Fatigue crack growth of aircraft aluminum alloys

The microstructural characteristics and the influence of existing corrosion on fatigue crack growth in 2024 T351 aircraft aluminium alloy are investigated. Examined is the elongated grain morphology due to the rolling process that exhibited higher crack growth resistance than the microstructure of the sheet material with smaller equiaxed grains. Moreover, plate microstructure with high purity composition offered better damage tolerance characteristics in contrast to the conventional sheet microstructure. Shown is the need to account for the influence of pre-existing corrosion on the aluminum alloys in order to obtain more reliable results from fatigue and damage tolerance analyses of components with corroded areas. © Springer Science+Business Media B.V. 2008

Fatigue performance of pre-corroded 6xxx aluminum alloy laser beam welds with dissimilar heat treatment

The role of existing corrosion damage on the fatigue performance of 6156 AA laser beam welds in T3 state, with additional post weld heat treatment T8, has been assessed. The welds were subjected to salt fog environment for 720 hours and then metallographically examined to characterize corrosion behaviour. The corrosion results demonstrate that T3/T8 treatment provides high corrosion susceptibility in the weld area, where localized damage in the form of large pits prevails. Fatigue performance of corroded samples is drastically degraded by the presence of corrosion pits which act as stress raisers and accelerate crack initiation in the corroded samples. Fatigue cracks initiate at the root of corrosion pits on the large specimen surfaces in the weld metal area and propagate in through thickness direction. The obtained results have been compared to results from 6156 welds with T4 treatment in as welded conditions. © 2014 The Authors. Published by Elsevier Ltd

A critical assessment of multifunctional polymers with regard to their potential use in structural applications

Multi Wall Carbon Nanotubes (MWCNTs) and Polyhedral Oligomeric Silsesquioxanes (POSS) are common additives to simultaneously enhance electrical conductivity and flame resistance. In the present work, the synergistic effect of the addition of MWCNTs and two different POSS compounds, DodecaPhenyl POSS (DPHPOSS) and Glycidyl POSS (GPOSS), on the mechanical behavior of multifunctional polymers subjected both to quasi-static as well as to fatigue loading was investigated. The results of the mechanical tests were discussed supported by Scanning Electron Microscope (SEM) and Energy Dispersive Spectroscopy (EDS) analyses. The results showed that the incorporation of MWCNTs in the resin containing GPOSS determines a slight decrease in the flexural modulus compared to the unfilled resin. The material filled with MWCNTs and DPHPOSS shows a higher reduction of the flexural modulus as compared to the other analyzed materials. The same trend was observed also for the flexural strength; more than 50% decrease of the flexural strength of the material filled with MWCNTs and DPHPOSS is detected. As far as the fatigue is concerned, it seems that the incorporation of the flame retardants led to an appreciable decrease in the fatigue life. The decrease in the mechanical properties of the nanofilled resin loaded with DPHPOSS is most likely due to the presence of aggregates of DPHPOSS crystals in the matrix. This hypothesis is confirmed by EDX analysis which shows that DPHPOSS forms some small aggregates, whereas GPOSS, being molecularly solubilized in the epoxy formulation, shows mechanical performance more similar to the sample loaded only with carbon nanotubes