Abstract The digital photoelastic technique is used to characterise the necking behaviour of isotactic polypropylene (iPP) fibres. The effect of stretching rate on necking initiation is studied. The birth of necking is observed using photoelastic patterns of the stretched fibres to understand how the localised difference between the principle stresses grows to form a necking region. Finally, the formation of multiple necking regions is characterised photoelastically. These multiple necks are initiated using the same formation mechanism and conditions as if there is only a single necking region. It was evident that, fast stretching causes faster arrangement of molecular chains and hence decreases the time required for necking initiation. Recommendations are suggested for optimum mechanical processing conditions of iPP fibres to avoid failure by necking. Photoelastic patterns are given for illustration.

中文翻译：

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利用数字光弹性表征拉伸速度对颈缩现象影响的定量研究

摘要 数字光弹技术用于表征等规聚丙烯 (iPP) 纤维的颈缩行为。研究了拉伸速率对颈缩起始的影响。使用拉伸纤维的光弹性图案观察颈缩的产生，以了解主要应力之间的局部差异如何增长以形成颈缩区域。最后，多个颈缩区域的形成以光弹性为特征。这些多个颈缩使用相同的形成机制和条件启动，就好像只有一个颈缩区域一样。很明显，快速拉伸导致分子链的更快排列，因此减少了颈缩起始所需的时间。针对 iPP 纤维的最佳机械加工条件提出了建议，以避免因颈缩而失败。给出了光弹性图案以供说明。