How is impact damage in composites characterized and managed?

Impact damage in composites is critical due to internal damage not visible externally. Damage types: Matrix cracking - First damage mode, may not affect strength significantly; Delamination - Interlaminar separation, major strength/stiffness knockdown; and Fiber breakage - Severe impact, visible damage likely. BVID (Barely Visible Impact Damage): Damage with visible indication at threshold of detectability (~0.05 inch dent depth), Designs must tolerate BVID with ultimate load capability. Testing: Drop weight impact (ASTM D7136), CAI (Compression After Impact, ASTM D7137), Impact energy vs. damage size characterization. Design approaches: Damage tolerance - Design strain levels account for BVID; Damage resistance - Material/design choices to minimize damage; and Inspection - NDT methods to detect damage. Factors: Ply orientation (45-degree surface plies improve impact resistance), Toughened matrices (thermoplastic interlayers), and Protective features (paint, external structure). Repair: Scarf or stepped-lap bonded repairs, bolted repairs for field use.