Study On The Technology Of Longtitudinal Compressing And Muti-dimensional Bending Of Wood

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.