Statement: $,$ An M$12$ x $1\mathrm{.}25,$ class $9\mathrm{.}8$ bolt with rolled threads is preloaded to $85\%$ of its proof strength when

clamping a $5-$cm$-$thick sandwich of aluminum. Find the safety factors against fatigue failure,

yielding, and joint separation when a $2\mathrm{.}5-$kN $($peak$)$ fluctuating external load is applied. Use $99\%$

reliability.

Given:

Bolt diameter $,$d:$=12*$mm

Preload fraction f$\_($p$)$:$=0\mathrm{.}85$

Clamp length $,$l:$=50*$mm

Number of bolts N$\_($bolts $)$:$=1$

Applied load $,$P$\_($tot $)$:$=2\mathrm{.}5*$kN

Material properties for class $9\mathrm{.}8$ bolt:

Proof strength $,$S$\_($p$)$:$=650*$MPa

Yield strength $,$S$\_($y$)$:$=720*$MPa

Ultimate strength S$\_($ut$)$:$=900*$MPa

Young's modulus E$\_($bolt $)$:$=206\mathrm{.}8*$GPa

Member modulus $,$E$\_($memb $)$:$=71\mathrm{.}7*$GPa

I need help with this problem, other people have posted the problem, but I feel that they are incorrect due to miscalculations and lack of explanation. Any assistance would be greatly appreciated. Thank you.