## Materials Science and Engineering: An Introduction

$R = -0.50$
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: $R = \frac{σ_{min}}{σ_{max}} = \frac{-140 MPa}{280 MPa} = -0.50$