What are the certification challenges for adhesively bonded primary composite structures?

Adhesive bond certification challenges include: Bondline quality inspection limitations (no NDI method reliably detects weak bonds), Kissing bonds (contact without structural integrity) undetectable by conventional NDI, Environmental degradation concerns (moisture ingress, temperature cycling), Long-term durability data requirements, Manufacturing process sensitivity, and Static vs fatigue performance correlation. Certification approaches: Limit bond-critical structures to design where bondline failure detection is possible by other means (deformation, leakage), Include fasteners as fail-safe backup, Extensive process controls and coupon testing per batch, Accelerated aging tests, and Conservative knockdown factors. FAR 25.571 requires demonstrable inspection capability or fail-safe backup.