Parallel-to-Grain Compressive and Tensile Behavior of Paulownia Wood at Elevated Temperatures

Fast-grown Paulownia wood is extensively used as construction material in China. The mechanical properties of Paulownia wood at room temperature are well known. However, investigations of its mechanical behavior at elevated temperatures are very limited. To address this issue, thermal analysis was conducted to investigate the mass loss and reaction heat during water evaporation and thermal decomposition. Moreover, parallel-to-grain compressive and tensile tests were conducted on clear Paulownia wood specimens at temperatures ranging from 20 °C to 220 °C. It was found that kinking is the main failure mode of the compressive specimens, while transverse rupture was frequently observed in the tensile specimens. At 220 °C, the retention rates of the average parallel-to-grain compressive and tensile strengths were 38% and 42%, respectively. However, the strengths significantly increased as the temperature increased from 100 °C to 140 °C, due to the moisture evaporation and the hardening of the dry lignin. The design curve suggested by EN 1995-1-2 was very conservative (as much as 76%) at estimating the parallel-to-grain compressive strengths. However, the design curve was slightly nonconservative (less than 6%) at predicting the parallel-to-grain tensile strengths when the temperature was below 60 °C. Furthermore, a significant reduction (approximately 40%) in the deformation capacity was found when the temperature was higher than 180 °C.