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

The Korean Society of Mechanical Engineers (대한기계학회)
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A Numerical Approach to Spherical Indentation Techniques for Creep Property Evaluation

크리프 물성평가를 위한 구형압입 수치접근법

  • Lim, Dongkyu (Dept. of Mechanical Engineering, Sogang Univ.) ;
  • Lee, Jin Haeng (Reactor Mechanical Engineering Division, Korea Atomic Energy Research Institute) ;
  • Choi, Youngsick (Dept. of Mechanical Engineering, Sogang Univ.) ;
  • Lee, Hyungyil (Dept. of Mechanical Engineering, Sogang Univ.)
  • Received : 2013.03.12
  • Accepted : 2013.08.07
  • Published : 2013.10.01
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Abstract

In this study, the theory of spherical indentation based on incremental plasticity is extended to an indentation method for evaluating creep properties. Through finite element analysis (FEA), the point where the elastic strain effect is negligible and the creep strain gradient constant is taken as the optimum point for obtaining the equivalent strain rate and stress. Based on FE results for spherical indentation with various values of creep exponent and creep coefficient, we derive by regression an equation to calculate creep properties using two normalized variables. Finally a program is generated to calculate creep exponent and creep coefficient. With this method, we obtain from the load-depth curve creep exponents with an average error of less than 1.5 % and creep coefficients with an average error of less than 1.0 %.

본 연구에서는 증분소성이론에 기초한 구형압입이론을 크리프 물성을 평가하기 위한 압입이론으로 확장했다. 먼저 크리프변형률 기울기가 일정한 지점을 유효 응력-변형률속도 최적 관측지점으로 선정했다. 구형압입시험 전산모사를 이용해 크리프 지수와 계수를 변화시켜 가면서 이에 따른 재료의 거동을 무차원 변수들 (${\xi}$, ${\psi}$)의 회귀식으로 표현해 크리프 물성평가를 위한 새로운 수치 접근법을 구축했다. 이를 토대로 구형압입시험으로부터 재료의 크리프지수 및 계수를 예측하는 물성평가 프로그램을 개발했다. 압입 하중-변위 곡선으로부터 크리프지수는 평균 1.5%, 크리프계수는 평균 1.0% 이내의 오차범위에서 물성치들을 얻을 수 있다.

Keywords

References

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