CFRP flap and wing tracks bird impact damage prediction numerical calibration for airworthiness certification criteria

The aim of this work is to provide a robust and efficient method to design a flap assembly to be resistant to a full scale experimental bird strike in according to the airworthiness certifications. In particular this paper analyses the full assembly of a CFRP flap including wing track attachments ready to be tested a birdstrike scenario. Before to introduce the impact simulations on the entire flap, a dedicated model calibration, which fully reflect ASTM procedure of tensile and compression tests have been prepared and simulation results, have been compared with typical experimental tests expected for a CFRP material. Furthermore the dimensioning of the roller carriages, which are the links between the flap tracks, has represented a critical issue in the interference aspects between the flap and the wing box, then a detailed evaluation of the links allowed to size the fixture for a fullscale test case. Using of an iterative approach, all failure parameter requested have been properly tuned. Then the calibration impact projectile is introduced to study the interaction between the bird (equivalent gelatine) and the target including the equation of state and contacts. Flap object of this work is equipped on a medium rage turbojet aircraft of about one hundred twenty seats. The flap model is a single slotted flap fixed to the main component with two tracks respectively, staring from the wing root. The impact condition presents for all flap deflections not affected by wing, fan cowl and track shadow. This paper present the analysis of bird strike with flap assembled on wing tracks. For this particular topic, a dedicated session has been developed in order to apply the most representative track installation. Finally an extensive campaign of impacts were performed on the inboard flap. Particular attention on the track zones is dedicated when the flap is fully opened. These zones are very critical because failure of links is a failure of complete systems. Results of the impacts analysis are presented in terms of visual damage and history forces reaction on link and carriage. Moreover the strain of the most critical items will be surveyed (rear spar damage). Result overview allows the selection of the bird impact points based on links and composite failure criteria, in particular on the flap tracks metallic attachments, and lower skin and rear spar damage; Result of current work have allowed to establish robust criteria and to define most critical impact points need to be investigated by means of a strike test. Reducing number of shots a two location allow laboratories to perform test bus using of a unique test specimen saving time and cost. The conclusion of this activity is dedicated a comparison of test result performed and relevant analysis. For the two shots strain gauge and force reaction history acquisition will be compared.