Department of Industrial Engineering, University of Trento, 38123 Trento, Italy.
National Interuniversity Consortium of Materials Science and Technology (INSTM), 50121 Florence, Italy.
Molecules. 2020 Nov 16;25(22):5347. doi: 10.3390/molecules25225347.
Thin cyclic olefin copolymer (COC) foils were used as intrinsic thermoplastic healing agents in carbon fiber (CF)-reinforced epoxy laminates. COC films were produced by hot pressing and were interleaved in the interlaminar regions between each EP/CF lamina, during the hand layup fabrication of the laminates. Three samples were produced, i.e., the neat EP/CF laminate without COC, and two laminates containing COC layers with a thickness of 44 μm and 77 μm, respectively. It was observed that the fiber volume fraction decreased, and the porosity increased with the introduction of COC layers, and this effect was more evident when thick films were used. These two effects, combined with the sub-optimal adhesion between COC and EP, caused a decrease in the mechanical properties (i.e., the elastic modulus, flexural strength, interlaminar shear strength and interlaminar fracture toughness) of the laminates. Specimens subjected to mode I interlaminar fracture toughness test were then thermally mended under pressure by resistive heating, through the Joule effect of conductive CFs. A temperature of approximately 190 °C was reached during the healing treatment. The healing efficiency was evaluated as the ratio of critical strain energy release rate () of the healed and virgin specimens. Healed specimens containing COC layers of 44 μm and 77 μm exhibited a healing efficiency of 164% and 100%, respectively. As expected, the healing treatment was not beneficial for the neat EP/CF laminate without COC, which experienced a healing efficiency of only 2%. This result proved the efficacy of COC layers as a healing agent for EP/CF laminates, and the effectiveness of resistive heating as a way to activate the intrinsic healing mechanism.
薄型环状烯烃共聚物（COC）箔片被用作碳纤维（CF）增强环氧树脂层压板中的本征热塑性修复剂。COC 薄膜通过热压制成，并在层压板的每一层 EP/CF 层之间的层间区域中交错排列，在层压板的手工铺设制造过程中进行。制作了三个样品，即没有 COC 的纯 EP/CF 层压板，以及两个分别含有厚度为 44μm 和 77μm 的 COC 层的层压板。观察到纤维体积分数随着 COC 层的引入而降低，孔隙率增加，当使用较厚的薄膜时，这种效果更为明显。这两个效应，再加上 COC 和 EP 之间的次优附着力，导致层压板的机械性能（即弹性模量、弯曲强度、层间剪切强度和层间断裂韧性）下降。然后，通过 CF 的焦耳效应，通过电阻加热对承受模式 I 层间断裂韧性测试的试件进行热修复，在修复处理过程中达到约 190°C 的温度。通过比较修复和原始试件的临界应变能释放率（），评估修复效率。含有 44μm 和 77μm COC 层的修复试件的修复效率分别为 164%和 100%。正如预期的那样，对于没有 COC 的纯 EP/CF 层压板，修复处理没有益处，其修复效率仅为 2%。这一结果证明了 COC 层作为 EP/CF 层压板修复剂的有效性，以及电阻加热作为激活本征修复机制的有效方法。
