Fatigue Crack-Growth Resistance of Aluminum Alloys Under Spectrum Loading. Volume 1. Commercial 2XXX and 7XXX Alloys

摘要

The purpose of this program is to obtain metallurgical guidelines and test methodologies for selection and development of spectrum fatigue-resistant, high-strength aluminum alloys for application to aircraft structures. This volume (I) of this report describes the results of baseline characterization of two high-strength aluminum alloys, and compares these results to those obtained in the two previous phases of the program. Twelve commercial 2XXX and 7XXX aluminum alloys were chosen and characterized for 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-18 load spectrums. One of the spectrums was dominated by tension loads and the other contained tension and compression loads of nearly equal magnitude. The spectrum FCP testing was performed at the maximum peak stress of 145 MPa (21 ksi) with 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.