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    不同温度、载荷下应压木和正常木的拉伸蠕变特性

    Tensile creep characteristics of compression wood and normal wood under different temperatures and loads

    • 摘要:
      目的 探究马尾松应压木和正常木的拉伸蠕变特性对温度和载荷的响应规律,旨在为马尾松木材的高附加值利用提供数据参考和基础理论依据。
      方法 以应压木和正常木早材组织切片为研究对象,分别采用X射线衍射仪和动态力学分析仪测定试材的微纤丝角和拉伸应力–应变曲线;在50 ~ 170 ℃范围内,利用动态力学分析仪分别获得3个应力水平和不同恒定温度水平下应压木和正常木的拉伸蠕变曲线。
      结果 与正常木相比,应压木的基本密度、微纤丝角、拉伸应变、拉伸蠕变柔量和最终残余应变均较大,而拉伸应力和弹性模量较小。应压木或正常木的瞬时应变均略大于瞬时应变恢复应变量。应压木与正常木试样的瞬时应变、瞬时应变恢复量、60 min蠕变应变量和30 min蠕变恢复量均分别随温度、施加载荷的增大而增加;最终残余应变随温度升高而增加,而对施加载荷的响应无明显规律。在50 ~ 170 ℃范围内,单位应力增加引起应压木与正常木试样的瞬时应变增加量分别为0.063% ~ 0.076%和0.016% ~ 0.020%,拉伸黏弹变形增加量分别为0.078% ~ 0.095%和0.019% ~ 0.028%。
      结论 与正常木相比,单位应力对应压木的拉伸瞬时应变和黏弹变形增加量影响更为明显,应压木中较大的微纤丝角导致其抵抗外力变形的能力较弱。升高温度加剧了单位应力对应压木与正常木瞬时应变和拉伸黏弹变形的影响。

       

      Abstract:
      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 high value-added utilization of plantation wood.
      Method The tissue sections of earlywood (EW) 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 or NW specimens was slightly higher than instantaneous recovery strain. The instantaneous strain, instantaneous recovery strain, 60 min creep strain, and 30 min 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 intensifies the effect of per unit stress on instantaneous strain and tensile viscoelastic deformation for NW and CW specimens.

       

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