AI 中文总结
研究光老化聚丙烯三点弯曲时的表面裂纹形成，通过对比老化面与非老化面在拉伸侧的情况，发现脆化厚度梯度反映在弯曲应力 - 应变响应中，三点弯曲能有效探测光老化聚合物表面脆化。
AI 中文摘要
本研究采用三点弯曲试验，研究了具有深度依赖老化梯度的光老化聚丙烯（PP）中的表面裂纹形成。PP在紫外线（UV）照射下会脆化，且光氧化从照射表面向内进行，导致脆化在样品厚度上不均匀发展。对轻度光老化且未出现可见表面裂纹的PP样品进行两种配置的弯曲：老化表面在拉伸侧和相反表面在拉伸侧。老化表面在拉伸侧时，应力 - 应变曲线出现多个离散应力降，原位侧视图观察证实每个新表面裂纹的形成与应力降一致；相反表面在拉伸侧时未观察到明显应力降。结果表明脆化的厚度梯度直接反映在弯曲应力 - 应变响应中。单轴拉伸试验是评估力学性能的标准方法，但假设横截面名义上均匀变形，反映的是空间平均响应。三点弯曲在样品表面施加最大拉伸应变，能选择性探测脆化表面层，是检测光老化聚合物表面脆化的有效方法。
英文摘要
Using three-point bending, this study investigates surface-crack formation in photo-aged polypropylene (PP) that has a depth-dependent aging gradient. PP undergoes embrittlement under ultraviolet (UV) irradiation, and because the photo-oxidation proceeds inward from the irradiated surface, the embrittlement develops non-uniformly across the specimen thickness. PP specimens were mildly photo-aged by UV irradiation and had not yet developed visible surface cracks. Each specimen was bent in two configurations: with the UV-irradiated ("aged") surface on the tensile side, and with the opposite ("reverse") surface on the tensile side. When the aged surface was on the tensile side, the stress-strain curves exhibited several discrete stress drops, and in-situ side-view observation confirmed that the formation of each new surface crack coincided with a stress drop. In contrast, no clear stress drops were observed when the reverse surface was on the tensile side. These results show that the through-thickness gradient of embrittlement is directly reflected in the bending stress-strain response. Uniaxial tensile testing, the standard method for evaluating mechanical properties, formally assumes a nominally uniform deformation across the cross-section and therefore reflects the spatially averaged response. Three-point bending, by contrast, imposes the largest tensile strain at the specimen surface and thus selectively probes the embrittled surface layer, making it an effective method for detecting the surface embrittlement of photo-aged polymers.
Comments39 pages, 9 figures
