In this work, step-cycle tensile behavior of two bimodal polyethylene (PE) materials, a PE100 grade pipe material, XS10, and a PE100-RC (Resistant Crack) grade pipe material, XSC50, was comparatively investigated. By decomposing the strain into a recoverable part and an unrecoverable part, it was found that the deformation recovery capability of XSC50 during stretching was larger than that of XS10. Structural evolution characterized by in situ synchrotron small angle X-ray scattering indicated that the fragmentation of initial crystals in XSC50 occurred at lower strain than in XS10. Considering that XSC50 had relatively small lamellar thickness and similar crystallinity to XS10, we speculated that the larger deformation recovery capability of XSC50 during stretching probably derived from stronger entangled amorphous region caused by larger density of tie molecules and entanglements, which were usually regarded to have a significant influence on the slow crack growth (SCG) resistance of PE materials. As expected, the experimental result of strain hardening modulus test suggested that the deformation recovery capability during stretching was positively correlated with the SCG resistance for XS10 and XSC50 used in this work. The step-cycle tensile test had the potential to be developed into a supplement for comparison of SCG resistance of PE materials.

在这项工作中，比较研究了两种双峰聚乙烯（PE）材料，PE100级管材XS10和PE100-RC（抗裂）级管材XSC50的阶跃循环拉伸性能。通过将应变分解为可恢复部分和不可恢复部分，发现XSC50在拉伸过程中的变形恢复能力大于XS10。以原位为特征的结构演化同步加速器小角度X射线散射表明，XSC50中初始晶体的碎裂发生在比XS10中更低的应变下。考虑到XSC50具有相对较小的层状厚度和与XS10相似的结晶度，我们推测XSC50在拉伸过程中具有较大的变形恢复能力，可能是由较大的键分子和缠结密度引起的更强的纠缠非晶区所致，这些通常被认为具有对PE材料的抗慢速裂纹扩展（SCG）性能有重要影响。正如预期的那样，应变硬化模量测试的实验结果表明，拉伸过程中的变形恢复能力与本研究中使用的XS10和XSC50的SCG抵抗力呈正相关。