What is fatigue in any structural member?
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Fatigue is a condition in which material is subjected to cyclic or reverse loading, and the material will fail when it’s no of the designed cycle is over. Fatigue strength study is generally carried out in the case of the machine, and 80-85% of material failure in the machine is done fatigue failure.
The fatigue strength is found such that material can withstand maximum no of reverse Cycles.
The reduction in strength of a member due to cyclic loading is called fatigue. However, the fatigue reaches a constant point over a time. This point is called the endurance limit. The reduction in strength of the member, i.e., fatigue, cannot go beyond a certain value. That value is called as the ENDURANCE LIMIT and it is explained in this graph. The endurance limit mostly happens after 2 million loading cycles.
Fatigue is the gradual and progressive weakening of a structural member due to prolonged cyclic loading-unloading of the member for a large number of times at stress levels fairly below the ultimate strength or ultimate stress of the member.
It is important to note that fatigue doesn’t weaken the material due to the prolonged loading but due to multiple reversals of stress and strain for often around a million times.
Initially, micro cracks begin to appear. Now, it is known that stress concentration happens at these microcracks and all sharp openings, slots, and edges. The stresses at these spots can be 3 to 15 times that of the stress applied. This progresses the cracks. Gradually they keep building up till the material fails at the number of cycles depending on the magnitude of the load.
Though, below a certain threshold level of stress, fatigue failure doesn’t happen even at an infinite number of cycles. This stress level is called the endurance limit or fatigue limit. The number of cycles to failure decreases exponentially with increasing stress till it becomes one at the ultimate stress of the member
fatigue is the weakening of a material caused by cyclic loading (repetitive loading) like vehicle load on the bridge and human load on foot over bridge at railway stations
Structural fatigue is the process where a compound begins to develop cracks when loaded with a time-varying load. Fatigue is dependent on many factors, the main contributors to failure are ; no of load cycles. Thus, concrete fatigue refers to the phenomenon of rupture under repeated loadings, each of which is smaller than a single static load that exceeds the strength of the material.
Concrete fatigue refers to the phenomenon of rupture under repeated loadings, each of which is smaller than a single static load that exceeds the strength of material.