• Title/Summary/Keyword: pre-strain

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Monitoring System For The Subway Structures Using Prestrained FBG Sensors Fixed With Partially Stripped Fibers (부분탈피 고정방식 프리스트레인 가변형 광섬유격자센서를 이용한 지하철 구조물 변위 모니터링시스템)

  • Kim, Ki-Soo
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.21 no.6
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    • pp.607-613
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    • 2008
  • A monitoring system for the subway structures using prestrained FBG sensors fixed with partially stripped fibers was developed. The sensor packages had pre-strain controllable fixtures. Tensile and compressive strain of the structure could be measured without slip. The FBG sensor system was applied to the concrete lining structure in Taegu subway. Near the structure, the narrow tunnel construction, for the electric power cables and telecommunication cables, started. We wanted to measure the deformations of the subway structures due to the construction by the FBG sensor. The applied sensors had the gauge length of 1 meter to overcome the inhomogeneity of the concrete material with enough length. In order to fix tightly to the structure, the partially stripped parts of the sensor glued to the package and slip phenomenon between fiber and acrylate jacket was prevented. Prestrain of the sensor was imposed by controlling the two fixed points with bolts and nuts in order to measure compressive strain as well as tensile strain. The behavior of subway lining structure could be monitored very well.

Study on the Time Dependent Stress-Strain Behavior of Clay (점성토의 시간의존적 응력 - 변형 특성에 관한 연구)

  • 지인택;강우묵
    • Magazine of the Korean Society of Agricultural Engineers
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    • v.30 no.4
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    • pp.134-153
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    • 1988
  • This paper was carried out to investigate the existence of a unique stress- strain behavior by obtaining some factors influencing the time dependent stress- strain behavior of clay. The results obtained from this study were summarized as follows ; 1. The relationship between stress ratro and strain in normally consolidated clay was in- dependent on pre-shear consolidation pressure. Therefore, shear strain could be expressed as a function with stress ratio. 2. The constitutive equation of shear strain on Modified Carn Clay Model coincided better with the observed value than Cam Clay Model. 3. The relationships between deviator stress and shear strain, between pore water pressure and shear strain were unified by the mean equivalent pressure. 4. The shear strain contour in norrnally consolidated clay was increased linearly through origin, but that in overconsolidated clay was not in accordance with the result of the former. 5. Because the effective stress path of normally consolidated clay was unified by the mean equivalent pressure, state boundary surface in (e,p,q) space was transformed into two dimensional surface. But it was considered to be suitable that the unified stress- strain in overconsolidated clay be expressed by a function with overconsolidation ratio. 6. The deviator for constant strain was increased linearly with increment of strain rate ($\varepsilon$) on semi-log scale, but pore water pressure was decreased. 7. The behavior of stress relaxation was transformed from linear to curvilinear with inc - rement of strain rate before stress relaxation test, and pore water pressure was increased in total range. 8. The strain of creep was increased linearly with increment of time on semi-log scale. The greater the strain rate before creep test became, the greater the increment of strain of creep became. And the pore water pressure during creep test was increased generally with increment of time on semi-log scale.

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Controlled Formation of Surface Wrinkles and Folds on Poly (dimethylsiloxane) Substrates Using Plasma Modification Techniques

  • Nagashima, So;Hasebe, Terumitsu;Hotta, Atsushi;Suzuki, Tetsuya;Lee, Kwang-Ryeol;Moon, Myoung-Woon
    • Proceedings of the Korean Vacuum Society Conference
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    • 2012.08a
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    • pp.223-223
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    • 2012
  • Surface engineering plays a significant role in fabricating highly functionalized materials applicable to industrial and biomedical fields. Surface wrinkles and folds formed by ion beam or plasma treatment are buckling-induced patterns and controlled formation of those patterns has recently gained considerable attention as a way of creating well-defined surface topographies for a wide range of applications. Surface wrinkles and folds can be observed when a stiff thin layer attached to a compliant substrate undergoes compression and plasma treatment is one of the techniques that can form stiff thin layers on compliant polymeric substrates, such as poly (dimethylsiloxane) (PDMS). Here, we report two effective methods using plasma modification techniques for controlling the formation of surface wrinkles and folds on flat or patterned PDMS substrates. First, we show a method of creating wrinkled diamond-like carbon (DLC) film on grooved PDMS substrates. Grooved PDMS substrates fabricated by a molding method using a grooved master prepared by photolithography and a dry etching process were treated with argon plasma and subsequently coated with DLC film, which resulted in the formation of wrinkled DLC film aligning perpendicular to the steps of the pre-patterned ridges. The wavelength and the amplitude of the wrinkled DLC film exhibited variation in the submicron- to micron-scale range according to the duration of argon plasma pre-treatment. Second, we present a method for controlled formation of folds on flat PDMS substrates treated with oxygen plasma under large compressive strains. Flat PDMS substrates were strained uniaxially and then treated with oxygen plasma, resulting in the formation of surface wrinkles at smaller strain levels, which evolved into surface folds at larger strain levels. Our results demonstrate that we can control the formation and evolution of surface folds simply by controlling the pre-strain applied to the substrates and/or the duration of oxygen plasma treatment.

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The Change of Sagittal Alignment of the Lumbar Spine after Dynesys Stabilization and Proposal of a Refinement

  • Park, Won Man;Kim, Chi Heon;Kim, Yoon Hyuk;Chung, Chun Kee;Jahng, Tae-Ahn
    • Journal of Korean Neurosurgical Society
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    • v.58 no.1
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    • pp.43-49
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    • 2015
  • Objective : $Dynesys^{(R)}$ is one of the pedicle-based dynamic lumbar stabilization systems and good clinical outcome has been reported. However, the cylindrical spacer between the heads of the screws undergoes deformation during assembly of the system. The pre-strain probably change the angle of instrumented spine with time and oblique-shaped spacer may reduce the pre-strain. We analyzed patients with single-level stabilization with $Dynesys^{(R)}$ and simulated oblique-shaped spacer with finite element (FE) model analysis. Methods : Consecutive 14 patients, who underwent surgery for single-level lumbar spinal stenosis and were followed-up more than 24 months (M : F=6 : 8; age, $58.7{\pm}8.0$ years), were analyzed. Lumbar lordosis and segmental angle at the index level were compared between preoperation and postoperative month 24. The von Mises stresses on the obliquely-cut spacer ($5^{\circ}$, $10^{\circ}$, $15^{\circ}$, $20^{\circ}$, $25^{\circ}$, and $30^{\circ}$) were calculated under the compressive force of 400 N and 10 Nm of moment with validated FE model of the L4-5 spinal motion segment with segmental angle of $16^{\circ}$. Results : Lumbar lordosis was not changed, while segmental angle was changed significantly from $-8.1{\pm}7.2^{\circ}$ to $-5.9{\pm}6.7^{\circ}$ (p<0.01) at postoperative month 24. The maximum von Mises stresses were markedly decreased with increased angle of the spacer up to $20^{\circ}$. The stress on the spacer was uneven with cylindrical spacer but it became even with the $15^{\circ}$ oblique spacer. Conclusion : The decreased segmental lordosis may be partially related to the pre-strain of Dynesys. Further clinical and biomechanical studies are required for relevant use of the system.

Determination of Optimum Cu and Mn Contents in Cu-bearing Hot Rolled Steel Sheets (Cu첨가형 열연강판의 최적 Cu 및 Mn 첨가량 규명)

  • Yoon, Il-Sung;Yun, In-Taek;Cho, Yeol-Rae;Kim, In-Bae
    • Korean Journal of Materials Research
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    • v.8 no.3
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    • pp.274-279
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    • 1998
  • Optimum Cu and Mn contents in 0.05wt%C-Cu bearing hot rolled steel sheets were investigated by vickers hardness measurement, tensile test and transmission electron microscopy. It was determined that the optimum Cu and Mn contents were 1.2wt% and 0.75-0.85wt% respectively. It was confirmed by TEM observation that the coarse recipitates were fcc $\varepsilon$-Cu in 0.05%C-1.2%Cu-0.75%Mn-O.O4%Nb steel sheets. The Cu-bearing steel sheets having 780MPa of tensile strength could be fabricated by 10% pre-strain and aging treatment at $550^{\circ}C$ for 30min.

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Studies on the Morphology and Stainability of Chicken Spermatozoa (닭 정자(精子)의 형태(形態)와 염색성(染色性) 조사(調査))

  • Kwak, Soo-dong
    • Korean Journal of Veterinary Research
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    • v.27 no.1
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    • pp.1-7
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    • 1987
  • The present studies were designed to investigate the morphology and stainability of the chicken spermatozoa. Semen samples were collected by abdominal massage from 10 cocks of Arbor, Acres strain (egg breed) and 10 cocks of white Cornish strain (meat breed). The semen samples were diluted with Sarker's solution and were washed. Some of the semen smear slides were stained with seven differential stain methods and was compared with one another by light microscope. In addition to the staining already compared, the length of heads, middle pieces and tails of 400 spermatozoa of two chicken breed was measured with micrometer. The results obtained from these, studies were as follows: 1. Eosin stain appeared to give good results than hematoxylin, pre-treated protease and eosin or hematoxylin stain, pre-treated protease and hematoxylin-eosin stain, carbol-fuchsin, stain and Giemsa 9 technique in differential staining of spermatozoal three portions and pre-treated protease and eosin stain appeared as good staining methods for middle piece of spermatozoa. 2. The average length of chicken spermatozoa was $90.4{\pm}4.0{\mu}m$, and the average length of the head, middle piece and tail of spermatozoa was $13.0{\pm}0.5{\mu}m$, $3.8{\pm}0.2{\mu}m$ and $73.6{\pm}3.8{\mu}m$ lesoectively. 3. The average length of spermatozoa of Arbor Acres strain was $89.2{\pm}5.0{\mu}m$ and the average length of the head, middle piece and tail of spermatozoa was $12.9{\pm}0.5{\mu}m$, $3.8{\pm}0.2{\mu}m$ and $72.5{\pm}4.7{\mu}m$ respectively. The average length of spermatozoa of with Cornish was $91.6{\pm}3.0{\mu}m$ and the average length of the head, middle piece and tail of spermatozoa was $13.1{\pm}0.5{\mu}m$, $3.8{\pm}0.2{\mu}m$ and $74.7{\pm}2.8{\mu}m$ respectively.

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Strain energy release rates in the curved spar wingskin joints with pre-embedded delaminations

  • P.K. Mishra;A.K. Pradhan;M.K. Pandit ;S.K. Panda
    • Structural Engineering and Mechanics
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    • v.87 no.1
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    • pp.47-56
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    • 2023
  • Any pre-existed delamination defect present during manufacturing or induce during service loading conditions in the wingskin adherend invariably shows a greater loss of structural integrity of the spar wingskin joint (SWJ). In the present study, inter-laminar delamination propagation at the critical location of the SWJ has been carried out using contact and multi-point constraint finite elements available with commercial FE software (ANSYS APDL). Strain energy release rates (SERR) based on virtual crack closure technique have been computed for evaluation of the opening (Mode-I), sliding (Mode-II) and cross sliding (Mode-III) modes of delamination by sequential release of multi point constraint elements. The variations of different modes of SERR are observed to be significant by considering varied delamination lengths, material properties of adherends and radius of curvature of the SWJ panel. The SERR rates are seen to be much different at the two pre-embedded delamination ends. This shows dissimilar delamination propagation rates. The maximum is seen to occur in the delamination front in the unstiffened region of the wingskin. The curvature geometry and material anisotropy of SWJ adherends significantly influences the SERR values. Increase in the SERR values are observed with decrease in the radius of curvature of wingskin panel, keeping its width unchanged. SWJs made with flat FRP composite adherends have superior resistance to delamination damage propagation than curved composite laminated SWJ panels. SWJ made with Boron/Epoxy (B/E) material shows greater resistance to the delamination propagation.

A Study on the Mechanical Behavior of Preflex Beam under Different Preflexion Loading Conditions (재하방법에 따른 프리플렉스빔의 역학적 거동에 관한 연구)

  • 방한서;주성민;김규훈;안해영
    • Journal of Welding and Joining
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    • v.22 no.2
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    • pp.33-37
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    • 2004
  • Since the preflex beam is fabricated by welding, the pre-compressive stresses that should occur over the concrete pier are diminished by the welding residual stresses. For this reason distribution of welding residual stresses must be analyzed accurately and welding residual stresses should be relieved during the fabrication. In this study strain history, displacement of beam and re-distributed welding residual stresses by different loading conditions are measured and compared to choose more appropriate preflex condition.

Finite Element Analysis for the Relation between Hardness and Effective Strain (경도-유효변형률 관계에 관한 유한요소 해석)

  • Kwon, Soon-Goo;Park, Joon-Hong
    • Journal of the Korean Society of Industry Convergence
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    • v.2 no.2
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    • pp.125-130
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    • 1999
  • It is already known that hardness value of cold-forged product is in close conjunction with its effective strain. This paper presents the method to predict the relation between effective strains and hardness values by using FE-simulation of hardness test from the conception that hardness indicates resistance to plastic deformation. The results of FE-simulation for the material with pre-strain arc compared with those of experiments of the references to show the feasibility of the proposed method.

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Strain Decomposition Method in Hull Stress Monitoring System for Container Ship

  • Park, Jae-Woong;Kang, Yun-Tae
    • Journal of Ship and Ocean Technology
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    • v.7 no.3
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    • pp.56-65
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    • 2003
  • The hull monitoring systems of container ships with four long-base gages give enough information for identifying the hull girder loads such as bending and torsional moments. But such a load-identification for container ships has not been known. In this paper, a load-identification method is suggested in terms of a linear matrix equation that the measured strain vector equals to the multiplication of the transformation matrix and the desired strain component vector. The equation is proved to be mathematically complete by the property of positive-definite determinant of the transformation matrix. The method is applied to a hull stress monitoring system for 8100TED container ship during sea trial, and the estimated external loads illustrate reasonable results in comparison with the pre-estimated results. This moment decomposition concept has also been tested in real operation conditions. The typical phenomena over the Suez Canal illustrated very suitable results comparing with the physical understandings. Henceforth, one can effectively use the proposed concept to monitor the hull girder loads such as bending and torsional moments.