柱面加压法对木材表面密实的机理研究

Study on wood surface densification mechanism in cylinder method

木材表面密实化是提高木材表面密度和硬度的有效方法,以往研究中大多采用平压法,木材表面密度提高的同时中心层也得到了密实,损耗了材积,因此有必要探索一种低材积损耗的木材表面密实方法。采用柱面加压法对木材进行表面密实,以半无限平面的线载荷理论为基础,利用有限元分析软件对柱面加压法木材表面密实进行模拟,优选出了柱面加载头的半径大小,并进行实验验证,探求加载头半径对木材表面密实效果的影响。半无限平面的线载荷理论分析表明,柱面法加压时,应力分布由表层向下逐渐衰减,与平压法中力的等值传递相比更适合木材的表面密实,且圆柱体半径越小,表面密实效果越好;有限元模拟结果更直观地表明了柱面加压时的应力分布情况,密实层均集中于表层,且加载头半径越小,密实层越集中于表层且越密实,压缩量越大,表面密实层厚度越大且越密实,根据模拟结果优选加载头半径的大小为10 mm及以下;实验验证的结果与理论分析及有限元模拟结果一致,当采用半径5 mm加载头压缩3 mm时,表面密实层最大密度达到783 kg·m^-3,比未密实前提高了82.6%,表面硬度和耐磨性也显著提高,但材积损耗仅为12%,较平压法大大减少了材积损耗。柱面加压法较平压法更适合于木材的表面密实,提高木材表面性能的同时材积损耗大大减少。

Wood surface densification is an effective method to improve the density and hardness of wood,flat pressing method was widely used in previous studies,the density of wood surface increased while the central layer was also compressed,which caused the volume loss,so it is necessary to explore a method for efficient compression of wood surface.In the study,cylindrical compression method was used for wood surface densification,based on the linear loading theory of half infinite plane,finite element analysis software was used to simulate wood surface densification in cylinder method,the radius of cylindrical loading head was optimized,and experimental verification was carried out to explore the effect of loading head radius on the compression of wood surface.The linear loading theory of half infinite plane showed that the stress distribution was decreasing from the surface in cylindrical compression method,which was more suitable for wood surface densification compared with the equivalent transfer of stress in traditional flat pressing method,and the smaller the radius of the cylinder was,the better the surface compression effect was;the results of finite element simulation intuitively showed the stress distribution,the densified layer was concentrated on the surface,the smaller the radius of loading head was,the more concentrated on the surface and denser the compression layer was,and the larger the compression amount was,the thicker and denser the surface compression layer was,optimized radius of cylindrical loading head was 10 mm and below according to simulation results;the experimental results were consistent with theoretical analysis and finite element simulation results,when compressed by 3 mm with radius 5 mm loading head,the maximum density of the surface densified specimen could reached 783 kg·m^-3,which was 82.6%higher than undensified specimen,surface hardness and wear resistance were also significantly improved,but the volume loss was only 12%,the volume loss was greatly reduced compared with flat pressing method.Cylindrical compression method was more suitable for wood surface densification compared with flat pressing method,wood surface properties was increased while the volume loss was greatly reduced.