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By Claudio Schoen, Associate Professor at the University of São Paulo about Non-linear thinking. Research area – Materials Science (general), Materials Mechanics and Computational Thermodynamics.

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Back in year 1996 Walter Schütz, in his work “A history of fatigue” told the history on how Gassner in 1941, measuring the fatigue strength of high strength aluminum alloys of the series 7XXX (Al-Zn-Mg), and finding this was not much different from the lower strength, lower cost, alloys of series 2XXX (Al – Cu), warned that if they were used, for example, to build an airplane, this would lead to premature fatigue failures.

This argument is tricky and seems illogical. Aren’t the alloys of series 7XXX of higher strength compared to alloys 2XXX? And didn’t Gassner find out the fatigue strength was about the same? So why would the fatigue live be smaller if the 7XXX alloys were used?

The explanation for this apparent contradiction is simple. The only possible reason to use a higher strength alloy (especially when it is more expensive) in place of…

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