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Mechanical Properties Research of Wood Glue Joints

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Tutor: HuYingCheng
School: Northeast Forestry University
Course: Wood Science and Technology
Keywords: Birch,Gluing joint,Mechanical properties,Finite element,Nondestructive testing
CLC: TS653
Type: PhD thesis
Year:  2013
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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.
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