Year: 1959
Type: article
Abstract: Fatigue phenomena of tire cords are usually described by the S-N diagram as in the case of metals. The fatigue life increases as the static load decreases. The logarithm of fatigue life is related linearly to the static load above a limiting value of the static load, but when the static load decreases beyond the limiting value the linear relation does not hold, and the fatigue life increases so rapidly that it takes a very long time to measure that.Tire cords are so designed that each constituting cord (1650 den/2) is not subjected to a load above 1kg when the tires are in running state, and naturally, it is desirable that experimental observations should be performed under a load of about 1kg. However, practical measurements have hitherto been made under loads above 1kg, and the fatigue life under lower loads has been estimated by extraporating the linear part in the S-N diagram. Such a procedure may results in a error because the S-N diagrams for various kinds of cords are not parallel with each other, and also the linear relation does not hold under lower loads. Thus, the true fatigue life under running states should be measured only experimentally.The authors have tried to make a flexing fatigue tester of rotary type and made it possible to measure the fatigue life of various kinds of tire cords under a load of 1kg (per a cord). Further, they have obtained the so-called “master curve” from the present data and also from that obtained by the apparatus reported in Part 1 of this series, making comparisons among the S-N diagrams under a load ranging from 0.25 to 3.0kg per a cord.The results obtained are as follows: The textile cord does not show a clear fatigue limit, and the slope of the linear part in the S-N diagram depends on the sort of the fiber and also on the manufacturing conditions (As already reported in Part 2 of this series). The slope of the linear part in the S-N diagram may be explained by considering the tensile recovery of the fiber. The tensile recovery of a fiber which has been allowed fully to relax when manufactured is nearly 100% in fairly a wide range of extension, but decreases when the extension exceeds some limit. On the contrary, the fiber which has been stretched strongly in spinning process shows rather a low tensile recovery under a small elongation, which does not decrease much under a large elongation. The Topfam spinning rayon belongs to the former and the BX to the latter.If the fatigue of fiber arises from consumption of external energy, the fatigue may not occur in a range of the tensile recovery of 100%, but may increase as the tensile recovery decreases. The fatigue life of the fiber whose tensile recovery varies much with increasing elongation varies widely. From this we may explain the fact that the S-N diagram of the Topfam spinning rayon has a less steep and that of BX has a steeper slope.
Authors: Shigeta FUJIMOTO, Isao OKAMURA
Language: English
Subfield: Mechanics of Materials
Field: Engineering
Domain: Physical Sciences
Open Access status: bronze
OpenAlex ID: W2397136121