fatigue limit

fatigue limit is the highest stress that a material can withstand for an infinite number of cycles without breaking —called also endurance limit

The endurance limit, also known as fatigue limit, is a stress level below which a material has an "infinite" life. Infinite life is commonly considered to be 1 million cycles. Ultimate strength alone is explained here, its purpose on this page is to show how it is related to the endurance limit. 

The maximum stress that can be applied to a material during a specified number of stress cycles without causing failure of the material being stressed.