What is cyclic fatigue? Why is important for engineers to understand cyclic fatigue? Do materials all experience fatigue the same way?

Fatigue of a material is the loss of the strength of any material due to repeated application of stresses both tensile and compressive in a cyclic manner. Fatigue causes gradual loss of strength and is accompanied by initiation of cracks in the material. Once the crack has been formed the stress concentration at the crack exceeds the toughness of the material causing complete fracture of the material.

The materials the we use are constantly under action of cyclic stresses take an example of the suspension of vehicles and trains or the metal parts in an aeroplane or various bolts and nuts of a steel bridge. These components are under constant cyclic stresses and if failure occurs in such structures it will cause loss of life and property. Thus while designing any machine part we need to take into account the deterioration in the material that will occur due to such repeated loading, thus it becomes important to study this property of materials to better understand their behavior.

Fatigue in a material depends on the loading pattern meaning the rate of loading, magnitude of loading and type of loading also the fatigue strength of materials is different and is determined by endurance testing of the materials. Ductile materials have different fatigue properties as compared to brittle materials.