Scanning electron microscopy of fracture surfaces of carton composite materials

A microscopic study has been performed on carbon composite fracture surfaces, using the Scanning Electron Microscope (SEM). It appears that the SEM is a useful tool to examine the fracture surface characteristics of composite materials failing under different loading conditions.

Influence of gust spectrum variations on fatigue crack growth behaviour of damage tolerant aluminium-lithium sheet materials

Flight simulation fatigue growth tests were done on 1.6 mm thick sheets of the damage tolerant aluminium-lithium (Al-Li) alloys 2091-T84 and 8090-T81 in comparison with the industry standard conventional damage tolerant alloy 2024-T3. The flight simulation load spectrum, the gust spectrum MINITWIST, was used in four versions: untruncated,...

Fractographic and microstructural analysis of fatigue crack growth in Ti-6Al-4V fan disc forgings

The constant amplitude and flight simulation (TURBISTAN) fatigue crack growth behaviour of Ti-6A1-4V fan disc forgings tested in the AGARD engine disc cooperative test programme was investigated by fractographic and microstructural analysis. The crack growth curve shapes and fractographic characteristics were similar. Transitions in the fatigue...

Breukvlakonderzoek

In this report an attempt is made to give an overview of the various aspects involved in a fracture surface investigation, stating with a definition of fractography and why it is done. Then the equipment needed is discussed, including stereo-microscopes, optical microscopes, transmission and scanning electron microscopes, and micro-analysis...

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...

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...

Vacuum fatigue fracture in titanium alloy plate

Fractography of fatigue crack propagation in 2024-T3 nx 7075-T6 aluminium alloys tested in air and vacuum

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...

Evaluation of non-destructive inspection methods applied to milled step-down areas

The present report describes how fatigue cracks were produced in 102 specimens. After cracking these specimens were inspected non-destructively by means of eddy currents, ultrasonics. X-rays and penetrants, and the indications were recorded. Successively the specimens were exposed to corrosion whereafter the inspections were repeated. Upon...

Crack resistance, fracture toughness and instability in damage tolerant Al-Li alloys

A comparison is made of the crack resistance (R-curve), fracture toughness and instability behaviour of candidate damage tolerant aluminiumlithium alloys, 2091 and 8090, and the widely used conventional 2024-T3 alloy. The 2091 alloy was in three heat treatment conditions, T8X, TX and TY, all artificially aged. The 8090 alloy was in the T81...

Microstructural and fractographic analysis of fatigue crack propagation in 2024-T351 and 2324-T39

Differences in the fatigue crack propagation rates of 2024-T351 and 2324-T39 are explicable from differences in microstructures. The slope changes (transitions) in the crack propagation curves are probably associated with the plastic zone sizes being equal to certain microstructural dimensions. As a consequence of different chemical compostion...

Failure and cracking of Inconel 718 air supply manifold support rods: A service-related contribution to lEPG TA 31

In 1995 an air supply manifold support rod from a high-performance turbofan engine failed by bending fatigue. The rod material was Inconel 718, operating at about 550° in an air environment. Diagnostic aspects of the failure (fatigue in bending, Stage I and Stage II fatigue fracture characteristics, and interference colours due to fracture...

Damage assessment and preservation of an Egyptian silver vase (300 - 200 B.C.)

An Egyptian metal vase from the Ptolemaic period was investigated metallurgically and fractographically. The metal is nearly pure silver, and chemical analysis indicates it was obtained from the cupellation of lead. Despite its high purity (in archaeological terms) the metal is severely cracked and embrittled, with fractures mainly along grain...

Comparison of fracture toughness in titanium alloys IMI 550 and IMI 551

Fracture toughness tests on two high strength titanium alloys, IMI 550 and 551, showed that the higher strength alloy, IMI 551, had a much lower toughness. The alloys were very similar in microstructure and fracture mechanisms. A number of model formulations for predicting fracture toughness were compared with the experimental results. This...

Corrosion fatigue crack arrest in aluminium alloys

The economic life of airframes is largely determined by widespread initiation and growth of fatigue cracks at low stress intensities. Any factor reducing the low stress intensity fatigue damage rate could, if controllable, increase the structural durability. One such factor is corrosion fatigue crack arrest. Corrosion product build-up within a...