HA series servohydraulic testing machine
In the high cycle fatigue test (also S-N test) to DIN 50100, a material or component is stressed with a periodically changing (cyclic) load.
The high cycle fatigue test is used for the determination of finite life fatigue strength and high cycle fatigue strength for tensile, compression, flexure and torsion loading. Especially in the case of components, the high cycle fatigue test can determine weak points which can then be eliminated through construction or material alterations. Low cycle fatigue strength is not considered in high cycle fatigue testing—it is determined in the low cycle fatigue test.
In the high cycle fatigue test, the load amplitude and the mean load are constant during the single-stage fatigue test. Depending on the magnitude of the load amplitude, it can be applied with varying frequency before the specimen fails.
Mean, high and low stresses of the cyclic loading are constant for every high cycle fatigue test. For tests on the same S-N curve either only the mean stress, or only the ratio between high and low stress is changed.
Measured values of cyclic stress amplitude and number of cycles determined in several high cycle fatigue tests result in the S-N curve.
From the S-N diagram you can read the maximum number of load changes for a certain load amplitude.
The S-N curve is divided into three regions:
In double-logarithmic representation, the finite life fatigue range of the S-N curve is nearly straight. This straight line is also called finite life fatigue curve.
The position and slope of finite life fatigue curves depend on a number of influences: