【作者】 宋魁彦；

【导师】 李坚；

【作者基本信息】 东北林业大学 ， 木材科学与技术， 2008， 博士

【摘要】 木材顺纹压缩与多维弯曲技术蕴涵着多学科知识的交叉融合,具有一定的理论深度和显明的应用性,是当今备受关注的研究热点之一。该项研究,特别是在木材顺纹压缩应力.应变本构关系的建立、多维弯曲和定型技术等方面,可以填补迄今为止,尚无相关研究报道的缺憾。该技术可以拓宽木材应用领域,是一项科学、合理地利用木材资源,有利于环保的新技术。在未来的木制品设计和生产中,实体木材的多维弯曲可以改变木制品的造型和结构特征,为有效地利用木材创造了更加广阔的空间。本文以木材顺纹压缩与多维弯曲技术的研究为总目标,首先将木材进行软化处理,优化软化处理方法;其次,对软化处理后的木材进行顺纹压缩,建立木材顺纹压缩中应力一应变的本构关系,分析压缩和回弹中木材的弹性、弹塑性的变化规律;第三,对顺纹压缩木材在允许的应变范围内以获得较小弯曲曲率半径和实现多维弯曲,分析木材弯曲后的弹性、弹塑性的变化规律,初步建立木材单维弯曲中应力-应变的本构关系,确定木材单维和多维弯曲的最小曲率半径;第四,对于弯曲的曲线形零件进行定型处理,分析定型方法、定型过程中的各种条件变化对木材弯曲定型的影响。通过上述研究确定木材顺纹压缩与多维弯曲的技术。论文以东北重要的商品材榆木和水曲柳为试材,进行了木材顺纹压缩与多维弯曲技术的试验研究:(1)在软化处理试验中,分别对幼龄材与成熟材进行探索性试验,最终确定水热、水热-微波以及复配碱液处理作为本试验的软化处理方法,通过后续试验(顺纹压缩率、PDR以及弯曲曲率半径等)的结果,对软化后的木材,通过X-射线衍射仪测定相对结晶度、FTIR测试木材表面性质以及测定木材化学组分的变化等,探讨幼龄材、成熟材在三种软化处理后木材化学组成成分、相对结晶度等方面的变化规律。结果表明,三种软化处理均使木材各个化学组分产生不同程度的变化,特别是木质素、半纤维素和抽提物发生了不同程度的降解,总的降解趋势是复配碱液处理的降解幅度最大,水热处理的降解幅度最小;成熟材的各自化学组分的降解幅度小于幼龄材;相对结晶度由于抽提物的抽出和相应的化学组分降解均有不同程度的提高;尽管幼龄材的PDR大于成熟材,但是后续试验结果表明成熟材顺纹压缩效果好于幼龄材;水热-微波处理中B方案更适合木材顺纹压缩。(2)在顺纹压缩试验中,配备特制压缩模具与力学实验机结合,对软化后的木材进行顺纹压缩。测定了应力、应变、顺纹压缩率和PDR等指标,采用X射线微密度仪测定木材顺纹压缩前后密度变化,扫描电子显微镜观察木材顺纹压缩后细胞壁褶皱的变化情况等。分析得出,水热-微波处理的顺纹压缩率较大,复配碱液软化处理的顺纹压缩率较小;顺纹压缩应力是榆木小于水曲柳,各自的成熟材小于幼龄材:在同一顺纹压缩率下,各自幼龄材的PDR都大于成熟材;建立的顺纹压缩应力-应变本构关系中,各自分段区域符合线形的力学关系;压缩后木材的密度变化为成熟材密度大于幼龄材,而幼龄材的密度波动较大:分析压缩和回弹中的木材的弹性、弹塑性、密度变化以及顺纹压缩后细胞壁内形成褶皱的变化规律,揭示了木材顺纹压缩机理;得出适宜的木材顺纹压缩的工艺条件。(3)在多维弯曲的试验中,采用圆形和S型弯曲模具与力学试验机配合使用,分别对木材的弦向、径向进行了单维和多维弯曲,扫描电子显微镜观察弯曲后木材细胞壁褶皱的变化,通过调整圆形模具的半径及采用多维弯曲模具,求出单维和多维弯曲的最小曲率半径。研究表明,木材的材性、顺纹压缩率、PDR等因素对弯曲曲率半径有显著的影响,幼龄材的弯曲性能不如成熟材;在弯曲过程中,弯曲拉伸面的褶皱开始展平,而压缩面的褶皱开始恢复到木材压缩时的压缩率,而最终破坏点是在弯曲试材拉伸面的中间部位;从初步建立的单维弯曲应力-应变本构关系中,得出弯曲的初始阶段符合线形的力学关系;榆木单维和多维弯曲曲率半径远远小于水曲柳,而各自成熟材的弯曲曲率半径都小于幼龄材,木材弦向弯曲曲率半径小于径向:水热-微波软化处理获得的弯曲曲率半径最小,得出了木材多维弯曲的工艺参数。(4)在木材弯曲定型试验中,采用直接干燥、水热-干燥、微波-干燥定型方法。通过快速检测弯曲木材曲率回弹性,定点监测弯曲木材的含水率,采用预埋式探针式温度计和点测温度计,测定微波定型处理过程中木材温度的变化。综合分析得出,纤维饱和点是弯曲木材回弹的分界点,在纤维饱和点以下时,回弹速度几乎成直线上升,当超过纤维饱和点时,回弹速度开始缓慢增加;复配碱液软化处理的弯曲试材,后期定型效果最好,水热软化处理的试材,后期定型效果最差;幼龄材的定型效果通常好于成熟材;微波-干燥定型效果最好,直接干燥定型效果最差;揭示了弯曲定型机理,讨论了应力释放与定型的关系,分析定型过程中的各种条件变化对木材弯曲定型的影响。确定了木材弯曲的定型工艺。通过木材软化处理、顺纹压缩、木材单维弯曲和多维弯曲以及弯曲定型机理和工艺研究,确定了木材顺纹压缩与多维弯曲技术,为有限的木材资源科学地、合理地、高效地利用提供理论依据和实践指导。更多还原

【Abstract】 The longtitudinal compressing and muti-dimensional bending technology of wood is a inter-disciplinary forefront hot issue with enough applicational and theoretical values.This research,particularly the constitutive relationship established of wood’s stress and strain on the process of longtitudinal compressing and the research of multi-dimensional bending deformation technology,will fill in the blank of relevant research that having been reported. The technology can expand the field of wood’s application,and it is a new technology of scientific and rational use of timber resources and helpful to environmental protection.The multi-dimensional technology can change the shape and structure of wood products in design, and can create an even wider space of the effective use of wood.The final aim of this paper is to research the longtitudinal compressing and mutidimensional bending technology of wood.The first thing is to soften the wood,and find the best softening method.The next thing is to compress the softened wood on longtitudinal direction,establish the constitutive relationship of wood’s stress and strain on the process of longtitudinal compressing and analysis the change of flexibility and elastic-plastic properties on the process of compressing and rebounding.The third is to get smaller curvature radius, realize multi-dimensional bending,analysis the change of flexibility and elastic-plastic properties after bending,establish the constitutive relationship of wood’s stress and strain, preliminarily establish the constitutive relationship of wood’s stress and strain on the process of single dimensional bending,and assure the single and muti-dimensional bending minimal curvature radius.The forth one is to mold the bended curve parts and analysis the impact of different molding conditions on deformation.Through the research above,the longtitudinal compressing and muti-dimensional bending of wood are determined.The samples of this paper are elm and ash which is all important commodity lumbers, researching the longtitudinal compressing and muti-dimensional bending technology.(1) On the process of softening test,exploring experiments to young and mature wood were carried on separately to make sure the softening mothods of hydrothermal, hydrothermal- microwave and compound lye softening treatments finally.Through the results of the following up tests(ratio of longtitudinal Compressing,PRD,bending curvature radius, ect),properties of the softened wood were tested,for example the relative crystallinty tested by X-ray diffractometer,the surface properties as well as chemistry component’s changes and so on tested by FTIR to discuss the chemistry component and the changes of relative crystallinity.The results show that:the three softening methods can all change chemistry components of wood,particularly the lignins,hemicelluloses,and extracts of wood degradate with a different degree by the three softening methods.In all the softening degree through compound lye softening treatments is the most obvious and the softening degree through hydrothermal treatments is smallest.And the degradating degree of mature wood’s chemistry components is lower than the young one.The relative crystallinty increases because extracts of wood have gone and the degradating degree of chemistry components goes up.Though the PRD of the young wood is higher than mature one,the results of tests show that the longtitudinal compressive results of mature wood will be better than the young one.The B method of hydrothermal-microwave treatments is more suitable for longtitudinal compressing.(2) In the longtitudinal compressing tests,the softened wood were compressed on the longtitudinal direction through special compressive mold and mechanical testing machine together.The stress,strain,ratio of longtitudinal compressing and PRD were determined,and the density changes of wood before and after longtitudinal compressing were tested by Micro-X-ray mechine.The changes of cell wall’s folding situations after longtitudinal compressing were observed by the scanning electron microscopy.Analysis shows that the longtitudinal compressive degree of hydrothermal-microwave treatments is lager,and the one of compound lye softening treatments is smaller.The longtitudinal compressive stress of elm is less than ash’s,and the indicators above of mature wood is less than the young wood.If the longtitudinal compressive degree is the same,the PRD of young wood is all higher the mature wood.When establishing the constitutive relationship of wood’s stress and strain on the process of longtitudinal compressing,each region all obeys the mechanical linear relationship.The density changes of the mature wood are higher than the young one,but the density fluctuation of young wood is higher.Through analysising the the change of flexibility,elastic-plastic properties,density as well as the change of folding,mechanism of wood’s longtitudinal compressing is revealed and the suitable processing conditions of wood’s longtitudinal compressing are drawn.(3) In the multi-dimensional bending test,the circular and S-type curving molds were used to bend the wood on the longtitudinal and string direction.The folding changes of wood’s cell wall were observed by the scanning electron microscopy.The single and muti-dimensional bending minimal curvature radius was known by adjusting the radius of curving molds and using the multi-dimensional bending molds.The research indicates that the characters of wood,the ratio of longtitudinal compressing, the ratio of rebounding and other factors all impact on the bending curvature radius of wood obviously.The bending properties of young wood are worse than the mature one.On the process of bending,the folded cell wall on the stretched side becomes smooth,and the folded cell wall on the compressive side become the former compressive ratio,finally the broken point lies on the middle section of the stretched side of the bended wood.From the preliminary establishment of the constitutive relationship of wood’s stress and strain on the process of single dimensional bending,the bending preliminary stage conforms to the linear mechanics relations.The single and muti-dimensional bending curvature radius of elm is lower than ash, and the property of mature wood is lower than young wood.The curvature radius on the string direction of wood is lower than the longtitudinal one.The curvature radius through micro-wave softening treatment is the smallest.Finally the processing parameters of wood’s mutidimensional bending are known.(4) In the test of wood’s deformation after bending,directly drying,hydrothermal-dry, and microwave-dry deformations were used.The rebounding ratios of bending wood were detected quickly.The moisture content of bended samples was tested on the specific points. Temperature changes of the samples on the process of micro-wave deformation treatments are tested by the buried probe-type thermometer and the spot-type thermometer.The generalized analysis shows that boundary point of samples is the fiber saturation point (FSP).Below FSP,the rebounding ratio goes up in line;above FSP,the rebounding speed increased slowly,the deforming result of bending wood by compound lye softening treatments is the best,but the one by hydrothermal softening treatments is the worst.The deforming result of young wood is better than the mature one.The microwave-dry deforming result is the best; the directly drying deforming is the worst.Mechanism of wood’s bending deformation was revealed,the relationships of stress release and deformation were discussed,and the impacts of diffrerent conditions on bending deformation were analysised.Finally,the deformation craft of bending wood was determined.Through researching the softening treatments,longtitudinal compressing,single and multi-dimensional bending as well as bending deformation mechanism and craft of wood, wood’s longtitudinal compressing and multi-dimensional bending technology were determined. It provides theoretical and applicational instruction to use the limited timber resources effectively and reasonably.更多还原