疲劳应力集中系数（\( K_f \)）
| \( K_f \) | = | 无应力集中源时的疲劳强度 |
| 存在指定应力集中源时的疲劳强度 |
有无应力集中源的试验条件必须完全相同。
亦称疲劳缺口系数或疲劳强度降低系数。
见 Campbell[1]，第 257 页（另见 Juvinall[1]，第 254 页）。
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).