This can be found from charts for bending, axial loads and, torsion…
q=1+r​a​​1​ where this q can be plugged into the dynamic loading Stress Concentration equations
Also a​ is the Neuber constant
Where the Neuber constant can be calculated using…
Bending or Axial Loading
a​={0.246−3.08(10−3)Sut​+1.15(10−5)Sut2​−2.67(10−8)Sut3​1.24−2.25(10−3)Sut​+1.60(10−6)Sut2​−4.11(10−10)Sut3​​50≤Sut​≤250 kpsi,a​ units (inch)1/2340≤Sut​≤1700 MPa,a​ units (mm)1/2​
Torsional Loading
a​={0.190−2.51(10−3)Sut​+1.35(10−5)Sut2​−2.67(10−8)Sut3​0.958−1.83(10−3)Sut​+1.43(10−6)Sut2​−4.11(10−10)Sut3​​50≤Sut​≤250 kpsi,a​ units (inch)1/2340≤Sut​≤1700 MPa,a​ units (mm)1/2​