IMPROVEMENT OF COMPRESSIVE STRENGTH OF TIRE STEEL CODE FOR AUTOMOBILE

这个项目可以分为三个步骤。第一步是研究钢索在压缩试验中破坏模式的观察。第二步与钢丝的弯曲疲劳失效有关。最后，提出了钢索弯曲疲劳破坏的力学模型。(1)在压缩试验中观察到钢丝的疲劳破坏。虽然加载方式为压缩，但钢结构规范是屈曲和弯曲的。分析了绳增强橡胶的压缩刚度，证实了绳增强橡胶容易发生屈曲。即破坏模式为弯曲疲劳。(2)因此，结合弯曲试验和观察，对钢丝帘线的弯曲疲劳机理进行了研究。采用1×19、3+9、1×12、1×12+Wr和4×3结构进行调查。疲劳破坏是从外层钢丝开始的。然后芯线失效了。几何分析表明，最大的弯曲应力是在芯线中产生的。也就是说，在弯曲过程中，还有另一个因素会损坏帘子线。(3)提出了一种简化的力学模型来解释钢丝帘线的弯曲疲劳。考虑了钢丝间轴向摩擦力的影响。在弯曲过程中，摩擦力增加了金属丝的应力。该模型很好地解释了索结构之间的相对强度。

This project can be divided into three steps. The first step is a study on the observation of failure mode in steel cords during compression tests. The second step is associated with bending fatigue failure of steel cords. And in the last step, the authors propose a mechanical model of the bending fatigue failure steel cords.(1) Fatigue failure of steel wire was observed during compression tests. Although the loading mode was compression, the steel codes were buckling and bent. The authors analyzed the compression stiffness and confirmed that the buckling was easy to initiate for the cord-reinforced rubber. Namely, the failure mode was bending fatigue.(2) Therefore, the bending fatigue mechanism of steel cord was investigated caring out the bending tests and the observations. The constructions of 1×19, 3+9, 1×12, 1×12+Wr, and 4×3 were used for the investigation. The fatigue failure was initiated at the outer layer wires. Then the core wire was failed. A geometrical analysis revealed that the highest bending stress is initiated in the core wire. Namely, there are another factor to damage the cord wire during the bending.(3) A simplified mechanical model was proposed to explain the bending fatigue of steel cord. The authors consider the effect of friction force in wire axial direction between the wires. The friction force increases the stress in wire during the bending. The model reasonably well explains the relative strength between the cord constructions.