A Damage Tolerance and Fatigue Evaluation Approach for Composite Rotorcraft Airframe Structures

The paper presents a methodology to perform a damage tolerance evaluation for composite airframe principal structural elements (PSE). This methodology consists out of five steps, first a logic how to identify PSE (step 1), then a threat assessment (step 2) for them, followed by a coupon testing approach (step 3) for showing dent depths visibility thresholds. Then a coupon test approach is presented for showing no growth behavior of barely visible impact damages (BVID) for one design service goal (DSG) and design ultimate load (DUL) capability and for clearly visible impact damages (CVID) no growth behaviour for one inspection interval and minimum design limit load (DLL) capability is demonstrated (step 4). Those coupon test results are then used to determine allowable strain limits for sizing of PSE. Finally the results of step 4 are then validated by structural component tests (step 5) by application of a certain test sequence to cover both, static- and fatigue damage tolerance requirements, i.e. first application of DLL, then simulation of one DSG with BVID, then application of DUL, followed by a simulation of one inspection interval with CVID and repairs and finally check of residual strength capability which is minimum DLL for such parts.