• Title/Summary/Keyword: offset curve

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A Study on the Apparent Negative Crack Growth Phenomenon of J-R Curve(II) (J-R 곡선에서의 균열길이 감소현상에 관한 연구 (II))

  • 석창성;최용식
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.9
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    • pp.1627-1631
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    • 1992
  • It often occurs in J-R testing that some initial crack extension (.DELTA.a) data points have anomalous negative values. The reason for the apparent negative crack growth is due to the analysis method. The phenomenon as a possible source of error in determining $J_{IC}$ or J-R curve from partial unloading compliance experiments may be eliminated by the compliance correction equation or the offset technique. In this study, the correction methods are suggested and examined by the measurement of the actual crack length and $J_{JC}$ analysis.

Modified Offset Method for Determination of Stable Crack Onset Point on R Curve (R 곡선상의 안정균열개시점 결정을 위한 수정옾셋방법)

  • 안광주;최재강;박준수
    • Journal of the Korean Society of Safety
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    • v.14 no.3
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    • pp.18-24
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    • 1999
  • This paper were performed to evaluate the elastic-plastic fracture toughness $J_IC$ by the unloading compliance method for 1/2 CT specimen of A5083-H112 aluminum alloy. A modified offset method for negative crack growth effect is presented and compared with Voss offset method. We found that the modified offset method presented can be used efficiently for a determination of the stable crack onset. The $J_IC$ by Voss offset method can be overestimated, but the suggested offset method showed a high reliability within 5% of tolerence from the results by the multi-specimen method.

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Effects of Accelerated Iso-Thermal Aging on Elastic-Plastic Fracture Toughness and Fracture Resistance Curve by Unloading Compliance Method in SA533B Low Alloy Steel (제하 컴플라이언스법에 의한 SA533B강의 $J_1C$ 및 J-R 곡선에 미치는 열시효 영향)

  • 윤한기;차귀준
    • Journal of Ocean Engineering and Technology
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    • v.8 no.2
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    • pp.157-165
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    • 1994
  • Effect of an accelerated iso-thermal aging (375 degree C x 66days, 375 degree C x 200days) on elastic-plastic fracture resistance curve were examined in SA533B low alloy steel. Fracture toughness test are conducted by unloading compliance method at room temperature. But the apparent negative crack growth phenomenon, usually arise in partial unloading compliance test. The phenomenon of negative crack growth may be eliminated by the offset technique. There is no effect of aging on J sub(IC) and dJ/da in iso-thermal aged (375 degree C x 66 days) specimen, but there is very little effect in iso-thermal aged (375 degree C x 200 days) specimen.

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A Single-Center Experience of Robotic-Assisted Spine Surgery in Korea : Analysis of Screw Accuracy, Potential Risk Factor of Screw Malposition and Learning Curve

  • Bu Kwang Oh;Dong Wuk Son;Jun Seok Lee;Su Hun Lee;Young Ha Kim;Soon Ki Sung;Sang Weon Lee;Geun Sung Song;Seong Yi
    • Journal of Korean Neurosurgical Society
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    • v.67 no.1
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    • pp.60-72
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    • 2024
  • Objective : Recently, robotic-assisted spine surgery (RASS) has been considered a minimally invasive and relatively accurate method. In total, 495 robotic-assisted pedicle screw fixation (RAPSF) procedures were attempted on 100 patients during a 14-month period. The current study aimed to analyze the accuracy, potential risk factors, and learning curve of RAPSF. Methods : This retrospective study evaluated the position of RAPSF using the Gertzbein and Robbins scale (GRS). The accuracy was analyzed using the ratio of the clinically acceptable group (GRS grades A and B), the dissatisfying group (GRS grades C, D, and E), and the Surgical Evaluation Assistant program. The RAPSF was divided into the no-breached group (GRS grade A) and breached group (GRS grades B, C, D, and E), and the potential risk factors of RAPSF were evaluated. The learning curve was analyzed by changes in robot-used time per screw and the occurrence tendency of breached and failed screws according to case accumulation. Results : The clinically acceptable group in RAPSF was 98.12%. In the analysis using the Surgical Evaluation Assistant program, the tip offset was 2.37±1.89 mm, the tail offset was 3.09±1.90 mm, and the angular offset was 3.72°±2.72°. In the analysis of potential risk factors, the difference in screw fixation level (p=0.009) and segmental distance between the tracker and the instrumented level (p=0.001) between the no-breached and breached group were statistically significant, but not for the other factors. The mean difference between the no-breach and breach groups was statistically significant in terms of pedicle width (p<0.001) and tail offset (p=0.042). In the learning curve analysis, the occurrence of breached and failed screws and the robot-used time per screw screws showed a significant decreasing trend. Conclusion : In the current study, RAPSF was highly accurate and the specific potential risk factors were not identified. However, pedicle width was presumed to be related to breached screw. Meanwhile, the robot-used time per screw and the incidence of breached and failed screws decreased with the learning curve.

A method of Determination of Fracture Toughness of Reactor Pressure Vessel Steel by J Integral (J적분을 이용한 원자력 압력용기강의 파괴인성치의 결정)

  • 오세욱;임만배;김진선
    • Journal of Ocean Engineering and Technology
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    • v.9 no.1
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    • pp.111-119
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    • 1995
  • The elastic-plastic fracture toughness($J_{IC}$) and fracture resistance (J-R curve) of SA508-3 alloy steel used for nuclear reactor pressure vessel are investigated by using CT-type specimens. Fracture toughness tests are conducted by unloading compliance method and multiple specimen method at room temperature, -2$0^{\circ}C$ and 20$0^{\circ}C$. The apparent negative crack growth phenomenon which usually arises in partial unloading compliance test is well known. The negative crack growth phenomenon in determining J sub(IC) or J-R cure from partial unloading compliance experiments may be eliminated by the offset technique. In this study, the evaluation of $J_{IC}$ multiple specimen method recommended by the JSME gives the most reliable results by using half-size CT(similar-type) specimens.

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A Study on Generation of the Advanced Laser Scanning Path for Stereolithography using Voronoi Diagrams (Voronoi Diagram 을 이용한 Stereo;ithography 의 향상된 레이져 주사경로 생성에 관한 연구)

  • 이기현;최홍태;이석희
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 1997.04a
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    • pp.405-409
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    • 1997
  • Voronoi diagrams are applied in varios field such as NC toolpath generation, VLSI design and robot path planning because of their geometric charcteristics. In this paper, Voronoi diagrams are introduced on polygon constructed by line segments only and with constant offset. Bisector curves for two arbitrary objects, which is the combination of line segment and arc, are defined as parametric fuction where the parameter is used as offset. Offset curves are applied on the generation of laser scanning path for the stereolithography and shows a good result from several examples.

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Chip Timing Recovery Algorithm Robust to Frequency Offset and Time Variant Fading

  • Kang, Hyung-Wook;Lee, Young-Yong;Park, Hyung-Jin
    • Proceedings of the IEEK Conference
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    • 2002.07c
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    • pp.1948-1951
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    • 2002
  • In this paper, we propose a chip timing recovery algorithm that is robust to frequency offset and time variant fading environments for DS/CDMA. The proposed structure is a modified non-coherent Delay Locked Loop (DLL) that employs a decimator. Analytical expression for the proposed non-coherent DLL S-curve and steady-state timing jitter is derived and confirmed by computer simulation. The results show that the proposed structure can reduce a steady-state timing jitter of the regenerated spreading code replica to frequency offset and time-variant fading in mobile radio channel, especially in very low SNR.

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Evaluation of J-R Curve for Aluminum 5083 Alloy Weldment by Load Ratio Analysis (Load Ratio 해석에 의한 알루미늄 5083 합금 용접부의 J-R곡선 평가)

  • 윤한기;김연겸
    • Journal of Welding and Joining
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    • v.15 no.4
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    • pp.178-186
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    • 1997
  • The purpose of this study is to evaluate the J-R curve characteristics for the 5083 aluminum alloy weldment by the load ratio analysis. The results of the load ratio analysis are compared with those of the J-R curve which are obtained by the ASTM unloading compliance method. The crack length calculated by the load ratio analysis is agrees well with the measured final crack length. The slope of the exponential J-R curve estimated by the load ratio analysis is slightly smaller than that by the ASTM unloading compliance method. The exponential correlation of the J-R curve for the 5083 aluminum alloy base metal by the load ratio analysis is J = 93.88 ${\Delta}{\alpha}^{0.375}$. That for the weld metal and HAZ is J = 69.87 ${\Delta}{\alpha}^{0.389}$ and J = 70.59 ${\Delta}{\alpha}^{0.359}$ respectively. The J-R curve obtained by the ASTM unloading compliance method is overpredicted and should be offsetted due to the initial negative crack. On the other hand, the load ratio analysis method can evaluate the J-R curve by only load displacement curve without particular crack measurement equipment.

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An Algorithm to Speed Up the Rapid Prototyping (쾌속조형의 속도를 향상시키기 위한 알고리즘)

  • Ko, Min-Suk;Chang, Min-Ho;Wang, Gi-Nam;Park, Sang-Chul
    • Journal of the Korean Society for Precision Engineering
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    • v.25 no.3
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    • pp.157-164
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    • 2008
  • While developing physical prototype from CAD model, rapid prototyping mainly focuses on two key points reducing time and material consumption. So, we have to change from a traditional solid model to building a hollowed prototype. In this paper, a new method is presented to hollow out solid objects with uniform wall thickness to increase RP efficiency. To achieve uniform wall thickness, it is necessary to generate internal contour by slicing the offset model of an STL model. Due to many difficulties in this method, this paper proposes a new algorithm that computes internal contours computing offset model which is generated from external contour using wall thickness. Proposed method can easily compute the internal contour by slicing the offset surface defined by the sum of circle swept volumes of external contours without actual offset and the circle wept volumes. Internal contour existences are confirmed by using the external point. Presented algorithm uses the 2D geometric algorithm allowing RP implementation more efficient. Various examples have been tested with implementation of the algorithm, and some examples are presented for illustration.

Optimum Design of T-shaped Microstrip-line-fed Slot Antennas (T-모양 급전선을 갖는 마이크로스트립 슬롯 안테나의 최적 설계방법에 관한 연구)

  • 김권일;서영훈;박익모
    • The Journal of Korean Institute of Electromagnetic Engineering and Science
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    • v.12 no.4
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    • pp.562-569
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    • 2001
  • This paper presents the optimum design method for T-shaped microstrip-line-fed slot antennas on various substrates. Since the impedance bandwidth of the antenna depends highly on the vertical offset position and the length of horizontal strip conductor, we derived the formulas regarding these design parameters to get the maximum bandwidth. The formulas can compute the offset position and the length of horizontal strip conductor for any given substrate parameters. We compared the results obtained by using these design formulas and the one obtained by the simulation for each slot width, and it showed very good agreement.

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