Rc. Tang et al., EFFECT OF TEMPERATURE ON THE CREEP OF COMMERCIAL ORIENTED STRANDBOARDS UNDER CYCLIC RELATIVE-HUMIDITY, Forest products journal, 47(7-8), 1997, pp. 100-106
The effect of temperature on the flexural creep behavior of six commer
cial oriented strandboards (OSB products: A, B, C, D, E, and Fl, 23/32
inch (1.826 cm) thick with a span-rating of 24 inches (60.96 cm) on c
enter, under cyclic relative humidity (RH) was investigated. The speci
mens were preconditioned to equilibrium under 65 percent RH at 75 degr
ees F (23.9 degrees C) and then divided into two groups. The first gro
up was tested under environmental conditions of RH cyclically changed
from 65 to 95 percent on a 96-hour frequency at a constant temperature
of 75 degrees F. The second group was tested in the same RH cycle as
the first group, but the temperature was maintained at 95 degrees F (3
5 degrees C). Identical concentrated loads, equivalent to 16.5 percent
of the ultimate static bending strength evaluated at 65 percent RH an
d 75 degrees F for the weakest group among these six OSB products, wer
e applied to each specimen in both groups for 794 hours followed by a
286-hour recovery after the load was removed. Results indicated that e
ven though the structural wood composite panel products were manufactu
red under the same product standard, and given equivalent engineering
performance ratings commercially, a difference in creep performance do
es exist. Among the six OSB products, panels made of southern pine fla
kes and bonded with only liquid phenol-formaldehyde (LPF) or bonded wi
th powder phenol-formaldehyde (PPF) in the face and isocyanate resin (
ISO) in the core showed much better creep resistance than those made o
f aspen flakes and bonded with only PPF or bonded with only ISO or bon
ded with LPF in the face and ISO in the core. Noticeable differences i
n the creep resistance among the southern pine groups were not observe
d. However, among the aspen groups, ISO-bonded products had the lowest
creep and PPF-bonded products showed the highest. Under identical cyc
lical RH conditions of 65 <----> 95 percent, a considerable temperatur
e effect on the creep resistance was observed in the groups exposed to
the high-temperature environment.