• 한국해양공학회지
• /
• 제16권3호
• /
• pp.59-64
• /
• 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.

• 한국재료학회:학술대회논문집
• /
• 한국재료학회 1994년도 춘계 학술발표 강연 및 논문 개요집
• /
• pp.28-28
• /
• 1994

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2002년도 춘계학술대회 논문집
• /
• pp.35-40
• /
• 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.

• Composites Research
• /
• 제17권5호
• /
• pp.54-60
• /
• 2004

복합재의 사전변형률과 형상기억합금의 형상기억효과를 유발하는 형상기억합금의 상변화량과의 관계를 예측하기 위하여 Eshelby의 등가개재물법과 Mori-Tanaka의 평균장이론을 이용한 새로운 3차원 모델을 제안하였다. 복합재 모델은 가공경화 현상을 갖는 알루미늄을 모재로, 단섬유 TiNi 형상기억합금을 강화재로 사용하였다. 모델 해석에 의하면 사전 변형률이 지극히 작은 영역에서는 사전변형률이 모두 강화재의 형상기억 효과를 유발하고, 이 보다 큰 영역에서 사전 변형률은 강화재의 형상기억 효과와 모재의 소성변형에 의한 것으로 나타났다. 이러한 복합재의 강화기구는 모재의 가공경화 현상과 형상기억 효과에 의한 항복응력 증가를 분리하여 제시되어야 한다.

• Journal of Mechanical Science and Technology
• /
• 제19권7호
• /
• pp.1460-1468
• /
• 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.

• 대한기계학회논문집A
• /
• 제22권3호
• /
• pp.624-634
• /
• 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%.

• 대한기계학회논문집A
• /
• 제40권10호
• /
• pp.851-856
• /
• 2016

최근 미세가공기술이 발전함에 따라 생체분해성 소재 기반의 미소바늘 혹은 미소바늘 주사기에 대한 연구가 각광을 받고 있다. 일반적으로 생체분해성 소재는 기계적 강도가 낮아 생체분해성 소재 기반의 미소바늘은 피부조직 관통 시 구부려지거나 파손되는 문제점을 가지고 있다. 본 연구에서는 기계적 강도가 향상된 생체적합성 소재를 새로이 합성하는 대신에 미소바늘 삽입 전 피부조직에 1축 혹은 등2축 초기변형률을 가해 미소바늘의 피부조직 관통력을 감소시키는 방법에 대해 살펴본다. 실험에서는 1축 혹은 등 2축 초기변형률을 가해 준 돼지 피부조직에 미소바늘을 삽입시키면서 힘-시간 데이터를 획득함으로써 초기변형률에 의한 미소바늘의 관통력 변화를 측정하였다. 본 연구를 통해 미소바늘의 피부조직 관통력은 피부조직에 초기변형률을 가해주는 방법으로 감소시킬 수 있음을 확인하였다.

• 대한기계학회논문집A
• /
• 제26권7호
• /
• pp.1223-1231
• /
• 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.

• 대한기계학회논문집A
• /
• 제28권4호
• /
• pp.453-459
• /
• 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.

• 대한기계학회논문집A
• /
• 제25권1호
• /
• pp.25-31
• /
• 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.