In our today’s blog post about the fatigue strength of metals and alloys. Usually, this type of resistance is represented as S-N curves. Here the stress with the number of cycles to failure are related.
High temperature fatigue.
Temperature has a significant effect. It is well known that an increase in temperature always results in an decrease in the fatigue strength. But what is the quantification of this decrease? Right by alloy and temperature. And in the event that there is an overlap between a static load and high temperature vibration? In such cases, we will be in the presence of an extremely complex and worse behavior than that of the creep (that is, with an applied load statically)
Fatigue strength – Focus on creep.
As mentioned above, the creep is a phenomenon of growing over time deformation continuously. During this phenomenon the load remains constant instead. But what are the primary mechanisms? Mainly to the processes of hardening and recrystallization as
- crystallographic plans slip
- the fomation of subgrains
- the slide of grain boundaries.
And when you enable the creep? In the presence of a homologous temperature/To (ratio of metal temperature and melting temperature, expressed in K) of more than 0.4÷ 0.5. What promotes the creep strength? As a rule, all obstacles to the restoration as
- compact crystalline structure
- presence of thermally stable precipitates.
The thermal fatigue.
In addition to mechanical vibration, there are other sources of cyclic stresses. The variables thermal gradients, for example, can lead to plastic deformation. In addition, if these gradients are cyclical they may incur in cyclic deformations, inducing the break component.
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