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e1 for end bolts
3 . d0
αd =
p1 −
1
for inner bolts
3 . d0 4
Tension
resistance Ft,Rd =
k2 . fub . As
γM2
k2 = 0.9 for steel bolts
k2 = 0.5 for aluminium bolts
k2 = 0.63 for countersunk steel bolts
As is the tensile stress area of the bolt
Punching shear
resistance Bp,Rd =
0,6 . π . dm . tp . fu
γM2
dm is the mean of across points and across flats
of a bolt head or the nut or the outer
diameter of the washer
tp is the thickness of the plate under the bolt head
or the nut
Combined
shear
and tension
Fv,Ed +
Ft,Ed ≤ 1.0
Fv,Rd 1.4 . Ft,Ed
Fv,Ed is the load effect of shear
Ft,Ed is the load effect of tension
TABLE VI.5
74
ALUMINIUM IN COMMERCIAL VEHICULES CHAPTER VI DESIGN AND CALCULATION 74 | 75
Connection details that carry tensile
forces, and where the tensile
forces don’t go directly through
the bolts, additional forces in the
bolts have to be accounted for.
These forces are called prying
forces (Q) and they can be considerable
large. See the figure
VI.12.
FIGURE VI.12
N = FN + Q N = FN + Q
Q Q
2 FN
Truck bodies for beverage transport
75
EUROPEAN ALUMINIUM ASSOCIATION
8.1. Theory
Structures with repeating loads
may be susceptible to fatigue
when the number of load cycles
is high, even when the loads give
low stresses in the structure.
Fatigue failure starts with development
of a crack at a point with
stress concentrations. With continuous
repeating loads the crack
will grow, this will be shown as
one striation in the failure surface
for each load cycles. The distance
between the striations is
depending on the stress range
and that is giving the growing
speed. The stress range is
defined as the algebraic difference
between the stress peak
and the stress valley in a stress
cycle. At low stress ranges the
crack grows slowly and with high
stress range it grows fast. (Figure
VI.5)
8. Fatigue
Trailer fatigue testing in laboratory (Benalu)
76
ALUMINIUM IN COMMERCIAL VEHICULES CHAPTER VI DESIGN AND CALCULATION 76 | 77
Rules for fatigue design are given
in EN 1999-1-3. The rules are
based on quality levels given in
EN 1999-1-3 and EN 1090-3.
• The fatigue strength depends on:
• type of detail (design)
• stress range
• number of cycles
• stress ratio
• quality of manufacturing
FIGURE VI.13
σ
σmax
σm
σmin
3
1
2
T
0
σ3 σ3
Δσ
1. Stress peak
2. Stress valley
3. Stress cycle
Δσ Stress range
σ3 Stress amplitude
The picture is showing the striations in a fatigue failure surface of an aluminium tube.
77
EUROPEAN ALUMINIUM ASSOCIATION
The properties of the parent
material have very little influence
on the fatigue strength in practical
structures and components.
For connections the properties of
the parent material have no
influence at all. For a plate or
extrusion with no manufacturing
or only holes and notches the
standard deviate between EN
AW 7020 and all other structural
alloys.
The fatigue strength is given as
SN curves for the different
details. All detail categories given
in EN 1999-1-3 have their own
SN curve. A typical SN curve is
shown on the Figure VI.14.
1). Number of cycles (108) at
which the cut-off limit is defined
2). For low cycles fatigue, this
part of the curve may not be correct,
other calculation methods
are recommended (Annex F of
EN 1999-1-3). It shall be checked
that the maximum design stress
range don’t result in a tensile
stress exceeding the design stress
in ultimate limit state.
FIGURE VI.14
104 105 106 107 108 109
N
2)
a
c
m d 2
1
b
1
m1
NL 1)
2 . 10e
NC
5 . 10e
ND
Δσ
ΔσC
ΔσD
ΔσL
a. Fatigue strength curve b. Reference fatigue strength c. Constant amplitude fatigue limit d. Cut-off limit
S
78
5.1 63-4,3
Continuous
automatic
welding
B C
5.2 56-4,3 C C
5.3 45-4,3
Any backing
bars to be
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