The Effects of Rubber Core Diameter and the Number of Braided Outer Layers on the Compression and Fatigue Properties of Helical Composite Springs

In this study, nine kinds of helical composite springs were made of structures containing rubber core unidirectional laminates with braided outer layers (BUR). It aims to investigate the effects of rubber core diameter and the number of braided outer layers on the compression and fatigue properties of helical composite springs. According to the experimental results, the helical composite spring with a rubber core of 3 mm diameter and a single braided outer layer has the highest compression properties among those considered herein, its failure load in compression approximately equals 348.1kgf, and the corresponding spring constant is almost 11.6kgf/mm. In compression fatigue test of the helical composite springs, the pre-compression displacement and the maximum compression displacement were set to be 10% and 70% of the maximum static compression displacement, respectively. Three hundred thousands fatigue cycles were applied at the frequency of 3 Hz on each specimen. The experimental results show that the decrease of the failure loads in compression after fatigue test was less than 5% of the failure loads in compression at the beginning of fatigue test for all the helical composite springs except those with three braided outer layers, which satisfied the general requirement of commercial standard.