Fracture Mechanics
Session 16
8/15/2019
1
Fatigue life estimation by
Fatigue crack growth analysis
2
Fatigue crack growth analysis
Material characterization
Fatigue crack growth analysis
Material characterization
4
Fatigue crack growth analysis
Material characterization
Fatigue crack growth analysis
6
Fatigue crack growth analysis
7
Example
Determine no of total life cycles to failure
8
Stress intensity factor
Critical stress intensity factor
9
Critical crack length
10
11
Determine no of total life cycles to failure
12
Fatigue crack growth analysis
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Application : 5
8/15/2019
8/15/2019
8/15/2019
8/15/2019
Fatigue life estimation by
Strain based-life analysis (cyclic strain)
20
Strain-life analysis
Strain-life analysis has found broad acceptance in the
automotive and aerospace industries for component
design in the early stages of design.
It allows reasonable prediction of fatigue life in design
before components are available for actual fatigue
testing, which results in a reduction in the number of
design iterations and a speed up in the Product
development cycle. A number of specialized
computer programs are available to assist in the
design analysis.
21
High cycle and Low cycle fatigue
Strain-life analysis
Typical cyclic stress-strain loop.
23
Strain-life analysis
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Strain-life analysis
25
Strain-life analysis
26
Strain-life analysis
Typical strain-life curve for mild steel.
Both the elastic and plastic curves are approximated as straight
lines. At small strains or long lives, the elastic strain
predominates, and at large strains or short lives the plastic
strain is predominant.
27
Strain-life analysis
28
Strain-life analysis
29
Strain-life analysis
Stress analysis at a notch using Neuber’s analysis.
30
Strain-life analysis
31
Strain-life analysis
32
Strain-life analysis
Imp Equations
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Strain-life analysis
Imp Equations
34
Example
Strain-life analysis
Determine no of life cycles to initiate 1mm of crack
35
Strain-life analysis
Imp Equations
36
Example
Strain-life analysis
We have,
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Strain-life analysis
We have,
We have,
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Strain-life analysis
39
Strain-life analysis
We have,
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Strain-life analysis
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