Research On Gluing And Jointing In Length Of Bamboo Strips For Side-Pressed Bamboo Laminates

Bamboo has the characteristics of lightweight and shock resistance,a high strengthto-weight ratio,and its mechanical properties such as tensile strength,MOR,and MOE are very excellent.The side-pressed bamboo plywood has good mechanical properties and has the potential to make structural glulam skeleton members.Most of the current research focuses on the influence of various factors on the bamboo properties,and the comparison of the properties with other materials.There are few studies on the gluing properties and the joint form of the bamboo strips,which are the constituent units of the side-pressed bamboo plywood.In this paper,the bamboo strips prepared by bamboo are used as raw materials,and the gluing performance,joint form,and finger-jointing process of bamboo strips are studied through a combination of theoretical analysis and experimental exploration.The main research contents and results obtained are summarized as follows:1.The three factors that affect the gluing performance of bamboo strips(gluing surface,knot,gluing pressure)are used as variables.The effects of three factors on the bonding performance of bamboo strips were explored by testing the adhesive layer shear strength and impregnation peeling rate of the glued bamboo strips.The glued surface has a great influence on the shear performance,the shear failure occurs inside the bamboo,and the adhesive layer is not the weakest item.Bamboo joints have little effect on shear strength and have a significant negative impact on the peel resistance of bamboo strips.The study found that avoiding the overlapping of bamboo joints during the gluing process can meet the impregnation and peeling standards of structural glulam.The best gluing process is:near-green surface-near yellow surface gluing,the gluing pressure is 1.2MPa,and the position of the bamboo joints during gluing is avoided during the preparation process.2.The side-pressed bamboo laminates with butt joints were prepared.By comparing the static bending strength and elastic modulus of the jointed bamboo laminates and the non-joint laminates,the influence of the butt joints on the flexural properties of the bamboo strips was studied.Combined with the existing research results,the bending failure mode of the bamboo laminate is analyzed.The study found that the butt joint reduces the static bending strength and elastic modulus of the side-compressed bamboo laminate,and has a more significant effect on the static bending strength.When the proportion of joints is more than 1/7,the loss rate of static bending strength of bamboo laminates is more than 15%.The existence of joints makes the bending performance of side-pressed bamboo laminates decrease significantly,so the form of butt joints cannot meet the requirements of joint length.;When the proportion of joints is 1/9,the loss rate of static bending strength of bamboo laminates with joints is 8.99%,which is less than 10%,which can meet the performance loss requirements of general materials;when the proportion of joints is less than 1/12,the loss rate is less than 5%,and the bending performance of the bamboo laminate is greatly preserved.3.The bamboo strips were processed into tenon teeth with different degrees of engagement with four commonly used tenon milling inserts.The effects of fingerjointing shape and tenon fitness rate on the required finger-joining pressure,and the effects of joint shape,tenon fitness rate,and adhesive on the mechanical properties of finger-jointing bamboo strips were studied.The research found that the tenon fitness rate is positively correlated with the required finger joint pressure.The required pressure of the finger tendon is affected by the finger-jointing wedge angle and length.When the finger-jointing angle wedge angle is different,the finger joint pressure increases with the decrease of the angle;When the wedge angle is the same,the finger joint pressure decreases with the increase of length.When the tenon fitness rate reaches 0.3mm,the root of the finger tenon will be split during the lengthening process.The tensile strength and static bending strength of finger-jointed bamboo strips increased with the increase of joint length,and had no obvious effect on the elastic modulus;within the range of fitting degree,the tensile strength and static bending strength increased with the fitting degree.Bamboo finger tenon diameter section and end surface have poor wettability,and the gradient structure leads to uneven force when the finger tenon is pressed,making the phenolic resin adhesive unsuitable for bamboo finger joints;one-component polyurethane adhesives rely on relatively It has high polarity and activity,and has good adhesion properties,which can be used for longitudinal extension of bamboo strips.In the test range,the best finger joint parameters are tenon type Ⅳ:joint wedge angle 9.81°,tenon tooth length 25 mm,groove bottom width 1.2 mm,tenon fitness rate 0.2 mm,required finger joint Pressure 10.387 MPa.