now being processed in bulk form suitable for structural applications including impact. Bulk metallic glasses have many unique mechanical properties such as high yield strength and fracture toughness, good corrosion and wear resistance that distinguish them from crystalline metals and alloys. However, only a few studies could be found mentioning the dynamic response and damage of metallic glasses under impact or shock loading. In this study, we employed a small explosive detonator for the dynamic indentation on a Zr-based bulk amorphous metal in order to evaluate the damage behavior of bulk amorphous metal under impact loading. These results were compared with those of spherical indentation under quasi-static and impact loading. The interface bonded specimens were adopted to observe the appearances of subsurface damage induced during indentation under different loading conditions.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.176-179
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• 2005

Spray casting of hypereutectic Al-Si based alloy has been reported to provide distinct advantages over ingot metallurgy (IM) or rapid solidification/powder metallurgy (RS/PM) process in terms of microstructure refinement. Hypereutectic Al-Si based alloys have been regarded attractive for automotive and aerospace application, due to high specific strength, good wear resistance, low coefficient of thermal expansion, high thermal stability, and good creep resistance. In this study, hypereutectic Al-25Si-2.0Cu-1.0Mg alloy was prepared by OSPREY spray casting process. High temperature deformation behavior of the hypereutectic Al-Si based alloy has been investigated by applying the internal variable theory proposed by Chang et al. The change of strain rate sensitivity and Creep transition were analyzed by using the load relaxation test and constant creep test.

• Proceedings of the Korean Fiber Society Conference
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• 1998.10a
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• pp.207-210
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• 1998

Among the common textile fibers, wool has excellent wrinkle recovery. However, absorbed moisture plasticizes the structure and increases the rate of stress relaxation during wear deformation. Therefore, the wrinkle recovery of wool deteriorates under very high-humidity conditions and is of particular concern in men's lightweight suits, where the trend is toward wool fabrics of lightweight and bright color in which the wrinkles are emphasized. (omitted)

• Journal of Welding and Joining
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• v.12 no.2
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• pp.20-27
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• 1994

The laser marking system is widely used in many industrial manufacturing companies as an effective process, because it is versitile, clean, and fast to run. Minimal heat deformation and zero tool wear can be obtained using fast and non-contact process of laser marking. As an introductory level, the basic knowledges about laser marking system layout and its components are presented with diagrams. The effects, requirements, and application example of laser marking process are also described in this paper.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.285-288
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• 2001

Hypereutectic Al-25Si-X alloys, expected to be applied to the cylinder-liner-part of the engine-block of an automobile due to the excellent wear resistance, low density and low thermal expansion coefficient has been fabricated through a spray forming process. The obtained microstructure of the hypereutectic Al-25Si-X alloy appeared to consist of Al matrix and equiaxed Si particles of average diameter of $5-7{\mu}m$. To characterize the deformation behavior of this alloy, a series of load relaxation and compression tests have been conducted at temperatures ranging from RT to $500^{\circ}C$. The strain rate sensitivity parameter (m) of this alloy has been found to be very low (0.1) below foot and reached 0.2 at $500^{\circ}C$. During the deformation above 300'c in compression, strain softening has been observed. The diagram of extrusion pressure vs. ram-speed has been constructed, providing the extrusion condition of Al-25Si-X alloys.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.23 no.3
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• pp.259-265
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• 2014

When the brakes of a vehicle are applied, large amounts of heat are generated on the surfaces of the brake discs owing to friction between the discs and the brake pads. A high temperature gradient on the disc surfaces leads to thermal deformation and severe disc abrasion. Ultimately, the thermal deformation and disc wear give rise to a thermal judder phenomenon, which has a major effect on the stability of the vehicle. To investigate and propose a solution to these problems, thermoelastic instabilities under applied thermal and mechanical loads were analyzed using the commercial finite element package ANSYS by considering the contact surfaces between the discs and pads. Direct-contact three-dimensional finite elements between the discs and pads were applied to investigate the disc friction temperature, thermal deformation, and contact stress so that the thermal judder phenomenon on the surface of the disc could be predicted.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.05a
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• pp.20-23
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• 2001

Hypereutectic Al-25Si alloy, which is expected to be applied to the cylinder-liner-part of the engine-block of an automobile due to its excellent wear resistance, low density and low thermal expansion coefficient, has been fabricated through a spray forming process. The obtained microstructure of the hypereutectic Al-25Si alloy appeared to consist of Al matrix and equiaxed Si particles of average diameter of 5-7 mm. To characterize the deformation behavior of this alloy, a series of load relaxation and compression tests have been conducted at temperatures ranging from RT to $500^{\circ}C$. The strain rate sensitivity parameter (m) of this alloy has been found to be very low (0.1) below $400^{\circ}C$ and reached maximum value of about 0.2 at $500^{\circ}C$. During the deformation above $300^{\circ}C$ in compression, strain softening has been observed. The diagram of extrusion pressure vs. ram-speed has been constructed. The extrusion has been successfully conducted at the temperatures of $300^{\circ}C$ and above with the ratio of area reduction of 28 and 40 in this study.

• Tribology and Lubricants
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• v.11 no.5
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• pp.128-135
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• 1995

Atomic force microscopy/friction force microscopy (AFM/FFM) techniques are increasingly used for tribological studies of engineering surfaces at scales, ranging from atomic and molecular to microscales. These techniques have been used to study surface roughness, adhesion, friction, scratching/wear, indentation, detection of material transfer, and boundary lubrication and for nanofabrication/nanomachining purposes. Micro/nanotribological studies of single-crystal silicon, natural diamond, magnetic media (magnetic tapes and disks) and magnetic heads have been conducted. Commonly measured roughness parameters are found to be scale dependent, requiring the need of scale-independent fractal parameters to characterize surface roughness. Measurements of atomic-scale friction of a freshly-cleaved highly-oriented pyrolytic graphite exhibited the same periodicity as that of corresponding topography. However, the peaks in friction and those in corresponding topography were displaced relative to each other. Variations in atomic-scale friction and the observed displacement has been explained by the variations in interatomic forces in the normal and lateral directions. Local variation in microscale friction is found to correspond to the local slope suggesting that a ratchet mechanism is responsible for this variation. Directionality in the friction is observed on both micro- and macro scales which results from the surface preparation and anisotropy in surface roughness. Microscale friction is generally found to be smaller than the macrofriction as there is less ploughing contribution in microscale measurements. Microscale friction is load dependent and friction values increase with an increase in the normal load approaching to the macrofriction at contact stresses higher than the hardness of the softer material. Wear rate for single-crystal silicon is approximately constant for various loads and test durations. However, for magnetic disks with a multilayered thin-film structure, the wear of the diamond like carbon overcoat is catastrophic. Breakdown of thin films can be detected with AFM. Evolution of the wear has also been studied using AFM. Wear is found to be initiated at nono scratches. AFM has been modified to obtain load-displacement curves and for nanoindentation hardness measurements with depth of indentation as low as 1 mm. Scratching and indentation on nanoscales are the powerful ways to screen for adhesion and resistance to deformation of ultrathin fdms. Detection of material transfer on a nanoscale is possible with AFM. Boundary lubrication studies and measurement of lubricant-film thichness with a lateral resolution on a nanoscale have been conducted using AFM. Self-assembled monolyers and chemically-bonded lubricant films with a mobile fraction are superior in wear resistance. Finally, AFM has also shown to be useful for nanofabrication/nanomachining. Friction and wear on micro-and nanoscales have been found to be generally smaller compared to that at macroscales. Therefore, micro/nanotribological studies may help def'me the regimes for ultra-low friction and near zero wear.

• Tribology and Lubricants
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• v.26 no.1
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• pp.14-20
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• 2010

Tribological properties of nanoporous structured alumina film was investigated. Alumina film (AAO: anodic aluminum oxide) of $60{\mu}m$ thickness having nanopores of 45 nm diameter with 105 nm interpore-diatance was fabricated by mild anodization process. Reciprocating ball-on-flat sliding friction tests using 1 mm diameter steel ball as a counterpart were carried out with wide range of normal load from 1 mN to 1 N in an ambient environment. The morphology of worn surfaces were analyzed using scanning electron microscopy. The friction coefficient was strongly influenced by the applied normal load. Smooth layer patches were formed on the worn surface of both AAO and steel ball at relatively high load (100 mN and 1 N) due to tribochemical reaction and compaction of wear debris. These tribolayers contributed to the lower friction at high loads. Extremely thin layer patches, due to mild plastic deformation of surface layer, were sparsely distributed on the worn surface of AAO at low loads (1 mN and 10 mN) without the evidence of tribochemical reaction. Delaminated wear particles were generated at high loads by fatigue due to repeated loading and sliding.