Fatigue test under operational stresses

An Fatigue test under operational stresses is required when developing plant, machinery, individual components and the associated connections.

It is intended to confirm that the components or assemblies will keep working correctly and safely in continuous operation throughout their calculated service life. Static, dynamic and random loads are included in the test. The dynamic loads may be periodic or impact loads. Environmental influences (temperature, Humidity, corrosive media, radiation, etc.) are also taken into account.

Proof needs to be provided that plant and machinery can withstand the loads in any situation, including exceptional events.

Strength under operational stresses (sometimes referred to as engineering strength) is defined based on behaviour vis-à-vis:

• Creep stresses (e.g. turbines at high temperatures)
• Wear in the case of Friction couples (Gear wheels, rails and rail wheels)
• Special loads (denting, buckling, impacts e.g. on vehicles when driving over potholes)
• Vibration (fatigue) loadings, including cyclic ones with constant (Wöhler curve) or variable (Gassner curve) amplitude to determine the fatigue limit (e.g. for crankshafts, connecting rods), finite-life fatigue strength (for door hinges, etc.) or low cycle fatigue (for items such as reactor pressure vessels)