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van Leeuwen, H.P. (author), Schra, L. (author), Meulman, A.E. (author)Fatigue cracks were grown in rectangular specimens with a central notch. At a certain crack length, the crack was repaired, using a variety of methods. Fatigue loading was resumed and re-initiation and subsequent growth of the fatigue crack were studied. The repair methods evaluated comprised simple stopholes, brazed straps across the crack,...report 1970
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van Leeuwen, H.P. (author), van der Vet, W.J. (author), Schra, L. (author)Correlation diagrams show that fracture toughness and fatigue crack propagation resistance are closely related properties, while stress corrosion endurance is a crack tolerance property with different characteristics. The heat treatment effects on characteristic dimensions of the microstructure could generally be explained on the basis of...report 1970
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Schra, L. (author), van der Vet, W.J. (author), van Leeuwen, H.P. (author)Porgings were given a variety of heat treatments after which hardness, static tensile properties, fatigue properties, fracture toughness and stress corrosion resistance were determined. Microstructures were studied in the electron mcroscope using the thinfoil technique. The effect of heat treatment on the microstructure could be explained on the...report 1972
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- van Leeuwen, H.P. (author), Schra, L. (author), Boogers, J.A.M. (author) report 1972
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van Leeuwen, H.P. (author), Schra, L. (author)Material from forgings rejected after cracking in service was given a variety of heat treatments. Material aged to peak hardness was susceptible to SCC at all ageing temperatures. Overageing at temperatures around 160° C imparted a significant increase in SCC resistance while useful strength was retained. An additional one week ageing at 160° C...report 1973
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Schra, L. (author), van Leeuwen, H.P. (author)Data presented by Branger, and indicating an effect of loading rate on residual strength of aluminium alloys and steels, are analysed using fracture mechanics. It is found that the apparent effect is largely or wholly due to the combination of two causes i.e. - the static data pertain to systematically shorter crack lengths than the dynamic...report 1974
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Wanhill, R.J.H. (author), Schijve, J. (author), Jacobs, F.A. (author), Schra, L. (author)The following text is given in the format required for presentation at the Conference and Exhibition "Fatigue Testing and Design", to be held in the City University, London, 5-9 April 1976. The report gives a comparison between the fatigue performances of several sheet and forging materials under gust spectrum loading representing the lower wing...report 1975
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van Leeuwen, H.P. (author), Schra, L. (author)The literature is reviewed with respect to: - tests conducted to investigate crack re-initiation under dynamic load and arrest of a running crack - metallurgical sources of rate effects - available data for aerospace engineering materials - mechanical sources of rate effects, i.e. dynamic crack tip stresses and kinetic energy effects Conclusions...report 1975
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Schra, L. (author), van Leeuwen, H.P. (author)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...report 1976
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Schra, L. (author), van Leeuwen, H.P. (author), Meulman, A.E. (author)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...report 1976
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Wanhill, R.J.H. (author), Schra, L. (author)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...report 1976
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- Wanhill, R.J.H. (author), Jacobs, F.A. (author), Schra, L. (author) report 1976
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Schra, L. (author), van Leeuwen, H.P. (author)The tip of a growing stress corrosion crack was photographed at a magnification of 72 x and at 30 sec. intervals. The crack appeared to grow in a discontinuous manner. Crack reinitiation was preceded or accompanied by gas evolution.report 1977
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Schra, L. (author), van Leeuwen, H.P. (author)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...report 1977
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- Bartelds, G. (author), Schra, L. (author) report 1978
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't Hart, W.G.J. (author), Schra, L. (author)An experimental investigation.was performed on 80 mm thick plate material of 7OIO-T7651 and 7OIO-T73651 developed by Alcan Industries Ltd in U.K. The testing programme involved: tensile tests, fracture toughness, stress corrosion and fatigue tests. For comparison a similar investigation vas carried out on 7075-T7351 Alcoa plate material.report 1979
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Schra, L. (author)The engineering properties of the aluminium alloys AAT075-TT3, AAT175-TT36, AA705O-T736 and the German alloy AZ74.6l were compared. The properties involved were: strength, fracture toughness, fatigue crack propagation under different load spectra, and resistance to stress corrosion cracking both with respect to initiation and propagation. The...report 1979
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Wanhill, R.J.H. (author), 't Hart, W.G.J. (author), Schra, L. (author)The fatigue crack propagation resistances of 7010-T7651, 7010-T73651 and 7075-T7351 thick plate were compared for flight simulation (gust spectrum) loading conditions. 7075-T7351 was slightly superior, and it was shown that this superiority was not essentially due to the higher fracture toughness of this alloy. The influence of specimen...report 1979
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Schra, L. (author), Wanhill, R.J.H. (author)An extensive programme of notched fatigue testing of aluminium forging alloys has shown that the data result in two basic forms of S-N curve. Analytical approaches to constructing the S-N curves were less satisfactory than fitting the curves freehand. Since freehand curve fitting m\ist involve an element of subjectivity, guidelines for...report 1980
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't Hart, W.G.J. (author), Kolkman, H.J. (author), Schra, L. (author)The Jominy end-quench test was applied to extruded rods of the aluminium alloys 2024 and 7075 to obtain a decreasing quench rate over the length of the rods. Subsequently the alloys were heat treated to the conditions: 2024-T4, 2024-T6, 7075-T73. A corrosion investigation and a transmission electron microscopy investigation were performed to...report 1980