不同纹理方向栎木微小无疵试样板材蠕变特性

Orthotropic Creep Performance of Small Flawless Oak Board

【目的】考察高温高湿环境下不同锯切方向栎木板材的弯曲蠕变行为,为湿热条件下翘曲栎木板材展平整直工艺提供参考。【方法】制备4种不同锯切方向栎木试样(分别对应弦切板纵向、径切板纵向、径切板横向和弦切板横向),利用DMA-Q800型动态热机械分析仪测定不同锯切方向栎木试样在不同温度下的蠕变曲线,采用Burger模型和广义Kelvin模型对栎木短期蠕变曲线进行拟合,分析锯切方向对栎木试样各蠕变参数的影响,并对不同取向栎木板材蠕变特性进行评价。【结果】在70~90℃范围内,不同取向栎木板材蠕变和蠕变恢复均随温度升高而增大。在相同应力作用下,径切板纵向蠕变大于弦切板纵向蠕变,而径切板横向蠕变小于弦切板横向蠕变。Burger模型和广义Kelvin模型都可以较好地模拟栎木短期蠕变过程,Burger模型相关系数(R^2)大于0.90,广义Kelvin模型相关系数(R^2)大于0.99。在试验范围内,相同含水率下栎木试样的普弹模量和本体黏度均随温度升高而降低。在单个滞后时间的Burger模型拟合中,滞后时间随温度升高而增加,90℃时达到最大,栎木在90℃时最接近理想黏性体。不同锯切方向栎木板材本体黏度依次为弦切板纵向>径切板纵向>径切板横向>弦切板横向。【结论】升高温度可以降低栎木本体黏度,随温度升高栎木更易产生黏性形变;栎木板材横向相比纵向更易发生黏性形变;在板材纵向,径切板相比弦切板易发生黏性形变;在板材横向,径切板相比弦切板更难产生黏性形变。

【Objective 】 In order to clarify the softening and flattening mechanisms of oaks in different cutting directions,bending creep behavior of different oak boards（ longitudinal plain-sawed lumber,longitudinal quarter-sawed lumber,transverse plain-sawed lumber and transverse quarter-sawed lumber） were investigated by dynamic mechanical analysis（ DMA）.【Method 】 DMA creep curves of oak samples were analyzed and fitting by Burger model and general Kelvin model to evaluate the creep performance of different oak samples.【Result】 The results showed that both Burger model and general Kelvin model could describe creep characteristic of oak well,R-2 of Burger model is larger than 0. 90 and R-2 of general Kelvin model is larger than 0. 99. Under the same moisture content,the elastic module（ E0） and bulk viscosity（ ηn）,which were calculated by general Kelvin model,decreased with temperature increasing from 70 to 90 ℃.The retarded time（ τ＇）,which were calculated by Burger model,increased when the temperature increased from 70 to 90℃. According to ηn,it was the following order： longitudinal plain-sawed lumber longitudinal quarter-sawed lumber transverse quarter-sawed lumber transverse plain-sawed lumber. 【Conclusion 】 It was suggested that the higher the temperature,the much easier for the oak board flattening. Transverse warp of oak board was easier to flat than that of longitudinal warp. Longitudinal warp of plain-sawed lumber was harder to flat than quarter-sawed lumber. However,comparing to quarter-sawed lumber,restoration of transverse warp for plain-sawed lumber was easier.