• Title, Summary, Keyword: Pre-Strain

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A Prediction Model for Low Cycle Fatigue Life of Pre-strained Fe-18Mn TWIP Steel (Fe-18Mn TWIP강의 Pre-strain에 따른 저주기 피로 수명 예측 모델 연구)

  • Kim, T.W.;Lee, C.S.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • pp.259-262
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    • 2009
  • The influence of pre-strain in low-cycle fatigue behavior of Fe-18Mn-0.05Al-0.6C TWIP steel was studied by conducting axial strain-controlled tests. As-received plates were deformed by rolling with reduction ratios of 10 and 30%, respectively. A triangular waveform with a constant frequency of 1 Hz was employed for low cycle fatigue test at the strain amplitudes in the range of ${\pm}0.4{\sim}{\pm}0.6$ pct. The results showed that low-cycle fatigue life was strongly dependent on the amount of pre-strain as well as the strain amplitude. Increasing the amount of prestrain, the number of reversals to failure was significantly decreased at high strain amplitudes, but the effect was negilgible at low strain amplitudes. A new model for predicting fatigue life of pre-strained body has been devised adding a correction term of ${\Delta}E_{pre-strain}$ to the energy-based fatigue damage parameter.

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Effects of Pre-Strains on Failure Assessment Analysis to API 5L X65 Pipeline

  • Baek, Jong-Hyun;Kim, Young-Pyo;Kim, Woo-Sik;Seok, Chang-Sung
    • Journal of the Korean Society for Nondestructive Testing
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    • v.29 no.3
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    • pp.219-223
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    • 2009
  • This paper prescribed the structural integrity of the API 5L X65 pipeline subjected to tensile pre-strain. The effects of pre-strain on the mechanical properties of API 5L X65 pipe were substantially investigated through a variety of the experimental procedures. Axial tensile pre-strain of 1.5, 5 and 10% was applied to plate-type tensile specimens cut from the pipe body prior to mechanical testing. Tensile test revealed that yield strength and tensile strength were increased with increasing tensile pre-strain. The increasing rate of the yield strength owing to the pre-strain is greater than that of the tensile strength. However, the pre-strain up to 5% had a little effect on the decreasing of the fracture toughness. The structural integrity of the API 5L X65 pipeline subjected to large plastic deformation was evaluated through the fitness-for service code.

A Prediction Model for Low Cycle and High Cycle Fatigue Lives of Pre-strained Fe-18Mn TWIP Steel (Fe-18Mn TWIP강의 Pre-strain에 따른 저주기 및 고주기 피로 수명 예측 모델)

  • Kim, Y.W.;Lee, C.S.
    • Transactions of Materials Processing
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    • v.19 no.1
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    • pp.11-16
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    • 2010
  • The influence of pre-strain on low cycle fatigue behavior of Fe-18Mn-0.05Al-0.6C TWIP steel was studied by conducting axial strain-controlled tests. As-received plates were deformed by rolling with reduction ratios of 10 and 30%, respectively. A triangular waveform with a constant frequency of 1 Hz was employed for low cycle fatigue test at the total strain amplitudes in the range of ${\pm}0.4\;{\sim}\;{\pm}0.6$ pct. The results showed that low-cycle fatigue life was strongly dependent on the amount of pre-strain as well as the strain amplitude. Increasing the amount of prestrain, the number of reversals to failure was significantly decreased at high strain amplitudes, but the effect was negligible at low strain amplitudes. A new model for predicting fatigue life of pre-strained body has been suggested by adding ${\Delta}E_{pre-strain}$ to the energy-based fatigue damage parameter. Also, high-cycle fatigue lives predicted using the low-cycle fatigue data well agreed with the experimental ones.

Finite Element Damage Analysis Method for J-Resistance Curve Prediction of Cold-Worked Stainless Steels (조사취화를 모사한 스테인레스강의 파괴저항선도를 예측하기위한 유한요소 손상해석기법)

  • Seo, Jun Min;Kim, Ji Soo;Kim, Yun Jae
    • Transactions of the Korean Society of Pressure Vessels and Piping
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    • v.14 no.1
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    • pp.1-7
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    • 2018
  • Materials in nuclear power plants can be embrittled by neutron irradiation. According to existing studies, the effect of the material property by irradiation embrittlement can be approximately simulated by cold working (pre-strain). In this study, finite element damage analysis method using the stress-modified fracture strain model is proposed to predict J-Resistance curves of irradiated SUS316 stainless steel. Experimental data of pre-strained SUS316 stainless steel material are obtained from literature and the damage model is determined by simulating the tensile and fracture toughness tests. In order to consider damage caused by the pre-strain, a pre-strain constant is newly introduced. Experimental J-Resistance curves for various degrees of pre-strain are well predicted.

Fabrication and AE Characteristics of TiNi/ A16061 Shape Memory Alloy Composite

  • Park, Young-Chul;Lee, Jin-Kyung
    • Journal of Mechanical Science and Technology
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    • v.18 no.3
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    • pp.453-459
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    • 2004
  • TiNi/ Al6061 shape memory alloy (SMA) composite was fabricated by hot press method to investigate the microstructure and mechanical properties. Interface bonding between TiNi reinforcement and A1 matrix was observed by using SEM and EDS. Pre-strain was imposed to generate compressive residual stress inside composite. A tensile test for specimen, which under-went pre-strain, was performed at high temperature to evaluate the variation of strength and the effect of pre-strain. It was shown that interfacial reactions occurred at the bonding between matrix and fiber, creating two inter-metallic layers. And yield stress increased with the amount of pre-strain. Acoustic Emission technique was also used to nondestructively clarify the microscopic damage behavior at high temperature and the effect of pre-strain of TiNi/ Al6061 SMA composite.

Anisotropy in Gum and Black Filled SBR and NR Vulcanizates Due to Large Deformation

  • Park, Byung-Ho;G.R. Hamed
    • Macromolecular Research
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    • v.8 no.6
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    • pp.268-275
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    • 2000
  • After imposing a large pre-strain, anisotropy increases with increasing residual extension ratio. Gums have very low residual extension ratio and exhibit little anisotropy, while black filled SBR and especially sulfur-cured carbon black filled NR have large set and anisotropy. For carbon black filled rubber, samples subjected to tensile loading in perpendicular to the pre-strain direction have the same stress-strain curves shape as the sample without pre-strain (=isotropic samples), but slightly lower modulus. However, compared to isotropic or perpendicular directional samples to pre-strain direction, samples subjected to tensile loading in parallel to the pre-strain direction show low stress at low deformation, but have high stiffness at high deformation. Normalized anisotropy changes with strain. The normalized anisotropy for various deformations is a linear function of residual extension ratio.

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Characterization of the Material Properties of Sheet Metal for Auto-body at the High Strain Rate Considering the Pre-strain Effect (예비변형률 효과를 고려한 고변형률 속도에서의 차체용 강판의 물성 특성)

  • Kim, Seok-Bong;Lim, Ji-Ho;Huh, Hoon;Lim, Jong-Dae
    • Transactions of the Korean Society of Automotive Engineers
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    • v.12 no.3
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    • pp.204-210
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    • 2004
  • Most auto-body members fabricated by the sheet metal forming process. During this process the thickness and material properties of the sheet metal are changed with the residual stress and plastic strain. This paper deals with the material properties of the sheet metal at the high strain rate considering the pre-strain effect. Specimens are selected from sheet metals for outer panels and inner members, such as SPCEN, SPRC45E, SPRC35R and EZNCD. The specimens are prepared with the pre-strain of 2, 5 and 10 % by tensile elongation in Instron 5583, which could be equivalent to the plastic strain in sheet metal forming. High speed tensile tests are then carried out with the pre-stained specimens at the strain rate of 1 to 100/sec. The experimental result informs that the material properties are noticeably influenced by the pre-strain when the yield stress of the specimens is moderate as SPCEN, SPRC35R and EZNCD. The result also demonstrates that the ultimate tensile strength as well as the yield stress is increased as the amount of the pre-strain is increased.

Effect of Strain Rate and Pre-strain on Tensile Properties of Heat-treated A5082 and A6060 Aluminium Wrought Alloys (열처리한 A5082와 A6060합금의 인장특성에 미치는 변형율속도 및 예비변형율의 영향)

  • Lee, Choongdo
    • Journal of the Korean Society for Heat Treatment
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    • v.33 no.4
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    • pp.161-172
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    • 2020
  • The tensile property of A5082 and A6060 aluminium wrought alloys was investigated, in terms of the strain rate sensitivity on alloy conditions by heat treatment and bake hardenability on pre-strain prior to strain ageing. The tensile test was carried out in a range of strain rate of 4.17 × 10-5 s-1 ~ 4.17 × 10-5 s-1 in room temperature and the nominal range of pre-strain was 3.0 ~ 10.5%. The tensile deformation of A5082 alloys is characterized as typical case of dynamic strain ageing with negative strain rate sensitivity for all conditions, and the tensile strength indicates a similar level regardless of alloy conditions, except only in full annealed condition. The stress-relief annealing on A6060 alloys can induce practical decrease in strength level of over approximately 100 MPa without any ductility loss, compared to as-rolled condition, while a full annealed and aged condition leads remarkable strengthening effect with the decrease of tensile elongation. Additionally, the bake hardenability of A5082 alloy by strain ageing indicates a negative dependence upon the increase of pre-strain, while A6060 alloy exhibits a positive sign even in low level relatively compared with conventional SPCC.

Effects of the Pre-strain on Mechanical Properties of the Solid-Phase Formed Thermoplastic Composite (고상성형된 열가소성 복합재료의 성형 변형률이 기계적 특성에 미치는 영향)

  • Lee, Jung-Hui;Jo, Hyeon-Cheol;Lee, Gyeong-Yeop
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.8
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    • pp.1220-1226
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    • 2001
  • This study investigates the effects of the pre-strain level on mechanical properties of the solid-phase formed thermoplastic composite. A uniaxial solid-phase forming was performed at the temperature of 125$\^{C}$ and at the constant cross-head speed of 3mm/sec. The composite sheet was formed to various pre-strain levels of 10%, 20%, and 30%. Tension, flexural, and impact tests were carried out to characterize the material properties of a solid-phase formed part. Tensile and flexural strengths decreased with increasing the pre-strain level, while impact strength increased. Various microstructures of the formed part explained the above material behavior.

The Pre-Evaluation of Stability during Tunnel Excavation using Unconfined Compression Strength of Intact Rock or Rock Mass and Crown Settlement Data (터널천단변위와 암석 또는 암반의 일축압축강도를 이용한 시공 중인 터널의 예비 안정성 평가)

  • Park, Young Hwa;Moon, Hong Duk;Ha, Man Bok
    • International Journal of Highway Engineering
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    • v.17 no.6
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    • pp.27-32
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    • 2015
  • PURPOSES : It is difficult to estimate tunnel stability because of lack of timely information during tunnel excavation. Tunnel deformability refers to the capacity of rock to strain under applied loads or unloads during tunnel excavation. This study was conducted to analyze a methods of pre-evaluation of stability during tunnel construction using the critical strain concept, which is applied to the results of tunnel settlement data and unconfined compression strength of intact rock or rock mass at the tunnel construction site. METHODS : Based on the critical strain concept, the pre-evaluation of stability of a tunnel was performed in the Daegu region, at a tunnel through andesite and granite rock. The critical strain concept is a method of predicting tunnel behavior from tunnel crown settlement data using the critical strain chart that is obtained from the relationship between strain and the unconfined compression strength of intact rock in a laboratory. RESULTS : In a pre-evaluation of stability of a tunnel, only actually measured crown settlement data is plotted on the lower position of the critical strain chart, to be compared with the total displacement of crown settlement, including precedent settlement and displacement data from before the settlement measurement. However, both cases show almost the same tunnel behavior. In an evaluation using rock mass instead of intact rock, the data for the rock mass strength is plotted on the lower portion of the critical strain chart, as a way to compare to the data for intact rock strength. CONCLUSIONS : From the results of the pre-evaluation of stability of the tunnel using the critical strain chart, we reaffirmed that it is possible to promptly evaluate the stability of a tunnel under construction. Moreover, this research shows that a safety evaluation using the actual instrumented crown settlement data with the unconfined compression strength of intact rock, rather than with the unconfined compression strength of a rock mass in the tunnel working face, is more conservative.