• 한국산업융합학회 논문집
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• 제25권2_2호
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• pp.239-245
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• 2022

Using the fatigue limit (∆σ_unsm) and residual stress (σ_r) of the UNSM smooth specimen, the harmless maximum crack depth (a_hlm) according to the crack aspect ratio (As) was evaluated. In addition, the relationship between the minimum crack depth (a_NDI1, a_NDI2) detectable by non-destructive inspection(NDI), the crack depth (a₂₅, a₅₀) that reduces the fatigue limit by 25% and 50%, and a_hlm were evaluated. The harmless crack condition was determined by the deepest crack point (point A). Since a_hlm is larger than a₂₅ and a₅₀, a₂₅ and a₅₀ can secure the safety and reliability of steel via UNSM. Because a_NDI1 and a_NDI2 are larger than a₂₅ and a₅₀, cracks in a₂₅ and a₅₀ cannot be detected by non-destructive testing. Therefore it is necessary to apply more precise NDI.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 추계학술대회 논문집
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• pp.929-930
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• 2012

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2012년도 추계학술대회 논문집
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• pp.931-932
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• 2012

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 춘계학술대회 논문집
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• pp.521-522
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• 2010

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 춘계학술대회 논문집
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• pp.181-182
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• 2010

• 한국분말재료학회지
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• 제29권5호
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• pp.382-389
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• 2022

A typical trade-off relationship exists between strength and elongation in face-centered cubic metals. Studies have recently been conducted to enhance strength without ductility reduction through surface-treatment-based ultrasonic nanocrystalline surface modification (UNSM), which creates a gradient microstructure in which grains become smaller from the inside to the surface. The transformation-induced plasticity effect in Fe-Mn alloys results in excellent strength and ductility due to their high work-hardening rate. This rate is achieved through strain-induced martensitic transformation when an alloy is plastically deformed. In this study, Fe-6%Mn powders with different sizes were prepared by high-energy ball milling and sintered through spark plasma sintering to produce Fe-6%Mn samples. A gradient microstructure was obtained by stacking the different-sized powders to achieve similar effects as those derived from UNSM. A compressive test was performed to investigate the mechanical properties, including the yielding behavior. The deformed microstructure was observed through electron backscatter diffraction to determine the effects of gradient plastic deformation.

• 대한조선학회논문집
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• 제49권4호
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• pp.333-339
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• 2012

The main objective of the present study is to investigate the roles of the micro-dimpled surface on the drag reduction. To investigate the effectiveness of the micro-dimpled surface, the flat plates are prepared. The micro-size dimples are directly carved on the metal surface by ultrasonic nano-crystal surface modification (UNSM) method. Momentum of the main flow is increased by the dimple patterns within the turbulent boundary layer (TBL), however, there is no significant change in the turbulence intensity in the TBL. The influence of dimple patterns is examined through the flow field survey near the flat plate trailing edge in terms of the profile drag. The wake flow velocities in the flat plate are measured by PIV technique. The maximum drag reduction rate is 4.6% at the Reynolds number of $10^6{\sim}10^7$. The dimples tend to increase the drag reduction rate consistently even at high Reynolds number range.

• 대한기계학회논문집 C: 기술과 교육
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• 제1권1호
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• pp.115-121
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• 2013

최근 플랜트산업분야에서는 발전설비와 해양 플랜트 및 선박, 교량 건설등 핵심 구조물들에 대한 내구성 향상 및 평가를 위한 기술이 크게 확장 적용될 것으로 본다. 이에 본 연구에서는 초음파 탄성진동에너지를 이용한 초음파 나노표면개질(Ultrasonic Nanocrystalline Surface Modification) 기술과 초음파 피로시험(Ultrasonic Fatigue Test)기술을 통해서 현재까지 국내산업분야에서 활발하게 진행중인 적용사례를 분석하고자 하였으며. 플랜트분야 특히 발전설비와 해양선박 플랜트 및 교량 건설구조물들의 핵심 용접부에 대한 내구성 향상을 위해 크게 확장 적용될 수 있는 새로운 응용기술 연구방향에 대한 방법들을 제시하고자 한다.