Answer
$σ_{min} = -140 MPa$ and $σ_{max} = 280 MPa$
Work Step by Step
Given:
A fatigue test was conducted in which the mean stress was 70 MPa (10,000 psi), and the stress amplitude was 210 MPa (30,000 psi).
Required:
maximum and minimum stress levels
Solution:
Using Equation 8.14:
$σ_{m} = \frac{σ_{max}+σ_{min}}{2} = 70 MPa$
${σ_{max}+σ_{min}} =140 MPa$
Using Equation 8.16, we find:
$σ_{a} = \frac{σ_{max}-σ_{min}}{2} = 210 MPa$
${σ_{max}-σ_{min}} = 420 MPa$
Simultaneously solving the above expressions:
$σ_{min} = -140 MPa$ and $σ_{max} = 280 MPa$
