クリープにおける応力休止の影響について

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Structural members which are subject to load at high temperature are, in general, not in a steady condition of applied stress and temperature. In this paper, as one fundamental problems, the creep behavior under cyclic stress removal is discussed. If a specimen of metals is creeping under constant load, at high temperature and on the way, the load is removed, elastic strain and creep strain recovery which seems like elastic-after-effect occur. After the period of stress removal, when reloaded, creep recovery which is based on the recovery of work-hardning in each crystal, strain aging and precipitation in commercial materials, take place. When the cyceic stress removal is given creep curves, show the differences from steady load creep curve. As the a result of this experiment, creep curves of stress removal are shown upper or lower than steady load creep curves, But the difference between lower creep curve of stress removal and steady load curve is very small. So in this experiment, by considering creep recovery only, creep curve of stress removal can be estimated well. But as for cases when stress cycle or period of stress removal is changed, this result has some questions. As test temperature is rised, creep recovery is much remarkable. If stress amplitude is synchronized with temperature cycle, the influence of creep recovery is much striking. Experimental results may be summarized up as follows : (1) Under a high stress and high temperature, creep recovery is much remarkable. (2) In the eary stage of transient creep, creep recovery is much larger and therafter gradually decreases. In the stage of steady creep, creep recovery reaches almost constant value. (3) Strain increment in cyclic stress removal test is affected not only by creep recovery but also by precipitation, aging and phase change. Etc. (4) In this experiment, this strain increment is well expressed by the following equation : Δε=alog(1+Ct_r) Δε: strain increment, t_r: test time a,c: constant in constant strain, temperature and stress.
社団法人日本材料学会の論文
1963-03-15

クリープにおける応力休止の影響について

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