[论文解读] Use of Digital Image Correlation to study the effect of temperature on the development of plastic instabilities in a semi-crystalline polymer

Laurent Farge, Stéphane André+1 more|arXiv (Cornell University)|Nov 30, 2018

Polymer crystallization and properties参考文献 43被引用 10

一句话总结

本研究采用三维数字图像相关法（3D DIC）分析高密度聚乙烯（HDPE）在温度依赖下的塑性失稳行为。结果表明，在60 °C以下，应变局部化随温度升高而减弱；而在60 °C以上，出现第二个屈服点（E_Y₂），标志着片晶结构破坏的开始，且该点对应的临界应变具有温度无关性，颈缩稳定化由应变驱动机制主导，与Haward-Thackray模型相符。

ABSTRACT

The plastic deformation processes that occur in a tensily deformed High Density Polyethylene specimen were studied from full-field strain and strain rate measurements obtained by 3D DIC (Digital Image Correlation).The tensile tests were performed every 10{\ extdegree}C from room temperature to 120{\ extdegree}C . For temperatures below 60{\ extdegree}C , it is shown that the strain localization effect becomes less pronounced when the temperature increases. For temperatures higher than 60{\ extdegree}C , the material is found to exhibit double yielding behavior. By analyzing the DIC data in Lagrangian representation, it was possible to quantitatively highlight the strain localization effect that is specifically associated with the second yield. The second yield strain (E_{Y_2}) was measured and appeared to be independent of temperature. For temperatures smaller than 60{\ extdegree}C , it was found that the threshold strain corresponding to (E_{Y_2}) also marks the onset of the deformation process phase during which the volume strain strongly increases. Based on previous studies of our research team and on literature we concluded that the critical strain (E_{Y_2}) corresponds to the onset of the lamellar morphology destruction. At high strain levels, the neck stabilization phase was shown to proceed according to a strain driven scheme characterized by threshold strains that are temperature independent. The experimental values of the threshold strain marking the onset of the stabilization phase are found to be in good agreement with those found using the Haward-Thackray model.

研究动机与目标

• 研究温度对半结晶聚合物（如HDPE）中塑性失稳的影响。
• 利用全场测量方法量化不同温度下的应变局部化与变形演化行为。
• 通过临界应变阈值识别片晶形貌破坏的起始点。
• 评估实验测得的临界应变阈值与Haward-Thackray模型在颈缩稳定化预测上的一致性。

提出的方法

• 采用三维数字图像相关法（3D DIC）获取单轴拉伸试验过程中全场应变与应变率分布。
• 在室温至120 °C范围内，以10 °C为间隔进行单轴拉伸试验。
• 将DIC数据以Lagrangian表示法进行分析，以追踪变形演化并定位应变集中区域。
• 定量测量第二个屈服应变（E_Y₂）并将其与形貌变化相关联。
• 提取颈缩稳定化的临界应变阈值，并与Haward-Thackray模型的预测结果进行对比。
• 结合实验DIC数据与已有文献，解释片晶结构破坏的起始机制。

实验结果

研究问题

• RQ1 温度如何影响HDPE在单轴拉伸变形过程中应变局部化的形成？
• RQ2 第二个屈服点（E_Y₂）在塑性失稳与形貌变化起始中的作用是什么？
• RQ3 HDPE中颈缩稳定化的临界应变是否依赖于温度？
• RQ4 实验测得的颈缩稳定化临界应变是否与Haward-Thackray模型的预测一致？
• RQ5 E_Y₂在片晶结构破坏方面具有何种物理意义？

主要发现

• 在60 °C以下，随着温度升高，应变局部化效应减弱。
• 在60 °C以上，HDPE表现出双屈服行为，可观察到明显的第二个屈服点（E_Y₂）。
• 第二个屈服应变（E_Y₂）与温度无关，标志着体积应变显著增加的起始点。
• E_Y₂对应于片晶形貌开始破坏的临界应变。
• 颈缩稳定化通过应变驱动机制进行，其临界应变阈值与温度无关。
• 实验测得的颈缩稳定化临界应变与Haward-Thackray模型的预测结果具有良好一致性。