• Title/Summary/Keyword: High Strain

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Creep Behavior of High-Strength Concrete with Nylon Fibers at Elevated Temperatures (고온을 받은 나일론 섬유 보강 고강도 콘크리트의 크리프 거동)

  • Kim, Young-Sun;Lee, Tae-Gyu;Kim, Woo-Jae;Kim, Gyu-Yong
    • Journal of the Korea Concrete Institute
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    • v.23 no.5
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    • pp.627-636
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    • 2011
  • Recently, to prevent explosive spalling of high-strength concrete (HSC) members, the usage of nylon fiber instead of polypropylene fiber has increased. Past experimental studies have been conducted to examine the spalling and mechanical properties of HSC with nylon fibers when exposed to elevated temperature. However, the previous studies on HSC with nylon fibers subjected to high temperatures were performed only on the properties such as spalling, compressive strength, and elastic modulus rather than investigations on to the behaviors such as thermal strain, total strain, steady state creep, and transient creep. Therefore, in this study thermal strain, total strain, steady state creep, and transient creep of HSC mixed with nylon fibers with water to binder ratio of 0.30 to 0.15 were tested. The experimental results showed that nylon fibers did not affect the performance of HSC with nylon fibers at high temperatures. However, HSC with nylon fibers generated a larger transient creep strain than that of HSC without fibers and normal strength concrete.

Characterization of Dynamic Deformation Behavior of Al 7075-T6 at High Temperature by Using SHPB Technique (SHPB 기법을 사용한 고온에서의 Al 7075-T6 의 동적 변형 거동)

  • Lee, Ouk-Sub;Park, Jin-Su;Choi, Hye-Bin;Kim, Hong-Min
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.34 no.8
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    • pp.981-987
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    • 2010
  • The split Hopkinson pressure bar (SHPB) technique is extensively used to characterize material deformation behavior under high strain rate condition. In this study, the dynamic deformation behavior of aluminum 7075-T6 under a high strain rate and at a high temperature is investigated by using a modified SHPB set-up with the pulse shaper technique. The parameters used in the Johnson-Cook constitutive equation are determined by using the SHPB experimental results including the data on the effects of strain rate, temperature, strain hardening, and thermal softening of the material.

Analytical Study on Flexural Behavior of Alkali-Activated Slag-Based Ultra-High-Ductile Composite (알칼리활성 슬래그 기반 초고연성 복합재료의 휨거동 해석)

  • Lee, Bang Yeon
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.7 no.2
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    • pp.158-165
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    • 2019
  • The purpose of this study is to investigate analytically the flexural behavior of beam reinforced by an alkali-activated slag-based fiber-reinforced composite. The materials and mixture proportion were selected to manufacture an alkali-activated slag-based fiber-reinforced composite with high tensile strain capacity over 7% and compressive strength and tension tests were performed. The composite showed a compressive strength of 32.7MPa, a tensile strength of 8.43MPa, and a tensile strain capacity of 7.52%. In order to analyze the flexural behavior of beams reinforced by ultra-high-ductile composite, nonlinear sectional analysis was peformed for four types of beams. Analysis showed that the flexural strength of beam reinforced partially by ultra-high-ductile composite increased by 8.0%, and the flexural strength of beam reinforced fully by ultra-high-ductile composite increased by 24.7%. It was found that the main reason of low improvement in flexural strength is the low tensile strain at the bottom of beam. The tensile strain at bottom corresponding to the flexural strength was 1.38% which was 18.4% of tensile strain capacity of the composite.

Influence of Mo Addition on High Temperature Deformation Behavior of L12 Type Ni3Al Intermetallics

  • Han, Chang-Suk;Jang, Tae-Soo
    • Korean Journal of Materials Research
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    • v.26 no.4
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    • pp.167-172
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    • 2016
  • The high temperature deformation behavior of $Ni_3Al$ and $Ni_3(Al,Mo)$ single crystals that were oriented near <112> was investigated at low strain rates in the temperature range above the flow stress peak temperature. Three types of behavior were found under the present experimental conditions. In the relatively high strain rate region, the strain rate dependence of the flow stress is small, and the deformation may be controlled by the dislocation glide mainly on the {001} slip plane in both crystals. At low strain rates, the octahedral glide is still active in $Ni_3Al$ above the peak temperature, but the active slip system in $Ni_3(Al,Mo)$ changes from octahedral glide to cube glide at the peak temperature. These results suggest that the deformation rate controlling mechanism of $Ni_3Al$ is viscous glide of dislocations by the <110>{111} slip, whereas that of $Ni_3(Al,Mo)$ is a recovery process of dislocation climb in the substructures formed by the <110>{001} slip. The results of TEM observation show that the characteristics of dislocation structures are uniform distribution in $Ni_3Al$ and subboundary formation in $Ni_3(Al,Mo)$. Activation energies for deformation in $Ni_3Al$ and $Ni_3(Al,Mo)$ were obtained in the low strain rate region. The values of the activation energy are 360 kJ/mol for $Ni_3Al$ and 300 kJ/mol for $Ni_3(Al,Mo)$.

Measurement of Fiber Board Poisson's Ratio using High-Speed Digital Camera

  • Choi, Seung-Ryul;Choi, Dong-Soo;Oh, Sung-Sik;Park, Suk-Ho;Kim, Jin-Se;Chun, Ho-Hyun
    • Journal of Biosystems Engineering
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    • v.39 no.4
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    • pp.324-329
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    • 2014
  • Purpose: The finite element method (FEM) is advantageous because it can save time and cost by reducing the number of samples and experiments in the effort to identify design factors. In computational problem-solving it is necessary that the exact material properties are input for achieving a reliable analysis. However, in the case of fiber boards, it is difficult to measure their cross-directional material properties because of their small thickness. In previous research studies, the Poisson's ratio was measured by analyzing ultrasonic wave velocities. Recently, the Poisson's ratio was measured using a high-speed digital camera. In this study, we measured the transverse strain of a fiber board and calculated its Poisson's ratio using a high-speed digital camera in order to apply these estimates to a FEM analysis of a fiber board, a corrugated board, and a corrugated box. Methods: Three different fiber board samples were used in a uniaxial tensile test. The longitudinal strain was measured using the Universal Testing Machine. The transverse strain was measured using an image processing method. To calculate the transverse strain, we acquired images of the fiber board before the test onset and before the fracture occurred. Acquired images were processed using the image processing program MATLAB. After the images were converted from color to binary, we calculated the width of the fiber board. Results: The calculated Poisson's ratio ranged between 0.2968-0.4425 (Machine direction, MD) and 0.1619-0.1751 (Cross machine direction, CD). Conclusions: This study demonstrates that measurement of the transverse properties of a fiber board is possible using image processing methods. Correspondingly, these processing methods could be used to measure material properties that are difficult to measure using conventional measuring methodologies that employ strain gauge extensometers.

Design and Fabrication of Split Hopkinson Pressure Bar for Dynamic Mechanical Properties of Self-reinforced Polypropylene Composite (폴리프로필렌 자기 보강 복합재의 동적 물성 구축을 위한 Split Hopkinson Pressure Bar의 설계 및 제작)

  • Kang, So-Young;Kim, Do-Hyoung;Kim, Dong-Hyun;Kim, Hak-Sung
    • Composites Research
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    • v.31 no.5
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    • pp.221-226
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    • 2018
  • The Split Hopkinson Pressure Bar(SHPB) has been the most widely used apparatus to characterize dynamic mechanical behavior of materials at high strain rates between $100s^{-1}$ and $10,000s^{-1}$. The SHPB test is based on the wave propagation theory which was developed to give the stress, strain and strain rate in the specimen using the strains measured in the incident and transmission bars. In this study, the SHPB was directly designed and fabricated for the dynamic mechanical properties of fiber reinforced plastic (FRP) composites. In addition, this apparatus was verified for the validity by comparing the strain data obtained through the high speed camera and Digital Image Correlation(DIC) during the high strain rate compression test of the self-reinforced polypropylene composite (SRPP) specimen.

Viscoelastic Behavior of High Density Polyethylene Using High Tibial Osteotomy with Respect to the Strain Rate (근위경골절골술(HTO)용 X-밴드 플레이트에 적용되는 고밀도 폴리에틸렌(HDPE)의 변형률속도에 따른 점탄성거동)

  • Hwang, Jung-Hoon;Kim, Cheol-Woong
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.36 no.4
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    • pp.431-438
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    • 2012
  • The mechanical behavior of the polymeric material, HDPE depends on both time and temperature. The study of the tensile behavior at different strain rates is important in engineering design of the orthopedics device such as X-band plate. The mechanical properties and deformation mechanisms of HDPE are strongly dependent on the applied strain rate. Generally, the deformation behavior of HDPE based on the stress-strain curve is complex because of the highly inhomogeneous nature of plastic deformation, particularly that of necking. Therefore, we attempted to determine the mechanical behavior of HDPE in this study. Normally, tensile testing under various strain rates of the HDPE has been used to determine the mechanical behavior. We performed tensile tests at various strain rates (1 to 500 %/min) to analyze the viscoelastic behavior on increasing the strain rate. A tensile stress-strain curve was plotted from the data, and the point of transition was marked to calculate the transition stress, strain, and modulus.

A Study on a Highly Sensitive Strain Sensor based on Rayleigh Wave (레일리파 기반의 고감도 변형률 센서에 관한 연구)

  • Lee, Ki Jung;Jo, Minuk;Fu, Chen;Eun, Kyoungtae;Oh, Haekwan;Choa, Sung-Hoon;Yang, Sang Sik
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.63 no.4
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    • pp.495-501
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    • 2014
  • Piezoresistive-type, capacitive-type, and optical-type sensors have mainly been used for measuring a strain. However, in building a sensor network for remote monitoring using these conventional sensors there are disadvantages such as the complexity of a measuring system including wireless communication circuitry and high cost. In this paper, we demonstrates a highly-sensitive surface acoustic wave (SAW) strain sensor which is advantageous to harsh environments and wireless network. We designed and fabricated the SAW strain sensor. The SAW strain sensor attached on a specimen was tested with a tensile tester. The strain on the sensor surface was measured with a commercial strain gauge and compared with that obtained from strain analysis. The central frequency shift of the SAW sensor was measured with a network analyzer. The sensitivity of the SAW strain sensor is 134 $Hz/{\mu}{\varepsilon}$ which is high compared to previous results.

Investigation on the Vibrating Wire Strain Gauges for the Evaluation of Pipeline Safety in Extreme Cold Region (극한지 파이프라인 안정성 평가를 위한 진동현식 변형률 게이지 연구)

  • Kim, Hak Joon
    • The Journal of Engineering Geology
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    • v.26 no.4
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    • pp.583-591
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    • 2016
  • Vibrating wire (VW) strain gauges are widely used for the evaluation of pipeline safety in extreme cold region. The development of VW strain gauges for the low temperature environment is necessary because of the high cost of gauges sold in developed countries. Thermistors embedded in the regular VW strain gauges and PT 100 sensors embedded in the gauges specially manufactured for this study have gone through credibility tests for temperature measurements. The use of PT 100 is recommended at low temperature environments because thermistors have low credibility at temperatures below $-15^{\circ}C$. Strain measurements using regular VW strain gauges also show low accuracies as temperature goes down. VW strain gauges manufactured using inconel give high credibility of strain measurements at low temperatures. More reliable VW strain gauges for the low temperature environment will be developed in the near future.

The friction effects at high strain rates of materials under dynamic compression loads (동압축 하중을 받는 재료의 고변형도율에서의 마찰영향)

  • 김문생
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.3
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    • pp.454-464
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    • 1987
  • The objective of this research is to analyze and evaluate the dynamic flow curve of metals under impact loading at both high strain rate (.epsilon.=1/h dh/dt > 10$\^$3/m/s/m) and large strain (.epsilon.=In h/h$\_$0/ > 1.0). A test method for dynamic compression of metal disc is described. The velocity of the striker face and the force on the anvil are measured during the impact period. From these primitive data the axial stress, strain, and strain rate of the disc are obtained. The Strain rate is determined by the striker velocity divided by the specimen height. This gives a slightly increasing strain rate over most of the deformation period. Strain rates of 100 to 10,000 per second are achieved. Attainable final strains are 150%. A discussion of several problem areas is presented. The friction on the specimen surfaces, the determination of the frictional coefficient, the influence of the specimen geometry (h$\_$0//d$\_$0/ ratio) on the friction effect, the lock-up condition for a given configuration, the friction correction factor, and the evaluation of several lubricants are given. The flow function(stress verus strain) is dependent on the material condition(e.g., prior cold work), specimen geometry, strain rate, and temperature.