Research on stress relaxation behavior of polyarylate fiber and braided polyarylate ropes

Polyarylate ropes are increasingly utilized in flexible and deployable structures of spacecraft. However, their stress relaxation behavior can critically influence operational performance and structural stability. In this study, a novel stress relaxation experimental system and a stress relaxation model based on the generalized Maxwell model were developed to comprehensively investigate the stress relaxation behavior of polyarylate fiber and braided polyarylate ropes with varying pitch lengths under different load levels. The results indicate that polyarylate fibers exhibit similar steady-state relaxation rates under 25% and 50% of the breaking strength but relax significantly faster at 75%, as more molecular chain segments are activated. Polyarylate ropes with different pitch lengths show comparable stress decay patterns at 50% of the breaking strength, but ropes with shorter pitch lengths relax at higher rates under the same load. The stress relaxation model reveals two relaxation modes for fibers and three for ropes. The first relaxation mode and the second relaxation mode reflect the rapid molecular chain arrangement in primary relaxation and the restricted chain segments motion within the limited molecular structure space in the steady-state relaxation, respectively. The third relaxation mode, identified only in ropes, is mainly associated with the rearrangement of fibers and yarns during the rope relaxation process. These findings offer a clearer understanding of the multiscale stress relaxation mechanisms of polyarylate fibers and braided polyarylate ropes, and provide valuable guidance for optimizing the structural design deployable spacecraft systems.