In-situ damage self-sensing and strength recovery activated by self-electricity in carbon fibrous composites embedded with multi-functional interleaves

doi:10.1016/j.compositesa.2023.107777

Composites Part A: Applied Science and Manufacturing
复合材料 A 部分：应用科学与制造

Volume 175, December 2023, 107777
第 175 卷，2023 年 12 月，10777

https://doi.org/10.1016/j.compositesa.2023.107777 Get rights and content 获取权利和内容

Full text access 全文访问

Highlights 亮点

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Multifunctional interleaf with damage in-situ monitoring and damage in-situ healing functions.
具有原位损伤监测和原位损伤修复功能的多功能夹层板。
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CFRPs integrated with the multifunctional interleaf exhibit obvious/regular monitoring signal characteristics during the progressive damage process.
集成了多功能夹层板的碳纤维增强塑料在逐渐损坏过程中表现出明显/规律的监测信号特征。
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The out-of-plane strength of CFRPs integrated with the multifunctional interleaf can be self-healed by more than 90% after two damage-healing cycles.

Abstract 摘要

It is challenging to simultaneously in-situ monitor and then repair the delamination crack of carbon fiber reinforced plastics (CFRPs) without sacrificing the initial mechanical properties. Herein, two sandwich interleaves are prepared by using healable poly (ethylene-co-methacrylic acid), reinforced and conductive carbon nanotubes (CNTs), and shear-resistant epoxy columns, to achieve self-sensing and self-healing functionalities. The results reveal that both interleaves show significant self-resistance changes to damage initiation and tensile strength of the interleaves themselves can be restored to 67.9–69.1%. Also, the interleaved CFRP exhibits obvious resistance change features during the progressive damage process after multiple healings. Moreover, a self-healing efficiency of more than 90% to interlaminar shear strength after two damage-healing cycles can be obtained. Furthermore, the interleaf with more CNTs possesses higher initial and healed strength. Therefore, the proposed interleaves can be used to prepare CFRP structure with self-sensing and self-healing functions, thereby with improved service reliability and service life.
在不牺牲初始机械性能的前提下，同时对碳纤维增强塑料（CFRP）的分层裂纹进行原位监测和修复是一项挑战。在此，我们利用可愈合聚（乙烯-共甲基丙烯酸）、增强导电碳纳米管（CNT）和抗剪环氧树脂柱制备了两种夹层中间膜，以实现自传感和自愈合功能。研究结果表明，这两种交错结构对损伤起始都有显著的自抗性变化，交错结构本身的抗拉强度可恢复到 67.9%-69.1%。同时，交错的 CFRP 在多次愈合后的渐进损伤过程中表现出明显的抗性变化特征。此外，经过两次损伤-愈合循环后，层间剪切强度的自愈合效率可达 90% 以上。此外，含有更多碳纳米管的夹层具有更高的初始强度和愈合强度。因此，所提出的夹层可用于制备具有自感应和自修复功能的 CFRP 结构，从而提高使用可靠性和使用寿命。

Graphical abstract 图形摘要

Keywords 关键词

A. Multifunctional composites

A. Carbon nanotubes

B. Delamination

D. Non-destructive testing

A.多功能复合材料

A.碳纳米管

B.脱层

D.非破坏性测试

1. Introduction 1.导言

Carbon fiber reinforced plastics (CFRPs) have become one of the most important class of structural materials over the last decades due to its high specific strength/stiffness and good resistance to fatigue/corrosion [1], [2], [3]. However, CFRP laminates are susceptible to delamination due to the mismatch through-the-thickness properties induced by the fiber reinforcements and the polymer matrix. Once delamination occurs, the stiffness and strength of the CFRP structure might be reduced significantly, which eventually causes a serious failure during the service life [4]. Especially, with the development of informatization and intelligence, CFRPs with self-diagnosis and self-healing functions have attracted more and more attention [5]. Based on this, it is also important to develop laminated CFRPs with in-situ self-sensing and self-healing functions for delamination cracks.
过去几十年来，碳纤维增强塑料（CFRP）因其高比强度/刚度和良好的抗疲劳/耐腐蚀性[1] 已成为最重要的结构材料之一、[2]、[3] 。不过、CFRP 层压板容易受到脱层的影响，这是因为纤维增强层和聚合物基质引起的厚度不匹配特性。一旦发生分层，CFRP 结构的刚度和强度可能会显著降低、[4] 最终导致在使用寿命期间发生严重故障。特别是随着信息化和智能化的发展，具有自诊断和自修复功能的 CFRP 越来越受到人们的关注[5] 。在此基础上，开发具有分层裂纹原位自感应和自修复功能的层状 CFRP 也很重要。

In the early stages of damage, timely sensing of damage and subsequent maintenance or self-healing can improve the integrity of structure and avoid unexpected failures [5], [6]. Due to the conductivity of carbon fibers, Thorn et al. embedded a self-healing phenoxy film into CFRP and achieved in-situ damage sensing and self-healing by monitoring the thickness direction resistance of the laminates [7]. However, due to the insulation nature of the interleaved phenoxy film, sensing signals cannot be obtained during the initial delamination period, which inhibits electrons from passing through the thickness of the laminate [7]. In recent years, damage self-sensing technology based on embedded sensing elements has received increasing attention, such as carbon nanotube (CNT) network sensors [8], [9], [10], [11], which exhibit both structural enhancement and damage monitoring functions [12], [13], [14], [15]. According to literature reports, CNT network sensors can be introduced into fiberglass reinforced plastics (GFRPs) or CFRPs in the form of buckypapers (BPs) [13], [16], [17] or grids [18], [19], [20], suggesting that for CFRP and GFRP, the relative resistance change (ΔR/R₀%) at the delamination initiation stage can reach 1.7–12.2% [18], [19], [21] and 10–100% [13], [17], [20], respectively. Meanwhile, these CNT networks can significantly improve strength by 38–60% [18], [21] and toughness by 0–25% [17], [18], [20]. Apparently, the CNT network is an ideal embedded sensor for achieving self-sensing of laminate damage, but the monitoring sensitivity for delamination initiation in highly conductive CFRPs still needs to be improved. Therefore, it is necessary to design a conductive network with a reasonable conductive path density [22], which is sensitive to cracks, especially for CFRPs with insulated healing agents.
在损坏的早期阶段，及时感知损坏并进行后续维护或自我修复可提高结构的完整性，避免意外故障[5]、[6].由于碳纤维的导电性，Thorn 等人在 CFRP 中嵌入了自修复苯氧基薄膜，并通过监测层压板的厚度方向电阻[7] 实现了原位损伤传感和自修复。然而，由于交错苯氧基薄膜的绝缘性质，在最初的分层期间无法获得传感信号，这就抑制了电子穿过层压[7] 厚的层压[7] 。近年来，基于嵌入式传感元件的损伤自感应技术受到越来越多的关注，例如碳纳米管（CNT）网络传感器[8] 、[9], [10]、[11]、[12]，[13]、[14], [15]. 根据文献报道，CNT 网络传感器可以以降压纸（BP）[13] 的形式引入玻璃纤维增强塑料（GFRP）或 CFRP 中、[16]、[17] 或网格 [18] 、[19], [20]、表明对于 CFRP 和 GFRP，分层开始阶段的相对电阻变化 (ΔR/R₀%) 可达到 1。7-12.2% [18], [19]、[21] 和 10-100% [13] 、[17], [20], 分别。同时，这些 CNT 网络可将强度显著提高 38-60% [18] 、[21] 和韧性降低 0-25% [17] 、[18], [20] 。显然，CNT 网络是实现层压板损伤自感的理想嵌入式传感器，但对高导电性 CFRP 中分层起始的监测灵敏度仍有待提高。因此，有必要设计一种具有合理导电路径密度[22] 的导电网络，该网络对裂纹具有灵敏度，尤其适用于具有绝缘愈合剂的 CFRP。

In addition, once cracks appear, they can be repaired by introducing external healing agents into the polymer matrix or developing a healable matrix containing reversible bonds [23], [24], [25]. Among the proposed approaches, introducing poly (ethylene-co-methacrylic acid) (EMAA) into CFRPs is considered a promising method for crack repairing due to its low melting point (T_m) and good compatibility with epoxy resin [26], [27], [28]. Meanwhile, EMAA can be flexibly incorporated into CFRPs or GFRPs in various forms, such as particles [29], membranes [30], meshes [31], stitches [32] and woven z-filaments [33]. Moreover, an attractive advantage of EMAA is that it can covalently bind to an epoxy resin matrix, resulting in a special pressure conduction mechanism and excellent toughening effect [34], [35], [36], [37]. While, some works reported that EMAA with low strength/ stiffness will significantly reduce the flexural strength [30], [38], in-plane strength [27], [39] and interlaminar shear strength (ILSS) [29], [30], [32], [40], [41] of FRP laminates. But hopefully, due to the excellent strength and stiffness of CNTs, literatures reported that CNTs can be used to improve the mechanical properties of EMAA [30], [42]. Simultaneously, highly conductive CNTs exhibit excellent Joule heating effect, which can be developed for in-situ self-healing of internal cracks in CNTs modified composites [43], [44], [45].
此外，一旦出现裂缝，可通过在聚合物基质中引入外部愈合剂或开发包含可逆键的可愈合基质[23] 来修复、[24], [25].在提出的方法中在 CFRP 中引入聚（乙烯-共甲基丙烯酸）（EMAA）被认为是一种很有前景的裂缝修复方法，因为其熔点低（T_m）以及与环氧树脂 [26] 的良好兼容性、[27], [28].同时，EMAA 可以以各种形式灵活地融入 CFRP 或 GFRP 中、例如颗粒[29], 膜[30]、网格 [31]、缝合线[32] 和编织的 z-长丝 [33] 。此外，EMAA 的一个诱人优势在于它能与环氧树脂基质共价结合，从而产生特殊的压力传导机制和出色的增韧效果[34] 、[35], [36]、[37].一些研究报告指出，强度/刚度较低的 EMAA 会显著降低挠曲强度[30] 、[38], 平面内强度 [27]、[39] 和层间剪切强度（ILSS）[29] 、[30]、[32], [40]、[41] 玻璃钢层压板。但是，由于 CNT 具有优异的强度和刚度，文献报道称 CNT 可用于改善 EMAA [30] 的机械性能、[42].同时，高导电性 CNT 表现出卓越的焦耳加热效应，可用于 CNT 改性复合材料内部裂缝的原位自愈合[43][43] 、[44], [45].

Thus, the focus of this work is to achieve in-situ self-sensing and self-healing of CFRP by monitoring the thickness resistance during the delamination process and using electrical-heating method. Two sandwich interleaves consisting of CNTs, EMAA and epoxy/epoxy columns were prepared, in which, EMAA and CNTs can achieve complementary mechanical properties and both can form good interface bonding with epoxy resin. Also, CNTs can form a continuously conductive networks at the interlaminar interface, thereby connecting the conductive paths in the thickness direction of CFRP, and ultimately resistance monitoring and electrical-heating self-healing can be achieved. Moreover, epoxy fine columns possess shear resistance. Firstly, the self-healing efficiency of the two interleaves were evaluated by tensile testing the interleaves themselves. Then, in-situ self-sensing of delamination as well as self-healing of ILSS of the interleaved CFRP were investigated systematically. Moreover, how the two interleaves affect the ILSS and flexural strength of the CFRP was comprehensively compared. Finally, the failure mechanisms and crack self-healing effect was understood by X-ray CT images.
因此，这项工作的重点是通过监测分层过程中的厚度电阻和使用电加热方法，实现 CFRP 的原位自传感和自修复。制备了两种由 CNTs、EMAA 和环氧树脂/环氧树脂柱组成的夹层交织物，其中，EMAA 和 CNTs 可实现机械性能互补，并都能与环氧树脂形成良好的界面粘合。CNT 还能在层间界面形成连续导电网络，从而连接 CFRP 厚度方向上的导电路径，最终实现电阻监测和电热自愈。此外，环氧树脂细柱还具有抗剪性能。首先，通过对交织层本身进行拉伸测试，评估了两种交织层的自修复效率。然后，对交错 CFRP 的分层原位自感应和 ILSS 自修复进行了系统研究。此外，还综合比较了两种交错层如何影响 CFRP 的 ILSS 和抗弯强度。最后，通过 X 射线 CT 图像了解了其失效机理和裂纹自愈合效果。

2. Experimental 2.实验

2.1. Materials 2.1 材料

EMAA pellets (Model 426628) was obtained from Sigma-Aldrich, with a weight fraction of methacrylic acid (with carboxyl groups: –COOH) about 15%, a T_m of 76 °C and a melt flow index of 60 g/10 min at 190 °C. Amino-functionalized (–NH₂) CNTs in Dimethylformamide suspension were purchased from Times Nano Co. (PR China), where the content of NH₂-CNTs is about 2.44 wt%. NH₂-CNTs are 8–15 nm in diameter and 30–50 μm in length, with a weight fraction of –NH₂ within dry CNTs about 0.45%. The epoxy resin used in this work was diglycidyl ether of bisphenol A (DGEBA, Araldite® LY1564, Huntsman) mixed with a primary amine cure agent (DMDC, Aradur® 2954, Huntsman) at the stoichiometric ratio of 100:35 w/w, and the glass transition temperature is 140 °C. Laminates were made using above epoxy resin and a unidirectional carbon fiber fabric (Shenying Carbon Fiber co., PR China), with an areal density of 300 g/m².
EMAA 颗粒（型号 426628）购自 Sigma-Aldrich，甲基丙烯酸（含羧基：-COOH）的重量分数约为 15%，T_m 为 76 °C，190 °C 时的熔体流动指数为 60 g/10 min。二甲基甲酰胺悬浮液中的氨基官能化（-NH₂ ）CNT 购自时代纳米（中国）有限公司，其中 NH₂-CNT 的含量约为 2.44 wt%。NH₂-CNT 的直径为 8-15 nm，长度为 30-50 μm，干 CNT 中 -NH₂ 的重量分数约为 0.45%。这项工作中使用的环氧树脂是双酚 A的二缩水甘油醚（DGEBA，Araldite® LY1564，亨斯迈）与伯胺固化剂（DMDC，Aradur® 2954，亨斯迈）以 100：35 w/w，玻璃转变温度为 140 ℃。层压板由上述环氧树脂和单向碳纤维织物（中国神鹰碳纤维有限公司）制成，单向碳纤维织物的平均密度为 300 g/m²。

2.2. Preparation 2.2.准备工作

Firstly, porous EMAA membranes were prepared by hot-pressing with a thickness about 90 μm, a porosity of 22.7% and a distance of 1.60 mm between the centers of two adjacent pores (see in Fig. 1a, the detailed preparation can be seen in Section 1 of Supporting Information). Then, a porous CNT layer (with periodic circular holes) was made by spraying CNT suspension on the porous EMAA membrane with a total CNT areal density of 10 g/m². After that, the above CNT/EMAA films were purified with nitric acid and deionized water, followed by infiltrating with epoxy resin and cured (60 °C for 4 h and post-cured at 150 °C for 2 h). Finally, two different sandwich interleaves with periodic neat epoxy column arrays were obtained, as shown in Fig. 1b, where epoxy fine columns (0.8 mm in diameter) have higher strength and modulus than EMAA, which act like z-pins and can improve the shear resistance of the interleaf. One interleaf consists of two face-layers of CNT/epoxy and a core-layer of EMAA/epoxy (named CEC, there is a small amount of CNTs on the surface of EMAA), while the other consists of two face-layers of EMAA/epoxy and a core-layer of CNT/epoxy (named ECE). Similarly, tensile specimens of CEC and ECE were prepared according to ASTM D1708 standard (shown in Fig. 1c). To compare, neat porous EMAA membrane (without CNTs) was also infiltrated with epoxy to prepare EMAA/EP specimens. The weight fractions of CNT + EMAA in EMAA/EP, CEC and ECE specimens are 18.4%, 17.3% and 23.9%, respectively.
1a、详细的准备工作可参见的第 1 节。dl-uid="6"> 支持信息）。然后，在多孔 EMAA 膜上喷洒 CNT 悬浮液，制成多孔 CNT层（带有周期性圆孔），CNT 总密度为 10 g/m²。然后，用硝酸和去离子水净化上述 CNT/EMAA 薄膜，再用环氧树脂浸润并固化（60 °C 4 小时，150 °C 2 小时）。最后，如图 1b所示，获得了两种不同的夹层互叶，其中环氧细柱（直径 0.8 毫米）的强度和模量均高于 EMAA，其作用类似于 Z 形销，可提高互叶的抗剪性。一种夹层由两层 CNT/ 环氧树脂面层和一层 EMAA/ 环氧树脂芯层组成（命名为 CEC，EMAA 表面有少量 CNT），另一种由两层 EMAA/ 环氧树脂面层和一层 CNT/ 环氧树脂芯层组成（命名为 ECE）。同样，根据 ASTM D1708 标准制备了 CEC 和 ECE 拉伸试样（如图 1c 所示）。为了进行比较，还用环氧树脂浸润了纯多孔 EMAA 膜（不含 CNT），以制备 EMAA/EP 试样。在 EMAA/EP、CEC 和 ECE 试样中，CNT + EMAA 的重量分数分别为 18.4%、17.3% 和 23.9%。

Carbon fiber fabric infiltrated with epoxy (The detailed process is provided in Section 1 of Supporting Information) was cut and laid up one by one to form unidirectional laminates ([0°]₆ for short beam shear (SBS) test and [0°]₁₀ for bending test). The uncured CEC or ECE interleaf was respectively introduced into the middle interfaces of the CFRP laminates. Meanwhile, base CFRP without interleaf was also fabricated for comparison. All laminates were cured in a hot-press with the same curing temperature as afore-mentioned and accompanied by a pressure of 0.7 MPa. The fiber volume fractions of the cured laminates are about 53%, with thicknesses of 2.04 ± 0.03 mm for SBS specimens and 3.40 ± 0.04 mm for flexural specimens, respectively.
用环氧树脂浸润碳纤维织物（详细过程见 Section 1 中的支撑信息）逐一切割和铺设，形成单向层压板（[0°]₆ 用于短梁剪切（SBS）试验，[0°]₁₀ 用于弯曲试验）。未固化的 CEC 或 ECE 中间膜分别被引入 CFRP 层压板的中间界面。同时，为了进行比较，还制作了不含中间膜的 CFRP 基材。所有层压板均在热压机中固化，固化温度与前述相同，固化压力为 0.7 兆帕。固化层压板的纤维体积分数约为 53%，SBS 试样的厚度为 2.04 ± 0.03 毫米，挠曲试样的厚度为 3.40 ± 0.04 毫米。

2.3. Characterization 2.3 特性

According to ASTM D1708 standard, the mechanical–electrical responses and self-healing ability of CEC and ECE interleaves were evaluated by uniaxially tension with a loading rate of 2 mm/min, as shown in Fig. 1c. The electrodes were set at the opposite ends of the specimens to avoid affecting the mechanical properties. The electrode areas were polished with fine sandpaper, then coated with conductive silver glue and cured at 60 °C for 5 h. Copper wires was soldered to the cured conductive silver glue to ensure the stability of the electrodes. Simultaneously, the other end of the copper wires was connected to a Keithley 2450 digital multimeter to record the static electrical resistance (R₀) and dynamic resistance (R) during the loading process. Once the load reaches its maximum and starts to decline, the test is stopped immediately. In order to in-situ repair the crack, the fractured specimens were clamped to make the fractured surfaces contact with each other, followed by electrical-heating to 150 °C and holding for 1 h. The power supply is MP3020D (MAISHENG) and some temperature fields were recorded by the FLIR ONE infrared camera. Meanwhile, the fractured EMAA/EP specimens were heated in an oven for 1 h (at 150 °C) to achieving self-healing. The healed specimens were tested again to evaluate the recovery of the tensile properties and the damage self-sensing ability. The self-healing efficiency was calculated by dividing the self-healing value from the original value.
根据 ASTM D1708 标准，以 2 mm/min 的加载速率单轴拉伸评估了 CEC 和 ECE 交织物的机械电气响应和自愈能力，如图 1c 所示。电极设置在试样的两端，以避免影响机械性能。用细砂纸打磨电极区域，然后涂上导电银胶，在 60 °C 下固化 5 h 。铜线被焊接到固化的导电银胶上，以确保电极的稳定性。同时，铜线的另一端连接到吉时利 2450 数字万用表，以记录加载过程中的静态电阻（R₀ ）和动态电阻（R ）。一旦载荷达到最大值并开始下降，测试就会立即停止。为了对裂纹进行原位修复，将断裂的试样夹紧，使断裂面相互接触，然后电加热至 150 °C，并保持 1 小时。同时，将断裂的 EMAA/EP 试样在烤箱中加热 1 小时（150 °C）以实现自愈合。对愈合后的试样再次进行测试，以评估其拉伸性能的恢复情况和损伤自感能力。自愈效率的计算方法是将自愈值除以原始值。

According to ISO 14130 standard, specimens for SBS tests were set as 20.4 mm × 10.2 mm, with a span length of 10.2 mm and a loading rate of 1 mm/min (see in Fig. 1d). Similarly, the real-time R was continuously recorded during the SBS testing. The electrodes were set on the upper and bottom surfaces of the specimens. The testing was stopped when the load reached its maximum. Then, the delaminated SBS specimens were clamped (The clamping system is only necessary to put the surfaces to be healed in contact) and healed at 150 °C for 1 h by using electrical-heating, followed by re-testing to obtain the first healed ILSS and corresponding real-time R. Once again, the damaged specimens were healed and tested, and finally the second healed ILSS and real-time R were obtained. To obtain the evolution of defect or crack density, the SBS specimens before and after damage were scanned by an X-ray CT scanner (YXLON FF85, Germany).
根据 ISO 14130 标准，SBS 试验的试样设定为 20.4 mm × 10.2 mm，跨长为 10.2 mm，加载速率为 1 mm/min（见图 1d）。同样，在 SBS 测试期间连续记录实时 R 。电极设置在试样的上下表面。当载荷达到最大值时，测试停止。然后，将分层 SBS 试样夹紧（夹紧系统只需使待愈合表面接触即可），在 150 °C 下通过电加热愈合 1 小时，然后重新测试，以获得首次愈合的 ILSS 和相应的实时 R。再次对受损试样进行愈合和测试，最后得到第二次愈合的 ILSS 和实时 R 。为了获得缺陷或裂纹密度的变化情况，用 X 射线 CT 扫描仪（YXLON FF85，德国）扫描了损伤前后的 SBS 试样。

Finally, a three-point bending test was conducted according to ASTM D7264 standard to evaluate the effect of CEC or ECE interleaves on the strength of the CFRP laminates. The specimens were 130.6 mm long and 13 mm wide, and the span length and loading rate were set as 108.8 mm and 1 mm/min, respectively, as seen in Fig. 1e. In each case, five specimens were tested to demonstrate the repeatability of experimental results. In addition, microscopic views of some fractured surfaces were observed by the FESEM machine (MIRA3 TESCAN, Czech Republic).
最后，根据 ASTM D7264 标准进行了三点弯曲试验，以评估 CEC 或 ECE 夹层对 CFRP 层压板强度的影响。如 Fig.在每种情况下，都测试了五个试样，以证明实验结果的可重复性。此外，还使用 FESEM 机器（MIRA3 TESCAN，捷克共和国）观察了一些断裂表面的微观视图。

3. Results and discussion
3.结果和讨论

3.1. Self-sensing and self-healing ability of the interleaves themselves
3.1.交错线本身的自感应和自修复能力

The initial tensile stress–strain curves of the CEC and ECE interleaves are respectively given in Fig. 2a and 2b (Result of EMAA/EP is given in Fig. S1 of Supporting Information), suggesting that the stress–strain curves show a nonlinear response, with small load drops associated to the developments of cracks in the specimen. Fig. 2c-d present the obtained tensile strength and modulus of EMAA/EP, CEC and ECE specimens. When compared to the EMAA/EP, the original tensile strength and modulus of CEC (50.7 MPa and 1.17 GPa) are improved by 15.0% and 10.4%, and the gains for ECE (38.2 MPa and 1.03 GPa) are −13.4% and −2.8%, respectively. This means that the tensile properties of CEC are better than those of ECE, as the former contains more CNTs and epoxy. After healing the fractured CEC and ECE specimens, the obtained tensile stress–strain curves are presented in Fig. 2e and 2f, which show that the fracture loads are decreased somewhat. Also, the self-healing efficiencies of tensile strengths of EMAA/EP, CEC and ECE are respectively obtained as 72.3%, 67.9 % and 69.1 %, which is higher than that reported in the literature (only 45.7–52.6%) [41]. And the self-healing efficiencies of tensile moduli are respectively calculated as 91.5%, 86.3 % and 90.3 %. That is the CEC and ECE possess good electrical-thermal self-healing ability to their macro-cracks. Also, because the healed area is mainly filled with EMAA, which becomes the weakest part of the specimens, thus, the healed strength and modulus are less than the original values. Therefore, the self-healing efficiency is less than 100%.
Fig.2a 和 2b（EMAA/EP 的结果见图。支持信息的 S1）、这表明应力-应变曲线显示了非线性响应，试样中裂纹的发展与小的载荷下降有关。图 2c-d 显示了 EMAA/EP、CEC 和 ECE 试样获得的拉伸强度和模量。与 EMAA/EP 相比，CEC 的原始拉伸强度和模量（50.7 MPa 和 1.17 GPa）分别提高了 15.0% 和 10.4%，ECE 的提高幅度（38.2 MPa 和 1.03 GPa）分别为 -13.4% 和 -2.8%。这说明 CEC 的拉伸性能优于 ECE，因为前者含有更多的 CNT 和环氧树脂。断裂的 CEC 和 ECE 试样愈合后，得到的拉伸应力-应变曲线见图 2e 和 2f，表明断裂载荷有所降低。此外，EMAA/EP、CEC 和 ECE 拉伸强度的自愈率分别为 72.3%、67.9 % 和 69.1 %，高于文献报道（仅为 45.7-52.6 %）[41] 。经计算，拉伸模量的自愈率分别为 91.5%、86.3% 和 90.3%。这说明 CEC 和 ECE 对其宏观裂纹具有良好的电热自愈合能力。此外，由于愈合区域主要由 EMAA 填充，而 EMAA 成为试样最薄弱的部分，因此愈合后的强度和模量均小于原始值。因此，自愈合效率低于 100%。

Fig. 2a and 2b also give the ΔR/R₀%-strain curves of the CEC and ECE specimens during the original tests, in which, the ΔR/R₀% change trend could be divided into three stages, i.e., nearly keep unchanged (stage I), slowly and steadily increasing stage (II) and rapid increasing stage (III). At stage I, the ΔR/R₀% nearly keeps unchanged due to small linear elastic deformation and Poisson’s ratio effect. As shown in Fig. 2g, before loading, CNTs in the CEC or ECE specimens are wrapped in epoxy or EMAA and intertwined to form a good conductive network, which is slightly affected by the initial small deformation stage. At stage II, the ΔR/R₀% changes slowly and steadily (less than 1%), and this is because the increase in relative distance between CNTs can lead to a corresponding increase in tunnel resistance or disconnection of local conductive paths, as shown in Fig. 2h. As for the stage III, the ΔR/R₀% increases rapidly due to the disconnection or fracture of CNTs, which is induced by the fracture of the specimens, as shown in Fig. 2i.
Fig.2a 和 2b 还给出了 CEC 和 ECE 试样在原始测试期间的 ΔR/R₀% 应变曲线、其中，ΔR/R₀% 变化趋势可分为三个阶段，即ΔR/R₀% 变化趋势。e.,几乎保持不变（第 I 阶段）、缓慢稳步上升阶段（第 II 阶段）和快速上升阶段（第 III 阶段）。在第一阶段，由于线性R/R₀% 的弹性变形和泊松比效应较小，ΔR/R₀% 几乎保持不变。如 Fig.2g，在加载前，CEC 或 ECE 试样中的 CNT 被环氧树脂或 EMAA 包裹并交织在一起，形成良好的导电网络，这在最初的小变形阶段会受到轻微影响。在第二阶段，ΔR/R₀% 变化缓慢而稳定（小于 1%）、2h. 至于第 III 阶段，由于 CNT 的断开或断裂，ΔR/R₀% 迅速增加、如 Fig.2i.

As for the healed CEC and ECE specimens, the obtained ΔR/R₀%-strain curves also given in Fig. 2e and 2f, respectively. Where, the change trend of ΔR/R₀% can also be divided into an invariant stage (I), a steady-state increase stage (II) and rapid increase stage (III), respectively. At stage II, the ΔR/R₀% changes about 6% for the CEC and 16% for the ECE, and the latter is larger due to containing more insulated EMAA. After healing, some CNTs are reconnected by the re-bonding of EMAA, as shown in Fig. 2j, and the healed area is filled with EMAA, resulting in a higher contact resistance between CNTs, thus the variation of ΔR/R₀% at stage II after healing (6–16%) is greater than that at the stage II during the original loading (about 1%). Similarly, at the stage III, the ΔR/R₀ grows rapidly due to the quickly disconnection of CNTs and the fracture of the specimens. Therefore, the obtained ΔR/R₀%-strain curves demonstrate that the CEC and ECE possess in-situ damage self-sensing abilities. Moreover, the damaged-healed specimens exhibit better self-sensing sensitivity of damage.
至于愈合的 CEC 和 ECE 试样，得到的 ΔR/R₀% 应变曲线也分别在图 2e 和 2f 中给出。2e 和 2f。其中，ΔR/R₀% 的变化趋势也可分别分为不变阶段（I）、稳态上升阶段（II）和快速上升阶段（III）。在Ⅱ阶段，CEC 的ΔR/R₀% 变化约为 6%，ECE 的变化约为 16%，后者由于含有更多绝缘的 EMAA 而变化更大。如 Fig.2j ，愈合区域充满了 EMAA，导致 CNT 之间的接触电阻增大，因此愈合后第二阶段的 ΔR/R₀% 变化（6-16%）大于原始加载时第二阶段的变化（约 1%）。同样，在第 III 阶段，由于 CNT 快速断开和试样断裂，ΔR/R₀ 增长迅速。因此，获得的 ΔR/R₀% 应变曲线表明，CEC 和 ECE 具有原位损伤自感能力。此外，损伤愈合后的试样表现出更好的损伤自感灵敏度。

Fig. 3a gives the fractured CEC specimen (for example), infrared temperature field under healing, and the healed specimen, respectively. It shows that the fractured CEC can be completely self-healed by Joule heating at about 150 °C. As shown in Fig. 3b, carboxyl groups within molten EMAA react with hydroxyl/amine groups in epoxy/CNT-NH₂ during the healing process, where superheated water micro-bubbles occur [35], [46] and which force molten EMAA to flow into the cracks of the specimens, thereby repairing the damage. Fig. 3c presents the fractured SEM cross-section of the CEC after the healing (the second fracture), which shows an obvious sandwich structure similar to Fig. 1b. A zoomed view of CNT/EP layer in Fig. 3c is given in Fig. 3d, indicating that CNTs are well infiltrated with epoxy and some CNTs are pulled out or broken, which will consume more energy and help increase the tensile performance. Besides, a zoomed view of EMAA/EP layer in Fig. 3c is presented in Fig. 3e, and some wave-like micro-pores are observed in the contact area between EMAA and epoxy, which are caused by water micro-bubbles during the healing process (see in Fig. 3b). This suggests that the pressure transfer mechanism of EMAA is still effectively achieved in the composite materials composed of EMAA, epoxy, and CNTs. SEM images of EMAA/EP and ECE is given in Fig. S2 of Supporting Information.
图 3a 分别给出了断裂的 CEC 试样（例如）、愈合时的红外温度场和愈合后的试样。它表明，断裂的 CEC 可在约 150 °C 的焦耳加热下完全自愈。如 Fig.3b 熔融 EMAA 中的羧基与环氧树脂/CNT-NH₂ 中的羟基/胺基在愈合过程中发生反应，过热的水产生微气泡[35] 、[46] 并迫使熔化的 EMAA 流入试样的裂缝中，从而修复损伤。Fig.3c 展示了 CEC 愈合（第二次断裂）后的断口 SEM 截面图，显示出明显的夹层结构，与图 1b 类似。图 3c 中的 CNT/EP 层放大图见图 3。3d，表明 CNT 与环氧树脂充分浸润，部分 CNT 拔出或断裂，这将消耗更多能量，有助于提高拉伸性能。此外，图中 EMAA/EP 层的放大图也显示了这一点。 3c 在 Fig.3e，在 EMAA 和环氧树脂的接触区域观察到一些波状微孔，这是愈合过程中水微泡造成的（见 Fig.）这表明在由 EMAA、环氧树脂和 CNT 组成的复合材料中，EMAA 的压力传递机制仍然有效。EMAA/EP 和 ECE 的扫描电镜图像见 S2 的支持信息。

3.2. In-situ self-sensing and self-healing the delamination crack
3.2.分层裂缝的原位自感应和自修复

3.2.1. In-situ self-sensing the delamination crack
3.2.1 原位自感应分层裂缝

The SBS load–displacement (δ) and ΔR/R₀%-δ curves of the base, CEC and ECE interleaved CFRPs after two damage-healing circles are indicated in Fig. 4a-g. The first derivative curves of ΔR/R₀%-δ (d(ΔR/R₀%)/dδ-δ) responses are also plotted in Fig. 4a-g, which highlights the ΔR/R₀% change in slope and helps to identify the initiation and propagation of delamination cracks. The first derivative of ΔR/R₀%, d(ΔR/R₀%)/dδ, represents the change magnitude in relative resistance variation per unit of displacement. A significant pulse on the d(ΔR/R₀%)/dδ-δ curves indicates a jump of the ΔR/R₀%. According to the inflection on the ΔR/R₀%-δ curves or jump points on the d(ΔR/R₀%)/dδ-δ curves, the change trend of damage process can be roughly divided into four stages, i.e., linear stage (I), accumulation of matrix microcrack (stage II), initiation and steady-state propagation of delamination crack (stage III), and rapid/multi- delamination and failure stage (IV). During the stage I, both ΔR/R₀% and d(ΔR/R₀%)/dδ nearly keep unchanged due to the small linear deformation and the complete conductive network in CFRPs. When entering the stage II, the deformation continues to increase, which on the one hand increases the tunnel resistance [21] and contact resistance, and on the other hand leads to microcracks in the matrix. Thus, both ΔR/R₀% and d(ΔR/R₀%)/dδ increase obviously and nonlinearly. Meanwhile, the stage II can also be seen as the accumulation of matrix microcracks. At the end of the stage II, the accumulation of matrix microcracks forms the initiation of main delamination crack (Also, the deformation reaches its critical value), therefore, the d(ΔR/R₀%)/dδ jumps significantly (While the ΔR/R₀% tends to deflect, because of the fracture of conductive paths) due to the initiation of main delamination crack (Breakage of local conductive paths). Then, the delamination crack propagates relatively stably (stage III). However, bending loading leads to the closure of the delaminated surfaces, and the fractured conductive paths form new conductive paths again, resulting in a slow increase in ΔR/R₀% while the d(ΔR/R₀%)/dδ tends to decrease. Finally, at stage IV, the main delamination crack propagates quickly and some adjacent minor delamination cracks will occur, which leads to a stepwise change in ΔR/R₀% and a local jump in d(ΔR/R₀%)/dδ. For the base CFRP (see in Fig. 4g), the changes of ΔR/R₀% and d(ΔR/R₀%)/dδ from I to III stages are similar to those of the CEC/ECE CFRPs, but the ΔR/R₀% decreases during the IV stage. This is because more exposed carbon fibers will form more conductive paths, which decrease the interfacial contact resistance significantly.
基座的 SBS 载荷-位移（δ ）和 ΔR/R₀%-δ 曲线、Fig.4-g。ΔR/R₀%-δ (d(ΔR/R₀%)/dδ-δ) 的响应也绘制在图 4 中。4g ，突出显示了 ΔR/R₀% 的斜率变化，有助于识别分层裂纹的产生和扩展。ΔR/R₀% 的一阶导数 d(ΔR/R₀%)/dδ 表示每单位位移的相对电阻变化幅度。d(ΔR/R₀%)/dδ- 上的明显脉冲δ 曲线表示 ΔR/R₀% 的跳跃。根据 ΔR/R₀%-δ 曲线上的拐点或 d(ΔR/R₀%)/dδ-δ 曲线上的跳跃点、损坏过程的变化趋势可大致分为四个阶段，即e.,线性阶段（I）、基体微裂纹的积累阶段（II）、分层裂纹的产生和稳态扩展阶段（III）以及快速/多重分层和破坏阶段（IV）。在阶段 I、ΔR/R₀% 和 d(ΔR/R₀%)/dδ 几乎保持不变，这是因为 CFRP 的线性变形较小，且具有完整的导电网络。进入第二阶段后，变形继续增大，一方面增加了隧道电阻[21] 和接触电阻，另一方面导致基体出现微裂缝。因此ΔR/R₀% 和 d(ΔR/R₀%)/dδ 明显非线性增加。同时，第二阶段也可以看作是基体微裂纹的积累。在第二阶段结束时，基体微裂纹的积累形成了主分层裂纹的起始（同时，变形达到临界值），因此、d(ΔR/R₀%)/dδ 显著跃升（而 ΔR/R₀% 趋于偏转、由于主分层裂纹的产生（局部导电路径断裂），导电路径会断裂。）然后，分层裂纹相对稳定地扩展（第三阶段）。然而，弯曲荷载会导致分层表面闭合，断裂的导电路径会重新形成新的导电路径、导致 ΔR/R₀% 而 d(ΔR/R₀%)/dδ 则呈下降趋势。最后，在第 IV 阶段，主分层裂纹迅速扩展，并出现一些相邻的次要分层裂纹、这导致ΔR/R₀% 发生阶跃变化，d(ΔR/R₀%)/dδ 出现局部跳跃。对于基础 CFRP（见图。 4g）、R/R₀% 和 d(ΔR/R₀%)/d 的变化。uid="76">R/R₀%)/dδ 从 I 到 III 阶段与 CEC/ECE CFRP 相似、但在 IV 阶段，ΔR/R₀% 有所下降。这是因为更多暴露在外的碳纤维将形成更多导电路径，从而显著降低界面接触电阻。

Besides, Fig. 4h gives the R in the thickness direction of CEC/ECE interleaved CFRPs during the two damage-healing processes. It shows that the R of CEC interleaved CFRP is about an order of magnitude smaller than that of ECE interleaved CFRP. Also, the R will increase after damage (delamination fracture), and it once again decreases when the specimens are healed. Each healed R is slightly higher than the initial values, because the healed area contains more insulated EMAA. Therefore, from Fig. 4a, 4d and 4 g, it can be seen that the CEC/ECE interleaved CFRPs and the base CFRP all exhibit significant self-sensing ability towards damage or damage evolution, but the damage evolution characteristics of the first two are more obvious (Fig. 4a and 4d). Moreover, the healed CEC/ECE interleaved CFRPs exhibit better stability and high-resolution d(ΔR/R₀%)/dδ signals (Fig. 4b, 4c, 4e and 4f), which can clearly distinguish the initiation and propagation of delamination (stage II), as well as more adjacent delamination when approaching failure (Some jumps of the d(ΔR/R₀%)/dδ during the stage IV).
此外，图 4h 给出了两种损伤愈合过程中 CEC/ECE 交错 CFRP 在厚度方向上的 R 值。结果表明，CEC 交错 CFRP 的 R 比 ECE 交错 CFRP 的 R 小一个数量级。此外，R 在损坏（分层断裂）后会增大，而在试样愈合后会再次减小。每个愈合的 R 都略高于初始值，因为愈合区域包含更多的绝缘 EMAA。因此，从图 4a、4d 和 4g，可以看出 CEC/ECE 交错 CFRP 和基体 CFRP 都对损伤或损伤演变表现出明显的自感能力，但前两者的损伤演变特征更为明显（Fig.4a 和 4d）。此外、此外，愈合后的 CEC/ECE 交错 CFRP 具有更好的稳定性和高分辨率 d(ΔR/R₀%)/dδ 信号（Fig.4b、4c、4e 和 4f），可以清楚地区分分层的开始和扩展（第 II 阶段），以及接近破坏时更多的邻近分层（第 IV 阶段中 d(ΔR/R₀%)/dδ 的一些跳跃）。

3.2.2. In-situ self-healing the delamination crack and the ILSS
3.2.2.原位自修复分层裂纹和 ILSS

After the 1st and 2nd healings, the load-δ curves of CEC/ECE interleaved CFRPs (Fig. 4b-c and 4e-f) exhibit more significant nonlinearity than these of the original specimens (Fig. 4a and 4d). The obtained ILSS from two damage-healing cycles is given in Fig. 4i, indicating that the 1st and 2nd healing efficiencies of ILSS are 93.0% and 91.8% for the CEC interleaved CFRP, and 90.9% and 91.6% for the ECE interleaved CFRP, respectively. This result is consistent with previous study (54–109%) [29], [30], [40]. Namely, the CEC and ECE interleaves show good healing ability to the delamination cracks of CFRP. Besides, comparing with the base CFRP (average ILSS is 46.8 MPa), the original ILSS of the CEC interleaved CFRP and the ECE interleaved CFRP are only decreased by 8.8% and 15.8%, respectively, and the decrease is significantly lower than those of previous reports (decreased by 22–38%) with neat EMAA interleaf [29], [30], [31], [40].
4b-c 和 4e-f）比原始试样（Fig.）Fig. 4i给出了两个损伤愈合周期获得的ILSS，表明CEC交错CFRP的ILSS第一次和第二次愈合效率分别为93.0%和91.8%，ECE交错CFRP的ILSS第一次和第二次愈合效率分别为90.9%和91.6%。这一结果与之前的研究（54-109%）[29] 一致、[30], [40].也就是说，CEC 和 ECE 交织层对 CFRP 的分层裂缝具有良好的愈合能力。此外，与基体 CFRP（平均 ILSS 为 46.8 MPa）相比，CEC 交错 CFRP 和 ECE 交错 CFRP 的原始 ILSS 分别仅降低了 8.8% 和 15.8% ，明显低于以往报告中使用整齐 EMAA 交错叶 [29] 的情况（降低了 22-38%）、[30]、[31], [40].

Fig. 4i also reveals that the self-healing efficiency of ILSS is less than 100%, which can be understood by the 3D X-ray CT images and optical views shown in Fig. 5. As an example, Fig. 5a and 5b display the original and the first damaged 3D X-ray CT reconstruction images of the CEC interleaved CFRP (Results of ECE interleaved CFRP are given in Fig. S3 of Supporting Information), respectively. The initial volume fraction of manufacturing defects is 0.94%, and the defect density increases to 1.35% due to the occurred delamination cracks after the 1st damage. The delamination cracks can be seen obviously, as indicated in Fig. 5b and 5c. After the 1st healed, the middle main delamination crack can be nearly completely healed (with healing interleaf), as seen in Fig. 5d and 5e, but the adjacent minor delamination cracks cannot be healed. Thus, the defect density after the 1st healing is still 0.77%, which is less than the initial defect density of 0.94%. This means that some manufacturing defects near the healing agent zone have been healed. The defects and cracks in other positions cannot be repaired, so there is still a certain defect density (0.77%). Because of the small manufacturing defects and relatively large unhealed cracks, therefore, the healing efficiency of ILSS is less than 100%. Also, due to the increased EMAA in the middle interface (weaker strength), the 2nd delamination mainly occurs at this interface (see in Fig. 5f), which can be healed again (see in Fig. 5g), but the healing efficiency of ILSS further decreases because of more filled EMAA.
Fig.Fig.例如，Fig.5a 和 5b 显示了 CEC 交错 CFRP 的原始图像和首次损坏的 3D X 射线 CT 重建图像（ECE 交错 CFRP 的结果见 Fig. 支持信息的 S3）。制造缺陷的初始体积分数为 0.94%，缺陷密度由于第一次损坏后出现的分层裂纹而增加到 1.35%。图 5b 和 5c 中可以明显看到分层裂纹。第 1 次愈合后，中间的主要分层裂纹几乎可以完全愈合（带有愈合夹层），如图 5d 和 5e，但相邻的次要分层裂纹无法愈合。因此，第一次愈合后的缺陷密度仍为 0.77%，小于初始缺陷密度 0.94%。这说明愈合剂区域附近的一些制造缺陷已经愈合。其他位置的缺陷和裂纹无法修复，因此仍存在一定的缺陷密度（0.77%）。由于制造缺陷较小，而未愈合的裂纹相对较大，因此 ILSS 的愈合效率低于 100%。此外，由于中间界面的 EMAA 增加（强度较弱），第二次分层主要发生在该界面（见图 5）。5f），它可以再次愈合（见Fig.

3.3. Further verification of the effect of CEC/ECE on the CFRP strength
3.3.进一步验证 CEC/ECE 对 CFRP 强度的影响

To further evaluate the effect of the CEC and ECE on the strength of CFRP, Fig. 6a presents the flexural load–displacement curves of the base, CEC and ECE interleaved CFRPs. The ECE interleaved CFRP shows obvious nonlinearity due to more tough EMAA existing at the middle interface, simultaneously accompanied by lower ultimate bearing load. However, the load bearing of the CEC interleaved CFRP is similar to that of the base CFRP. As given in Fig. 6b, the obtained flexural strengths and moduli are 701.2 MPa and 69.0 GPa for the base CFRP, 685.3 MPa and 69.0 GPa for the CEC interleaved CFRP, and 601.0 MPa and 66.5 GPa for the ECE interleaved CFRP, respectively. Compared to the base CFRP, reductions in flexural strength and modulus are obtained as 2.3% and 0.0% for the CEC interleaved CFRP, and 14.3% and 3.6% for the ECE interleaved CFRP, respectively. While, neat EMAA interleaf may decrease the flexural strength of FRPs by 23–44% [30], [38]. Thus, Fig. 6a and 6b demonstrate that the sandwich self-healing interleaf composed of EMAA, CNTs, and epoxy exhibits relatively less negative effect on bending strength, especially for the CEC interleave CFRP, which shows a slight effect on bending strength of CFRP and reduces the ILSS of CFRP only by 8.8% (see in Fig. 4i). This is attributed to the strengthening effect of CNTs and the shear resistance of epoxy columns (see in Fig. 1b). Therefore, the CEC interleaf possesses excellent in-situ self-sensing and self-healing abilities for damage or cracks.
为了进一步评估 CEC 和 ECE 对 CFRP 强度的影响，图 6a 显示了基底、CEC 和 ECE 交错 CFRP 的挠曲载荷-位移曲线。ECE 交错 CFRP 显示出明显的非线性，原因是中间界面存在更坚韧的 EMAA，同时伴随着较低的极限承载负荷。然而，CEC 交错 CFRP 的承载力与基体 CFRP 相似。如图 6b 所示，获得的弯曲强度和模量分别为 701.2 MPa 和 69.0 GPa，CEC 交错 CFRP 为 685.3 MPa 和 69.0 GPa，ECE 交错 CFRP 为 601.0 MPa 和 66.5 GPa。与基体 CFRP 相比，CEC 交错 CFRP 的抗弯强度和模量分别降低了 2.3% 和 0.0%，ECE 交错 CFRP 的抗弯强度和模量分别降低了 14.3% 和 3.6%。[30] 而纯 EMAA 交错层可能会使玻璃纤维增强材料的抗弯强度降低 23-44%、[38].因此，Fig.6a和 6b 表明，由 EMAA、CNT 和环氧树脂组成的夹层自修复夹层对弯曲强度的负面影响相对较小，尤其是 CEC 交错 CFRP，对 CFRP 的弯曲强度影响轻微，仅使 CFRP 的 ILSS 降低了 8.8%（见Fig.）这归功于 CNT 的增强效应和环氧树脂柱的抗剪性（见图 1b）。因此，CEC夹层具有出色的原位自感应和自修复能力，可修复损坏或裂纹。

Fig. 6c-e provide the SEM images of the fractured side-sections of the flexural specimens. For the base CFRP, compressive fracture and slight delamination mainly occur in the compression region (Fig. 6c1-c2). Fig. 6d1-d2 show that a more meandering compression fracture and more delamination cracks occur in the CEC interleaved CFRP. A zoomed view of the middle interface (Fig. 6d2) reveals that the delamination crack propagates inside the CEC interleaf and many CNTs are pulled out from epoxy resin. It is interesting that for the ECE interleaved CFRP (Fig. 6e1), the ultimate failure is mainly due to the delamination of multiple interfaces. And the main delamination occurs at the middle interface and within the ECE interleaf, also accompanied by pulling-out of CNTs (Fig. 6e2). Fig. 6c-e demonstrate that both CEC and ECE interleaves would change the fracture patterns of CFRP, especially for the ECE with weaker EMAA, and the enhanced mismatch between adjacent carbon fiber layers would result in a severe delamination. Therefore, from this perspective, the CEC is also superior to the ECE.
图 6c-e 提供了挠曲试样断裂侧截面的扫描电镜图像。对于基底 CFRP，压缩断裂和轻微分层主要发生在压缩区域（Fig.）Fig.放大中间界面（Fig.有趣的是，对于 ECE 交错 CFRP（Fig.而主要的分层发生在中间界面和 ECE 夹层内，同时还伴随着 CNT 的拔出（图 6e2）。Fig.因此，从这个角度来看，CEC 也优于 ECE。

4. Conclusions 4.结论

This work develops two sandwich interleaves (CEC and ECE) composed of crack-healable EMAA, reinforced and conductive CNTs, and shear-resistant epoxy columns, which show damage self-sensing and self-healing functions, as well as appropriate mechanical properties. The results reveal that the two interleaves exhibit reasonable sensitivity to the initiation and evolution of damage, and the damage self-sensing sensitivity of the healed sample is higher (the ΔR/R₀% variation is about 6.0–16.0%) than the original values (with a variation of ΔR/R₀% about 0.7–1.0%). Simultaneously, the tensile strength and modulus of the interleaves themselves can be healed by 67.9–69.1% and 86.3–90.3%, respectively, and the interleaf with more CNTs possesses higher initial and healed strength/modulus. Also, the CFRP interleaved with CEC and ECE exhibits more obvious characteristics of progressive damage self-sensing. Namely, at the initiation of delamination, the ΔR/R₀% suddenly increases rapidly and the d(ΔR/R₀%)/dδ jumps significantly. During the delamination propagation, the ΔR/R₀% changes in a stepwise manner while the d(ΔR/R₀%)/dδ is relatively stable, occasionally accompanied by a jump in the d(ΔR/R₀%)/dδ induced by delamination near the middle interface. Meanwhile, the 1st and 2nd self-healing efficiencies of ILSS for the interleaved CFRP can reach more than 90%. Moreover, the CEC interleaf shows little negative impact on the ILSS (-8.8%) and flexural strength (-2.3%) of CFRP, which is significantly superior to previous study on neat EMAA interleaf (The gain is −44∼–22%). Therefore, the CEC can be used to prepare CFRP structures with self-sensing and self-healing functions. Of course, for an actual CFRP structure, the easy delamination position can be obtained by numerical simulation according to the service load type, and then the introduction location of the interleaves can be selected.
这项研究开发了两种夹层交织物（CEC 和 ECE），它们由可裂纹愈合的 EMAA、增强型导电 CNT 和抗剪切环氧柱组成，具有损伤自感应和自愈合功能以及适当的机械性能。结果表明，两种交错材料对损伤的发生和演变表现出合理的灵敏度，愈合样品的损伤自感灵敏度（ΔR/R₀% 变化率约为 6.0-16.0%）相比（变化率ΔR/R₀% 约为 0.7-1.0%）。同时，交错层本身的拉伸强度和模量可分别愈合 67.9%-69.1% 和 86.3%-90.3%，且含有更多 CNT 的交错层具有更高的初始强度和愈合强度/模量。此外，与 CEC 和 ECE 交错的 CFRP 还表现出更明显的渐进式损伤自感特征。也就是说，在分层开始时、ΔR/R₀% 突然迅速增加，d(ΔR/R₀%)/dδ 显著跃升。在去层传播过程中、ΔR/R₀% 以逐步变化，而 d(ΔR/R₀%)/dδ 则相对稳定、偶尔伴随着中间界面附近分层引起的 d(ΔR/R₀%)/dδ 跳变。同时，交错 CFRP 的 ILSS 第一和第二自愈效率可达 90% 以上。此外，CEC夹层对CFRP的ILSS（-8.8%）和抗弯强度（-2.3%）的负面影响很小，明显优于之前对纯EMAA夹层的研究（增益为-44∼-22%）。因此，CEC 可用于制备具有自感应和自修复功能的 CFRP 结构。当然，对于实际的 CFRP 结构，可根据使用载荷类型通过数值模拟获得易分层位置，然后选择夹片的引入位置。

CRediT authorship contribution statement
CRediT 作者贡献声明

Qin Ouyang: Methodology, Investigation, Formal analysis, Writing – original draft, Visualization. Ling Liu: Conceptualization, Methodology, Resources, Writing – review & editing, Supervision, Funding acquisition. Zhanjun Wu: Resources.
欧阳钦： 方法学、调查、形式分析、写作-原稿、可视化。刘玲：概念化、方法学、资源、写作--审阅和编辑、指导、资金获取。吴占军：资源。

Declaration of Competing Interest
竞争利益声明

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
作者声明，他们没有任何可能会影响本文所报告工作的已知经济利益或个人关系。

Acknowledgements 致谢

This research is financially supported by the National Natural Science Foundation of China (Grant No: 11972256).
本研究得到国家自然科学基金资助（批准号：11972256）。

Appendix A. Supplementary data
附录 A.补充数据

The following are the Supplementary data to this article:Download: Download Word document (9MB)

Supplementary data 1.

以下是本文的补充数据： Download: Download Word document (9MB)

Supplementary data 1.

Data availability 数据可用性

Data will be made available on request.
数据将应要求提供。

References

[1]
K. Tian, T.E. Tay, V.B.C. Tan, A. Haris, E. Chew, V.N.H. Pham, et al.
Improving the impact performance and residual strength of carbon fibre reinforced polymer composite through intralaminar hybridization
Compos A Appl Sci Manuf, 171 (2023), p. 107590
View PDF View article View in Scopus Google Scholar
[2]
J.L. Liu, J. Zhi, H.L. Wong, E.S. Sugeng, T.E. Tay, V.B.C. Tan
Effect of ply blocking on the high-speed impact performance of thin-ply CFRP laminates
Compos Sci Technol, 228 (2022), p. 109640
View PDF View article View in Scopus Google Scholar
[3]
Y. He, K.e. Duan, L. Yao, J. Tang, J. Zhang, D. Jiang, et al.
Synergistic toughening on CFRP via in-depth stitched CNTs
Compos B Eng, 254 (2023), p. 110605
View PDF View article Google Scholar
[4]
Q. OuYang, X. Wang, L. Liu
High crack self-healing efficiency and enhanced free-edge delamination resistance of carbon fibrous composites with hierarchical interleaves
Compos Sci Technol, 217 (2022), p. 109115
View PDF View article View in Scopus Google Scholar
[5]
Y. Zhao, Q. Liu, R. Li, S.V. Lomov, S.G. Abaimov, K.e. Xiong, et al.
Self-sensing and self-healing smart fiber-reinforced thermoplastic composite embedded with CNT film
J Intel Mat Syst Str, 34 (13) (2023), pp. 1561-1571
Crossref View in Scopus Google Scholar
[6]
M.-H. Yu, J.-S. Lee, H.-S. Kim
Machine learning-based damage sensing and self-healing of carbon fiber/nylon composites via addressable conducting networks
Struct Health Monit, 22 (5) (2023), pp. 3401-3415
Crossref View in Scopus Google Scholar
[7]
T.D.S. Thorn, Y.i. Liu, X. Yao, D.G. Papageorgiou, P. Robinson, E. Bilotti, et al.
Smart and repeatable easy-repairing and self-sensing composites with enhanced mechanical performance for extended components life
Compos A Appl Sci Manuf, 165 (2023), p. 107337
View PDF View article View in Scopus Google Scholar
[8]
D. Xiang, X. Zhang, E. Harkin-Jones, W. Zhu, Z. Zhou, Y. Shen, et al.
Synergistic effects of hybrid conductive nanofillers on the performance of 3D printed highly elastic strain sensors
Compos A Appl Sci Manuf, 129 (2020), p. 105730
View PDF View article View in Scopus Google Scholar
[9]
X. Zhang, D. Xiang, W. Zhu, Y. Zheng, E. Harkin-Jones, P. Wang, et al.
Flexible and high-performance piezoresistive strain sensors based on carbon nanoparticles@polyurethane sponges
Compos Sci Technol, 200 (2020), p. 108437
View PDF View article View in Scopus Google Scholar
[10]
D. Xiang, X. Zhang, Y. Li, E. Harkin-Jones, Y. Zheng, L. Wang, et al.
Enhanced performance of 3D printed highly elastic strain sensors of carbon nanotube/thermoplastic polyurethane nanocomposites via non-covalent interactions
Compos B Eng, 176 (2019), p. 107250
View PDF View article View in Scopus Google Scholar
[11]
X. Zhang, D. Xiang, Y. Wu, E. Harkin-Jones, J. Shen, Y. Ye, et al.
High-performance flexible strain sensors based on biaxially stretched conductive polymer composites with carbon nanotubes immobilized on reduced graphene oxide
Compos A Appl Sci Manuf, 151 (2021), p. 106665
View PDF View article View in Scopus Google Scholar
[12]
S.-J. Joo, M.-H. Yu, W.S. Kim, H.-S. Kim
Damage detection and self-healing of carbon fiber polypropylene (CFPP)/carbon nanotube (CNT) nano-composite via addressable conducting network
Compos Sci Technol, 167 (2018), pp. 62-70
View PDF View article View in Scopus Google Scholar
[13]
G. Yang, X.u. Feng, W. Wang, Q. OuYang, L. Liu, Z. Wu
Graphene and carbon nanotube-based high-sensitive film sensors for in-situ monitoring out-of-plane shear damage of epoxy composites
Compos B Eng, 204 (2021), p. 108494
View PDF View article View in Scopus Google Scholar
[14]
X.F. Sánchez-Romate, Á. Coca, A. Jiménez-Suárez, M. Sánchez, A. Ureña
Crack sensing mechanisms of Mode-II and skin-stringer joints between dissimilar materials by using carbon nanotubes
Compos Sci Technol, 201 (2021), p. 108553
View PDF View article View in Scopus Google Scholar
[15]
S.C. Brown, C. Robert, V. Koutsos, D. Ray
Methods of modifying through-thickness electrical conductivity of CFRP for use in structural health monitoring, and its effect on mechanical properties – a review
Compos A Appl Sci Manuf, 133 (2020), p. 105885
View PDF View article View in Scopus Google Scholar
[16]
J. Li, Z. Zhang, J. Fu, Z. Liang, K.R. Ramakrishnan
Mechanical properties and structural health monitoring performance of carbon nanotube-modified FRP composites: a review
Nanotechnol Rev, 10 (1) (2021), pp. 1438-1468
Crossref View in Scopus Google Scholar
[17]
L. Shen, L. Liu, W. Wang, Y. Zhou
In situ self-sensing of delamination initiation and growth in multi-directional laminates using carbon nanotube interleaves
Compos Sci Technol, 167 (2018), pp. 141-147
View PDF View article View in Scopus Google Scholar
[18]
G. Yang, X.u. Feng, W. Wang, Q. OuYang, L. Liu
Effective interlaminar reinforcing and delamination monitoring of carbon fibrous composites using a novel nano-carbon woven grid
Compos Sci Technol, 213 (2021), p. 108959
View PDF View article View in Scopus Google Scholar
[19]
G. Yang, Q. OuYang, J. Ye, L. Liu
Improved tensile and single-lap-shear mechanical-electrical response of epoxy composites reinforced with gridded nano-carbons
Compos A Appl Sci Manuf, 152 (2022), p. 106712
View PDF View article View in Scopus Google Scholar
[20]
X. Chen, S. Cheng, S. Wang, K. Wen, C. Shi, J. Zhang, et al.
Embedding stretchable, mesh-structured piezoresistive sensor for in-situ damage detection of glass fiber-reinforced composite
Compos Sci Technol, 233 (2023), p. 109926
View PDF View article Google Scholar
[21]
H. Zhang, Y. Liu, M. Kuwata, E. Bilotti, T. Peijs
Improved fracture toughness and integrated damage sensing capability by spray coated CNTs on carbon fibre prepreg
Compos A Appl Sci Manuf, 70 (2015), pp. 102-110
View PDF View article View in Scopus Google Scholar
[22]
D. Xiang, L. Wang, Y. Tang, E. Harkin-Jones, C. Zhao, P. Wang, et al.
Damage self-sensing behavior of carbon nanofiller reinforced polymer composites with different conductive network structures
Polymer, 158 (2018), pp. 308-319
View PDF View article View in Scopus Google Scholar
[23]
A. Cohades, C. Branfoot, S. Rae, I. Bond, V. Michaud
Progress in self-healing fiber-reinforced polymer composites
Adv Mater Interfaces, 5 (17) (2018), p. 1800177
View in Scopus Google Scholar
[24]
M.O.H. Cioffi, A.S.C. Bomfim, V. Ambrogi, S.G. Advani
A review on self-healing polymers and polymer composites for structural applications
Polym Compos, 43 (11) (2022), pp. 7643-7668
Crossref View in Scopus Google Scholar
[25]
S. Islam, G. Bhat
Progress and challenges in self-healing composite materials
Mater Adv, 2 (6) (2021), pp. 1896-1926
View article Crossref View in Scopus Google Scholar
[26]
T. Yang, J. Zhang, A.P. Mouritz, C.H. Wang
Healing of carbon fibre–epoxy composite T-joints using mendable polymer fibre stitching
Compos B Eng, 45 (1) (2013), pp. 1499-1507
View PDF View article View in Scopus Google Scholar
[27]
K. Pingkarawat, C.H. Wang, R.J. Varley, A.P. Mouritz
Mechanical properties of mendable composites containing self-healing thermoplastic agents
Compos A Appl Sci Manuf, 65 (2014), pp. 10-18
View PDF View article View in Scopus Google Scholar
[28]
R.J. Varley, D.A. Craze, A.P. Mouritz, C.H. Wang
Thermoplastic healing in epoxy networks: exploring performance and mechanism of alternative healing agents
Macromol Mater Eng, 298 (11) (2013), pp. 1232-1242
Crossref View in Scopus Google Scholar
[29]
A. Azevedo do Nascimento, F. Fernandez, F. S. da Silva, E. P.C. Ferreira, J.D. D. Melo, A.P. Cysne Barbosa
Addition of poly (ethylene-co-methacrylic acid) (EMAA) as self-healing agent to carbon-epoxy composites
Compos A Appl Sci Manuf, 137 (2020), p. 106016
View PDF View article View in Scopus Google Scholar
[30]
Y.a. Gao, L. Liu, Z. Wu, Z. Zhong
Toughening and self-healing fiber-reinforced polymer composites using carbon nanotube modified poly (ethylene-co-methacrylic acid) sandwich membrane
Compos A Appl Sci Manuf, 124 (2019), p. 105510
View PDF View article View in Scopus Google Scholar
[31]
A.D. Snyder, Z.J. Phillips, J.S. Turicek, C.E. Diesendruck, K.B. Nakshatrala, J.F. Patrick
Prolonged in situ self-healing in structural composites via thermo-reversible entanglement
Nat Commun, 13 (1) (2022), p. 6511
View in Scopus Google Scholar
[32]
T. Yang, Y. Du, Z.M. Li, C.H. Wang
Mechanical properties of self-healing carbon fiber-epoxy composite stitched with mendable polymer fiber
Polym Polym Compos, 22 (3) (2014), pp. 329-336
Crossref View in Scopus Google Scholar
[33]
T.W. Loh, R.B. Ladani, A. Orifici, E. Kandare
Ultra-tough and in-situ repairable carbon/epoxy composite with EMAA
Compos A Appl Sci Manuf, 143 (2021), p. 106206
View PDF View article View in Scopus Google Scholar
[34]
K. Pingkarawat, C.H. Wang, R.J. Varley, A.P. Mouritz
Self-healing of delamination cracks in mendable epoxy matrix laminates using poly[ethylene-co-(methacrylic acid)] thermoplastic
Compos A Appl Sci Manuf, 43 (8) (2012), pp. 1301-1307
View PDF View article View in Scopus Google Scholar
[35]
S. Meure, D.-Y. Wu, S.A. Furman
FTIR study of bonding between a thermoplastic healing agent and a mendable epoxy resin
Vib Spectrosc, 52 (1) (2010), pp. 10-15
View PDF View article View in Scopus Google Scholar
[36]
R.B. Ladani, K. Pingkarawat, A.T.T. Nguyen, C.H. Wang, A.P. Mouritz
Delamination toughening and healing performance of woven composites with hybrid z-fibre reinforcement
Compos A Appl Sci Manuf, 110 (2018), pp. 258-267
View PDF View article View in Scopus Google Scholar
[37]
R.B. Ladani, A.T.T. Nguyen, C.H. Wang, A.P. Mouritz
Mode II interlaminar delamination resistance and healing performance of 3D composites with hybrid z-fibre reinforcement
Compos A Appl Sci Manuf, 120 (2019), pp. 21-32
View PDF View article View in Scopus Google Scholar
[38]
G. de Souza, J.R. Tarpani
Interleaving CFRP and GFRP with a thermoplastic ionomer: the effect on bending properties
Appl Compos Mater, 28 (2) (2021), pp. 559-572
Crossref View in Scopus Google Scholar
[39]
K. Pingkarawat, A.P. Mouritz
Stitched mendable composites: Balancing healing performance against mechanical performance
Compos Struct, 123 (2015), pp. 54-64
View PDF View article View in Scopus Google Scholar
[40]
C.H. Wang, K. Sidhu, T. Yang, J. Zhang, R. Shanks
Interlayer self-healing and toughening of carbon fibre/epoxy composites using copolymer films
Compos A Appl Sci Manuf, 43 (3) (2012), pp. 512-518
View PDF View article View in Scopus Google Scholar
[41]
W. Wang, Q. Ouyang, L. Liu, Z. Wu
Novel nanotube/poly(ethylene-co-methacrylic acid)/epoxy composite adhesive possessing in-situ electrical-heating activated crack healing function
Compos A Appl Sci Manuf, 150 (2021), p. 106599
View PDF View article View in Scopus Google Scholar
[42]
R. Calderón-Villajos, A.J. López, L. Peponi, J. Manzano-Santamaría, A. Ureña
3D-printed self-healing composite polymer reinforced with carbon nanotubes
Mater Lett, 249 (2019), pp. 91-94
View PDF View article View in Scopus Google Scholar
[43]
A. Jiménez-Suárez, J. Martín-González, X.F. Sánchez-Romate, S.G. Prolongo
Carbon nanotubes to enable autonomous and volumetric self-heating in epoxy/polycaprolactone blends
Compos Sci Technol, 199 (2020), p. 108321
View PDF View article View in Scopus Google Scholar
[44]
H. Kim, A.L. Yarin, M.W. Lee
Self-healing corrosion protection film for marine environment
Compos B Eng, 182 (2020), p. 107598
View PDF View article View in Scopus Google Scholar
[45]
Q. Ouyang, L. Liu, Z. Wu
Electrothermally self-healing delamination cracks in carbon/epoxy composites using sandwich and tough carbon nanotube/copolymer interleaves
Polymers, 14 (20) (2022), p. 43133
Google Scholar
[46]
K. Pingkarawat, C. Dell’Olio, R.J. Varley, A.P. Mouritz
Poly(ethylene- co -methacrylic acid) (EMAA) as an efficient healing agent for high performance epoxy networks using diglycidyl ether of bisphenol A (DGEBA)
Polymer, 92 (2016), pp. 153-163
View PDF View article View in Scopus Google Scholar

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2024, Composites Part A: Applied Science and Manufacturing
Citation Excerpt :
By applying heat and pressure for a time after damage, delamination damages can be recovered with mechanical properties of the laminates restored [12,25–32]. Ouyang et al. utilised poly(ethylene-co-methacrylic acid) (EMAA) thermoplastic interleaves to toughen and repair CF/epoxy laminates in a variety of modes [25–27]. The EMAA films contain an array of 0.8 mm diameter holes with a 22.7 % porosity, which result in stiff epoxy columns after thermoset resin curing, to enhance interlaminar stiffness and provide shear resistance.
Thermoplastic interleaving is a well-established approach to toughen carbon fibre thermoset laminates, studied over the past five decades. Recently, it has been revisited to create functional smart composites with damage sensing and repair capabilities with a renewed focus on the sustainability and longevity of components. However, the introduction of thermoplastic films within the interlaminar region often lowers fibre volume fraction and performance at elevated temperature, while the addition of impermeable continuous films during manufacture may also limit compatible fabrication methods. Moreover, the incorporation of dielectric thermoplastic films inevitably reduces through-thickness electrical conductivity and prevents accurate damage sensing of delamination in carbon fibre laminates. In this study, strategies of using discontinuous interleaving to improve both fracture toughness and thermomechanical properties of carbon fibre epoxy laminates, with the ability to monitor delamination damage and restore mechanical properties after a short healing step have been explored. Both the interleaving design and the physical properties of the thermoplastic were assessed, which has not been addressed previously. Interleaving high molecular weight thermoplastic with decreasing interleaf width and distance between interleaf zones results in increased fracture toughness (+347 %), by creating a superior toughened interlaminar zone, forcing a migration of delamination into the intralaminar region. A repair efficiency of 77 % was achieved when using a lower molecular weight of thermoplastic; however, the lack of thermoplastic over the entire fracture surface area affects the repairing performance universally. Damage sensing and thermomechanical properties were significantly improved compared to continuous interleaving, demonstrating that discontinuous thermoplastic interleaving strategies offer a favourable combination of toughening, thermal performance and accurate damage sensing for multifunctional high-performance composites.
Smart Carbon Fiber-Reinforced Polymer Composites for Damage Sensing and On-Line Structural Health Monitoring Applications
2024, Polymers
Effects of particle size and particle concentration of poly (ethylene-co-methacrylic acid) on properties of epoxy resin
2024, Journal of Applied Polymer Science

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[1] [1]
K. Tian, T.E. Tay, V.B.C. Tan, A. Haris, E. Chew, V.N.H. Pham, et al.
Improving the impact performance and residual strength of carbon fibre reinforced polymer composite through intralaminar hybridization
Compos A Appl Sci Manuf, 171 (2023), p. 107590
View PDF View article View in Scopus Google Scholar

[2] [2]
J.L. Liu, J. Zhi, H.L. Wong, E.S. Sugeng, T.E. Tay, V.B.C. Tan
Effect of ply blocking on the high-speed impact performance of thin-ply CFRP laminates
Compos Sci Technol, 228 (2022), p. 109640
View PDF View article View in Scopus Google Scholar

[3] [3]
Y. He, K.e. Duan, L. Yao, J. Tang, J. Zhang, D. Jiang, et al.
Synergistic toughening on CFRP via in-depth stitched CNTs
Compos B Eng, 254 (2023), p. 110605
View PDF View article Google Scholar

[4] [4]
Q. OuYang, X. Wang, L. Liu
High crack self-healing efficiency and enhanced free-edge delamination resistance of carbon fibrous composites with hierarchical interleaves
Compos Sci Technol, 217 (2022), p. 109115
View PDF View article View in Scopus Google Scholar

[5] [5]
Y. Zhao, Q. Liu, R. Li, S.V. Lomov, S.G. Abaimov, K.e. Xiong, et al.
Self-sensing and self-healing smart fiber-reinforced thermoplastic composite embedded with CNT film
J Intel Mat Syst Str, 34 (13) (2023), pp. 1561-1571
Crossref View in Scopus Google Scholar

[6] [6]
M.-H. Yu, J.-S. Lee, H.-S. Kim
Machine learning-based damage sensing and self-healing of carbon fiber/nylon composites via addressable conducting networks
Struct Health Monit, 22 (5) (2023), pp. 3401-3415
Crossref View in Scopus Google Scholar

[7] [7]
T.D.S. Thorn, Y.i. Liu, X. Yao, D.G. Papageorgiou, P. Robinson, E. Bilotti, et al.
Smart and repeatable easy-repairing and self-sensing composites with enhanced mechanical performance for extended components life
Compos A Appl Sci Manuf, 165 (2023), p. 107337
View PDF View article View in Scopus Google Scholar

[8] [8]
D. Xiang, X. Zhang, E. Harkin-Jones, W. Zhu, Z. Zhou, Y. Shen, et al.
Synergistic effects of hybrid conductive nanofillers on the performance of 3D printed highly elastic strain sensors
Compos A Appl Sci Manuf, 129 (2020), p. 105730
View PDF View article View in Scopus Google Scholar

[9] [9]
X. Zhang, D. Xiang, W. Zhu, Y. Zheng, E. Harkin-Jones, P. Wang, et al.
Flexible and high-performance piezoresistive strain sensors based on carbon nanoparticles@polyurethane sponges
Compos Sci Technol, 200 (2020), p. 108437
View PDF View article View in Scopus Google Scholar

[10] [10]
D. Xiang, X. Zhang, Y. Li, E. Harkin-Jones, Y. Zheng, L. Wang, et al.
Enhanced performance of 3D printed highly elastic strain sensors of carbon nanotube/thermoplastic polyurethane nanocomposites via non-covalent interactions
Compos B Eng, 176 (2019), p. 107250
View PDF View article View in Scopus Google Scholar

[11] [11]
X. Zhang, D. Xiang, Y. Wu, E. Harkin-Jones, J. Shen, Y. Ye, et al.
High-performance flexible strain sensors based on biaxially stretched conductive polymer composites with carbon nanotubes immobilized on reduced graphene oxide
Compos A Appl Sci Manuf, 151 (2021), p. 106665
View PDF View article View in Scopus Google Scholar

[12] [12]
S.-J. Joo, M.-H. Yu, W.S. Kim, H.-S. Kim
Damage detection and self-healing of carbon fiber polypropylene (CFPP)/carbon nanotube (CNT) nano-composite via addressable conducting network
Compos Sci Technol, 167 (2018), pp. 62-70
View PDF View article View in Scopus Google Scholar

[13] [13]
G. Yang, X.u. Feng, W. Wang, Q. OuYang, L. Liu, Z. Wu
Graphene and carbon nanotube-based high-sensitive film sensors for in-situ monitoring out-of-plane shear damage of epoxy composites
Compos B Eng, 204 (2021), p. 108494
View PDF View article View in Scopus Google Scholar

[14] [14]
X.F. Sánchez-Romate, Á. Coca, A. Jiménez-Suárez, M. Sánchez, A. Ureña
Crack sensing mechanisms of Mode-II and skin-stringer joints between dissimilar materials by using carbon nanotubes
Compos Sci Technol, 201 (2021), p. 108553
View PDF View article View in Scopus Google Scholar

[15] [15]
S.C. Brown, C. Robert, V. Koutsos, D. Ray
Methods of modifying through-thickness electrical conductivity of CFRP for use in structural health monitoring, and its effect on mechanical properties – a review
Compos A Appl Sci Manuf, 133 (2020), p. 105885
View PDF View article View in Scopus Google Scholar

[16] [16]
J. Li, Z. Zhang, J. Fu, Z. Liang, K.R. Ramakrishnan
Mechanical properties and structural health monitoring performance of carbon nanotube-modified FRP composites: a review
Nanotechnol Rev, 10 (1) (2021), pp. 1438-1468
Crossref View in Scopus Google Scholar

[17] [17]
L. Shen, L. Liu, W. Wang, Y. Zhou
In situ self-sensing of delamination initiation and growth in multi-directional laminates using carbon nanotube interleaves
Compos Sci Technol, 167 (2018), pp. 141-147
View PDF View article View in Scopus Google Scholar

[18] [18]
G. Yang, X.u. Feng, W. Wang, Q. OuYang, L. Liu
Effective interlaminar reinforcing and delamination monitoring of carbon fibrous composites using a novel nano-carbon woven grid
Compos Sci Technol, 213 (2021), p. 108959
View PDF View article View in Scopus Google Scholar

[19] [19]
G. Yang, Q. OuYang, J. Ye, L. Liu
Improved tensile and single-lap-shear mechanical-electrical response of epoxy composites reinforced with gridded nano-carbons
Compos A Appl Sci Manuf, 152 (2022), p. 106712
View PDF View article View in Scopus Google Scholar

[20] [20]
X. Chen, S. Cheng, S. Wang, K. Wen, C. Shi, J. Zhang, et al.
Embedding stretchable, mesh-structured piezoresistive sensor for in-situ damage detection of glass fiber-reinforced composite
Compos Sci Technol, 233 (2023), p. 109926
View PDF View article Google Scholar

[21] [21]
H. Zhang, Y. Liu, M. Kuwata, E. Bilotti, T. Peijs
Improved fracture toughness and integrated damage sensing capability by spray coated CNTs on carbon fibre prepreg
Compos A Appl Sci Manuf, 70 (2015), pp. 102-110
View PDF View article View in Scopus Google Scholar

[22] [22]
D. Xiang, L. Wang, Y. Tang, E. Harkin-Jones, C. Zhao, P. Wang, et al.
Damage self-sensing behavior of carbon nanofiller reinforced polymer composites with different conductive network structures
Polymer, 158 (2018), pp. 308-319
View PDF View article View in Scopus Google Scholar

[23] [23]
A. Cohades, C. Branfoot, S. Rae, I. Bond, V. Michaud
Progress in self-healing fiber-reinforced polymer composites
Adv Mater Interfaces, 5 (17) (2018), p. 1800177
View in Scopus Google Scholar

[24] [24]
M.O.H. Cioffi, A.S.C. Bomfim, V. Ambrogi, S.G. Advani
A review on self-healing polymers and polymer composites for structural applications
Polym Compos, 43 (11) (2022), pp. 7643-7668
Crossref View in Scopus Google Scholar

[25] [25]
S. Islam, G. Bhat
Progress and challenges in self-healing composite materials
Mater Adv, 2 (6) (2021), pp. 1896-1926
View article Crossref View in Scopus Google Scholar

[26] [26]
T. Yang, J. Zhang, A.P. Mouritz, C.H. Wang
Healing of carbon fibre–epoxy composite T-joints using mendable polymer fibre stitching
Compos B Eng, 45 (1) (2013), pp. 1499-1507
View PDF View article View in Scopus Google Scholar

[27] [27]
K. Pingkarawat, C.H. Wang, R.J. Varley, A.P. Mouritz
Mechanical properties of mendable composites containing self-healing thermoplastic agents
Compos A Appl Sci Manuf, 65 (2014), pp. 10-18
View PDF View article View in Scopus Google Scholar

[28] [28]
R.J. Varley, D.A. Craze, A.P. Mouritz, C.H. Wang
Thermoplastic healing in epoxy networks: exploring performance and mechanism of alternative healing agents
Macromol Mater Eng, 298 (11) (2013), pp. 1232-1242
Crossref View in Scopus Google Scholar

[29] [29]
A. Azevedo do Nascimento, F. Fernandez, F. S. da Silva, E. P.C. Ferreira, J.D. D. Melo, A.P. Cysne Barbosa
Addition of poly (ethylene-co-methacrylic acid) (EMAA) as self-healing agent to carbon-epoxy composites
Compos A Appl Sci Manuf, 137 (2020), p. 106016
View PDF View article View in Scopus Google Scholar

[30] [30]
Y.a. Gao, L. Liu, Z. Wu, Z. Zhong
Toughening and self-healing fiber-reinforced polymer composites using carbon nanotube modified poly (ethylene-co-methacrylic acid) sandwich membrane
Compos A Appl Sci Manuf, 124 (2019), p. 105510
View PDF View article View in Scopus Google Scholar

[31] [31]
A.D. Snyder, Z.J. Phillips, J.S. Turicek, C.E. Diesendruck, K.B. Nakshatrala, J.F. Patrick
Prolonged in situ self-healing in structural composites via thermo-reversible entanglement
Nat Commun, 13 (1) (2022), p. 6511
View in Scopus Google Scholar

[32] [32]
T. Yang, Y. Du, Z.M. Li, C.H. Wang
Mechanical properties of self-healing carbon fiber-epoxy composite stitched with mendable polymer fiber
Polym Polym Compos, 22 (3) (2014), pp. 329-336
Crossref View in Scopus Google Scholar

[33] [33]
T.W. Loh, R.B. Ladani, A. Orifici, E. Kandare
Ultra-tough and in-situ repairable carbon/epoxy composite with EMAA
Compos A Appl Sci Manuf, 143 (2021), p. 106206
View PDF View article View in Scopus Google Scholar

[34] [34]
K. Pingkarawat, C.H. Wang, R.J. Varley, A.P. Mouritz
Self-healing of delamination cracks in mendable epoxy matrix laminates using poly[ethylene-co-(methacrylic acid)] thermoplastic
Compos A Appl Sci Manuf, 43 (8) (2012), pp. 1301-1307
View PDF View article View in Scopus Google Scholar

[35] [35]
S. Meure, D.-Y. Wu, S.A. Furman
FTIR study of bonding between a thermoplastic healing agent and a mendable epoxy resin
Vib Spectrosc, 52 (1) (2010), pp. 10-15
View PDF View article View in Scopus Google Scholar

[36] [36]
R.B. Ladani, K. Pingkarawat, A.T.T. Nguyen, C.H. Wang, A.P. Mouritz
Delamination toughening and healing performance of woven composites with hybrid z-fibre reinforcement
Compos A Appl Sci Manuf, 110 (2018), pp. 258-267
View PDF View article View in Scopus Google Scholar

[37] [37]
R.B. Ladani, A.T.T. Nguyen, C.H. Wang, A.P. Mouritz
Mode II interlaminar delamination resistance and healing performance of 3D composites with hybrid z-fibre reinforcement
Compos A Appl Sci Manuf, 120 (2019), pp. 21-32
View PDF View article View in Scopus Google Scholar

[38] [38]
G. de Souza, J.R. Tarpani
Interleaving CFRP and GFRP with a thermoplastic ionomer: the effect on bending properties
Appl Compos Mater, 28 (2) (2021), pp. 559-572
Crossref View in Scopus Google Scholar

[39] [39]
K. Pingkarawat, A.P. Mouritz
Stitched mendable composites: Balancing healing performance against mechanical performance
Compos Struct, 123 (2015), pp. 54-64
View PDF View article View in Scopus Google Scholar

[40] [40]
C.H. Wang, K. Sidhu, T. Yang, J. Zhang, R. Shanks
Interlayer self-healing and toughening of carbon fibre/epoxy composites using copolymer films
Compos A Appl Sci Manuf, 43 (3) (2012), pp. 512-518
View PDF View article View in Scopus Google Scholar

[41] [41]
W. Wang, Q. Ouyang, L. Liu, Z. Wu
Novel nanotube/poly(ethylene-co-methacrylic acid)/epoxy composite adhesive possessing in-situ electrical-heating activated crack healing function
Compos A Appl Sci Manuf, 150 (2021), p. 106599
View PDF View article View in Scopus Google Scholar

[42] [42]
R. Calderón-Villajos, A.J. López, L. Peponi, J. Manzano-Santamaría, A. Ureña
3D-printed self-healing composite polymer reinforced with carbon nanotubes
Mater Lett, 249 (2019), pp. 91-94
View PDF View article View in Scopus Google Scholar

[43] [43]
A. Jiménez-Suárez, J. Martín-González, X.F. Sánchez-Romate, S.G. Prolongo
Carbon nanotubes to enable autonomous and volumetric self-heating in epoxy/polycaprolactone blends
Compos Sci Technol, 199 (2020), p. 108321
View PDF View article View in Scopus Google Scholar

[44] [44]
H. Kim, A.L. Yarin, M.W. Lee
Self-healing corrosion protection film for marine environment
Compos B Eng, 182 (2020), p. 107598
View PDF View article View in Scopus Google Scholar

[45] [45]
Q. Ouyang, L. Liu, Z. Wu
Electrothermally self-healing delamination cracks in carbon/epoxy composites using sandwich and tough carbon nanotube/copolymer interleaves
Polymers, 14 (20) (2022), p. 43133
Google Scholar

[46] [46]
K. Pingkarawat, C. Dell’Olio, R.J. Varley, A.P. Mouritz
Poly(ethylene- co -methacrylic acid) (EMAA) as an efficient healing agent for high performance epoxy networks using diglycidyl ether of bisphenol A (DGEBA)
Polymer, 92 (2016), pp. 153-163
View PDF View article View in Scopus Google Scholar

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