Determine the fatigue strength of medium carbon steel:
For determining the fatigue strength of medium carbon steel 15 specimens, identical in all respect were tested in cantilever rotating beam fatigue testing machine. The ultimate tensile strength of steel was known to be 550 MPa and test began at 275 MPa with a fixed step of 5 MPa. Determine the fatigue strength if results obtained are described below.
As a first step plot survival (o) and failure (x) pattern form visual depiction. From the plot it is seen that the lowest level at which survival is obtained is σo = 275 MPa. Calculations are made by the help of the table.
Figure: Failures Survival Pattern
Eq. (22) is utilized for calculating fatigue strength, σe.
σ e = 275 + 5 (( 7/8) + (1/2))
= 281.875 MPa.
Say 282 MPa (Ans.)