Characteristics of shrinkage stress of wood during drying under high temperature and high pressure steam conditions
-
摘要: 该研究利用新开发的耐热、耐压应力传感器，采用夹具束缚试件在干燥过程中的收缩变形，考察了高温高压蒸汽条件下，伴随试件干燥过程的收缩应力发生、发展特征及粘弹性特性，旨在为探索减少木材干燥缺陷和内部残留应力的高温快速干燥工艺条件提供理论基础和科学依据.该文着重探讨了100℃以上的高温高压过热蒸汽条件下，试件从饱水到全干状态或明显开裂为止，收缩应力的连续测定方法，并对其径向和弦向收缩应力的发生发展特征进行了初步探讨。研究结果表明，在高温热处理(相对湿度为0)过程中，径向的收缩应力相当大，约为弦向的2倍；而在其他相对湿度条件下，情况却相反，相对湿度60%、80%条件下，弦向的收缩应力反而变得比径向大。试件在180℃的高温高压过热蒸汽干燥过程中，随着相对湿度的增加，收缩应力明显下降，应力得到有效抑制。即使在相对湿度100%的高温条件下干燥，木材仍然存在收缩应力。Abstract: Shrinkage stresses and viscoelasticity of wood during drying under superheated steam above 100℃ were studied using a newly developed load cell which is capable of measuring shrinkage stresses of wood inside an autoclave under high temperature and pressure. The shrinkage stresses along radial and tangential directions of a wood sample were continuously measured from its saturated condition until it was completely dried or significant cracks occurred under superheated steam above 100℃. The results showed that during the drying process under high temperature with 0 relative humidity (RH) , the shrinkage stress in the radial direction of the test specimen was about 2 times higher than that in the tangential direction. However, when samples were dried at 60 and 80 RH, the shrinkage stress in the tangential direction was higher than that in the radial direction. The shrinkage stresses were effectively restrained and dramatically decreased with increase of RH during the drying process under superheated steam at 180℃. It was also found that shrinkage stress still existed even under superheated steam at 100 RH.
-
计量
- 文章访问数: 3328
- HTML全文浏览量: 76
- PDF下载量: 74
下载:
