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RISS 인기검색어
- 검색키워드
- 저자 : Keyoung-Jin Chun (검색결과 94 건)
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Keyoung Jin Chun,Robert P. Hubbard 대한기계학회 2009 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.23 No.7
A new “standard nonlinear solid” reduced relaxation function has been developed to describe the measured relaxation responses of tendons with 3% and 4% strain levels. This new reduced relaxation function has been used in modeling tendon responses with the quasi-linear viscoelastic law. Unlike the reduced relaxation functions employed in previous studies, the present function closely fits the measured relaxation responses for both the short term of the first few seconds and the long term of 22 hours. The relaxation responses of the anatomically paired tendons were found to be more alike than those from different sites.
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Tendon Responses Depending on Different Anatomical Locations
Keyoung Jin Chun,Robert P. Hubbard 대한기계학회 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.7
The objectives of this work focus on the difTerences in responses of paired tendons from different anatomical locations. Tendon specimens were obtained from the hindlimbs of canines and frozen to -70℃. After being thawed, specimens were mounted in the immersion bath,<br/> preloaded to 0.13 N, and then subjected to 3% or 4% of the initial length at a strain rate of 5%hec. It was found that the mechanical responses of anatomically paired tendons were nearly the same within each pair but different between pairs of tendons from different anatomical locations. Although f1exor tendons had much larger cross-sectional area than the others, such as peroneus or extensor tendons, the stiffness of the flexor tendons were much lower than the others throughout their stress-strain responses. The nature and causes of these differences in the<br/> stiffness are not fully known. However, it is clear that differences in the mechanical response of tendons and other connective tissues are significant to the musculoskeletal performance.
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Sectional Differences in Tendon Response
Keyoung Jin Chun,Robert P. Hubbard 대한기계학회 2003 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.17 No.8
The objectives of this work here focus on the differences in responses to multiple cyclic tests of different sections along the length of the same tendon. Tendon specimens were obtained from the hindlimbs of canines and frozen to -70℃. After thawing. specimens were mounted in the immersion bath at room temperature (22℃), preloaded to 0.13 N and then subjected to 3% or 4% of the initial length at a strain rate of 5%/sec. It was found that different sections of the same long tendons had different resistances to deformation. In general. the bone end sections were stiffer and carried greater loads for a given strain than the muscle end sections, and the mid-portions were the least stiff and carried the smallest loads for a given strain. The results of this study offer new information about the mechanical responses of collagenous tissues. We know more about their responses to multiple cyclic extensions and how their responses are different from the positions along the length of the tendon specimen. The nature and causes of these differences in the stiffness are not fully known. However, it is clear that differences in the mechanical response of tendons and other connective tissues are significant to musculoskeletal performance.
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Development of a Functional Fixator System for Bone Deformity Near Joints
Keyoung Jin Chun,Ho Jung Lee 대한기계학회 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.2
A functional external fixator system for bone deformity near the joints using worm gear was developed for curing the angle difference in fracture bones while the lengthening bar was developed for curing the differences in length, also in fracture bones. Both experiments and FE analysis were performed to compare the elastic stiffness in several loading modes and to improve the functional external fixator system for bone deformity near joints. The FE model using compressive and bending FE analysis was applied due to the angle differentiations. The results indicate that compressive stiffness value in the experiment was 175.43N/㎜, bending stiffness value in the experiment was 259.74N/㎜, compressive stiffness value in the FEA was 188.67N/㎜, and bending stiffness value in the FEA was 285.71N/㎜. Errors between experiments and FEA were less than 10% in both the compressive stiffness and the bending stiffness. The maximum stress (157㎫) applied to the angle to the angle of the clamp was lower than the yield stress (176.4㎫) of SUS316L. The degree of stiffness in both axial compression and bending of the new fixator are about 2 times greater than other products, with the exception of EBI (2003).
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A study of exhaust valve and seat insert wear depending on cycle numbers
Chun, Keyoung Jin,Kim, Jae Hak,Hong, Jae Soo Elsevier 2007 Wear: An international journal on the science and Vol.263 No.7
<P><B>Abstract</B></P><P>This study investigated the wear of the seating faces of the exhaust valve and seat insert that have influence on an engine's performance depending on mileage (cycle numbers).</P><P>Exhaust valves and seat inserts that are commonly used for commercial vehicles were used as test specimens. The cycle numbers for tests were 2×10<SUP>6</SUP>, 4×10<SUP>6</SUP>, 6×10<SUP>6</SUP> and 8×10<SUP>6</SUP>, and the test speeds were 10 and 25Hz. All other parameters such as temperature (350°C), fuel (LPG) and load (1960N) were fixed.</P><P>The 10Hz tests indicated that the average maximum roughness (Rmax) of the valve increased at the rate of 7.76μm/10<SUP>6</SUP> cycles starting from 29.42μm at the 2×10<SUP>6</SUP> cycles, and that the average Rmax of the seat insert increased at the rate of 8.57μm/10<SUP>6</SUP> cycles starting from 34.19μm at the 2×10<SUP>6</SUP> cycles. The 25Hz tests indicated that the average Rmax of the valve increased at the rate of 1.58μm/10<SUP>6</SUP> cycles starting from 74.2μm at the 2×10<SUP>6</SUP> cycles, and that the average Rmax of the seat insert increased at the rate of 1.25μm/10<SUP>6</SUP> cycles starting from 83.95μm at the 2×10<SUP>6</SUP> cycles. The tribochemical reaction product covered the base metals of the valve and seat insert, preventing the wear of the base metals, and included O, V, S and Al, which are the compositions of the two base metals. The tribochemical reaction product observed on the valve had cracks, and it was also noticed that the seat inserts were laid one upon another.</P><P>As cycle numbers became greater, the Rmax of the seating faces of the valve and seat insert also increased, and the wear rate rose significantly depending on the Hz (RPM). The wear mechanism of the valve and seat insert was investigated through the tribochemical reaction.</P>
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Development of a Functional Fixator System for Bone Deformity Near Joints
Chun, Keyoung-Jin,Lee, Ho-Jung The Korean Society of Mechanical Engineers 2006 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.20 No.2
A functional external fixator system for bone deformity near the joints using worm gear was developed for curing the angle difference in fracture bones while the lengthening bar was developed for curing the differences in length, also in fracture bones. Both experiments and FE analysis were performed to compare the elastic stiffness in several loading modes and to improve the functional external fixator system for bone deformity near joints. The FE model using compressive and bending FE analysis was applied due to the angle differentiations. The results indicate that compressive stiffness value in the experiment was 175.43N/mm, bending stiffness value in the experiment was 259.74 N/mm, compressive stiffness value in the FEA was 188.67 N/mm, and bending stiffness value in the FEA was 285.71 N/mm. Errors between experiments and FEA were less than $10\%$ in both the 'compressive stiffness and the bending stiffness. The maximum stress (157 MPa) applied to the angle of the clamp was lower than the yield stress (176.4 MPa) of SUS316L. The degree of stiffness in both axial compression and bending of the new fixator are about 2 times greater than other products, with the exception of EBI (2003).
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속도변화에 따른 엔진 밸브 및 시트 인서트의 마모에 관한 연구
전경진(Keyoung Jin Chun),홍재수(Jae Soo Hong) 한국자동차공학회 2003 한국 자동차공학회논문집 Vol.11 No.6
The minimization of valve and seat insert wear is a critical factor in the pursuit of engine performance improvement. In order to achieve this goal, we have developed a new simulator, which can generate and control high temperatures up to 900℃and various speeds up to 80㎐ during motion, just like an actual engine. The wear simulator is considered to be a valid simulation of the engine valve and seat insert wear process with various speeds during engine activity.<br/> The objective of this work focuses on the different degrees of wear from two different test speeds (10㎐ & 25㎐). For this study, the temperature of the outer surface of the seat insert was controlled at 350℃, the cycle number was 2.1 × 106, and the test load was 1960N. The wear depth and surface roughness were measured before and after the testing using a confocal laser scanner. It was found that a higher speed (25㎐) causes more wear than a lower speed (10㎐) under identical test conditions (temperature, cycle number and test load). In the wear mechanism, adhesive wear, shear strain and abrasive wear could be observed.<br/>
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