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like the case in Figure 6.21 at high compaction. Furthermore, there
are all VTC strands
on the face layers with high stiffness thus contributed the most to the modulus.
The results of Figure 6.22 also show interfacial effects have a large contribution
to the overall stiffness of the panel. There is linear increase of the stiffness as a function
of compaction.
6000
7000
8000
9000
10000
11000
12000
13000
14000
15000
0.50
0.55
0.60
0.65
0.70
0.75
0.80
Density (g/cm
3
)
MO
E
(
MP
a
)
HROM
1/Dt=0
1/Dt=0.02
Figure 6.22. Simulated modulus versus overall panel density for different values of 1/D
t
for commercial OSB with surface VTC strands.
6.7 Summary and Conclusions
The vertical density profile influences the overall OSB panel stiffness. In
processing, the manufacturer usually demands higher density at the
surface to carry the
higher load in bending for structural applications. To know the specific density profile at
different levels of compaction, manufacturers could benefit from
optimization during
processing and manufacturing of OSB. During processing, manufacturers usually obtain
the stiffness and vertical density profile by trial and error. From the relationship between
148
vertical density profile and stiffness at
different levels of compaction, the manufacturer
can tailor the process to achieve high load carrying panels. Moreover,
enhanced strand
(VTC) on the surface layer increases density.
Additionally, reducing yield stress of the surface strands in 2D simulations gave
an increase in density for the face. Reducing yield stress and moduli at the face layers in
2D increases the density at the surface area. In 2D, reducing moduli at the surface layers
had more effect on the density profile than reducing the yield stress. Furthermore,
increasing compaction rate increases the density at the surface of the panel.
The simulation of density profile in 3D showed different results than the 2D. In
3D, the Poisson’s expansion resulted in no increase in density of the surface. There is
some increase in density of the surface when there is no gap on the surface layer. Unlike
the 2D, there is no increase in density profile of the surface when reduced yield stress of
the surface strands. However, in 3D reducing moduli at the surface
layers had an effect
on the density profile of the surface strands. Furthermore, 3D model of MPM is able to
look into interior structure or morphology of the panel.
Finally, to fully model the vertical density profile, moisture content gradient and a
temperature profile is needed. A better plasticity model to account for densification is
needed because the traditional plasticity model did not allow for plastic densification
after yielding occurred. As all results all densification is due to by elastic deformation.
Additionally, the simulations may need to be done on 3D. More work
is needed to get the
same simulation results for the vertical density profile as experimental results.
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