Types of material fatigue

Material fatigue is a generic term for processes that occur in a material as a result of a cyclic load and consequently lead to an impairment of the function or even to the failure of a component. These processes are therefore based on material damage, which gradually increases as the load increases and ultimately ends in complete failure of the component. These processes are therefore based on material damage, which gradually increases as the time of loading expands and ultimately ends in a complete failure of the component. Depending on the component, this is the complete break or already the crack initiation. The appearance, the causes and the influences that lead to this malfunction are very diverse.

Depending on the type of stress, the fatigue processes can be divided into:

• Mechanical fatigue
• Thermal fatigue
• Thermomechanical fatigue
• Creep fatigue

In mechanical fatigue, the damage processes inside the material are caused by cyclic mechanical loads at largely constant temperatures. It is the most common cause of component failure due to material fatigue in many areas of technology. Examples of this are endless, whether wheel hub, wishbone, connecting rod or spindle of a machine tool, all these components recognize recurring loads that lead to corresponding fatigue.

If the stress is not caused by changing mechanical loads, but by changing thermal conditions in a component, it is referred to as thermal fatigue. It always occurs when thermal expansion is hindered as a result of uneven heating.

The combination of these previously mentioned two types of loading leads to technically frequent thermomechanical fatigue, often abbreviated as TMF. Here, too, there are countless practical examples. The blades of a gas turbine, the exhaust manifold or the piston of an internal combustion engine are only a few of them.

Another type of continuous material damage is creep fatigue. Especially with materials with a high tendency to creep, progressive or cyclically changing plasticizing leads to fatigue, which can develop to breakage. This failure mechanism is particularly important for soft solder connections such as those found in numerous electrical circuit boards.