An abstract of the thesis of

PF Adhesive Coverage
1/
D
t
(m
m
/M
P
a
)
1% 25% 100%
1% 25% 100%
VTC Strand
Normal Strand
Figure 2.6. Measured adhesive compliance for PF resin on unmodified (normal strands) 
and VTC for different adhesive coverage. 

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28 
0
0.03
0.06
0.09
0.12
0.15
0.18
0.21
1/
D
t
(mm/
M
P
a
)
1% 25% 100%
1% 25% 100%
1% 25% 100%
VTC Strand
Normal Strand
PF resin
PVA Based
 
Figure 2.7. Interfacial compliance for specimens with various adhesive surface coverage 
area for VTC and normal strand with PF and PVA. 
2.4 Summary and Conclusions 
There was consistency in the values for specimen k for continuous bond lines 
(large amount of PF resin, 100%) compared to the k for 25%, and 1% adhesive coverage. 
Using shear-lag theory, we extracted the interfacial parameter 
D
t
given specimen 
mechanical properties and geometries. The interfacial property varied significantly from 
discrete drops (1% coverage) to continuous bond line (100%). The interfacial property is 
highest for 100% and smallest for 1% adhesive coverage. There was a 60% increase in 
interfacial property from 1% to 25% adhesive coverage for normal strands with PF resin. 
The interfacial property 
D
t
, is higher for PF resin than for PVA wood glue. 
D
t
is also 

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29 
higher for VTC strands than for normal hybrid poplar strands. As the level of adhesive 
increased from 1% to 100% coverage, the stiffness of the interface could become stiffer 
than the wood itself (negative values of 
D
t
). This may be due to the penetration of the 
resin into the wood cell and consequently creating interfacial region stiffer than the wood. 
In addition to the smoother surface of VTC strands, VTC strand allow less resin 
penetration into wood cells. Despite less penetration, the bond line 
D
t
was higher. 
Perhaps, less adhesive penetration into the wood cells of VTC strands made more 
adhesive available at the surface to make a better bond line. Therefore, more work is 
needed to confirm how penetration of resin into wood cells affects the interfacial stiffness 
parameter. The observation here suggests penetration is not needed for good stress 
transfer (high 
D
t
) and might even be somewhat detrimental to good composites.