Delamination due to interlaminar fracture has limited the application of composite materials in highly integrity-sensitive structural systems. The novelty of this experimental and statistical investigation is twofold: (i) the effects of the size of multi-wall carbon nanotube (MWCNT) bundles and their interphase with the surrounding matrix on the multimodal fracture toughness and crack propagation regime; (ii) the effectiveness of single lamina vs. multiple laminas on fracture toughness in carbon fiber nanocomposites. The Atomic Force Microscopy Peak Force Quantitative Nanomechanics Mapping (AFM PFQNM) technique was utilized to characterize the CNT bundle size and interphase. Weibull analysis of a myriad of 480 CNT bundle sizes and interphases confirmed a high scatter in the data with more occurrences at the larger size. Two different nanocomposite laminates were considered: (i) laminates with 1wt% CNT in all laminas (FCNT); (ii) laminates with 1wt% CNT in the middle layer in front of the pre-crack (CNT). The average size of the CNT bundles and the interphase thickness were 549.7 nm and 22.9 nm in the CNT laminates and 480.1 nm and 22.2 nm in the FCNT laminates. The ratio of interphase thickness to CNT bundle size was higher in FCNT than in CNT, confirming a better stiffening effect due to the nano reinforcement of FCNT laminates. Weibull moduli of mode I initiation and propagation and mode II initiation for laminates with CNT in all laminas, FCNT, are higher than reference and CNT laminates, confirming a higher crack energy consistency. The Mode I initiation and propagation and mode II initiation fracture energies of CNT and FCNT were (15% and 10%), (38% and 44%), and (1.7% and 9.6%) higher than those without CNT. Mixing 1wt% CNT with all laminas expanded the mixed-mode I-II fracture envelope function by 21%. Unlike FCNT laminates, CNT laminates do not considerably improve the mixed-mode I-II fracture toughness. Crack deflection and a more arduous crack path due to the rigid CNT bundles increased the crack energy and delayed the crack propagation.

层间断裂导致的分层限制了复合材料在对完整性高度敏感的结构系统中的应用。该实验和统计研究的新颖性是双重的：(i) 多壁碳纳米管 (MWCNT) 束的尺寸及其与周围基体的界面对多峰断裂韧性和裂纹扩展机制的影响；(ii) 单层与多层对碳纤维纳米复合材料断裂韧性的影响。原子力显微镜峰值力定量纳米力学映射 (AFM PFQNM) 技术用于表征 CNT 束尺寸和界面。对无数 480 个 CNT 束大小和相间的 Weibull 分析证实了数据的高度分散，在较大尺寸处出现的次数较多。考虑了两种不同的纳米复合材料层压板：(i) 所有层板中含有 1wt% CNT 的层压板 (FCNT)；(ii) 在预裂纹 (CNT) 前面的中间层中使用 1wt% CNT 的层压板。CNT 束的平均尺寸和界面厚度在 CNT 层压板中分别为 549.7 nm 和 22.9 nm，在 FCNT 层压板中分别为 480.1 nm 和 22.2 nm。FCNT 中的相间厚度与 CNT 束尺寸之比高于 CNT，证实了由于 FCNT 层压板的纳米增强而具有更好的硬化效果。所有层板中具有 CNT 的层压板的模式 I 引发和传播以及模式 II 引发的威布尔模量 FCNT 高于参考和 CNT 层压板，证实了更高的裂纹能量一致性。CNT和FCNT的I型起爆和传播以及II型起爆断裂能分别为（15%和10%），（38% 和 44%）和（1.7% 和 9.6%）高于没有 CNT 的那些。将 1wt% CNT 与所有薄层混合，将混合模式 I-II 断裂包络函数扩展了 21%。与 FCNT 层压板不同，CNT 层压板不会显着提高混合模式 I-II 断裂韧性。由于刚性 CNT 束导致的裂纹偏转和更艰难的裂纹路径增加了裂纹能量并延迟了裂纹扩展。