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 MP_a and test began at 275 MP_a with a fixed step of 5 MP_a. Determine the fatigue strength if results obtained are described below.

Solution

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 σ_o = 275 MPa. Calculations are made by the help of the table.

Figure: Failures Survival Pattern

Eq. (22) is utilized for calculating fatigue strength, σ_e.

Substituting

σ _e  = 275 + 5 (( 7/8) + (1/2))

= 281.875 MPa.

Say 282 MP_a    (Ans.)