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showing the most uniform radial stresses for 4. Test results
Fig 3
the 120° head with an rld value of 0.85, 4.1 Tensile shear tests under
material flow being well balanced in both quasi- static loading
radial and tangential directions, Fig.6. Fig.7 In order to avoid incurring high tooling costs
shows the radial compressive stresses on the and save time, modified parts readily available
outside of the shank for splines with different in the market - mandrels of the Huck BOM
geometries and rld values. blind rivets - were used. These were annealed
to a soft condition, knurled on a lathe and
subsequently hardened, Fig. 8. The increase in
diameter of the shaft with standard knurling
tools was relatively small, limiting the radial
expansion of the shank. Two-shear lap
specimens, Fig. 8, were used for the tests
Mesh and boundary conditions for because the lock ring could not be deformed
2D analysis. Parameters used in the in the desired manner with the available
model: sheet thickness 2 + 2mm, setting equipment.
hole diameters: top sheet 10.2mm,
bottom sheet 9.8mm.
Fig 8
studies were performed for optimising the
Fig 6
geometry of the components of the rivet.
Based on the results, a 3D model of a repre-
sentative section was built, comprising a slice
3D-Model showing form fit and
with one of 8 identical splines, Figs. 3 and 4.
stress distribution, 120˚ spline,
The main parameters (e.g. materials, friction
rld= 0.85mm. Material flow
coefficients…) were maintained.
closes gaps.
Three different geometries of such splines
were investigated: keys with triangular heads,
included angles 120° and 150°, respectively,
and one round type, Fig. 5.
Fig 4
Tensile shear test results Form-fit lock
bolt versus M8.8 bolt with specimen
geometry, and lock bolt mandrel.
Specimen: Sheet thickness 2mm;
Material: AA6062T6; width: 40mm;
overlap: 40mm.
For the purpose of comparison, similar
specimens using M8 nuts and bolts, class 8.8,
tightened to 25Nm were prepared. The results
of the tensile shear tests are shown in Fig. 8,
the bolted joints slipping at approximately
Meshed 3D-FEM Model
Fig 7 4.7kN; the form-fit lock bolt joints with the
Hole fill was achieved in the simulations with
modified mandrel (without lock rings, without
all three spline geometries. The results
force-fit), show first signs of plastic
Radial contact-stress distribution at
showed that the spline with the 120°
deformation at about 10kN, [8, 9].
triangular head performed best, 3D analysis
the shank/work piece interface
with different spine geometries.
4.2 Fatigue tests results and discussion
Fig 5
Fatigue tests were performed with blind
rivets, lock bolts and corresponding bolted two
3.1 Evaluation of the results of the shear lap specimens. The nominal diameter of
FEM simulation the lock bolts was 6mm and 8mm; that of the
The results of the simulation verified the blind rivets, 9.6mm. M6, M8 and M10 class
design concept. Hole fill was possible even 8.8 bolted joints, were used for
when the two holes had diameters with a comparison. The material of the specimens
difference of 0.4mm. As could be shown in the was AA6062T4, thickness 2.5mm. In the case
investigations, the shape of the key head of the 6mm joints, the specimen material was
influences the force required for achieving hole 1.5mm H340 steel sheet. The width of the
Triangular spline geometry
fill and the distribution of radial compressive specimens was 40mm and the overlap 50mm.
forces between shank and work piece. The hole diameters for the M6, M8 and
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