What is fatigue failure and what is a Wöhler curve?

Material fatigue test

• Similar springs are subjected to cyclical stresses of decreasing magnitude
• Each spring failure is plotted as a point on the curve, according to the number of cycles to failure
• Springs that withstand the stresses for more than 10 million cycles are considered to be durable
• The almost horizontal part of the curve defines the fatigue limit of the spring