Effects of flight load spectrum variations on fatigue life of riveted specimens and crack propagation in sheet made of Alclad 7075-T6

Riveted specimens that are considered representative for F-27 type wing structure were subjected to comparative flight simululation test in which the gust load severity and Ground-Air-Ground cycle were systematically varied. The effect of these variations on crack propagation behaviour was studied by means of crack growth tests on 2 mm sheet...

The effect of gust alleviation on fatigue in 2024-T3 Alclad

Fatigue tests under flight simulation loading were done on simple notched 2024-T3 Alclad sheet specimens. Reduction of the gust load amplitudes resulted in an increase of crack initiation life but hardly influenced crack propagation. Reduction of the overall stress level increased both initiation and crack propagation life. The observed...

Engineering application of fracture mechanics to flight simulation fatigue crack propagation

Heat treatment studies of aluminium alloy type 7050 forgings. Interim report no. 3: Corroded-specimen fatigue tests and SCC propagation tests

The influence of previous corrosion on the fatigue life was investigated. It was foimd that a slight corrosive attack could drastically reduce the fatigue life. The damaging effect of corrosion was greater for the alloy AA 7050 than for AZ 74.61. It could be established that fatigue cracks initiated from various corrosion pits. A second series...

The effect of sheet thickness on flight simulation fatigue crack propagation in 2024-T3, 7475-T761 and mill annealed Ti-6A1-4V

Flight simulation fatigue crack propagation tests were carried out on 2024-T3, 7475-T761 and mill annealed Ti-6A1-4V sheet in thicknesses up to 3 nim and representative for traJisport aircraft lower wing skin stiffened panels of end load capacities 1.5 and 3 MN/m. There was a significant effect of sheet thickness on crack propagation. Thinner...

The effect of sheet edge working on the fatigue life under flight-simulation loading

Fatigue tests under flight-simulation loading have been performed on unnotched Alclad 2024-T3, anodised 2.0 mm thick sheet specimens, manufactured according to several machine-shop processes applied in the air craft industry. From the results it appears that milling is preferable to stamping. Rounding off the edges is also advantageous. The...

Flight simulation fatigue crack propagation evaluation of candidate lower wing skin materials with particular consideration of spectrum truncation

Flight simulation fatigu-e crack propagation tests were carried out on 2024-T3, 7475-T761 and mill annealed Ti-6A1-4V sheet in thicknesses up to 3 miri and representative for transport aircraft lower wing skin stiffened panels of end load capacities 1.5 and 3 MN/m. The performance of 2024-T3 was much superior, owing mainly to greater retardation...

A non-stationary model for atmospheric turbulence patches, for the prediction of aircraft design loads

In this report a model for atmospheric turbulence is proposed. It is assumed that atmospheric turbulence appears in patches and that within the patches the turbulence can be described as a modulated Gaussian process. Statistical properties of this model and of atmospheric turbulence are compared. Using data from various sources a probability...

Environmental effects on crack grwoth in flight-simulation tests on 2024-T3 and 7075-T6 material Supplement: Compilation of test data from an investigation on the effect of environment on crack growth under flight-simulation loading

Flight-simulation tests based on a standardized gust load spectrum were carried out in normal air, very dry air and salt water. Specimen thicknesses were t = 2 mm and t = 10 mm, mean stress in flight was 70 or 55 MN/m². In all cases a significant effect of the environment was found. Fatigue lives for t = 10 ram were much shorter than for t = 2...

Effects of crack plane orientation transitions on flight simulation fatigue crack propagation in a high strength aluminium alloy (7050)

The effects of flat to slant fracture transitions on flight simulation fatigue crack propagation in specimens of 7O5O aluminium alloy forgings are discussed. For specimens containing flat, shearlipped, or full slant fractures at similar crack lengths the crack resistance (R curve) approach appears to provide an explanation for differences in the...

The significance of cladding for fatigue of aluminium alloys in aircraft structures

Flight-simulation tests were carried out on sheet specimens notched "by an open hole (Kt = 2.66). The material was 2024-T3 in three conditions; Alclad, bare and chemically milled. The crack initiation period and the crack propagation period were considerably shorter for the Alclad material. The significance of the cladding, both for constant...

Heat treatment studies of aluminium alloy forgings of the AZ 74.61 type. Interim report no. 3: Fatigue crack propagation performance under manoeuvre spectrum loading

The fatigue crack propagation performance of the alloy AZ 74.61 under manoeuvre spectrum loading was studied. The crack propagation behaviour was also compared with that of the American forging alloy AA 7050, not only for simulated manoeuvre loading but also for simulated gust loading and programme loading. It was found that, at comparable...

Equations for the response of an airplane to non-stationary atmospheric turbulence patches

In this report a method is described to calculate the load exceedance curve for a linear system having a finite, modulated Gaussian process as input. The derivation is based on the use of ensemble averages, defined as the expected values at a certain point of time. The equations can be used for any airplane-transfer function for which the Power...

Heat treatment studies of aluminium alloy type 7050 forgings. Interim report no. 2: The effect of heat treatment on a variety of engineering properties

The effect of variety of heat treatments on various engineering properties was studied with the aim to derive an optimum heat treatment. The engineering properties comprised Vickers hardness, short-time tensile strength, fatigue crack propagation resistance, fracture toughness and stress corrosion resistance. The test results were compared with...

Comparison between the statistical discrete gust method and the power spectral density method

The Power Spectral Density method and the Statistical Discrete Gust Method to calculate aircraft design loads due to atmospheric turbulence are compared qualitatively and quantitatively on the basis of the load exceedance curves for certain aircraft models. It is shown that both methods are related to each other, giving the same results for...

Fracture toughness and fatigue properties of the new aluminium alloy 7475-T76

Residual strength tests have been performed on 610 mm wide centre cracked panels. During the tests, stable crack growth was filmed and crack opening displacements were measured. Fracture toughness was determined using the method of Feddersen. Flight simulation fatigue tests were carried out to investigate the crack propagation properties. A...

An evaluation of the mission analysis concept for the definition of gust design loads

The mission analysis concept for defining design loads is assessed and compared with the current design procedure based on Design Envelope Concepts. Although the Mission Analysis Concept permits design loads of equal probability of exceedance to be obtained for all components, this does not imply that a fixed failure probability for the aircraft...