Metal Fatigue


Metal Fatigue
Metallic fatigue occurred at both low and high temperature. It is considered mainly from the perspective of the interaction between the microstructure, the deformation mode, and the mechanical state (Pineau, et al., 2016). The fatigue strength of metals is depending on the crack growth resistance provided by the grain boundaries, the phase boundaries, and various dislocations present in the material (Vallellano, et al., 2009). Therefore, fatigue crack initiation position and the minimum load cycle number before initiation of fatigue are essential to determine in the fatigue analysis. (Topaç, et al., 2009).

Fatigue is a type of failure that takes place in the structures when exposed to dynamic forces. Those dynamic forces will produce dynamic stresses and give rise to fatigue failure of structures. The real-life example is fatigue failure of vehicle’s axle housing arisen due to dynamic stresses that induce by rough and uneven road surface (Topaç, et al., 2009). Next, fatigue failures are commonly aircraft component and the statistics indicated that fatigue failures account for approximately 60 % of the total failures (Bhaumik, et al., 2008). There are many factors that affect the fatigue of tools such as complicated stress cycles, engineering design, manufacturing and inspection, service conditions and environment, and materials (Bhaumik, et al., 2008).

Fatigue life denotes as number of stress cycles under particular stress magnitude, the fatigue failures will take place. According to study done by Pineau, et al., (2016), the conventional total fatigue life, NT is summation of initiation life, Ni and number of cycles consumed in crack propagation, Np. Next, fatigue life is affected by creep, fatigue and oxidation at high temperature (Pineau, et al., 2016). The fatigue process comprises of three stages, first stage is crack initiation, second stage is crack propagation as shown in Figure 1. Third stage is final failure which is cracking. These three stages start as a small crack is forming, then cracks growing bigger and lastly cracking.


Figure 1: Fatigue failure

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