Interlaminar to intralaminar mode I and II crack bifurcation due to aligned carbon nanotube reinforcement of aerospace-grade advanced composites
Interlaminar to intralaminar mode I and II crack bifurcation due to aligned carbon nanotube reinforcement of aerospace-grade advanced composites
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DOI：
10.1016/j.compscitech.2020.108014
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发表时间：
2020-04-12
影响因子：
9.1
通讯作者：
Wardle, Brian L.
中科院分区：
文献类型：
--
作者：
Ni, Xinchen;Furtado, Carolina;Wardle, Brian L.
航空航天级单向碳微纤维增强环氧预浸料复合材料层压板在相对较弱的层间区域通过均匀分布的垂直排列碳纳米管（A-CNT）的高密度（> 100亿纳米纤维/厘米（2））进行增强，从而创建了一种称为“纳米缝合”的分层结构。这种纳米缝合层压材料已被证明可以提高层压材料的面内和层间剪切强度。在这里，根据 ASTM 标准，通过分别对单向 0 度层压板进行双悬臂梁和端部缺口弯曲测试，对 I 型和 II 型断裂行为以及相关的增韧机制进行实验研究。通过显微镜和微计算机断层扫描（CT）对裂纹表面的研究表明，在模式I和II中，层间裂纹从层间预裂纹分叉到层内区域，然后在与纳米缝合层间区域平行的层内区域内扩展，形成稳定状态的“层内分层”。这种之前未观察到的现象归因于 A-CNT 将层间韧性增加到导致层间裂纹分叉到韧性较差的层内区域的水平。显微镜和μ CT 分析表明，A-CNT 不会增加层间厚度，并且在模式 I 和 II 中将裂纹驱动到裂纹萌生 1-2 nun 内的层内区域，模式 II 中的“层内分层裂纹距层间区域（层压板中心线）的距离比模式 I 更大（分别为（大约）30 μ m 和（大约）15 pm）。模式 I 中裂纹分叉的有限元模拟预测，由于 A-CNT 在稳态下在层内区域扩展裂纹，层间韧性至少会增加 10%，正如实验所观察到的，先进复合材料中这种独特的裂纹行为为了解 A-CNT 引起的增强效果提供了新的见解，从而影响层压板的宏观断裂和失效行为，并为增强层压板提供了新的机会。
Aerospace-grade unidirectional carbon microfiber reinforced epoxy prepreg composite laminates were reinforced in the relatively weak interlaminar regions with high densities (>10 billion nanofibers per cm(2)) of uniformlydistributed vertically aligned carbon nanotubes (A-CNTs), creating a hierarchical architecture termed "nano stitch". Such nanostitched laminates have been shown to increase laminate in-plane and interlaminar shear strengths. Here, the Mode I and Mode II fracture behavior and associated toughening mechanisms are investigated experimentally by performing double cantilever beam and end-notched flexure tests, respectively, of unidirectional 0 degrees laminates following the ASTM Standards. Investigation of the crack surfaces via microscopy and micro-computed tomography (CT) show that in both Mode I and II, the interlaminar crack bifurcates into the intralaminar region from the interlaminar precrack, and then propagates within the intralaminar region parallel to the nanostitched interlaminar region as an "intralaminar delamination" in steady state. This before unobserved phenomenon is attributed to the A-CNTs adding interlaminar toughness to a level that causes the interlaminar crack to bifurcate into the less tough intralaminar region. Microscopy and mu CT analyses reveal that the A-CNTs do not increase the interlaminar thickness, and drive the crack into the intralaminar region within 1-2 nun of crack initiation in both Mode I and II, with the distance of the "intralaminar delamination- crack from the interlaminar region (at the laminate centerline) being greater in Mode II than in Mode I ((similar to)30 mu m vs. (similar to)15 pm, respectively). Finite element simulation of the crack bifurcation in Mode I predicts a minimum of 10% increase in interlaminar toughness due to the A-CNTs to propagate the crack in the intralaminar region in steady state, as observed experimentally. This unique crack behavior in advanced composites provides new insights into the magnitude and effects of reinforcement induced by A-CNTs that influence the macroscopic fracture and failure behavior of laminates, and suggests new opportunities for toughening laminates.