Accu157
Apr 05, 2009, 07:55 PM
http://www.experimentalhelo.com/Anodizing&Fatigue.pdf
Basically, aluminum parts that are anodized are not necessarily being helped in the endurance department, and MANY r/c model helicopters have anodized parts under oscillating stress. Not just helicopters, cars, boats, etc. And anodizing is considered an aesthetic selling point. From this article perspective, anodizing is hardly an upgrade that cannot be blown off as irrelevant. A guy crashed a real helicopter due to this, and it only had a couple hundred hours of flight time.
To the layman: (deliberately avoiding engineering talk)
The tighter the curvature of a part, the greater the stress on that curving element you are looking at. While you may be putting only say, 20 pounds of force on that tube, the internal forces are several thousand pounds per square inch. Aluminum itself is fine stress wise, but when a cleaner is used on it, the etching can produce tiny fissures in the steel that have extremely tight curvature. Stretch and compress several thousand times later (perhaps several hundred thousand), that little fracture continues to progress molecule by molecule, break by break. Now, the cleaning process (using particular cleaner types in the article) can produce these little cracks. Anodizing, produces a layer on the aluminum (essentially ruby) that cannot handle the stresses whatsoever, but it looks nice. The aluminum oxide + coloring breaks in tiny lines, and is strongly adhered to the aluminum. That tiny fracture is then put into the aluminum. Wash, rinse, repeat, CRACK! Again and again until it works it way through. The article references a strong recommendation to not anodize flight critical components, and look at what the modeling world has done. Much higher frequencies than on the real thing (higher rate of fracturing), not necessarily the same forces. The article also says that many mechanical engineers are not familiar with this problem. Anyway, this is modeling science, so perhaps we can find a way to analyze this possible problem. The live cycle of an anodized part under controlled testing was reduced by a factor of 5.7. That is a lot.
Basically, aluminum parts that are anodized are not necessarily being helped in the endurance department, and MANY r/c model helicopters have anodized parts under oscillating stress. Not just helicopters, cars, boats, etc. And anodizing is considered an aesthetic selling point. From this article perspective, anodizing is hardly an upgrade that cannot be blown off as irrelevant. A guy crashed a real helicopter due to this, and it only had a couple hundred hours of flight time.
To the layman: (deliberately avoiding engineering talk)
The tighter the curvature of a part, the greater the stress on that curving element you are looking at. While you may be putting only say, 20 pounds of force on that tube, the internal forces are several thousand pounds per square inch. Aluminum itself is fine stress wise, but when a cleaner is used on it, the etching can produce tiny fissures in the steel that have extremely tight curvature. Stretch and compress several thousand times later (perhaps several hundred thousand), that little fracture continues to progress molecule by molecule, break by break. Now, the cleaning process (using particular cleaner types in the article) can produce these little cracks. Anodizing, produces a layer on the aluminum (essentially ruby) that cannot handle the stresses whatsoever, but it looks nice. The aluminum oxide + coloring breaks in tiny lines, and is strongly adhered to the aluminum. That tiny fracture is then put into the aluminum. Wash, rinse, repeat, CRACK! Again and again until it works it way through. The article references a strong recommendation to not anodize flight critical components, and look at what the modeling world has done. Much higher frequencies than on the real thing (higher rate of fracturing), not necessarily the same forces. The article also says that many mechanical engineers are not familiar with this problem. Anyway, this is modeling science, so perhaps we can find a way to analyze this possible problem. The live cycle of an anodized part under controlled testing was reduced by a factor of 5.7. That is a lot.