Please explain crack initation and propagation during metal fatigue? Explain factors that affect fatigue life and solutions to prevent fatigue failure. Explain environmental effects on fatigue behavior of materials.
Design Against Fluctuating Loads
Machine elements are subjected to varieties of loads, some components are subjected to static loads, while some machine components are subjected to fluctuating loads, whose load magnitude tends to fluctuate. The components of a machine, when rotating at a high speed, are subjected to a high degree of load, which fluctuates from a high value to a low value. For the machine elements under the action of static loads, static failure theories are applied to know the safe and hazardous working conditions and regions. However, most of the machine elements are subjected to variable or fluctuating stresses, due to the nature of load that fluctuates from high magnitude to low magnitude. Also, the nature of the loads is repetitive. For instance, shafts, bearings, cams and followers, and so on.
Design Against Fluctuating Load
Stress is defined as force per unit area. When there is localization of huge stresses in mechanical components, due to irregularities present in components and sudden changes in cross-section is known as stress concentration. For example, groves, keyways, screw threads, oil holes, splines etc. are irregularities.
Please explain crack initation and propagation during metal fatigue? Explain factors that affect fatigue life and solutions to prevent fatigue failure. Explain environmental effects on fatigue behavior of materials.
![Table 5.2
A Tabulation of
Diffusing
Species
D(m²/s)
Host Metal
QJ/mol)
Diffusion Data
Interstitial Diffusion
Fe (a or BCC)
1.1 x 10-
87,400
Fe (y or FCC)
2.3 x 10-
148,000
Fe (a or BCC)
5.0 x 10-7
77,000
N°
Fe (y or FCC)
9.1 x 10-
168,000
Self-Diffusion
Fe
Fe (a or BCC)“
Fe (y or FCCY
2.8 x 10-
251,000
Fe
5.0 x 10-
284,000
Cu (FCC)
Al (FCC)
Cu
2.5 x 10-
200,000
Al
2.3 x 10-
144,000
Mg
Mg (HCP)
1.5 x 10
136,000
Zn
Zn (HCP)
1.5 x 10-
94,000
Mo
Mo (BCC)
1.8 x 10-
461,000
Ni
Ni (FCC)
1.9 x 10
285,000
Interdiffusion (Vacancy)
Cu (FCC)
Zn (HCP)
Zn
2.4 x 10-
189,000
Cu
2.1 x 10-
124,000
Cuf
Al (FCC)
6.5 x 10-
136,000
Mg
Al (FCC)
1.2 x 10-
130,000
Cuf
Ni (FCC)
2.7 x 10-
256,000
Ni
Cu (FCC)
1.9 x 10-
230,000
*There are two sets of diffusion coefficients for iron because iron experiences a phase trans-
formation at 912°C; at temperatures less than 912°C, BCC a-iron exists; at temperatures
higher than 912°C, FCC y-iron is the stable phase.](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fc40b2f61-3db2-429b-87a4-eaeaa483f227%2F40d2ad82-c9ce-4eb8-bc8c-709d5eb780e7%2Fibu2fri_processed.png&w=3840&q=75)
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