Toughening and repairability of high-strength CFRP by interlayer resin structure control

研究了含离聚体夹层的单向碳纤维/环氧复合材料层合板在I型和II型载荷下的层间断裂韧性。层间断裂的裂纹路径通常在层间树脂富集区被阻止。在本研究中，增韧的层间树脂扩展到层间/基板界面。由于裂纹路径位于增韧区域内，因此这种新的增韧概念有望获得优异的层间性能。利用离聚体的高粘结性能，对分层复合材料的可维修性进行了试验。研究结果总结如下：(1)层间树脂结构的控制用12~200 mm厚的离聚体夹层成型单向碳纤维/环氧层压板。EPMA分析表明，离聚体层与基碳纤维/环氧树脂层之间形成了界面相。这些中间相含有离聚体、环氧树脂和碳纤维的混合物。(2)层间断裂韧性…在I型和II型载荷下，离聚体交织的CF/环氧层压板的粗糙度均远高于基板。(3)离聚体厚度效应I型层间韧性随离聚体夹层的增加先增大后趋于平缓。对于II型加载，韧性随着离聚体厚度的增加而不断增加，达到9~10kJ/m^2，是已报道结果中最高的之一。(4)I型分层疲劳由于裂纹路径在离聚体/相界面处或在界面区内，被纤维阻挡，因此保持了较高的抗裂纹扩展能力，而不随裂纹长度的增加而增加。(5)可维性虽然不加离聚体膜的热压效果不佳，但离聚体膜的修复带来了与原始层合板相当的韧性。较少

Interlaminar fracture toughness under mode I and II loadings was investigated for unidirectional CF/epoxy laminates with ionomer interleaf. Crack path of interlaminar fracture is often arrested within the interlayer resin rich region. In the present study, the toughened interlayer resin was expanded to the interlayer/base lamina interphase. Since the crack path was located inside the toughened region, excellent interlaminar properties are expected by this new toughening concept. Using the high bonding properties of ionomer, the repairability of delaminated composites was also tried. The results are summarized as follows :(1) Control of interlayer resin structureUnidirectional CF/epoxy laminates was molded with ionomer interleaf of the thickess of 12 to 200 mm. EPMA analysis revealed that interphases were formed between the ionomer layer and the base CF/epoxy laminas. These interphases contain a mixture of ionomer, epoxy and carbon fibers.(2)Interlaminar fracture toughnessThe fracture t … More oughness of ionomer interleaved CF/epoxy laminates was much higher than that of base CF/epoxy laminates both under mode I and II loadings. For mode I loading, the high level of the toughness was kept constant with the crack growth.(3)Ionomer thickness effectMode I interlaminar toughness initially increased with the increase of ionomer interleaf, and then leveled off. For mode II loading, the toughness continuously increased with the ionomer thickness, and reached 9 to 10 kJ/m^2, which is one of the highest among already reported results.(4)Mode I delamination fatigueHigh crack growth resistance was kept without respect to the increment of the crack length because the crack path was at the interface of the ionomer/interphase or inside the interphase region, arrested by fibers.(5)RepairabilityThe delaminated specimen was hot-pressed again, and the interlaminar toughness change was investigated. Although hot-pressing without additional inomer film gave poor results, the repair with ionomer film brought the toughness comparable to the virgin laminates. Less