原态毛竹环状收缩应变表征及机理研究

摘要

In order to explore the shrinkage mechanism of bamboo culm which has hollow cavity,bamboo culm (Phyllostachys pubescens) samples were prepared to observe and measure the shrinkage behavior under 40 ℃ environment,and the shrinkage strain field on cross section of bamboo culm was in-situ characterized and analyzed by digital speckle correlation method(DSCM).The results indicated that the moisture content (MC) of bamboo culm declined quickly and then turned gentle,the curve showed ExpAssoc function trend,and the MC differences between samples displayed minor with time prolonged.The annular shrinkage strain of bamboo green and bamboo yellow were observed at the same time,while the shrinkage of bamboo green was greater than that of bamboo yellow without obvious difference(P＞0.05),however the shrinkage in axial direction was significantly slight compared with bamboo green shrinkage(P＜0.05).The annular shrinkage was certified by the opposite strain in Y direction near the upper and lower edges of fine crack in bamboo green,and the greater shrinkage of bamboo green was also visual via the X direction strain change from bamboo green to the cavity.The crack coming from the inner stress for the hydrone evaporation taken place in the bamboo green which is known for excellent mechanical property.Therefore,reducing or releasing the inner stress induced by shrinkage is the key point to protect bamboo culm from splitting.%为探究原态竹材收缩特性,以毛竹(Phyllostachys pubescens)筒材为研究对象,研究其在40℃环境下的收缩行为,并采用数字散斑相关方法表征竹壁原位收缩应变.结果表睨:竹筒含水率下降速率由快至缓,呈ExpAssoc指数,各试样含水率随干缩时间趋同明显;竹青和竹黄同时呈环状收缩,竹青收缩程度大于竹黄,差异不显著(P＞0.05);竹筒顺纹收缩甚微,与竹青相比差异显著(P＜0.05);裂缝两侧Y方向收缩应变相反,印证了其环状收缩,非裂缝部位X方向应变表明从竹青到竹黄收缩应变急剧减小.竹青是干缩应力集中部位,是裂纹发生源,减少或释放该应力是原态竹材防裂的关键.