----[Please read http://ercoupers.com/disclaimer.htm before following any advice in this forum.]----At 01:34 PM 2/10/2006, [EMAIL PROTECTED] wrote:
Is stress corrosion cracks in rivets unique to Ercoupes, what causes it, can it be prevented
would it not apply to all aircraft, which comes first the crack or the corrosion?
Check out the FAA web site and get a copy of AC43-4a (broadband suggested).
Excerpt from same:
a. Stress Corrosion Cracking. Stress corrosion cracking is an intergranular cracking of the metal which is caused by a combination of stress and corrosion (see Figures 2-12 through 2-14). Stress may be caused by internal or external loading. Internal stresses are produced by nonuniform deformation during cold working, by unequal cooling from high temperatures, and by internal structural rearrangement involving volume changes. Internal stresses are induced when a piece of structure is deformed during an assembly operation, (i.e., during pressing in bushings, shrinking a part for press fit, installing interference bolts, installing rivets, etc.). Concealed stress is more important than design stress, because stress corrosion is difficult to recognize before it has overcome the design safety factor. The level of stress varies from point to point within the metal. Stresses near the yield strength are generally necessary to promote stress corrosion cracking, but failures may occur at lower stresses. Specific environments have been identified which cause stress corrosion cracking of certain alloys. Salt solutions and seawater may cause stress corrosion cracking of high strength heat treated steel and aluminum alloys. Methyl alcohol hydrochloric acid solutions will cause stress corrosion cracking of some titanium alloys. Magnesium alloys may stress corrode in moist air. Stress corrosion may be reduced by applying protective coatings, stress relief heat treatment, using corrosion inhibitors, or controlling the environment. Shot peening a metal surface increases resistance to stress corrosion cracking by creating compressive stresses on the surface which should be overcome by applied tensile stress before the surface sees any tension load. Therefore, the threshold stress level is increased.
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