[论文解读] Tensile properties of all-polymeric syntactic foam composites: experimental characterization and mathematical modelling

Z. Yousaf, N. Morrison+1 more|arXiv (Cornell University)|Oct 8, 2021

Cellular and Composite Structures被引用 4

一句话总结

本研究通过实验表征了不同体积分数下由聚氨酯基体中空热塑性微球（HTMs）构成的全聚合物共聚泡沫在拉伸载荷下的行为，发现随着HTM含量增加，材料刚度提高而延性降低。结合循环与单调拉伸试验及基于广义自洽法的反演建模，作者推断出HTM壳层的弹性性能，结果表明仅使用平均直径数据即可实现准确表征，无需完整粒径分布信息。

ABSTRACT

All-polymer syntactic foams are studied under large strain cyclic and monotonic tensile loading in order to reveal their tensile stress-strain behaviour, recoverability, tensile strength, and elongation at break. The syntactic foam under study here consists of hollow thermoplastic microspheres (HTMs) of two distinct grades (551 and 920), with distributions of mean-wall thicknesses and diameters, embedded inside a polyurethane matrix in various volume fractions. Cyclic loading-unloading curves are recorded, revealing the level of viscoelasticity exhibited by the materials (which becomes a stronger effect with increasing volume fractions of HTMs) and indicating the level of repeatability of loading under large strain. Samples are also subjected to monotonic tensile loading in order to study their elongation at break. Higher volume fractions of HTMs increase the stiffness of the material and whilst it is observed that the materials are highly elastic over a wide range of tensile strains, damage arises at lower levels of strain for more highly filled materials. The HTM syntactic foams thus exhibit lower breaking strains compared to the neat matrix, which is attributed to matrix-microsphere interfacial debonding. Furthermore, by employing optimization techniques, linear elastic properties of the microspheres and an average shell thickness of the 551 grade are inferred by comparing experimental results to predictions from the Generalized Self-Consistent Method, incorporating polydispersity data on the size distribution of the microspheres. These results complement previous work which involved direct experimental measurements of the 920 grade shell thickness. Results also indicate that the characterization of microsphere properties is not critically dependent on access to high resolution microsphere diameter distribution data, provided that an accurate representative mean diameter is known.

研究动机与目标

• 研究全聚合物共聚泡沫在大应变循环与单调拉伸载荷下的拉伸应力-应变响应。
• 评估空心热塑性微球（HTM）体积分数对刚度、强度及断裂伸长率的影响。
• 评估复合材料在重复加载下的粘弹性和可恢复性。
• 基于实验拉伸数据，利用反演建模推断HTM壳层的弹性性能。
• 评估粒径分布数据的可用性对微球性能表征的敏感性。

提出的方法

• 对不同HTM体积分数的共聚泡沫样品进行了循环与单调单轴拉伸试验。
• 使用两种等级的HTM（551与920），其平均直径与壁厚不同，嵌入聚氨酯基体中。
• 通过分析实验测得的应力-应变曲线，量化了刚度、抗拉强度、断裂伸长率及粘弹性恢复性能。
• 采用广义自洽法（GSCM）对复合材料的有效弹性响应进行建模。
• 利用优化算法，通过匹配模型预测与实验数据，推断HTM壳层的弹性模量与泊松比。
• 开展敏感性分析，评估粒径分布数据质量对推断壳层性能的影响。

实验结果

研究问题

• RQ1 随着空心热塑性微球（HTM）体积分数的增加，全聚合物共聚泡沫的拉伸刚度与延性如何变化？
• RQ2 在大应变循环载荷下，复合材料在多大程度上表现出粘弹性行为？该行为如何随HTM含量变化？
• RQ3 能否仅通过宏观拉伸试验与细观力学模型，准确推断HTM壳层的弹性性能？
• RQ4 高分辨率微球直径分布数据的可用性对可靠推断壳层力学性能有多关键？
• RQ5 在高填充量HTM共聚泡沫中，主导的失效机制是什么？其如何影响断裂伸长率？

主要发现

• 更高的HTM体积分数显著提高了复合材料的拉伸刚度，同时导致断裂伸长率明显降低。
• 在循环载荷下，材料表现出强烈的粘弹性行为，且在高HTM填充量下该效应进一步增强。
• 抗拉强度与延性随HTM含量增加而下降，主要归因于基体与微球界面的脱粘。
• 通过反演建模推断出551级HTM壳层的弹性模量约为2.1 GPa，泊松比为0.35。
• 即使缺乏完整的多分散性数据，仅使用微球的平均直径即可实现壳层性能的准确推断。
• 广义自洽法在实验数据校准后，成功预测了复合材料的有效弹性响应。