Fatigue stress concentration factor (\( K_f \))

\( K_f \)	=	Fatigue strength without stress concentrator
		Fatigue strength with specified stress concentrator

The test conditions with and without the stress concentrator must be identical.

Also called fatigue notch factor or fatigue strength reduction factor.

See Campbell[1], p. 257 (also Juvinall[1], p. 254).