Abstract The mechanical and crack sensing capabilities of CFRP-metal Mode-II coupons and skin-stringer T-joints under bending conditions with carbon nanotube (CNT) doped adhesive films are explored. Different surface treatments of the aluminium substrate are tested (grit blasting and sandpaper brushing). Mode-II energy fracture slightly increases with CNT addition due to the nanoparticle toughening effect when the surface treatment is adequate. However, in the case of brushed specimens, the enhanced lubricant properties of CNTs leads to the promotion of weak interfaces between adhesive and metal substrate. The electrical resistance increases with the load nose displacement with a good correspondence to the crack length. A crack opening effect is herein noticed in the last stages of the Mode-II tests due to the difference between the stiffness of metal and CFRP adherents, which is reflected in a sudden increase of the electrical resistance. These results have been also validated by theoretical analysis. Electromechanical response of T-joints shows a similar behaviour with an increasing sensitivity when placing a CFRP stringer, due to a more prevalent crack opening observed in this type of specimens. Therefore, crack sensing capabilities are demonstrated at both coupon and sub-element level.

中文翻译：

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利用碳纳米管对异种材料之间的模式 II 和蒙皮-纵梁接头的裂纹传感机制

摘要 研究了碳纳米管 (CNT) 掺杂粘合剂薄膜在弯曲条件下 CFRP-金属 II 型试样和皮肤纵梁 T 接头的机械和裂纹传感能力。测试了铝基板的不同表面处理（喷砂和砂纸刷）。当表面处理足够时，由于纳米颗粒的增韧效应，模式 II 的能量断裂会随着 CNT 的加入而略微增加。然而，在拉丝试样的情况下，碳纳米管增强的润滑性能导致粘合剂和金属基材之间的弱界面的促进。电阻随着负载鼻位移的增加而增加，与裂纹长度有很好的对应关系。由于金属和 CFRP 粘合剂的刚度不同，在模式 II 测试的最后阶段注意到裂纹打开效应，这反映在电阻的突然增加上。这些结果也得到了理论分析的验证。T 型接头的机电响应显示出类似的行为，并且在放置 CFRP 纵梁时，由于在此类试样中观察到的裂纹开口更为普遍，因此灵敏度会增加。因此，裂纹传感能力在试样和子元件级别都得到了证明。T 型接头的机电响应显示出类似的行为，并且在放置 CFRP 纵梁时，由于在此类试样中观察到的裂纹开口更为普遍，因此灵敏度会增加。因此，裂纹传感能力在试样和子元件级别都得到了证明。T 型接头的机电响应显示出类似的行为，并且在放置 CFRP 纵梁时，由于在此类试样中观察到的裂纹开口更为普遍，因此灵敏度会增加。因此，裂纹传感能力在试样和子元件级别都得到了证明。