Research on Fatigue Testing Method of Bolts for Quality Assurance

1977年，ISO发布了关于螺纹紧固件疲劳试验方法的标准。目前该标准正在修订中。标准修订稿中包括“质量控制试验”，但对该项目的描述非常简单。疲劳强度是螺栓的重要质量特性之一，如何对这一特性进行质量保证是螺栓用户和供应商需要解决的问题之一。从上述观点出发，对保证螺栓质量的疲劳试验方法进行了研究，得到如下结果：（1）作为试样，准备了M10-8.8的螺栓和M10-8的螺母（8.8和8为强度性能等级），采用ISO标准修订草案中规定的14 S-N试验方法。在这种情况下，一系列试验中所需的试样数量为14。(2)作为质量保证的测试方法，在讨论了几种方法之后，提出了两种方法。(3)方法1是对14个S-N试验方法进行简化得到的，所需试件数量为8个。(4)建议的方法2是基于螺栓疲劳极限的估计标准值，所需的试验样本数只有4个。(5)针对这两种方法，进行了较大范围的实验，阐明了它们的优缺点。从质量保证的角度来看，发现方法2优于方法1。

In 1977 the ISO standard on fatigue testing method of threaded fasteners was published. Now the revision of this standard is in progress. The draft of revised standard includes "Quality control test", but the description on this item is very simple. In order to apply this item to the practical situation, many problems should be investigated.The fatigue strength is one of the important quality characteristics of bolts, and how to carry out the quality assurance for this characteristic is one of the problems to be solved for users and suppliers of bolts. From the above standpoint, the fatigue testing method of bolts for quality assurance is investigated, and the obtained results are as follows:(1) As the specimens, the bolts of M10-8.8 and the nuts of M10-8 (8.8 and 8 are strength property classes) are prepared, and the 14 S-N testing method specified in the draft of revised ISO standard is applied. In this case the required number of test specimens in a series of test is 14.(2) As the testing method for quality assurance, two methods are proposed after several methods have been discussed.(3) The proposed method 1 is obtained by the simplification of 14 S-N testing method, and the required number of test specimens is 8.(4) The proposed method 2 is based on the estimated standard values of fatigue limits of bolts, and the required number of test specimens is only 4.(5) Concerning these two methods, the experiments in the wider range are carried out, and their merits and demerits are clarified. From the viewpoint of quality assurance, it is found that the method 2 is better than the method 1.