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Extension of the Theta Projection Concept in Multi-Axial and Stress-Change Creep Behavior

Theta 投影概念在多轴和应力变化蠕变行为中的扩展

基本信息

批准号：
04650061
负责人：
KOBAYASHI Ken-ichi
金额：
$ 1.34万
依托单位：
Chiba University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1992
资助国家：
日本
起止时间：
1992 至 1993
项目状态：
已结题

项目摘要

The purpose of this project is to estimate creep behavior at the stress-change state or under multi-axial stresses with a help of both the theta projection concept and the strain hardening law.(1)Initially a series of constant-load creep tests were conducted on austenitic stainless steel AISI type 304 at 923K.Four parameters in the theta projection concept were computed for each creep curve using the non-linear least square method. Since these parameters were well expressed as an exponential function of the applied stress, creep curves even under unknown stresses could be easily drawn.(2)Stress-change creep tests were performed between the stresses of 90MPa and 140MPa. After the specimens were crept at the initial stress of 90MPa for 50, 100, 200, 300 and 400 hours, the applied stress was increased to 140MPa. These hours when the creep tests were interrupted corresponded to the primary, secondary, and (former, middle, and latter part of) tertiary creep respectively.(3)Creep behavior after the change of the applied stress was calculated using the proposed method. The estimation curves were compared with the experiments. When the interrupted points were places within the former part of the tertiary stage of creep, they well agreed each other. However the calculation were underestimated over the range of the middle part of the tertiary stage. Then we concluded that the application of the theta projection concept should be limited within the initial part of the tertiary creep if the strain hardening law as employed together.(4)The experiments reported here were the results when the stress was increased after some creep deformation. However we should investigate whether this method can also be applied to the stress-change creep test after the applied stress was decreased.

本项目的目的是借助θ投影概念和应变硬化规律来估计应力变化状态下或多轴应力下的蠕变行为。(1)对AISI 304型奥氏体不锈钢在923K温度下进行了一系列恒载蠕变试验。利用非线性最小二乘法计算了每条蠕变曲线的theta投影概念中的4个参数。由于这些参数很好地表示为施加应力的指数函数，因此即使在未知应力下也可以很容易地绘制蠕变曲线。(2)在90MPa ~ 140MPa应力范围内进行应力变化蠕变试验。试件在初始应力为90MPa下爬行50、100、200、300和400小时后，外加应力增加到140MPa。蠕变试验中断的时间分别对应于初级、次级和（前、中、后）三级蠕变。(3)应用该方法计算了外加应力变化后的蠕变行为。将估计曲线与实验结果进行了比较。当断续点位于第三纪蠕变前段时，它们相互吻合得很好。然而，在第三纪中期的范围内，计算结果被低估了。然后我们得出结论，如果同时采用应变硬化规律，θ投影概念的应用应限于三级蠕变的初始部分。(4)本文所报道的试验均为蠕变后应力增加的结果。但该方法是否也适用于外加应力降低后的应力变化蠕变试验，还有待研究。