How do you avoid fatigue failure?

Answer 1

Fatigue failure is the progressive failure of a material when it is repeatedly strained below its breaking point but at a level suffucient to cause fatigue. See Wikipedia article in links for lots more details. To avoid fatigue failure either: Reduce Stress Concentration (Kt) of your design. Use large radius or blend radius. For a flat plate with a hole, you can calulate the Kt. Surprisingly, you can drill a hole on each side of a hole to reduce the Kt---but it could reduce the overall static strength. Also, alter the bolt or rivet patterns. If the fatigue stress cycles from zero stress to peak stress, you can reduce the fatigue effect by raising the mean stress level. This is why it is helpful to increase the torque on a bolt. The higher torque increases the stress on the bolt so the stress will not drop to zero. Apply Shot Peen to finish of the part. This will remove any imperfections on the finish and will apply a compressive layer that helps keep a crack from initiating. There are other finishes that will also do the same. Perform a fatigue analysis using standard fatigue S-N curves and calcuate the predicted Fatigue Life of the part under the loads and spectrum that you plan for your part. Divide the calculated life by 4 and use this as the fatigue life for the part and plan to remove the part from service when it reaches this time. Suspect that since this question is in the mechanical engineering section the below answer is not the one the questioner was looking for but since it is also true..... Try not to do the same repetitive things too often. If you type on a keyboard year after year that part of your mind is going to tire out. Try new activities. Dont do the same thing all day. Get good sleep. Eat good food. Lots of fluids and fruit.