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방건웅(G . W . Bahng),탁내형(N . H . Tak),(T . Poizin) 한국열처리공학회 2001 熱處理工學會誌 Vol.14 No.6
N/A For the establishment of the world wide unified scales of the Rockwell hardness test with conical indenters, round robin test was carried from 1998 to 2000. The pilot laboratory was MPA-NRW and 12 laboratories from 11 countries participated in this RRT Rockwell hardness of 74 specially prepared blocks was measured for the scales of C, A, D, 45N, 30N, and 15N and the results were compared. It was found that the geometric form of indenter affects on the results very significantly and standardization in the measurement and evaluation of indenter should be established in short time for the reliable hardness measurement. KRISS showed good results in general for all of the ranges except 15N scale which showed relatively large difference compare to the mean value. It was concluded that poor control in loading velocity of the dash pot was the major reason.
방건웅(G. W. Bahng),탁내형(Nae Hyung Tak),봉하헌(Ha Heon Bong) 한국열처리공학회 2002 熱處理工學會誌 Vol.15 No.3
N/A Shore hardness test was developed in 1906 to overcome the limit of Brinell hardness test. However, the detailed requirements on the tester was not clearly specified except the scale, i.e., 100 HS for high carbon steel and 10 HS for soft brass. As a result, the shore hardness was used for quite long time without well established standards. For the establishment of hardness standards, standard tester, standard procedure, and standard hardness block must be provided. So far the standard of Shore hardness was maintained by correlating Shore hardness scale to Vickers hardness through converting equation. This is the so called converted Shore hardness and it is not the true Shore hardness standard strictly. In this paper, the possibility of establishing Shore hardness standard based on the Shore standard hardness tester is reported.
방건웅(G . W . Bahng),탁내형(N . H . Tak) 한국열처리공학회 2001 熱處理工學會誌 Vol.14 No.5
N/A To improve the reliability of hardness test results, Rockwell hardness round robin test was carried out for 10 laboratories. The test condition was the same with the ISO(International Standards Organization) standards. Korea Research Institute of Standards and Science(KRISS) supplied the hardness standard blocks and an indenter to laboratories for the measurement. The participating laboratories measured hardness of the specified areas on the blocks for 6 times with their own indenter as well as common indenter, respectively, and report the results to KRISS. The result showed that quits large amount of the differences came from the indenter and it is necessary to change indenter with better quality for improved reliability in hardness measurement.
극저온 시험장치의 제작과 AISI 300계열 스테인리스강의 극저온 인장변형거동
이해무,남승훈,허용학,이주진,방건웅 대한금속재료학회(대한금속학회) 1990 대한금속·재료학회지 Vol.28 No.11
For practical application of cryogenic engineering, development and characterization of structural materials for use at low temperatures are essential. For these purposes, a system for mechanical testing at liquid helium temperature was developed and it was shown that the precision and accuracy of the system met the requirements of standards for materials testing machines. Using this system, tensile deformation behavior of AISI 304, 316 and 310S austenitic stainless steels at cryogenic temperatures was investigated. Tests were conducted on round, tensile specimens having a 6.25㎜ diameter at 4, 77, and 295 K and loading rate was 0.5㎜/min. Serrations were observed in all alloys at 4 K. The stress-displacement curves at 77 and 4 K showed different tendency from those at 298 K. As the testing temperature decreased, ultimate strengths of 304 and 316 were largely increased compared to the increase of yield strengths, but the increase of ultimate strength of 310S was almost the same to that of yield strength. Type 310S had the highest yield strength and the lowest tensile strength at all temperatures. These tensile characteristics were considered to be strongly affected by austenite stability.
방건웅,권동일 대한금속재료학회(대한금속학회) 1992 대한금속·재료학회지 Vol.30 No.6
A smooth specimen subjected to cyclic loading undergoes different stages of crack growth behavior; three distinct crack growth regimes exist, namely the regime of microstructually small cracks, the regime of physically small cracks and the long crack regime. The limits of these different crack growth regimes can be evaluated in terms of characteristic crack lengths which are functions of material and mechanical parameters. A log △σ-log a diagram is used to derive estimates of these characteristic. crack lengths. The approach presented relies on relations between material strength and grain size, on the one side, and on fracture mechanics quantities depending on the applied load such as the size of the plastic zone ahead of the crack tip, on the other side.