目的 为研究双向拉伸聚丙烯(Biaxially Oriented Polypropylene，BOPP)薄膜在重复拉伸使用后的弹性模量变化以及应变变化趋势。方法 以26 μm BOPP薄膜为研究对象，以1、1.5、2、2.5、3、3.5、4 N为最大加载力分别进行加载周期为15次的单轴循环拉伸试验，总结对比循环次数以及加载力对弹性模量及棘轮应变的影响，分析薄膜性能变化趋势。结果 通过对比同一加载应力不同循环下的弹性模量以及棘轮应变，发现在预设加载力下随着循环次数增加，薄膜弹性模量呈增大趋势，且增大幅度逐渐减小，其棘轮应变与弹性模量变化趋势一致;通过取均值对比不同加载力下的弹性模量以及棘轮应变变化，发现薄膜弹性模量随加载力增大而先增大后减小，最大应变以及最小应变均随加载力的增加而增大。结论 通过试验研究得出了BOPP薄膜在循环拉伸中弹性模量及棘轮应变随加载力、循环次数增大的变化趋势;对薄膜性能变化有了一定的预测，并为实际加工中的张力选择提供了指导性建议。

The work aims to study the changes in elastic modulus and plastic deformation trend of biaxially oriented polypropylene (BOPP) films after repeated stretching use. With 26 μm BOPP films as the research object, uniaxial cyclic tensile tests were conducted with a maximum loading force of 1, 1.5, 2, 2.5, 3, 3.5, and 4 N for 15 loading cycles. The effects of the cycle number and loading force on the elastic modulus were summarized and compared, and the trend of film performance changes was analyzed. By comparing the elastic modulus and ratcheting strain under different cycles under the same loading stress, it was found that under the preset loading force, the elastic modulus showed an increasing trend with the increase of the cycle number, and the increasing amplitude gradually decreased. The ratcheting strain and the change trend of the elastic modulus were consistent. By comparing the elastic modulus and ratcheting strain changes under different loading forces by taking the mean, it was found that the elastic modulus first increased and then decreased with the cycle number, while the maximum and minimum strains both increased with the number of cycles. The experiment shows that the elastic modulus and the ratcheting strain of BOPP films increase with the increase of loading force and cycle number. It provides certain predictions about the changes in film properties and provides guidance for the selection of tension in actual processing.