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스패클 패턴을 이용한 변형률속도와 하중방향에 따른 R-값의 측정
허지향(J. Huh),김유종(Y. J. Kim),이홍오(H. O. Lee),김교성(K. S. Kim),허훈(H. Huh) 한국소성가공학회 2010 한국소성가공학회 학술대회 논문집 Vol.2010 No.10
This paper introduces a method to measure r-value from the speckled pattern with respect to the strain rate and loading direction. The r-values were calculated with high speed camera by analyzing the deformation history during the static and dynamic tensile tests. A digital image processing Matlab code for tracking of selected points was constructed to measure the longitudinal and transversal strain from the speckled pattern, which was made by spraying black paints on the white paint coated tensile specimen. Using suggested method, r-values of 590TRIP 1.2t and 7800P 1.0t were measured with the variation of the strain rate (0.001 /s~ 100 /s) and loading direction (rolling direction, diagonal direction, and transverse direction).
변형률속도에 따른 SPCC 강판의 항복곡면 발전에 관한 연구
허지향(J. Huh),허훈(H. Huh) 한국소성가공학회 2012 한국소성가공학회 학술대회 논문집 Vol.2012 No.5
This paper investigates the effect of strain rate on the yield surface evolution of spec steel sheet. Uniaxial tensile tests were carried out for spec steel sheets at the strain rate ranged from 0.001 s<SUP>-1</SUP> to 100 s<SUP>-1</SUP> to obtain flow stresses and r-alues at various loading angles. Based on the experimental data, yield surfaces of spec were constructed at different strain rates with Hi1l48 yield function. Subsequent yield surfaces were constructed and compared with the initial yield surfaces to investigate the strain rate effect on the yield surface evolution. It was found that the strain rate sensitivity on the anisotropy of the yield surface decreases as the deformation goes on.
변형률 속도에 따른 고강도 강판의 이방성 변화에 관한 연구
허훈(H. Huh),허지향(J. Huh),이창후 한국소성가공학회 2011 한국소성가공학회 학술대회 논문집 Vol.2011 No.5
This paper investigates the effect of strain rate on anisotropy of advanced high strength steel sheets. Uniaxial tensile tests were carried out for TRIP590 and 780DP steel sheets at the strain rate ranged from 0.001/sec to 100/sec to measure the yield stress and r-values at various loading angle. R-values were measured by digital image correlation technique. Based on the experimental data, Hill48 and Yld2000-2d yield functions were tested to describe plastic anisotropy of the materials. Initial yield loci were constructed for the two materials using the Yld2000-2d yield function, which was observed to describe anisotropy appropriately. It was found that the shape of the initial yield loci changes along with the strain rate, and the anisotropy decreases as the strain rate increases.