Tensile creep behavior of earlywood between compression wood and normal wood under different temperature and load levels

Objective This research was carried to explore the difference in tensile creep behavior between compression wood (CW) and normal wood (NW) from masson pine (Pinus massoniana) under different temperature and load levels, aiming to provide the data reference and theoretical basis for the high value-added utilization of plantation wood.

Method The tissue section of earlywood between CW and NW were used as research objects, and the microfiber angle (MFA) and tensile stress-strain curve were characterized by X-ray diffraction and dynamic mechanical analyzer, respectively. Dynamic mechanical analyzer was also used to determine tensile creep for CW and NW specimens in the temperature range of 50 ℃ to 170 ℃ and at three stress levels.

Result Compared with NW, the basic density, MFA, tensile strain, creep compliance and creep strain at stable stage of CW were larger, while the tensile stress and modulus of elasticity were smaller. The instantaneous strain of CW and NW specimens were slightly higher than instantaneous recovery strain. The instantaneous strain, instantaneous recovery strain, 60-minute creep strain, and 30-minute creep recovery of CW and NW specimens increased with increasing temperature and stress level, respectively. Furthermore, the creep strain at stable stage increased with increasing temperature, while its response to load level was not obvious. In the temperature range from 50 to 170 ℃, the increase of instantaneous strain caused by per unit stress for CW and NW was 0.063%−0.076% and 0.016%−0.020%, respectively. And the increase of creep strain in 60 min caused by per unit stress for CW and NW was 0.078%- 0.095% and 0.019%-0.028%, respectively.

Conclusion Compared with NW, per unit stress shows obvious influence on the increase of tensile instantaneous strain and viscoelastic deformation, and CW with larger MFA has less ability to resist external deformation. The increasing temperature intensify the effect of per unit stress on the instantaneous strain and tensile viscoelastic deformation for NW and CW specimens.