【作者】 卢伟；

【导师】 胡英成；

【作者基本信息】 东北林业大学 ， 木材科学与技术， 2013， 博士

【摘要】 木材是人类应用最早的材料之一,由丁木材本身具有天然纹理和色泽、易加工、质轻而强重比大、可生物降解、隔声、隔热、绝缘等优点,使木质材料在人类发展的历程中发挥了极其重要的作用。在钢材、水泥、木材、塑料这四大工程材料中,木材是惟一的可再生材料。木质材料已被广泛应用于家具、建筑、乐器、船舶、车辆、医疗器械等各个行业。为了对木质材料进行正确合理的有效使用,就需要了解木材及其连接件的物理力学性能。因此本文针对以桦木为材料的几种胶接接头的力学性能进行了相关理论和试验的研究。论文首先提出了课题的研究背景和研究意义,对木质胶接技术和检测手段进行了阐述,对国内外胶接接头的应力分析、无损检测方法和蠕变特性进行了总结和论述,确定了论文的研究方向和主要研究内容。胶接接头的应力分布是一个复杂的力学问题,本文提出利用三角级数求和的方法,从理论上推导了胶接接头的应力分布区域及解析解的大小,为木质胶接接头应力的分析和求解提供了一种新的理论方法。对桦木搭接胶接接头力学性能进行了正交试验研究。主要研究胶合长度l、试件厚度h和试件宽度b三因素对其力学性能的影响。得到各因素对最大拉伸载荷影响的强弱关系为b>l>h,最优方案为b3l3h3；也得到各因素对拉伸强度影响的强弱关系为h>l>b,最优方案为h1l3b1。得到各因素对弹性模量(MOE)影响的强弱关系为l>h>b,最优方案为l3h1b3；也得到各因素对静曲强度(MOR)影响的强弱关系为h>l>b,最优方案为h1l3b3,弯曲性能的综合最优方案为l3h1b3。并利用Matlab软件构建了搭接接头力学性能的曲面模型和预测方程。对桦木盖板胶接接头力学性能进行三组单因素试验研究。三个因素分别为盖板长度(胶合长度)l、盖板厚度h1、试件和盖板同厚(h=h1),研究它们对接头力学性能的影响。发现拉伸载荷和拉伸强度随胶合长度l的增加而增加,拉伸载荷随盖板厚度h1的增加而增加,而拉伸强度却随盖板厚度h1的增加而略有减小,拉伸载荷和拉伸强度随试件和盖板同厚(h=h1)的增加而减小；弯曲载荷、MOE和MOR都随胶合长度l的增加而增加,随盖板厚度h1或试件和盖板同厚(h=h1)的增加而减小。对桦木斜接胶接接头的力学性能进行了单因素试验研究。研究三种斜率(1：4、1:8、1：12)对其力学性能的影响。斜率k由1：4变到1：8,胶合长度增加20mm,接头的拉伸载荷与拉伸强度增加了2.5倍；由1：8变到1：12,胶合长度也增加20mm,而拉伸载荷与拉伸强度只增加了29.49%；弯曲载荷、MOE和MOR都随斜率的减小而增加。因此斜率越小,斜接接头力学性能越好。对桦木指接胶接接头的力学性能进行了试验研究。研究三种斜度α(1：8、1：10、1：12)对其弯曲力学性能的影响。弯曲载荷、MOE和MOR都随斜度的减小而增加。因此斜度越小,指接接头力学性能越好。利用ANSYS有限元法对桦木胶接接头的力学性能进行了仿真分析,在仿真等效应力图中各种接头受力变形呈现不同程度对称分布,在胶合区域存在应力集中现象。搭接接头应力峰值随胶合长度l的增加而逐渐减小；随试件厚度h的增加,拉伸应力峰值增大,而弯曲应力峰值略有减小。盖板接头的应力峰值也随胶合长度l的增加而逐渐减小；随盖板厚度hl的增加,拉伸应力峰值而减小,随试件和盖板同厚(h=h1)的增加而增大；弯曲应力峰值随盖板厚度hl或试件和盖板同厚(h=h1)的增加而略有增大。斜接接头弯曲应力峰值随斜率k的减小而减小。指接接头由上到下的胶合面的弯曲剪切应力由负变正,数值由大到小再变大,剥离应力峰值在胶合面的中间区域,由上到下峰值逐渐减小,而且斜度越小,应力峰值越小。接头的仿真分析与胶接接头应力理论分析结论存在一致性,可以利用ANSYS有限元对接头的力学性能进行仿真分析。对桦木胶接接头进行了弯曲蠕变试验。搭接和盖板接头的抗弯曲蠕变现象相近似,其抗弯曲蠕变性能随胶合长度和试件厚度(或盖板厚度)的增加而增强,而且接头在蠕变的过程中,会出现突变再恢复的现象。斜接接头的抗弯曲蠕变在140h(第六天)左右发生一次大突变,比原木的突变发生要早,变异量也大,而且变异量随斜率减小而增加。从曲线整体看,斜接接头比搭接和盖板接头的蠕变曲线要光滑平整,也没有蠕变突变再恢复的现象。并利用对数方程和乘幂方程对蠕变曲线进行了回归分析,获得的回归方程精度很高,可以被用来预测各类胶接接头的蠕变过程。利用快速傅里叶变换(FFT)分析技术的弯曲振动法对四种桦木胶接接头进行无损检测。得到动态弹性模量Ef和破坏试验获得的拉伸强度σ(斜接接头除外)、MOE及MOR之间存在明显的相关性,回归关系高度显著,获得的回归方程可进行接头强度预测。将胶接接头应用到单板层级材(LVL)中,结果表明,通过设计合理的接头类型和结构尺寸,可以满足LVL等木质复合材料不同工作场合的使用性能,有效地提高LVL的力学性能和利用率。本文通过试验检测、理论推导和有限元分析的方法对木质胶接接头进行了力学性能的评价及其影响规律的研究,获得的理论模型及预测模型对于木质接头的实践应用有着积极的作用。更多还原

【Abstract】 Wood is one of the earliest application materials in human history. The advantages of wood are light mass, high strong-heavy ratio, biodegradability, comfortability of vision and touch, sound insulation, heat insulation and etc, and play an important role in the development process of human. In the four engineering materials of steel, wood, plastics and cement, wood is the only renewable material. Wood materials have been used widely in construction, furniture, musical instruments, vehicles, ships and medical instruments. In order to make the correct and reasonable use of wood materials, physical and mechanical performances of wood and wood fittings, the related theory and experiments of mechanical performances of several gluing joints made birch have been done in this paper.The research background and significance of the topic have been put forward firstly, gluing technology and testing methods of wood have also been illustrated, the glue joint stress analysis, nondestructive testing methods and creep characteristics of wood joints both in abroad and at home have been summarized and discussed, thus research direction and research contents have been determined.Stress distribution of gluing joint rubber is a complex mechanical problem, this paper puts forward the method by using trigonometric series summation, the stress distribution and the analytical solutions have been deduced theoretically, a new theory method of the stress analysis and solution of wood gluing joint has been provided.Orthogonal experiment research of mechanical performance of birch lap gluing joint has been carried. The main three research factors are agglutination lengthι, specimen width h and specimen thickness b. The relationship of all the factors on the maximum tensile load is b>l> h, the optimal scheme is b3ι3h3; also the relationship of all the factors on the tensile strength is h>l>b, the optimal scheme is b3ι3h3. the relationship of all the factors on MOE is l>h>b, the optimal scheme is h1ι3h3; Also the relationship of all the factors on MOR is h>l>b, the optimal scheme is h1ι3h3, the optimal solution scheme of bending performance is h1ι3h3. And by using Matlab software, surface model and prediction model of joint mechanical properties have been builded.Three groups of factor experiment research have been carried for the mechanical performances of birch cover plate gluing joints. The three factors influencing mechanical property are gluing length, cover plate thickness and specimen and cover plate with the same thickness. Tensile load and tensile strength increase with the increase of gluing length, tensile strength slightly and reduces with cover plate thickness, tensile load and tensile strength decrease with the increase of cover plate thickness, Bending load, MOE and MOR all increase with the increase of gluing length, decrease with the increase of the cover plate thickness, and decrease with the increase of the thickness of specimen and cover plate.Single factor experiment research of mechanics performance of the birch scarf gluing joints has been carried. When the slope k change from1:4to1:8, the tensile load of joints increased2.5times, When the slope k change from from1:8to1:12, the tensile load increased only29.49%; Bending load, MOE and MOR also decrease with the slope increase. So the smaller the slope, the better the mechanics performance is.Experiment research of mechanics performance of the birch finger joints has been carried. The influence of three slopeα (1:8,1:10,1:12) on the bending mechanical properties has been discussed. Bending load, MOE and MOR are all increased with the decrease of slope. So the smaller the slope, the better the mechanics performance is.Simulation analysis of mechanical performance of the birch gluing joints has been done by using the ANSYS finite element method, the different degree symmetric distributions are present in the simulation equivalent stress graghs, the stress concentration phenomenon of shear stress and stripping stress exists in the gluing regions; the peak values of lap joints decrease with the increase of the gluing lengthι; with the increasing of specimen thickness, the peak tensile stress increase and the peak bending stress increase slightly. The peak tensile stress values of cover plate joints also decrease with the increase of the gluing lengthι; with the increasing of cover plate thickness h1the peak tensile stress decrease, with the increasing of both h andh-h1, the peak tensile stress increase; the peak bending stress increase with the increasing of h or h=h1. The peak bending stress decreases with the decreasing of the slopes k. The bending shear stress of the finger joint changed from negative to positive values from the top layer to the bottom layer, the peak stripping stress exist in the middle areas of gluing area, and gradually decreased from top to low. The smaller the slope, the smaller the peak stress is.From the above results, there is a same changing tendency with the theory analysis, so ANSYS finite element method can be used to simulate the mechanical performances of gluing joints.Bending creep test of birch gluing joint has been done. Creep phenomena of lap and cover plate joints are similar, flexural creep properties increase with the increase of gluing length and specimen thickness (or cover plate thickness), and mutation recovery phenomenon appears in the creep process. A big mutation has happened in140hour (the sixth day) around, which is earlier than the log opponent; the variation amount is also larger and increases with the slope decrease. From the overall of the curves, the creep curves are more smoothly and have no creep mutations recovery phenomenon. The regression analysis using the logarithmic equation and power equation has carried, the precision of regression curve is high, and can be used to predict of various gluing joint creep process. Nondestructive testing of four types brich gluing joints have been done by using the bending vibration method of FFT analysis technology, obvious correlation relationships between dynamic elastic modulus Ef and the tensile strength a got by damaging test(except scarf joints), the significant relationship has existed between MOE and MOR, the regression is highly obvious, the regression equation can predict the joint strength.When applying the veneer joint for veneer lumber (LVL) application, the results show that, through the reasonable design of the joint type and structure size, can meet LVL wood composite materials different application requirements, effectively improve the mechanical properties and utilization of LVL.Mechanical properties and the influence law of wood gluing joints have been researched by using experimental testing, theory derivation and finite element analysis methods in the paper, the obtained theory model and prediction model have a positive effect for the practical application of wood joints.更多还原