• Title/Summary/Keyword: Compressive Stress

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Analysis and Design Programming of RC Beams Strengthened with Carbon Fiber Sheets (탄소섬유시트로 보강된 RC보의 해석 및 설계 프로그램 개발)

  • 김성도;김성수
    • Journal of the Korean Society for Railway
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    • v.7 no.4
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    • pp.319-325
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    • 2004
  • In this study, analysis and design programs of bending of RC beams strengthened with fiber sheets are developed by using Visual Basic Language. The program consists two groups, ultimate strength method and nonlinear flexural analysis method. Ultimate strength method regards concrete compressive stress as a rectangular stress block and do not consider tensile stress of concrete and load-deflection curves. On the other hand, nonlinear flexural analysis considers tensile stress of concrete, load-deflection curves, state of stress distribution and failure strain of strengthening material. Also, the analysis method used in this study regards nonlinear flexural stress as compressive stress of concrete. This program can be a good tool for determining the bending strength of strengthened RC beams and estimating the amount of fiber sheets for practical use.

Stress Behavior of PSG/SiN Film for Passivation in Semiconductor Memory Device (반도체 소자의 표면보호용 PSG/SiN 절연막의 스트레스 거동)

  • Kim, Yeong-Uk;Sin, Hong-Jae;Ha, Jeong-Min;Choe, Su-Han;Lee, Jong-Gil
    • Korean Journal of Materials Research
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    • v.1 no.1
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    • pp.46-53
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    • 1991
  • The stress of PSG (Phosphosilicate glass), USG (Undoped-silicate grass) and SiN films, which are mainly used as passivation layers in semiconductor memory devices, deposited by CVD methods has been studied as a function of film thickness and holding time in air. The stress of the PSG film or the USG film is increased in tensile state with increasing film thickness. On the other hand the stress level of the SiN film in compressive stress does not change as film thickness changes. The stress of PSG film shows the drastic change from the tensile stress to the compressive stress after the film is left 2 days in air. FTIR spectra indicated that the stress variation was due to the penetration of water molecule. It looks possible to recover the stress of about $2.5{\times}{10^9}dyne/cm^2$ by annealing treatment at $300^{\circ}C$ for 20min. The total stress of multi-layered films having the PSG film is determined mainly by the stress variation of PSG layer with holding time. The total stress of multi-layered film appears to have a functional relationship with the stress in the thickness of each film. The resistance against stress-migration of sputtered Al line increases with increasing the tensile stress for the PSG film or the USG film.

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The Residual Stress of TiN Thin Film Deposited by PECVD (PECVD에 의해 증착된 TiN 박막의 잔류응력)

  • Song, K.D.;Nam, D.H.;Lee, I.W.;Lee, G.H.;Kim, M.I.
    • Journal of the Korean Society for Heat Treatment
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    • v.6 no.2
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    • pp.70-78
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    • 1993
  • The presence of a residual stress in a thin film affects the properties and performances of the film, so the study of stress in a film must be very important. In this study, therefore, considering the characteristics of PECVD process, it was discussed that the residual stress, measured by $sin^2{\Psi}$ method, fo TiN films deposited on substrates with different TECs (thermal expansion coefficients) changed with film thickness. As a results, it was obtained that the residual stress of TiN film was compressive stress about all kinds of substrates and increased with film thickness. Also, the compressive residual stresses of TiN films increased in Si, Ti, STS304 order. According to the above results, we confirmed that the changes of residual stress of TiN film with substrates were due to the thermal stress originated form the difference in the TECs of the film and substrates, and that the intrinsic stress had dominating effect on the residual stress of TiN film deposited by PECVD. And in this study, the intrinsic stress of TiN film was compressive stress in spite of the Zone 1 structure. It is due to the entrapment of impurities in grain boundary or void.

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Characteristics of Compressive Strength of Geogrid Mixing Reinforced Lightweight Soil (지오그리드 혼합 보강경량토의 압축강도특성 연구)

  • Kim, Yun-Tae;Kwon, Yong-Kyu;Kim, Hong-Joo
    • Journal of the Korean Geotechnical Society
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    • v.22 no.7
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    • pp.37-44
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    • 2006
  • This paper investigates strength characteristics and stress-strain behaviors of geogrid mixing reinforced lightweight soil. The lightweight soil was reinforced with geogrid in order to increase its compressive strength. Test specimens were fabricated by various mixing conditions including cement content, initial water content, air content and geogrid layer and then unconfined compression tests were carried out. From the experimental results, it was found that unconfined compressive strength as well as stress-strain behavior of lightweight soil was strongly influenced by mixing conditions. The more cement content that is added to the mixture, the greater its unconfined compressive strength. However, the more initial water content or the more air foam content, the less its unconfined compressive strength. It was observed that the compressive strength of reinforced lightweight soil increased reinforcing effect by the geogrid for most cases. Stress-strain relation of geogrid mixing reinforced lightweight soil showed a ductile behavior rather than a brittle behavior. In reinforced lightweight soil, secant modulus ($E_{50}$) also increased as its compressive strength increased due to the inclusion of geogrid.

Effect of pulse shaper in SHPB technique on dynamic deformation behavior of an NBR rubber (SHPB 기법에서 Pusle shpaer 가 내유 고무(NBR)의 동적 변형 거동에 미치는 영향)

  • 김성현;이억섭;이종원
    • Proceedings of the Korean Society of Precision Engineering Conference
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    • 2004.10a
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    • pp.634-637
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    • 2004
  • This paper presents a Split Hopkinson Pressure Bar(SHPB) technique to obtain compressive stress-strain data for rubber materials. An experimental technique that modifies the conventional Split Hopkinson Pressure Bar(SHPB) has been developed for measuring the compressive stress-strain responses of materials with low mechanical impedance and low compressive strengths such as rubber. This paper introduces an all-polymeric pressure bar which achieves a closer impedance match between the pressure bar and the specimen materials. In addition, we are a pulse shaper to lengthen the rising time of the incident wave to ensure stress equilibrium and homogeneous deformation of a rubber materials. It is found that the modified technique can be determine the dynamic deformation behavior of an NBR rubber more accurately.

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Compressive Creep Behavior of Fruits

  • Kim, M.S.;Park, J.M.
    • Proceedings of the Korean Society for Agricultural Machinery Conference
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    • 1993.10a
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    • pp.1329-1339
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    • 1993
  • Creep tests were performed to determine the nonlinear viscoelastic properties of apples and pears with the creep experiment apparatus designed in this study. Compressive creep characteristics of fruits were tested at two kinds of storage conditions, four periods of storage and three levels of initial stress. Ten replications were made at each treatment combination. The creep behavior of the fruits could be well described by the nonlinear viscoelastic model as a function of initial stress and time. however, for each level of initial stress applied, the compressive behavior of the samples was satisfactorily represented by Burger's model. For all sample fruits, the longer the samples was stored, the higher the instantaneous elastic strain was observed, and the creep progressed at a high rate. These phenomena were even more remarkable on the fruit stored at the normal temperature storage rather than at the low temperature storage.

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Study on the characteristics of shot peened material (쇼트피닝에 의한 재료의 특성에 관한 연구)

  • 이승호
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.7 no.2
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    • pp.15-22
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    • 1998
  • The effects of shot peening an the fatigue strength are studied in this paper. Applying the multistage shot peening on the material. the relation between the residual stress and fatigue strength compressive is investigated. Observing tensile strength elongation. reduction of area. hardness. and roughness. the results can be summarized as follows ; 1.The change of mechanical properties is small before and after the shot peening is carried out. The change of hardness is also small in high hardness material. 2.The surface roughness does not affect the fatigue strength. but the surface roughness is improved by multi-stage shot peening. 3.The fatigue strength of multi-stage shot peening material is 756MPa and is 1.78 times higher than that of un-peened material. 4.The maximum compressive residual strength of multi-stage shot peening material is -792MPa the fatigue strength seems to be improved by residual stress.

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Characterization of Piezoelectric Microspeaker Fabricated with C-axis Oriented ZnO Thin Film (C-축 배향된 ZnO 박막을 이용하여 제작한 압전형 마이크로 스피커의 특성 평가)

  • Yi Seung-Hwan;Seo Kyong-Won;Ryu Kum-Pyo;Kweon Soon-Young
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.19 no.6
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    • pp.531-537
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    • 2006
  • A micromachined piezoelectric microspeaker was fabricated with a highly c-axis oriented ZnO thin film on a silicon-nitride film having compressive residual stress. When it was measured 3 mm away from the microspeaker in open field, the largest sound pressure level produced by the fabricated microspeaker was about 91 dB at around 2.9 kHz for the applied voltage of $6\;V_{peak-to-peak}$. The key technologies to these successful results were as follows: (1) the usage of a wrinkled diaphragm caused by the high compressive residual stress of silicon-nitride thin film, (2) the usage of the highly c-axis oriented ZnO thin film.

The Improvement of Compressive Residual Stress by Warm Shot Peening (온간 쇼트피닝에 의한 압축잔류응력의 변화)

  • Lee Seung-Ho;Shim Dong-Suk;Kim Gi-Jeon
    • Journal of the Korean institute of surface engineering
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    • v.37 no.5
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    • pp.273-278
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    • 2004
  • The requirements of getting spring steel with higher fatigue strength have been increased to achieve the weight reduction of a vehicle. As the possible increment in fatigue strength by using the conventional shot peening treatment is found to be limited, it is necessary to modify the shot peening treatment. In this study, to investigate the effects of warm shot peening on increasing fatigue strength, tests are conducted on spring steel SAE9524. By the results of rotating bending fatigue tests, the fatigue strength increases up to 23.8% in warm shot peening specimens at $200^{\circ}C$ compared with conventional shot peening. The major reason why the warm shot peening is effective to the improvement of fatigue strength is the increment of the compressive residual stress, which can be effectively formed by shot peening under the condition of warm temperature than room temperature.

The Improvement of Fatigue Properties by 2-step Shot Peening (2단쇼트피닝에 의한 피로특성의 향상)

  • 이승호;심동석
    • Journal of the Korean institute of surface engineering
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    • v.36 no.6
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    • pp.475-479
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    • 2003
  • In this study, to investigate the effects of 2-step shot peening at the surface of spring steel, tests are conducted on spring steel and shot peened specimens. Various tests are accomplished to evaluate mechanical properties influenced by shot peening process, and fatigue tests are also performed to evaluate the improvement of fatigue strength. And then the residual stresses are examined. The mechanical properties of material did not change so much by shot peening. However, the fatigue strength of notched specimen remarkably increased. In the case of 1-step shot peening, fatigue strength increased by about 20% than unpeened specimen. Especially, in the case of 2-step shot peening, fatigue strength increased by about 40%, because the residual compressive stress at surface was higher than that of 1-step shot peened specimen. The fatigue strength and life are closely related to the value and position of maximum compressive residual stress by shot peening.