Methodology for Evaluation of Fatigue Crack-Growth Resistance of Aluminum Alloys under Spectrum Loading

摘要

The purpose of this program is to obtain guidelines and test methodologies for selection and development of spectrum resistant, higher strength aluminum alloys for application to aircraft structures. The results described in this report present baseline characteristics of a number of high strength aluminum alloys for use in the future phases of this investigation. Seven commercial 2XXX and 7XXX aluminum alloys were chosen and have been characterized with respect to chemical composition, microstructure, tensile properties and fracture toughness. Fatigue crack propagation (FCP) tests were conducted on specimens of each alloy for both constant-amplitude loading (including the near-threshold region) and two F-18k load spectra. One of the spectra was dominated by tension loads and the other contained tension and compression loads of nearly equal magnitude. The spectrum FCP testing was performed at maximum peak stress of 145 MPa (21 ksi) as well as limited testing at 103 and 169 MPa (15 and 24.5 ksi) to obtain additional data at the low and high end of the crack-growth range. Pertinent fracture surface features were documented on the spectrum fatigue specimens.