Accelerated weathering (AW) tests have become a requirement for many wood composite products. This project monitored temperature and moisture content of specimens undergoing AW exposure for the following standards: ASTM D3434 (automatic boil test), CSA O112.9 (boil-dry-freeze), and PS2 (Section 7.17, 6-cycle VPS). Each AW procedure was conducted with three types of specimens that differed by geometry and size. Using fine-wire thermocouples, temperature was measured in the center of the specimen during AW regimes. Average MC of specimens was determined by weight measurements, along with a final oven-dry weight. MC gradient was determined by periodic destructive testing, by removing a specimen from the AW environment and promptly cutting into sections for a gravimetric MC determination. Results include plots of temperature and MC as a function of time and/or cycle. Mechanical tests were performed on the weathered specimens, as well as dry control specimens.
Geometries included lap-shear in tension, compression shear blocks and short-span shear in bending (SSB) which was manufactured using laminated veneer lumber (LVL). Direct comparisons between AW methods were conducted through non-linear regression by fitting the VPS and BDF data to equivalent cycles of the ABT. The SSB specimens showed to retain the greatest amount of strength after mechanical testing while the compression-shear block geometry had the greatest overall loss in strength. Lap-shear specimen mechanical results yielded the greatest variability among all three AW regimes. Temperature measurements were as expected within the lap-shear and compression block geometries, indicating that they were receptive to the exposure conditions. The SSB geometry, showed to be the least responsive to changes in temperature throughout exposure conditions in ASTM D3434.
MC measurements, taken after each test’s respective drying phase, showed to be under the fiber-saturation point within CSA 0112.9 and PS2 6-cycle vacuum pressure soak test, as expected. Results of ASTM D3434 showed that there was essentially no occurrence of drying among all three specimen geometries