Fatigue Testing Machine

A fatigue testing machine is a device used to repeatedly load a material or component so engineers can study how it fails under cyclic stress rather than a single overload. German engineer August Wohler built early apparatus of this kind to repeatedly load railway axles, after being appointed in 1852 to investigate why axles were fracturing; his work over the following two decades established what became known as the Wohler curve, or S-N curve, relating the stress a part experiences to the number of cycles it can survive before failing. Wohler presented his findings internationally at the Paris Exposition of 1867, and his research demonstrated that fatigue failure begins as a crack that grows from a surface defect until the remaining material can no longer bear the load, addressing a serious nineteenth century safety problem in which sudden fatigue fractures of railway components caused numerous accidents.