Numerical simulation of the load carrying capability of composite rotorcraft airframe structures, taking into account the effect of disbonds in the damage tolerance and fatigue evaluation

摘要

Authorities require among others a damage tolerance and fatigue evaluation for so called Principal Structural Elements (PSE) of composite rotorcraft airframe structures (see FAR 29.573). This includes a threat assessment followed by an assessment of the residual strengths of these parts after e.g. impacts and discrete flaws like large disbonds, and finally a so called no-growth substantiation under fatigue load has to be performed, regarding any kind of damages which are barely visible.This paper focusses on the residual strength determination of PSE with large disbonds. Traditionally this is done by a large test program during which the damage size of typical layups induced by e.g. impacts or disbonds is determined. In a second step the residual strength of such parts with damage is measured in tests as well. New simulation techniques based on fracture mechanics that are now available in commercial finite element (FEM) codes and have been successfully used to simulate some of the most important phenomena driving damage tolerance evaluation: Delaminations caused by impact damages, residual strength after impact damage and proof of stability of structures with large disbonds. The results look promising and may simplify the substantiation effort in the future.