高温高压蒸汽条件下木材的拉伸应力松弛

Tensile stress relaxation of wood under high temperature and pressurized steam.

为进一步探讨木材在高温高压蒸汽干燥过程中的应力释放机理,该研究以日本柳杉木材为研究对象,利用新开发的耐热、耐压应力传感器和专用夹具,对高温高压蒸汽条件下木材的拉伸应力松弛特性进行了较为详细、全面的系统研究.结果表明:温度条件对木材应力松弛的影响远比应变水平的影响显著,随着温度的增加、木材应力松弛急剧增大,残余应力迅速下降;木材应力的松弛除了受温度的影响外,受环境相对湿度的影响显著.无论木材的径向还是弦向,其拉伸应力松弛过程中的残余应力和木材干燥过程中的最大收缩应力随温度变化的关系十分吻合.该结果充分证明了木材在高温高压过热蒸汽干燥过程中的收缩应力显著降低,是由于收缩变形而引起的收缩应力在长时间处于拉伸状态下应力释放所致.

This research aims to provide theoretical proof for the further study on the mechanism of stress relaxation during drying under high temperatures and pressurized steam. In this study, Japanese sugi （Cryptomeria japonica D. Don） was used as the experimental materials. Tensile stress relaxation during drying under high temperatures and pressurized steam was discussed using a specially developed load cell, which was capable of measuring stress under high temperature and pressurized steam inside an autoclave. The results showed that the effect of temperature on stress relaxation was much more significant than that of strain level. Stress relaxation dramatically increased and the remaining stress rapidly decreased with temperature enhancing. Stress relaxation was not only affected by the temperature, but also greatly affected by the environmental relative humidity. It was also found that, irrespective of radial or tangential direction, the remaining stress during tensile stress relaxation as well as the maximum shrinkage stress during drying had a good relationship with temperature. The results clarified that the significant reduction of shrinkage stress during drying under high temperature and pressure superheated steam was attributed to the relaxation of shrinkage stress caused by shrinkage deformation due to long-time tensile status.