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304스테인레스鋼의 高溫 크리이프 變形機構에 관한 硏究
白南柱,韓圭澤,裵宰賢 부산대학교 공과대학 1985 硏究報告 Vol.29 No.-
This study is concerned with high temperature creep mechanism of SUS 304. Creep tests were conducted at uniaxial stresses 10㎏/㎟ to 25㎏/㎟ and at temperature 575℃ to 775℃, for the purpose of investigating steady state creep mechanism at high temperature. Stress dependence of apparent activation energy and stress exponent are obtained. From theories and these experimental results, it is suggested that the steady state creep mechanism of SUS 304 at high temperature can be correlated with the model of nonconservative motion of jogs on screw dislocations dependent on lattice self-diffusion.
統一型 構成式을 適用한 非彈性 解析의 向上에 關한 硏究
白南柱,李相梅 부산대학교 공과대학 1985 硏究報告 Vol.29 No.-
In this paper the unified constitutive equation represented by internal variables is modified considering stress dependence of strain hardening function A(σ), in order to enhance the accuracy of inelastic analysis. Strain softening due to dynamic recovery is made slightly an addition to the unified model. The modified model simulates the deformation behavior including cyclic hardening/softening. Calculated results were good agreement with experimental results.
白南柱,韓圭澤 부산대학교 공과대학 1986 硏究報告 Vol.32 No.-
The forming limit diagram is assessed as a means of estimating the forming characteristics of sheet metal. Material characteristics that influence plastic instability and forming limit strain is investigated through hydraulic bulging test by using of steel sheet and aluminum sheet. Of all properties that influence forming limit strain, work hardening exponent n and normal antisotropy parameter R and strain rate are found to have the most effect on limit strain. Experiments have shown that forming limit strain is lowered with increasing strain rate. Further, it is found that correlation exists between strain rate and the work hardening exponent.
反復荷重을 받는 SUS 304鋼의 크리이프 擧動에 관한 硏究
白南柱,姜大敏,獨孤郁,許官道 부산대학교 공과대학 1985 硏究報告 Vol.29 No.-
The creep behavior of SUS 304 under cyclic loading has been studied, Square-wave loading between stresses σ₁(26㎏/㎟ or 18㎏/㎟) and σ₂(13㎏/㎟ or 9㎏/㎟) for times t₁(0.05h or 0.1h) and t₂(0.5h~12h) at 600℃ and 700℃. At high temperature and low stress, recovery did not accumulate from cycle to cycle. But at low temperature and high stress, recovery accumulated from cycle to cycle, and the creep rate steadily accelerated. In both cases the predicting strain-time relation is more accurate than strain-hardening method and time-hardening method.
白南柱,姜大敏,白雲景 부산대학교 공과대학 1984 硏究報告 Vol.27 No.-
Modern technological progress demands the use of materials at high temperatures. One of the most critical factors in considering such applications-perhaps the most critical one-is creep behavior. This creep curve has three stages of creep at a given stress and temperature. The first stage of creep is known as primary creep and is the period where the metal is hardening, that is, the creep rate is decreasing with time, stable substructures develop during this stage of creep. The second stage of creep, secondary creep, is characterized by a constant rate of creep and the creep substructures remain essentially unchanged with straining. The third stage of creep, tertiary creep, is quite often associated with localized necking and also with the formation of cavities (especially near grain boundaries), eventually leading to tensile creep failure. In this study, creep tests on Al 7075 are analyzed and predicted creep behavior of Al 7075 using a graphical optimization procedure to solve the constitutive equation proposed by T.H. Dawson and D.A.Woodford. Experimental conditions used creep test are as follows: Stresses: 18.7, 20, 21.2, 30 (MPa) Temperature: 300℃ gause length of creep specimens: 50nm material of creep test: Al 7075
白南柱,白成官,姜大敏 부산대학교 공과대학 1984 硏究報告 Vol.28 No.-
In this paper, creep tests on Al 7075 alloy are analyzed using a graphical optimization procedure to solve the constitutive equation at 220℃ under various stress and the calculated values of the constitutive equation are good agreement with the expermental values. In addition to the above study, the apparent energies Qc have been obtained during creep of Al 7075 alloy at 81.15Mpa under 210℃~230℃, the calculated values of the constitutive equation as well as experimental values are used for obtaining stress component(n) at 220℃ under 81.15Mpa~99.87Mpa and the internal stress σi have been determined during creep of Al 7075 alloy at 220℃ under 81.15~87.39Mpa, for the purpose of predicting the secondary creep mechanism at high temperature. According to these results, it is concluded that the steady state creep mechanism of Al 7075 alloy at high temperature was believed a dislocation climb, but at high stress a dislocation intersection process.