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为了弄清楚岩石的蠕变性,需要连续进行某种长达数十年的试验。本文介绍此种试验方法之一。试件加工成20cm长的梁,并高度磨光其上表面,把它弯成向上凸,其最大弯曲应力宜为20bar或稍小一些。当观测时,把一块光学平板放在磨光的面上使产生单色光的干涉条纹,对干涉条纹进行分析,就可确定上表面的轮廓。试件的挠度应减小到观测时的轮廓与弯曲前已确定了的初始轮廓之间的差值。如此继续进行试件的挠度观测,就可绘制出蠕变曲线。根据作者的经验,文中叙述了应用上述方法必须注意的事项和可能遇到的问题,并举了一些具体的例子。 弯曲试验有着能比较容易地探测变形的优点,缺点是应力状态不象压缩或拉伸试验那样简单。但在文章的最后部分,作者给出了在屈服应力等于零时,由弯曲试验得到的蠕变曲线与由压缩或拉伸试验得到的蠕变曲线不相上下,并且从熊谷(Kumagai)和伊藤的长达23年以上的蠕变试验,得出了重要结论,就是岩石没有屈服应力。
In order to understand the creep of rock, it is necessary to carry out some kind of continuous tests for decades. This article describes one of the test methods. The specimen was machined into a 20-cm long beam, and its upper surface was highly polished, and it was bent into an upwardly convex shape with a maximum bending stress of 20 bar or less. When observing, an optical plate is placed on the polished surface to generate interference fringes of monochromatic light, and the interference fringes are analyzed to determine the contour of the upper surface. The deflection of the test specimen shall be reduced to the difference between the contour of the observation and the initial contour determined before bending. The creep curve can be drawn by continuing the deflection observation of the specimen. According to the author’s experience, the article describes the matters that must be taken care of and the problems that may be encountered when applying the above methods, and gives some specific examples. The bending test has the advantage of being able to detect deformations relatively easily, the disadvantage being that the stress state is not as simple as a compression or tensile test. But in the last part of the article, the authors gave that when the yield stress is equal to zero, the creep curve obtained from the bending test is comparable to the creep curve obtained from the compression or tensile test, and it is from Kumagai and Ito. The creep tests for more than 23 years have come to the important conclusion that there is no yield stress in rocks.