How do you design bonded repairs for composite aircraft structures?

Bonded composite repairs restore damaged structure to required capability. Repair types: Scarf repair - Tapered removal and replacement, flush surface, best load transfer; Stepped lap - Discrete step transitions, similar to scarf; and External patch - Bonded doubler, simplest but adds thickness. Design process: Assess damage extent (NDT), Determine required strength restoration, Design patch geometry (taper ratio, overlap, ply orientation), and Select repair materials (matching or equivalent). Analysis: Adhesive shear stress distribution, Load eccentricity effects, Environmental knockdowns (hot/wet adhesive properties), and Static and fatigue capability. Critical factors: Surface preparation - Contamination removal, peel ply or abrasion, moisture removal; Cure - Field repairs may use vacuum-bag/heat blanket (lower properties than autoclave); and Inspection - Verify bond quality, repair boundaries. Certification: Repairs to SRM (Structural Repair Manual) are pre-approved, Major repairs require engineering approval (DER). Field constraints often limit repair options; damage limits define repairable vs. replace decisions.