Abstract: Ultrahigh molecular weight polyethylene (UHMWPE) fibers have a highly oriented crystalline chain structure. This special structure contributes them with excellent physical and mechanical properties. UHMWPE fibers are considered to be the material with the highest specific strength and specific modulus in the world. Additionally, they exhibit low density, excellent moisture absorption, exceptional chemical resistance, high impact strength, and remarkable wear resistance. These outstanding characteristics make them indispensable in various industrial sectors such as aerospace, automotive engineering, national defense, textile manufacturing, chemical engineering, and medical technology. With so many excellent properties, the UHMWPE fiber has its shortcomings, for instance, poor temperature resistance, bad composite adhesion and creep resistance. The creep behavior makes UHMWPE fibers unstable in product size and shape, which greatly limits their application in composite materials, ropes and other fields. Therefore, improving the creep resistance of UHMWPE fibers has been the focus of researchers. By exploring the evolution of condensed matter structure of UHMWPE fibers during multistage thermal stretching, the creep rule of fibers under different conditions and the change rule of fiber properties after creep behavior, the article can provide theoretical support for improving the creep resistance of fibers. In order to study the creep properties of ultrahigh strength UHMWPE fibers during multistage thermal drawing, fiber samples with different thermal stretching rates were collected in different sections on actual industrial production lines. The condensed matter structure, mechanical properties and creep properties of chemical fibers during thermal stretching were studied by means of two-dimensional wide-angle X-ray diffractometer, universal testing machine and creep property tester. The variation of fiber creep rates under different temperatures and stresses, as well as the correlation between creep size and fiber structure and mechanical properties, were analyzed. The results showed that with tiered thermal stretching grading, the rate of crystallization and orientation of the fibers could reach 88.97% and 0.973 respectively, which indicated that not only the mechanical properties of the fibers but the creep resistance were improved. When the test temperature was less than 70 ℃, the creep behavior of the fiber was not obvious. It demonstrated two distinct stages of rapid and gradual increase with increasing applied stress, while the transition time between these stages decreased as both temperature and applied stress rose. The creep behavior of the fiber, however, exhibited a continuous acceleration when the temperature reached 90 ℃. Furthermore, it was observed that the magnitude of stress directly influenced the extent of creep acceleration during later stages. When the fiber creeped by 10%, its breaking strength showed an increasing trend, and when it creeped by more than 20%, its mechanical properties became worse.

Key words: UHMWPE, condensed matter structure, creep behavior, mechanical properties, thermal tensile

摘要： 蠕变行为是限制超高强型超高分子量聚乙烯（UHMWPE）纤维应用领域的关键因素。为研究超高强型UHMWPE纤维在多级热拉伸过程中的蠕变行为，以工业生产线上不同热拉伸倍率纤维为样品，采用二维广角X射线衍射仪、万能试验机和化纤高强丝蠕变性能测试仪，表征纤维在热拉伸过程中的凝聚态结构、力学性能和蠕变行为。分析了不同温度、应力下纤维蠕变率的变化规律，以及蠕变大小与纤维结构和力学性能的相关性。结果表明：随着热拉伸的分级进行，纤维的结晶和取向度分别可达88.97%和0.973，同步改善了纤维的力学性能和抗蠕变性能。当测试温度低于70 ℃时，纤维蠕变不明显；随着施加应力的增加，蠕变表现出快速增加和缓慢增长两个阶段，两个阶段的转变时间点随着温度和施加应力的增加而缩短。但当温度达到90 ℃时，纤维的蠕变呈现不断加速的结果，施加应力越大，后期的蠕变加速度也越大。当纤维发生10%的蠕变后，其断裂强力得到提高，而当蠕变超过20%时，力学性能转而变差。

关键词: 超高分子量聚乙烯（UHMWPE）, 凝聚态结构, 蠕变行为, 力学性能, 热拉伸