대한기계학회논문집A (Transactions of the Korean Society of Mechanical Engineers A)

  • 제32권1호
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  • Pages.35-42
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  • 2008
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  • 1226-4873(pISSN)
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  • 2288-5226(eISSN)
대한기계학회 (The Korean Society of Mechanical Engineers)
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유한선단반경을 갖는 원뿔형 압입자에 의한 영률평가 수치접근법

A Numerical Approach to Young's Modulus Evaluation by Conical Indenter with Finite Tip-Radius

  • 이진행 (서강대학교 대학원 기계공학과) ;
  • 김덕훈 (서강대학교 대학원 기계공학과) ;
  • 이형일 (서강대학교 기계공학과)
  • 발행 : 2008.01.01
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초록

본 연구에서는 원뿔형 압입자를 이용한 압입시험의 기초 유한요소해석으로부터 자기유사성을 나타내는 Kick's law 계수 C의 영향을 조사하고, 선단반경의 변화가 하중-변위 곡선에 미치는 영향을 회귀분석을 통해 살펴보았다. 아울러 항복강도와 변형경화지수 등의 변수들이 재료 영률평가에 미치는 영향을 분석하였다. 기존 영률 평가에 널리 사용되는 탄성이론에 기초한 Pharr 등의 식을 일반적인 탄소성 금속재료에 적용하기 위하여 다양한 재료에 대한 유한요소해석을 수행하였다. 재료 영률평가 시 압입자 선단반경과 압입깊이의 영향을 최소화하기 위해 Pharr 등의 식에 수정된 보정계수 k를 도입한 영률예측식을 제시하였다. 새로운 영률예측식은 텅스텐 카바이드와 다이아몬드 압입자일 때 모두 2%내의 평균 오차범위에서 각 재료의 영률을 평가할 수 있다.

Instrumented sharp indentation test is a well-directed method to measure hardness and elastic modulus. The sharp indenter such as Berkovich and conical indenters have a geometrical self-similarity in theory, but the self-similarity ceases to work in practice due to inevitable indenter tip-blunting. In this study we analyzed the load-depth curves of conical indenter with finite tip-radius via finite element method. Using the numerical regression data obtained from Kick's law, we first confirmed that loading curvature is significantly affected by tip radius as well as material properties. We then established a new method to evaluate Young's modulus, which successfully provides the value of elastic modulus with an average error of less than 2%, regardless of tip-radius and material properties of both indenter and specimen.

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참고문헌

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