Respuesta :
Answer:
Actaul endurance stress = 190.826 MPa
Explanation:
we know ultimate tensile strength S_{UT} for AISI 3149 steel is 689.5 MPa
endurance of material Sn = 0.5 Sut
[tex]= 0.5 \times 689.5 = 344.75 MPa[/tex]
surface factor
[tex]K_{surf} a Sut^b[/tex]
for mechanical surface a = 4.51 and b = - 0.265
PUTTING ALL VALUE
[tex]K_{surf} = 0.79[/tex]
size modification factor Ksize
equivalent diameter [tex]de = 0.808\times (hb)^{1/2}[/tex]
where b =w = 30 mm and h = 60 mm
so de is 34.2805 mm
[tex]K_{size} = [\frac{d}{7.62}]^{-0.107}[/tex]
[tex]K_{size} = [\frac{34.28}{7.62}]^{-0.107} = 0.85[/tex]
Loading factor
for reversal bending load Kb = 1
Reliability factor
[tex]K_{rel} = 1 - 0.08 Za[/tex]
we know for 99% reliablity Za = 2.326
[tex]K_{rel} = 1 - 0.08\times 2.326 = 0.814[/tex]
so Actaul endurance stress of materail
[tex]Se' = Se\times K_{surf} \times K_{size} Kb \K_{real}[/tex]
[tex]= 344.75\times 0.8\times 0.85\times 1\times 0.814[/tex]
= 190.826 MPa
