"A steel rotating-beam test specimen has an ultimate strength of 120 kpsi. Estimate the life of the specimen if it is tested at a completely reversed stress amplitude of 70 kpsi."

life (N) of the specimen is 117000  cycles

Explanation:

given data

ultimate strength Su = 120 kpsi

stress amplitude σa = 70 kpsi

solution

we first calculate the endurance limit of specimen Se i.e

Se = 0.5× Su   .............1

Se = 0.5 × 120

Se = 60 kpsi

and we know strength of friction f  = 0.82

and we take endurance limit Se is = 60 kpsi

so here coefficient value (a) will be

a =     ......................1  

put here value and we get

a =  

a = 161.4  kpsi

so coefficient value (b) will be

b =  

b =    

b = −0.0716

so here number of cycle N will be  

N =  

put here value  and we get

N =  

N = 117000

so life (N) of the specimen is 117000  cycles

i think its

when it gains or loses electrons