b$)$ W$$hler$-$curves $(\frac{S}{N}-$curves$)$ can be used to illustrate the fatigue behaviour of

materials. Please describe the stress$-$scenario that has been applied to create

below shown W$$hler$-$curve with the help of given values for $R$ and $F.(4$ P$)$

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 $?(6$ P$)$

d$)$ The shown W$$hler$-$curve does not cover stress$-$amplitudes above $180$ MPa

and below $70$ MPa. Please explain.