Table 11. Moisture content of the wet flexural specimens of RPC and Douglas fir (DF).
(Nominal dimensions of all specimens: 38.1 38.1 406.4 mm, 1.5 1.5 16 in.)
Specimen
No. of
No. of hours
Average dry
Average wet
Moisture
Avg. moisture
density (lb/in.3)
density (lb/in.3)
type
specimens
in water
absorbed (%)
absorption/hr
RPC-WD
7
383
0.032
0.037
15.6
0.0407
RPC-WCD
7
48
0.032
0.033
3.1
0.0646
DF-WD
7
265
0.018
0.022
22.2
0.0838
DF-WCD
7
219
0.018
0.0198
8.2
0.0374
SI conversion factors: 1 lb = 0.454 kg, 1 in. = 25.4 mm.
Douglas fir also decreased with moisture ingres-
sion (22.2%). The flexural strength decreased
approximately 17.7%, and the flexural modulus
approximately 29.7%. Like RPC, the low tempera-
ture (30C, 22F) increased the S and Ef values,
S by approximately 23.7%, and Ef by 18.8%. When
wet and cold, the value of S still increased, about
20%, the Ef did not; rather it shows a very minor
decrease (1.5%).
Discussion
The RPC material investigated here is a new
material. Its mechanical properties were largely
Figure 54. Fracture and crack orientations from flexural
unknown before these tests. In fact, the material
was produced in large size beams (152.4 203.2
tests. (Top is RPC material, and bottom is Douglas fir.)
mm, 6 8 in.) for the first time only when this
project was underway. After the manufacturer
direction of the specimen. Evidently, mode II fail-
addressed the issue of large sized wood chip con-
ure dominated the mechanism. In the RPC the
tamination, the material looked homogeneous.
crack nucleated by exceeding the tensile strength
Because of the limited scope of this investigation,
at the bottom layer of the beam and then propa-
no major microstructural analysis was under-
gated virtually through the thickness, indicating
taken, but it was suspected that the pultrusion
the dominance of mode I failure. The flexural
type manufacturing process would introduce a
strength difference between these two materials
degree of variation with grain orientation and
is thus obvious. As shown in Table 12, the Dou-
densification. The results of the compression, ten-
glas fir flexural strength is about seven times that
sion, and flexure tests are compiled in Table 13.
of the RPC, and the Ef is about 3.6 times. How-
The compression tests showed that the major
ever, as stated before, like the RPC, the S and Ef of
Table 12. Comparison of flexural properties from test data for RPC and
Douglas fir.
Type of specimen
Flexural strength S
Flexural modulus Ef
and test condition
(psi)
(psi)
RPC dry, room temp. DD
872.3
26,574.3
RPC wet, room temp. WD
783.1 (10.2% decrease)*
17,838.6 (32.8% decrease)*
RPC dry, at 30C. DCD
1424.5 (63.3% increase)*
53,389.9 (100.9% increase)*
RPC wet, at 30C. WCD
1322.8 (51.6% increase)*
54,141.3 (103.7% increase)*
Doug fir dry, room temp. DD
6057.1
96,057.4
Doug fir wet, room temp. WD
4985.4 (17.7% decrease)
67,481.7
(29.7% decrease)
Doug fir dry, 30C. DCD
7492.1 (23.7% increase)
114,089.4
(18.8% increase)
Doug fir wet, 30C. WCD
7266.1 (20.0% increase)
94,607.3
(1.5% decrease)
* Relative to dry room temperature (baseline) data.
SI conversion factors: 1 psi = 6.89 kPa, (30C = 22F)
38
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