Endurance strength of screw joints
Metric thread
M1
M1.2
M1.6
M2
M3
M4
M5
M6
M8
M10
M12
M14
M16
M20
M24
M30
M36
M42
-
8.8
9.8
10.9
12.9
Joint stiffness factor C
m
=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
load at yield F
0.2
kN
endurance strength
σ
e
MPa
maximum value of load fluctuation bolt
1
P
b
=2A
t
σ
e
kN
load fluctuation clamped material
P
m
=
P
b
(1-C
m
)/C
m
kN
Minimum value of preload
F
i,min
=
F
m
+P
m
kN
Maximum value of preload
F
i,max
=F
0.2
−P
b
kN
Maximum value of load fluctuation
P=
P
b
+
P
m
kN
1
In infinite life or safe stress designs stresses higher then the endurance limit are avoided and a factor of safety is taken into account. Most rotating and oscillating components must sustain over 10^6 load cycles during service life and thus are to be designed for infinite fatigue life.
www.tribology-abc.com