How do you perform damage tolerance analysis for composite structures?

Composite damage tolerance ensures structure safely carries loads with damage present. Damage categories: Manufacturing - Porosity, delamination, foreign objects; Service - Impact (BVID to VID), fatigue, environmental; Accidental - Major impact, penetration. Analysis approach: Define damage scenarios per AC 20-107B, Determine damage sizes (BVID at inspection threshold), Analyze residual strength with damage present, and Establish inspection intervals if needed. Methods: No-growth approach - Demonstrate damage doesn't grow under repeated loads, simplifies inspection; Slow-growth approach - Predict growth, inspect before critical; and Arrested growth - Damage grows then arrests at design feature. Analysis tools: Fracture mechanics for delamination growth (GIc, GIIc criteria), Progressive damage analysis (FEA), and Empirical knockdown factors for initial sizing. Testing: CAI establishes design strain limits, Fatigue testing validates no-growth, and Residual strength testing verifies analysis. Certification requires showing adequate residual strength throughout inspection interval with assumed damage.