The type of specimen used depends on the testing machine and on the aim of the test. Factors like geometry, machining, thermal treatments, grain size and superficial finishing of the specimen have great influence on the fatigue resistance.
One specimen has three main parts: the gauge length, the grip section and the transition section. The gauge length is the place where the stress, strain, temperature and environmental conditions are measured, it is also the place where the crack appears. The grip sections are designed to transmit the load from the headlocks of the machine and they have to be identical on both sides. The transition zones between the grip sections and the gauge length are designed with smooth radii in order to minimise the stress concentration.
The different standards define basic configurations for cylindrical specimens.