Revelando os 6 fatores que afetam as propriedades de fadiga dos materiais

Revealing the 6 factors that affect the fatigue properties of materials

If the cyclic stress is shown in the sequence 1-2-3-4, and the average stress is represented by S I, the addition of a compressive residual stress S will result in a new stress level of 1′-2′-3 ′-4′, which is a superposition of the original voltage sequence and -S resolution . This leads to a reduction in the mean stress for S ' resulting in improved fatigue performance.

Common methods for increasing component life include surface shot peening, cold extrusion of parts, and the introduction of residual compressive stress on their surface.

The resistance of the material has a direct impact on its fatigue performance. Higher material strength leads to a lower level of cyclic stress and therefore a longer service life and better life extension effects.

Shot peening is especially effective in areas with stress gradients or notch stress concentrations.

Surface nitriding or carburizing treatments can improve the surface strength of the material and induce compressive residual stress, which contribute to improved fatigue performance.

Test results indicate that nitriding or carburizing treatments can double the fatigue limit of steel. This effect is even more pronounced in specimens with notches.

Influence of environment and temperature

The SN curve of materials is normally obtained under room temperature and atmospheric conditions. Fatigue in corrosive environments such as seawater, acids and alkalis is called corrosion fatigue.

The presence of corrosive media has a detrimental effect on fatigue.

Corrosion fatigue is a complex process that involves mechanical and chemical actions and its failure mechanism is complex.

There are several factors that influence corrosion fatigue, and the general trend is as follows:

  1. The effect of load cycle frequency is significant. In non-corrosive environments, frequency has little effect on the SN curve of materials over a relatively wide frequency range (such as 200 Hz). However, in corrosive environments, as the frequency decreases, the time experienced by the same number of cycles increases, providing sufficient time for corrosion to have a significant impact on the decline in fatigue performance.
  2. Semi-immersion in corrosive media (such as seawater) is more unfavorable than complete immersion.
  3. Corrosion-resistant steels with good corrosion and fatigue resistance perform better than common carbon steels, which show a significant decrease in their fatigue limit, or even its complete disappearance, in corrosive environments.
  4. The fatigue limit of metallic materials generally increases with decreasing temperature. However, as the temperature decreases, the fracture toughness of the material also decreases, leading to brittleness at low temperatures. Once cracks occur, instability fracture is more likely to occur. High temperatures reduce the strength of materials, can cause creep and are unfavorable to fatigue. It should also be noted that the compressive residual stress introduced to improve fatigue performance will also disappear with increasing temperature.

Conteúdo relacionado

Back to blog

Leave a comment

Please note, comments need to be approved before they are published.