#### Answer

$R = -0.50$

#### 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).
$σ_{min} = -140 MPa$ and $σ_{max} = 280 MPa$
Required:
stress ratio
Solution:
Using Equation 8.17:
$R = \frac{σ_{min}}{σ_{max}} = \frac{-140 MPa}{280 MPa} = -0.50$