How is the building block approach used for composite structure certification?

The building block approach progressively validates composite design through test levels. Levels: Coupons - Material properties (tension, compression, shear), Environmental effects, Large sample sizes for statistics; Elements - Structural features (holes, joints, impact), Failure modes, Moderate sample sizes; Subcomponents - Multi-element structures (panels with stiffeners, joints), Structural behavior validation; Components - Full-scale sections, Combined loading, Single article typical; and Full-scale - Complete structure test. At each level: Analysis predictions verified against test, Analysis methods calibrated, and Failure modes confirmed. CMH-17 guidance: Test matrix defined by criticality, Sample sizes per statistical requirements, and Environmental conditioning. Benefits: Risk reduction through progressive testing, Analysis methods validated at each level, and Cost-effective compared to full-scale only. Certification: Compliance documentation at each level, Failure mode correlation, and Margin demonstration. This approach is standard for composite primary structure certification.