1976 年 42 巻 494 号 p. 215-220
The spring limit test is utilized as a practical testing method for the evaluation of mechanical characteristics of metals for springs. However, the spring limit value Kb for representing the characteristics is defined in a conventional manner and the effects of the testing conditions on the value have not been investigated. In this paper, a new testing method in terms of the up-and-down method and linear regression analysis is proposed and the effects of the testing conditions on Kb value measured by the cantilever method are investigated. It is revealed that the free length of the cantilever must be 80-150 times of the thickness of the specimen in order to have correct values. The relation between the maximum bending stress and the permanent deflection can be assumed to be linear within the range of Kb±10σK (σK; the standard deviation of Kb). By this new method, the spring limit value Kb can be estimated without the strain history. The accuracy of the estimated value of Kb is about ± 1.0% (95% confidence interval) when the number of specimens is 15.