Abstract Epoxy is a material of choice for demanding applications thanks to its high chemical stability, stiffness, and strength. Yet, its brittle fracture behavior is an important downside for many sectors. Here, we show that the addition of electrospun thermoplastic nanofibers is a viable toughening strategy to design nanofiber reinforced epoxy materials with excellent toughness. Moreover, the use of transparent film-like specimens allowed in-situ imaging during mechanical testing. Optical and scanning electron microscopy, digital image correlation and crack length measurements are used to analyze the toughening mechanisms responsible for high toughening efficiency in detail. The addition of polyamide and polycaprolactone nanofibers resulted in an increased plastic energy uptake up to 100%. In-situ observation of the crack tip showed that the main energy-absorbing mechanism was due to bridging nanofibers. There was a profound decrease in toughening efficiency when nanofibers lacked sufficient adhesion with the matrix only when they were oriented parallel with the crack growth direction. The profound understanding of such underlying mechanisms opens up material design in applications where high toughness is required like adhesives, coatings, and fiber-reinforced composite laminates.

中文翻译：

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通过原位光学和扫描电子显微镜研究热塑性纳米纤维增强环氧树脂具有优异抗裂性的增韧机制

摘要 环氧树脂由于其高化学稳定性、刚度和强度而成为要求苛刻的应用的首选材料。然而，其脆性断裂行为是许多行业的一个重要缺点。在这里，我们表明添加电纺热塑性纳米纤维是设计具有优异韧性的纳米纤维增强环氧树脂材料的可行增韧策略。此外，使用透明薄膜样样品允许在机械测试期间进行原位成像。使用光学和扫描电子显微镜、数字图像相关性和裂纹长度测量来详细分析导致高增韧效率的增韧机制。添加聚酰胺和聚己内酯纳米纤维导致塑料能量吸收增加高达 100%。裂纹尖端的原位观察表明，主要的能量吸收机制是由于纳米纤维的桥接。当纳米纤维仅在与裂纹扩展方向平行时才与基体缺乏足够的粘附力时，增韧效率会显着降低。对此类潜在机制的深刻理解为需要高韧性的应用（如粘合剂、涂料和纤维增强复合层压板）开辟了材料设计之路。