DEVELOPMENT OF AN IMPROVED MODEL FOR PREDICTING FATIGUE CRACK GROWTH IN ALUMINIUM ALLOY HELICOPTER AIRFRAME COMPONENTS

摘要

The National Aerospace Laboratory NLR in the Netherlands has embarked on the research programme 'HeliDamTol', which aims to improve the capability of assessing the severity of in-service fatigue cracks in helicopter airframes. The present paper briefly describes and discusses the programme and the programme status, with particular emphasis on the work involved in the development of an improved Strip Yield model for predicting fatigue crack growth in aluminium alloy helicopter airframe components. This research model has been developed as a Matlab application and due to its open and easy architecture it can also serve as a platform to test new concepts that might arise regarding the constraint behaviour of the material at the crack tip, fatigue crack growth propagation laws, etc. The model has been used to demonstrate that the apparently unique relation between the cyclic crack tip opening displacement and the effective cyclic stress intensity factor exists only under the condition of no-crack-closure. Further research will be conducted to investigate whether the use of the cyclic crack tip opening displacement as a fatigue crack growth correlating parameter will enhance the capability to predict crack growth under variable amplitude loading.