Bolt joint under dynamic loading
Metric thread :
M1
M1.2
M1.6
M2
M3
M4
M5
M6
M8
M10
M12
M14
M16
M20
M24
M30
M36
M42
-
3.6
4.6
4.8
5.6
5.8
6.8
8.8
9.8
10.9
12.9
Initial tensile stress : σ
i
·R
p0.2
Minimum value of clamping force: F
m
kN
Joint stiffness factor C
m
=k
b
/(k
b
+k
m
)
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
initial tensile stress σ
t
=
α
R
p0.2
MPa
load at yield F
0.2
= R
p0.2
A
t
kN
initial preload F
i
= σ
t
A
t
kN
load fluctuation bolt P
b
=F
0.2
- F
i
kN
amplitude of bolt stress
σ
at
= ½
P
b
/A
t
MPa
endurance strength of the bolt
σ
e
MPa
load fluctuation clamped material P
m
=
P
b
(1-C
m
)/C
m
kN
clamping force F
m
= F
i
-P
m
kN
Total load fluctuation P
= P
b
+ P
m
kN
Warning: Amplitude of dynamic bold stress > Endurance Strength:
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.
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