• Title, Summary, Keyword: Prestrain

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Creep Behavior of High Temperature Prestrain in Austenitic 25Cr-20Ni Stainless Steels (오스테나이트계 25Cr-20Ni 스테인리스강의 고온 예변형에 의한 크리프 거동)

  • 박인덕;남기우;안석환
    • Journal of Ocean Engineering and Technology
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    • v.16 no.3
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    • pp.59-64
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    • 2002
  • In the present study, we examined the influence of prestrain on creep strength of Class M alloy(STS310S) and Class A(STS310J1TB) alloys containing precipitates. Prestrain was given by prior creep at a higher stress than the following creep stresses. Creep behaviour before and after stress change and creep rate of pre-strained specimens were compared with that of virgin specimens. Pre-straining produced the strain region where the strain rate was lower than that of a virgin specimen both for STS310J1TB and STS310S steels. The reason for this phenomenon was ascribable to the viscous motion of dislocations, the interaction between dislocations and precipitates in a STS310J1TB steel, and the interaction of dislocations with sub-boundaries in a STS310S steen which has the higher dislocation density and smaller subgrain size resulted from pre-straining at higher stress.

Creep Behavior of High Temperature Prestrain in Austenitic 25Cr-20Ni Stainless Steels (오스테나이트계 25Cr-20Ni 스테인리스강의 고온예변형에 의한 크리프 거동)

  • Park, In-Duck;Nam, Ki-Woo;Ahn, Seok-Hwan
    • Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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    • pp.35-40
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    • 2002
  • In the present study, we examined the influence of prestrain on creep strength of Class M alloy(STS310S) and Class A(STS310J1TB) alloys containing precipitates. Prestrain was given by prior creep at a higher stress than the following creep stresses. Creep behaviour before and after stress change and creep rate of pre-strianed specimens were compared with that of virgin specimens. Pre-straining produced the strain region where the strain rate was lower than that of a virgin specimen both for STS310J1TB and STS310S steels. The reason for this phenomenon was ascribable to the viscous motion of dislocations, the interaction between dislocations and precipitates in a STS310J1TB steel, and the interaction of dislocations with sub-boundaries in a STS310S steel which has the higher dislocation density and smaller subgrain size resulted from pre-straining at higher stress.

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An Analytical Study on Prestrain and Shape Memory Effect of Composite Reinforced with Shape Memory Alloy (형상기억합금 강화 복합재의 사전 변형률과 형상기억 효과에 대한 이론적 고찰)

  • 이재곤;김진곤;김기대
    • Composites Research
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    • v.17 no.5
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    • pp.54-60
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    • 2004
  • A new three-dimensional model for predicting the relationship between the prestrain of the composite and the amount of phase transformation of shape memory alloy inducing shape memory effect has been proposed by using Eshelby's equivalent inclusion method with Mori-Tanaka's mean field theory. The model composite is aluminum matrix reinforced with short TiNi fiber shape memory alloy, where the matrix is work-hardening material of power-law type. The analytical results predicted by the current model show that most of the prestrain is induced by the plastic deformation of the matrix, except the small prestrain region. The strengthening mechanism of the composite by the shape memory effect should be explained by excluding its increase of yield stress due to the work-hardening effect of the matrix.

A Theoretical Comparison of Two Possible Shape Memory Processes in Shape Memory Alloy Reinforced Metal Matrix Composite

  • Lee Jae Kon;Kim Gi Dae
    • Journal of Mechanical Science and Technology
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    • v.19 no.7
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    • pp.1460-1468
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    • 2005
  • Two possible shape memory processes, austenite to detwinned martensite transformation and twinned martensite to detwinned martensite transformation of a shape memory alloy have been modeled and examined. Eshelby's equivalent inclusion method with Mori-Tanaka's mean field theory is used for modeling of the shape memory processes of TiNi shape memory alloy reinforced aluminum matrix composite. The shape memory amount of shape memory alloy, plastic strain and residual stress in the matrix are computed and compared for the two processes. It is shown that the shape memory amount shows differences in a small prestrain region, but the plastic strain and the residual stress in the matrix show differences in the whole prestrain region. The shape memory process with initially martensitic state of the shape memory alloy would be favorable to the increase in the yield stress of the composite owing to the large compressive residual stress and plastic strain in the matrix.

A study on the development of photoelastic model material with shape memory effect (형상기억효과를 가진 투과형 광탄성 실험용 모델재료 개발에 관한 연구)

  • Lee, Hyo-Jae;Hwang, Jae-Seok;Shimamoto, Akira
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.22 no.3
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    • pp.624-634
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    • 1998
  • The photoelastic model material with shape memory effect and the molding processes for the material are developed in this research. The matrix and fiber of the photoelastic model material developed in this research are epoxy resin (Araldite to hardner 10 to 3 (weight ratio)) and wire of $Ti_50-Ni_50$ shape memory alloy, respectively. It is called Ti50-Ni50 Shape Memory Alloy Fiber Epoxy Composite $(Ti_50-Ni_50SMA-FEC).$ Ti50-Ni50 SMA-FEC is satisfied with the requirements of the photoelastic model material and can be used as a photoelastic model material. The maximum recovering strain of $Ti_50-Ni_50$SMA-FEC is occurred at $80^{\circ}C$ in any prestrain of $Ti_50-Ni_50$ shape memory alloy fiber and in any fiber volume ratio. Recovering strain(force) is increased with the increment of the prestrain and the fiber volume ratio. The best prestrain of $Ti_50-Ni_50$SMA-FEC is 5% for the recovering force among 1%, 3%, 5%.

Prestrain-induced Reduction in Skin Tissue Puncture Force of Microneedle (초기변형률에 의한 미소바늘의 피부조직 관통력 감소)

  • Kim, Jonghun;Park, Sungmin;Nam, Gyungmok;Yoon, Sang-Hee
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.40 no.10
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    • pp.851-856
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    • 2016
  • Despite all the recent advances in biodegradable material-based microneedles, the bending and failure (especially buckling) of a biodegradable microneedle during skin tissue insertion remains a major technical hurdle for its large-scale commercialization. A reduction in skin tissue puncture force during microneedle insertion remains an essential issue in successfully developing a biodegradable microneedle. Here, we consider uniaxial and equibiaxial prestrains applied to a skin tissue as mechanophysical stimuli that can reduce the skin tissue puncture force, and investigate the effect of prestrain on the changes in skin tissue puncture force. For a porcine skin tissue similar to that of humans, the skin tissue puncture force of a flat-end microneedle is measured with a z-axis stage equipped with a load cell, which provides a force-time curve during microneedle insertion. The findings of this study lead to a quantitative characterization of the relationship between prestrain and the skin tissue puncture force.

Fabrication and Characterization of TiNi Shape Memory Alloy Fiber Reinforced 6061 Aluminum Matrix Composite by Using Hot Press (핫프레스법에 의한 TiNi/Al6061 형상기억복합재료의 제조 및 기계적 특성에 관한 연구)

  • Park, Dong-Sung;Lee, Jun-Hee;Lee, Guy-Chang;Park, Young-Chul
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.26 no.7
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    • pp.1223-1231
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    • 2002
  • Al alloy matrix composite with TiNi shape memory fiber as reinforcement has been fabricated by hot pressing to investigate microstructures and mechanical properties. The analysis of SEM and EDS showed that the composites have shown good interface bonding. The stress-strain behavior of the composites was evaluated at temperatures between 363K and room temperature as a function of prestrain, and it showed that the yield stress at 363K was higher than that of the room temperature. Especially, the yield stress of this composite increases with increasing the amount of prestrain, and it also depends on the volume fraction of fiber and heat treatment. The smartness of the composite is given due to the shape memory effect of the TiNi fiber which generates compressive residual stress in the matrix material when heated after being prestrained. Microstructural observation has revealed that interfacial reactions occur between the matrix and fiber, creating two intermetallic layers.

Effect of Room Temperature Prestrain on Creep Life of Austenitic 25Cr-20Ni Stainless Steels (오스테나이트계 25Cr-20Ni 스테인리스강의 실온예변형이 크리프 수명에 미치는 영향)

  • Park, In-Duck;Ahn, Seok-Hwan;Nam, Ki-Woo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.28 no.4
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    • pp.453-459
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    • 2004
  • 25Cr-20Ni series strainless steels have an excellent high temperature strength high oxidation and high corrosion resistance. However, further improvement can be expected of creep strength by work hardening prior creep. In the present study, the effect of prestraining at room temperature on the creep behavior of a Class M(STS310S) and a Class A(STS310J1TB) alloy containing precipitates have been examined. Prestaining was carried out at room temperature and range of prestrain was 0.5-2.5 % at STS310J1TB and 2.0-7.0% at STS310S. Creep behavior and creep rate of pre-strained specimens were compared with that of virgin specimens. Room temperature prestraining produced the creep life that is longer than that of a virgin specimen both for STS310J1TB and STS310S when creep test was carried out at the temperature lower than recrystallization temperature. The reason for this improvement of creep life was ascribable to the interaction between dislocations and precipitates in addition to the dislocation-dislocation interaction in STS310J1TB and the dislocation-dislocation interaction in STS310S. The beneficial effect of prestraining in STS310J1TB was larger than that of STS310S.

Evaluation of Elastic Modulus in a Particulate Reinforced Composite by Shape Memory Effect (형상기억입자 강화 복합체의 탄성계수 평가)

  • Kim, Hong-Geon
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.1
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    • pp.25-31
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    • 2001
  • The theoretical modeling to predict the modulus of elasticity by the shape memory effect of dispersed particles in a metal matrix composite was studied. The modeling approach is based on the Eshelbys equivalent inclusion method and Mori-Tanakas mean field theory. The calculation was performed on the TiNi particle dispersed Al metal matrix composites(PDMMC) with varying volume fractions and prestrains of the particle. It was found that the prestrain has no effect on the Yonugs modulus of PDMMC but the volume fraction does affects it. This approach has an advantage of definite control of Youngs modulus in PDMMCs.