Programmed Load Fatigue Tests on Notched and Welded Specimens of Al-Zn-Mg Alloys
MILITARY ENGINEERING EXPERIMENTAL ESTABLISHMENT CHRISTCHURCH (UNITED KINGDOM)
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The report describes constant amplitude and programmed load fatigue tests on notched and welded specimens in two high strength aluminium-zinc- magnesium alloys. It is shown that, with very few exceptions, the hypothesis that sigmanN 1 consistently underestimates life. For the notched specimens using the basic quadratic programme sigmanN varied from 0.8 to 14.8. For welded specimens using the same programme the value of sigmanN varied much less and was approximately 2.6 to 7.0 for pulsating tension loading. Changes in the order of application of programme blocks had a negligible effect on the values of sigmanN obtained. However, both for half tensile and for alternating loading, lower values of sigmanN were obtained. When a spectrum parallel to the constant amplitude S-N curve was used high values of sigmanN were obtained, except when the lowest stresses in the programme were omitted. This fact led to the belief that a possible reason for the high values of SIGMAnN is coaxing at the lowest stress levels in the programme.
- Metallurgy and Metallography