CREEP-BEHAVIOR OF SWEETGUM OSB - EFFECT OF LOAD LEVEL AND RELATIVE-HUMIDITY

Flexural creep behavior of laboratory-fabricated sweetgum oriented str andboard (OSB), under constant (65% and 95%) and cyclic (65% <--> 95% at a 96-hr. frequency) relative humidity (RH) conditions at 75-degrees -F (23.9-degrees-C) is presented. Two levels (4.5% and 6.5%) of resin content (RC) of phenol-formaldehyde were used in fabricating the test panels. Two load levels (20% and 40% of the modulus of rupture (MOR)) were chosen for the investigation. Load duration was 12 weeks followed by a 3-week recovery under constant 65 percent RH at 75-degrees-F. Co nstant high RH (95%) as well as the cyclic RH (65% <--> 95%) showed a great influence on the creep resistance and relative creep. At constan t low RH (65%), improvement of relative creep was observed when the RC was increased from 4.5 to 6.5 percent. The load-duration effect (cree p-rupture) became evident when the load level was increased from 20 to 40 percent MOR under constant 95 percent or cyclic 65 <--> 95 percent RH conditions.