• Title/Summary/Keyword: Pre-compressive Stress

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A Study on Nondestructive Evaluation of Share Memory Alloy Composite at High Temperature (고온에서의 형상기억복합재료의 비파괴평가에 관한 연구)

  • Kang, Dong-Hyun;Lee, Jin-Kyung;Park, Young-Choul;Ku, Hoo-Taek;Lee, Kyu-Chang
    • Proceedings of the KSME Conference
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    • 2001.11a
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    • pp.186-191
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    • 2001
  • Tensile residual stress happen by difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composite(MMC). In this study, TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress in matrix using shape memory effect of it. Pre-strain was added to generate compressive residual stress inside TiNi/A16061 shape memory alloy(SMA) composite. It was also evaluated the effect of compressive residual stress corresponding to pre-strains variation and volume fraction of TiNi alloy. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain difference of TiNi/A16061 SMA composite. In addition, two dimensional AE source location technique was applied to inspect the crack initiation and propagation in composite.

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Experimental study of Kaiser effect under cyclic compression and tension tests

  • Chen, Yulong;Irfan, Muhammad
    • Geomechanics and Engineering
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    • v.14 no.2
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    • pp.203-209
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    • 2018
  • Reliable estimation of compressive as well as tensile in-situ stresses is critical in the design and analysis of underground structures and openings in rocks. Kaiser effect technique, which uses acoustic emission from rock specimens under cyclic load, is well established for the estimation of in-situ compressive stresses. This paper investigates the Kaiser effect on marble specimens under cyclic uniaxial compressive as well as cyclic uniaxial tensile conditions. The tensile behavior was studied by means of Brazilian tests. Each specimen was tested by applying the load in four loading cycles having magnitudes of 40%, 60%, 80% and 100% of the peak stress. The experimental results confirm the presence of Kaiser effect in marble specimens under both compressive and tensile loading conditions. Kaiser effect was found to be more dominant in the first two loading cycles and started disappearing as the applied stress approached the peak stress, where felicity effect became dominant instead. This behavior was observed to be consistent under both compressive and tensile loading conditions and can be applied for the estimation of in-situ rock stresses as a function of peak rock stress. At a micromechanical level, Kaiser effect is evident when the pre-existing stress is smaller than the crack damage stress and ambiguous when pre-existing stress exceeds the crack damage stress. Upon reaching the crack damage stress, the cracks begin to propagate and coalesce in an unstable manner. Hence acoustic emission observations through Kaiser effect analysis can help to estimate the crack damage stresses reliably thereby improving the efficiency of design parameters.

Fracture Characteristic of TiNi/A16061 Share Memory Alloy Composite using Acoustic Emission Technique (AE 기법을 이용한 TiNi/A16061 형상기억복합재료의 파괴특성평가)

  • Lee, Jin-Kyung;Park, Young-Chul;Ku, Hoo-Taek;Park, Dong-Sung;Lee, Kyu-Chang
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.2
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    • pp.275-282
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    • 2002
  • Tensile residual stress happen by difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composite(MMC). In this study, TiNi fiber was used to solve the tensile residual stress as the reinforced material. TiNi fiber improves the tensile strength of composite by occurring compressive residual stress in matrix using shape memory effect of it. Pre-strain was added to generate compressive residual stress inside TiNi/A16061 composite. It was also evaluated the effect of compressive residual stress corresponding to pre-strains variation. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain difference of TiNi/A16061 shape memory alloy composite.

Fracture Characteristic of TiNi/A16061 Share Memory Alloy Composite at High Temperature using Acoustic Emission Technique (AE 기법을 이용한 TiNi/A16061 형상기억복합재료의 고온파괴특성평가)

  • Lee, Jin-Kyung;Park, Young-Choul;Kang, Dong-Hyun;Park, Dong-Sung;Lee, Kyu-Chang
    • Proceedings of the KSME Conference
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    • 2001.06a
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    • pp.72-77
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    • 2001
  • Tensile residual stress happen by difference of coefficients of thermal expansion between fiber and matrix is one of the serious problems in metal matrix composite(MMC). In this study, TiNi fiber was used to solve the tensile residual stress as the reinforced material. TiNi fiber improves the tensile strength of composite by occurring compressive residual stress in matrix using shape memory effect of it. Pre-strain was added to generate compressive residual stress inside TiNi/A16061 composite. It was also evaluated the effect of compressive residual stress corresponding to pre-strains variation. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain difference of TiNi/A16061 shape memory alloy composite.

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A Study on the Microscopic Damage Behavior and the Damage Position Evaluation of TiNi/Al6061 Share Memory Alloy Composite (TiNi/A16061 형상기억복합재료의 미시적 손상거동과 손상위치측정에 관한 연구)

  • Lee, Jin-Gyeong;Park, Yeong-Cheol;Gu, Hu-Taek;Lee, Gyu-Chang
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.9
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    • pp.1787-1794
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    • 2002
  • TiNi alloy fiber was used to solve the problem of the tensile residual stress as the reinforced material. TiNi alloy fiber improves the tensile strength of composite by occurring compressive residual stress in the matrix using shape memory effect. In order to generate compressive residual stress in TiNi/Al6061 shape memory alloy(SMA) composite, 1, 3 and 5% pre-strains were applied to the composite in advance. It was also evaluated the effect of compressive residual stress corresponding to the pre-strain variation and the volume fraction of TiNi alloy. AE technique was used to clarify the microscopic damage behavior at high temperature and the effect of pre-strain in TiNi/Al6061 SMA composite. The results of the microscopic damage evaluation of TiNi/Al6061 SMA composite under various pre-strain using AE technique can be divided into three stage corresponding to the AE signals. AE counts and events were useful parameters to evaluate the fracture mechanism according to the variation of pre-strain. In addition, two dimensional AE source location technique was applied for monitoring the crack initiation and propagation in composite.

Analysis of actively-confined concrete columns using prestressed steel tubes

  • Nematzadeh, Mahdi;Haghinejad, Akbar
    • Computers and Concrete
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    • v.19 no.5
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    • pp.477-488
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    • 2017
  • In this paper, an innovative technique for finite element (FE) modeling of steel tube-confined concrete (STCC) columns with active confinement under axial compressive loading is presented. In this method, a new constitutive model for the stress-strain relationship of actively-confined concrete is proposed. In total, 14 series of experimental STCC stub columns having active confinement were modeled using the ABAQUS software. The results obtained from the 3D model including the compressive strength at the initial peak point and failure point, as well as the axial and lateral stress-strain curves were compared with the experimental results to verify the accuracy of the 3D model. It was found that there existed a good agreement between them. A parametric study was conducted to investigate the effect of the concrete compressive strength, steel tube wall thickness, and pre-stressing level on the behavior of STCC columns with active confinement. The results indicated that increasing the concrete core's compressive strength leads to an increase in the compressive strength of the active composite column as well as its earlier failure. Furthermore, a reduction in the tube external diameter-to-wall thickness ratio affects the axial stress-strain curve and the confining pressure, while increasing the pre-stressing level has a negligible effect on the two.

An Experimental Study on Allowable Compressive Stress at Prestress Transfer in Pre-Tensioned Concrete Members (프리텐션된 콘크리트 부재의 프리스트레스 도입시 허용압축응력에 관한 실험적 연구)

  • Lee, Jeong Yeon;Lee, Deuck Hang;Kim, Kang Su;Park, Min Kook;Yoon, Sang Chun
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.16 no.4
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    • pp.9-17
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    • 2012
  • In the previous research, allowable compressive stress was analyzed based on strength theory, in which primary effect factors on the allowable compressive stress, such as eccentricity ratio, section type, section size, prestress and self-weight moment, were considered. As its results, allowable compressive stress equations were proposed. As a series of the previous research, this paper presents an experimental study on the prestress at transfer of pre-tensioned members with different eccentricity ratios. The results shows that ACI318-08 and EC2-02 are unconservative for the members under low eccentricity ratios, and they are conservative for the members under high eccentricity ratios. Compared to the code provisions, the results indicates that the proposed equation reasonably well evaluates the allowable compressive stresses for those with different eccentricity ratios.

Influence of pre-compression on crack propagation in steel fiber reinforced concrete

  • Abubakar, Abdulhameed U.;Akcaoglu, Tulin
    • Advances in concrete construction
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    • v.11 no.3
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    • pp.261-270
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    • 2021
  • In this study, a new understanding is presented on the microcracking behavior of high strength concrete (HSC) with steel fiber addition having prior compressive loading history. Microcracking behavior at critical stress (σcr) region, using seven fiber addition volume of 0.5, 0.75, 1.0, 1.25, 1.5, 1.75, and 2.0% was evaluated, at two aspect ratios (60 and 75). The specimens were loaded up to a specified compressive stress levels (0.70fc-0.96fc), and subsequently subjected to split tensile tests. This was followed by microscopic analyses afterwards. Four compressive stress levels as percentage of fc were selected according to the linearity end point based on stress-time (σ-t) diagram under uniaxial compression. It was seen that pre-compression has an effect on the linearity end point as well as fiber addition where it lies within 85-91% of fc. Tensile strength gain was observed in some cases with respect to the 'maiden' tensile strength as oppose to tensile strength loss due to the fiber addition with teething effect. Aggregate cracking was the dominant failure mode instead of bond cracks due to improved matrix quality. The presence of the steel fiber improved the extensive failure pattern of cracks where it changes from 'macrocracks' to a branched network of microcracks especially at higher fiber dosages. The applied pre-compression resulted in hardening effect, but the cracking process is similar to that in concrete without fiber addition.

A Study on the Analysis for Welding Residual Stress of Preflex Beam (PREFLEX BEAM 제작시의 용접부 역학적 특성에 관한 연구)

  • 방한서;주성민;안해영
    • Journal of Ocean Engineering and Technology
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    • v.17 no.6
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    • pp.65-71
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    • 2003
  • Since the preflex beam is fabricated through welding, the pre-compressive stresses that should occur over the concrete pier are diminished by the welding residual stresses. Therefore welding residual stresses must be relieved during the fabrication. Therefore, the analysis and examination of the accurate welding residual stress distribution characteristics are necessary. In this study, accurate distribution of welding residual stress of the preflex beam is analyzed by the finite element method, using 2 dimensional and 3 dimensional elements. Further, the thermo-mechanical behavior of the preflex beam is also studied. After the finite element analysis, real distribution of welding residual stress is measured using the sectioning method, and then is compared with the simulation results. The distribution of welding residual stress by finite analysis agreed well with the experimental results.

The Effect of a Compressive Follower Pre-load on the Ligament of Lumbar Spine and the Relationship with Low Back Pain (압축 종동 예하중이 요추 인대에 미치는 영향과 요통과의 관계)

  • Moon, Chang-Hyun;Chung, Tae-Eun;Sin, Hyo-Chol
    • Transactions of the Korean Society of Automotive Engineers
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    • v.18 no.6
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    • pp.63-69
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    • 2010
  • A noble model of the whole lumbar spine (L1~L5) considering all the passive elements, especially the ligaments of the lumbar spine was developed. The purpose of this study was to investigate the relationship between the shear stress of the AVB and the ALL and the effect of a compressive follower pre-load on all ligaments with various motions. The result shows that the shear stress at the AVB and the ALL are positively correlated. This indicates that the shear stress of the ligament can be used an index of low back pain. Regarding the effect of a follower pre-load, contrary to our expectation, the shear stress of the ligaments was not always reduced by applying follower pre-load; flexion was decreased and axial rotation did not change, while extension and lateral bending were increased.