Fatigue strength of screw joints
Metric thread
M1
M1.2
M1.6
M2
M3
M4
M5
M6
M8
M10
M12
M14
M16
M20
M24
M30
-
8.8
9.8
10.9
12.9
Joint stiffness factor C=k
b
/(k
b
+k
m
)
Minimum value of clamping force F
m
kN
pitch P
mm
pitch diameter d
2
mm
root diameter d
3
mm
tensile stress area A
t
=π/4 d
0
2
; d
0
=(d
2
+d
3
)/2
mm
2
ultimate tensile strength R
m
MPa
yield strength R
p0.2
MPa
maximum tensile load F
0.2
kN
fatigue strength
σ
a
MPa
maximum value of load fluctuation bolt
1
dF
b
=A
t
σ
a
kN
load fluctuation clamped material
dF
m
=d
F
b
(1-C)/C
kN
Minimum value of preload
F
i,min
=
F
m
+dF
m
kN
Maximum value of preload
F
i,max
=F
0.2
-dF
b
kN
Maximum value of load fluctuation
dF=
dF
b
+
dF
m
kN
1
The fatigue strength of the bolt can be fully exploited if F
i,min
<F
i,max
.
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