Question

Fatigue is one of the major factors that limit the use phase of a material. a) Please explain the general difference between \"creep\" and \"fatigue\". (2 P) b) Wöhler-curves (S/N-curves) can be used to illustrate the fatigue behaviour of materials. Please describe the stress-scenario that has been applied to create below shown Wöhler-curve with the help of given values for R and F. (4 P) 180 160 $R = -0.1$ $F = 2 \text{ Hz}$ 140 $R = \frac{\sigma_{min}}{\sigma_{max}}$ 120 $D = \sum \frac{n_i}{N_i}$ 100 80 60 $10^4$ $10^5$ $10^6$ $10^7$ $10^8$ $10^9$ $10^{10}$ c) With the help of above diagram please calculate damage D of the material after 250,000 cycles at 130 MPa and additional 4,000,000 cycles at 90 MPa. What do you conclude from your result? (6P) d) The shown Wöhler-curve does not cover stress-amplitudes above 180 MPa and below 70 MPa. Please explain. (3 P)

          Fatigue is one of the major factors that limit the use phase of a material.
a) Please explain the general difference between \"creep\" and \"fatigue\". (2 P)
b) Wöhler-curves (S/N-curves) can be used to illustrate the fatigue behaviour of
materials. Please describe the stress-scenario that has been applied to create
below shown Wöhler-curve with the help of given values for R and F. (4 P)
180
160
$R = -0.1$
$F = 2 \text{ Hz}$
140
$R = \frac{\sigma_{min}}{\sigma_{max}}$
120
$D = \sum \frac{n_i}{N_i}$
100
80
60
$10^4$
$10^5$
$10^6$
$10^7$
$10^8$
$10^9$
$10^{10}$
c) With the help of above diagram please calculate damage D of the material
after 250,000 cycles at 130 MPa and additional 4,000,000 cycles at 90 MPa.
What do you conclude from your result? (6P)
d) The shown Wöhler-curve does not cover stress-amplitudes above 180 MPa
and below 70 MPa. Please explain. (3 P)

Fatigue is one of the major factors that limit the use phase of a material.
a) Please explain the general difference between c̈reepänd f̈atigue.̈ (2 P)
b) Wöhler-curves (S/N-curves) can be used to illustrate the fatigue behaviour of
materials. Please describe the stress-scenario that has been applied to create
below shown Wöhler-curve with the help of given values for R and F. (4 P)
180
160
R = -0.1
F = 2 Hz
140
R = (σmin)/(σmax)
120
D = ∑(ni)/(Ni)
100
80
60
10^4
10^5
10^6
10^7
10^8
10^9
10^10
c) With the help of above diagram please calculate damage D of the material
after 250,000 cycles at 130 MPa and additional 4,000,000 cycles at 90 MPa.
What do you conclude from your result? (6P)
d) The shown Wöhler-curve does not cover stress-amplitudes above 180 MPa
and below 70 MPa. Please explain. (3 P)

Added by Ivan S.

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