• 대한기계학회논문집A
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• 제36권1호
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• pp.17-28
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• 2012

본 연구에서는 역해석 방법을 통해, 중심각이 서로 다른 두 삼각뿔 압입자를 이용하는 재료물성 평가법을 제안한다. 자기유사성을 갖는 첨단형 압입자를 사용한 압입시험 전산모사시, 동일 압입깊이에 대해 원뿔형 및 삼각뿔 압입자가 주는 하중-변위 곡선들이 다름을 확인했다. 따라서 삼각뿔형 압입자를 이용한 물성평가는 원뿔형 압입자와 별도로 독립적인 연구가 필수적이다. 먼저 다양한 재료들에 대한 삼각뿔 압입 유한요소해석들로 얻은 하중-변위 곡선들의 특징을 살폈다. 이를 토대로 압입자 반각이 다른 두 삼각뿔 압입자를 이용해 유한요소해석으로 얻은 하중-변위곡선들의 회귀분석으로 재료물성치를 얻는 이중 삼각뿔 압입물성평가 알고리듬을 제시했다. 제안된 물성평가법을 이용하면 다양한 재료에 대해 평균오차 3% 이내로 영률 및 항복강도, 변형경화지수의 예측이 가능하다.

• 대한기계학회논문집A
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• 제39권11호
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• pp.1079-1089
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• 2015

본 연구에서는 항복강도 1GPa 이상의 고강도재료에 대해 구형압입자를 이용한 물성평가법을 제시한다. 압입전산모사를 통해 하중-변위 관계를 응력-변형률 관계로 변환하는 네 압입변수에 대한 회귀식을 바탕으로, 고강도 물성평가용 프로그램을 작성했다. 이를 압입시험에 적용하면 단 한번의 하중-해중에서 얻어지는 데이터로 유효 응력-변형률곡선을 얻을 수 있다. 광범위한 재료들에 대해 구해진 물성치의 평균오차는 영률 0.3%, 항복강도 0.8 %, 변형경화지수 6.4 % 이내이다.

• 대한기계학회논문집A
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• 제26권5호
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• pp.960-968
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• 2002

In this research, the effects of fiber stacking sequence on damage behaviors of FML(Fiber Metal Laminates) subject to indentation loading. SOP (Singly Oriented Ply) FML and angle ply FML were fabricated to study fiber orientation effects and angle ply effects. FML were fabricated by using 1050 aluminum laminate and carbon/epoxy prepreg. To increase adhesive bonding strength, Al laminate was etched using FPL methods. The static indentation test were conducted by using UTM under the 2side clamped conditions. During the tests, load and displacement curve and crack initiation and propagation behaviors were investigated. As fiber orientation angle increases, the crack initiation load of SOP FML increases because the stiffness induced by fiber orientation is increased. The penetration load of SOP FML is influenced by the deformation tendency and boundary conditions. However, the macro-crack of angle ply FML was initiated by fiber breakage of lower ply because angle plies in Angle ply FML prevents the crack growth and consolidation. The Angle ply FML has a critical cross-angle which prevent crack growth and consolidation. Damage behavior of Angle ply FML is changed around the critical cross-angle.

• 한국분말재료학회지
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• 제18권1호
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• pp.64-72
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• 2011

Nondestructive instrumented indentation test is the method to evaluate the mechanical properties by analyzing load - displacement curve when forming indentation on the surface of the specimen within hundreds of micro-indentation depth. Resistance spot welded samples are known to difficult to measure the local mechanical properties due to the combination of microstructural changes with heat input. Particularly, more difficulties arise to evaluate local mechanical properties of resistance spot welds because of having narrow HAZ, as well as dramatic changed in microstructure and hardness properties across the welds. In this study, evaluation of the local mechanical properties of resistance spot welds was carried out using the characterization of Instrumented Indentation testing. Resistance spot welding were performed for 590MPa DP (Dual Phase) steels and 780MPa TRIP (Transformation Induced Plasticity) steels following ISO 18278-2 condition. Mechanical properties of base metal using tensile test and Instrumented Indentation test showed similar results. Also it is possible to measure local mechanical properties of the center of fusion zone, edge of fusion zone, HAZ and base metal regions by using instrumented indentation test. Therefore, measurement of local mechanical properties using instrumented indentation test is efficient, reliable and relatively simple technique to evaluate the tensile strength, yield strength and hardening exponent.

• 한국분말재료학회지
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• 제15권6호
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• pp.482-488
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• 2008

The indentation technique has been one of the most commonly used techniques for the measurement of the mechanical properties of materials due to its experimental ease and speed. Recently, the scope of indentation has been enlarged down to the nanometer range through the development of instrumentations capable of continuously measuring load and displacement. In addition to testing hardness, the elastic modulus of submicron area could be measured from an indentation load-displacement (P-h) curve. In this study, the hardness values of the constituent phases in Ti($C_{0.7}N_{0.3}$)-NbC-Ni cermets were evaluated by nanoindentation. SEM observation of the indented surface was indispensable in order to separate the hardness of each constituent phase since the Ti($C_{0.7}N_{0.3}$)-based cermets have relatively inhomogeneous microstructure. The measured values of hardness using nanoindentation were ${\sim}20$ GPa for hard phase and ${\sim}10$ GPa for binder phase. The effect of NbC addition on hardness was not obvious in this work.

• Composites Research
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• 제22권3호
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• pp.9-17
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• 2009

본 논문에서는 분자동력학 방법을 이용하여 Ag 필름/Cu기판에 대한 나노인덴테이션 특성을 파악하였다. 필름의 강성과 경도는 필름의 두께에 관계되어있으며, 임계범위 내에서, 그래인 크기가 증기하면 강성과 경도도 증가하는 것을 확인하였다. 5nm 두께 이하의 Ag필름/Cu기판의 강성과 경도는 벌크 Ag의 경우에 비해 낮은 값을 나타내었다. 특히 4nm 두께 이하의 Ag필름/Cu기판의 인덴테이션에 있어서, 전위 집적과 불일치 전위사이의 상호작용에 의해 계면상에서 꽃모양의 전위 루프가 발생 하였다. 이는 인덴테이션 하중과 변위 커브에서 하중이 저하되는 것과 관계있는 것으로 사료되고 있다.

• KSTLE International Journal
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• 제1권1호
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• pp.48-51
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• 2000

Surface damage accumulation of alumina ceramics under the cyclic stress state was analyzed. The alternating stress state in repeat pass sliding contact was simulated by a synchronized biaxial (normal and tangential) repeated indentation technique. Wear debris formation mechanism through damage accumulation and fatigue grain failure in both alumina ceramic balls and flat disks was confirmed, and the contact induced surface degradation due to fatigue cracking accumulation was quantified by measuring vertical contact displacement. Variation of structural compliance (slope of load-displacement curve) of two contacting bodies was expressed as a variation of the apparent elastic property, called pseudo-elastic constant, of the contact system.

• 대한토목학회논문집
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• 제34권2호
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• pp.415-424
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• 2014

기존 콘크리트 구조물 내력은 변위 및 스트레인 게이지를 통해 기지의 가력에 따른 변화량을 계측하고, 그 결과를 수치해석 결과와 비교하여 평가한다. 이는 결과적으로 현존 콘크리트의 잔류응력을 계측 평가하므로써 완성될 수 있다. 본 논문은 실험적 응력해석법의 일환으로 콘크리트 구조물에 대한 잔류응력을 비파괴적인 방식으로 평가하는 IITC (Instrumented Indentation Technique for Concrete) 시스템 개발과 관련된 것으로 콘크리트 구조물 표면에서 압입하중과 압입깊이와의 상관관계를 이용한 실험적 평가방법을 논하였다. 본 연구에서는 구성되는 H/W 및 분석용 S/W는 새롭게 개발하였으며, 다각도의 실험결과를 이용하여 콘크리트 구조물에서의 실험적 잔류응력 추정식을 창출하였고, 자동으로 잔류응력을 평가케 함으로써 콘크리트 구조물의 축성단계에서부터 유지관리 단계에까지 자유롭게 내력을 산정할 수 있도록 하였다.

• 한국세라믹학회지
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• 제54권4호
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• pp.314-322
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• 2017

This study investigates changes in the mechanical behavior, such as changes in indentation load-displacement curve, wear resistance and contact fatigue resistance of thermal barrier coatings (TBCs) by thermal cycling test and thermal shock test. Relatively dense and porous TBCs on nickel-based bondcoat/superalloy are prepared; the highest temperature applied during thermal durability test is $1350^{\circ}C$. The results indicate that the porous TBCs have relatively longer lifetime during thermal cycling and thermal shock tests, while denser TBCs have relatively higher wear and contact fatigue resistance. The mechanical behavior is influenced by sintering of the TBCs by exposure to high temperature during tests.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 춘계학술대회 논문집
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• pp.389-392
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• 2005

In the modern days, a galvannealed sheet steel(GA) instead of a cold rolled steel sheet has been widely used as an alternative to extend the life of automotive body. Accordingly, the mechanical properties of GA for automobiles were taken Into account and studied by comparing with the temperature variation on annealing in this study. To clarify the effect of surface features in the mechanical properties of GA, the several tests such as nanoindentation and FE-analysis were executed. For this goal use is made of the method of neural networks. The developed neural networks apply also to obtain reliable mechanical properties of the thin films. Load-displacement curve was computed by the analysis procedure and compared with experimental results.