In materials science , uses loads of fatigue caused by the weakness of material over and over again . This is a gradual localized structural damage that occurs when the material is exposed to cyclic loading . Stressvalues maximum value that caused this damage could be much less than the tensile strength of the material usually as surface tension , reduce or restrict the effort described below.
For the following reasons :
Fatigue happens when you download the materials and discharged several times. If you download a certain threshold , and microscopic cracks will begin to focus on the level of stress, and slip bands Pollutants ( PSBs ) and total interfaces . Finally, the crack reaches critical size , the crack suddenly released , and the structure will fail .
Fatigue life of ASTM, NF is defined as the number of stress cycles of a specific nature is to keep the specimen before failure occurs, the specific nature .
Fatigue properties :
• Fatigue is a process that has a degree of chance , showing the often large scatter even in controlled also .
• fatigue normally associated with tensile stress , were reported crack fatigue loads due to pressure .
• Increasing the amplitude of the applied stress , and longer life.
• dispersion tends to increase the fatigue life fatigue strength is .
• cumulative damage . The rest of the material to recover.
• 1837: Wilhelm Albert publishes the first article on fatigue . He designed the test machine to conveyor chains used in the Clausthal mines .
• 1842: William John Rankin Macquorn importance of stress concentrations in their research failed to recognize rail hubs . Versailles train crash in central fatigue .
• 1903: Sir James Alfred Ewing explains the origin of failure and fatigue cracks in the microstructure .
• 1910: OH Basquin log curve refers to the relationship between the SN, using test data and Lawler .
• 1945 AD : Miner popular AM (1924) A. Palmgren linear damage hypothesis as a tool design process .
• 1970: W. Elber mechanism and the importance of bridging the gap survey wedging effect of slowing the growth of fatigue cracks due to plastic deformation behind the crack tip .
High- cycle fatigue :
Historically , have been paying more attention in situations that require more than 104 cycles to failure in tension and the elastic deformation is concentrated in the first place.
Payment cycle fatigue , the material is generally a curve SN, also known as the curve is determined by Lawler . Is a graph of the amount of stress League (S) on a logarithmic scale of cycles to failure (N) is .
It is known in some cases, this process test coupon .
Probabilistic nature of fatigue :
This complex :
In practice , and the mechanical part of the complex , and often random , a series of loads , large and small , are located . To assess the safe life of this section :
1 reduces this complexity into a series of periodic shipments...