Fatigue Resistance of 787-composites
Join Date: Aug 2014
Location: Miami, FL
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I have to take issue with several posts here regarding metals. Steel is hardly some outlier metal or alloy in terms of having a fatigue endurance limit (basically the stress at which theoretically infinite cycles will not result in rupture).
In fact, many aluminum alloys at various tempers, titanium alloys at various agings, beryllium and other alloys all have specified fatigue endurance limits.
Here is a simple representative ranking of the ratio of fatigue strength to density of a sample of engineering metals/alloys:
titanium 10-2-3: 833,000 inches
beryllium hot-pressed: 597,000 inches
Ferrium M54 steel: 528,000 inches
aluminum 2024, T-4: 200,000 inches
You can see why titanium alloy 10-2-3 is a preferred alloy for aircraft landing gear.
Carbon fiber reinforced polymer (CFRP) is an extremely nice material, but it has been hyped to the point that many people are surprised to learn that it (only!) saves on the order of 10%-35% weight in most aircraft component applications vs aluminum alloys. It does have downsides versus metals, though, including being less rugged in service wrt external damage and wear.
In fact, many aluminum alloys at various tempers, titanium alloys at various agings, beryllium and other alloys all have specified fatigue endurance limits.
Here is a simple representative ranking of the ratio of fatigue strength to density of a sample of engineering metals/alloys:
titanium 10-2-3: 833,000 inches
beryllium hot-pressed: 597,000 inches
Ferrium M54 steel: 528,000 inches
aluminum 2024, T-4: 200,000 inches
You can see why titanium alloy 10-2-3 is a preferred alloy for aircraft landing gear.
Carbon fiber reinforced polymer (CFRP) is an extremely nice material, but it has been hyped to the point that many people are surprised to learn that it (only!) saves on the order of 10%-35% weight in most aircraft component applications vs aluminum alloys. It does have downsides versus metals, though, including being less rugged in service wrt external damage and wear.
Last edited by Mach Stall; 7th Dec 2015 at 22:11. Reason: clarity
