This paper describes the crack growth analysis and verification test for an A17075-T73 Main Rotor Damper Attachment Lug. The analysis involved 2D and 3D stress analysis using the MARC finite element code, stress intensity analysis using the FRANC3D and NASGRO codes, crack growth rate data fit with a closure model, and crack growth analysis using the NASGRO crack growth code. The crack growth testing involved fatigue testing using a load cylinder to introduce the vibratory damper loads, the introduction of notches at high stress locations as crack initiators, and the tracking of cracks using acetate replicates examined in a Scanning Electron Microscope (SEM). The predicted crack growth compared well with the measured crack growth on the lug surfaces. However the predicted and measured final crack shapes were somewhat different. The goal of detecting and tracking a crack from a 5 to 10 mil initial size in the damper attachment lugs was not achieved, although good crack growth data was obtained for cracks down to 70 mils. Based on the final stress and stress intensity analyses this is not surprising, since the AK tends to be below threshold for the 5 and 10 mil cracks. For the main rotor damper attachment lugs the stress intensities predicted by the FRANC3D code and the NASGRO lug corner crack model (CC03) were in good agreement. For the A17075-T73 main rotor damper attachment lugs crack growth analyses based on stress intensities from FRANC3D and NASGRO were in good agreement with replicate measured crack growth on the surface of the lugs. Examination of the fracture surfaces indicated that the final crack length in the bore of the hole was greater than the crack length on the surface (i.e. a/c less that one). The crack growth predictions resulted in a final crack shape with a/c greater than one. This suggests that the tested lugs may have more bending than predicted by the MARC finite element stress analysis. The crack growth analyses based on the FRANC3D stress intensities provided better crack shapes than the crack growth analysis based on the NASGRO stress intensities. This is because the FRANC3D stress intensities include the bending predicted by the MARC stress analysis but the NASGRO stress intensities do not include bending.
Crack growth analysis and test of a main rotor damper attachment lug
Analyse der Rissfortpflanzung und Test der Befestigung des Hauptrotordämpfers
AHS International Forum, 60 ; 193-201
2004
9 Seiten, 13 Bilder, 2 Tabellen, 11 Quellen
Conference paper
English
Rissfortpflanzung , Rotor (Drehflügel) , Hubschrauber , Mechanik , mechanisches Modell , numerische Simulation , Programmsystem , Finite-Elemente-Methode , Dauerschwingprüfung , Risseinleitung , experimentelle Untersuchung , mechanische Spannung , Schmieden , Spannungsanalyse , Rasterelektronenmikroskop