Interlocking fiber features for mixed-mode crack arrest in weakly bonded CFRP joints

Adhesive joints in carbon fiber reinforced plastic (CFRP) structures may contain weak bonds that are difficult to detect and can trigger mixed-mode crack propagation, leading to the use of redundant mechanical fasteners. To realize boltless aircraft adhesive structures, this study investigates crack arresters based on interlocking fiber features for suppressing mixed-mode crack propagation in weakly bonded joints. After establishing a reproducible weak bond preparation method, three interlocking fiber features were examined: Straight Interlocking Fiber Feature (SIFF), Mechanically Hooked Interlocking Fiber Feature (MHIFF), and Diagonally Interlocking Fiber Feature (DIFF). Crack lap shear static and fatigue tests were conducted to evaluate crack arresting performance. All interlocking fiber features arrested interfacial debonding at the fiber cross-link and enhanced static strength, with DIFF achieving the highest strength, up to 2.6 times that of a normally bonded joint without crack arresters. In fatigue tests, SIFF did not suppress mixed-mode crack propagation, whereas MHIFF and DIFF suppressed fatigue crack growth beyond the fiber cross-link up to 100,000 cycles. Among the three interlocking fiber features, DIFF exhibited the most favorable balance of mixed-mode fatigue crack suppression and structural simplicity, indicating high potential for practical applications. (188 words)