| Bamboo is a natural biological material with great variability in its stalk shape,physical and mechanical properties.In order to achieve the best use of materials,the classification of round bamboo was a prerequisite for the preparation of bamboo products with uniform performance,stability and designability.The traditional bamboo glued laminate was the plate square material,which was composed of fine-planned bamboo strips with small cross-sectional dimensions,and then prepared via bundling and gluing.Because of the small cross-sectional size of the constituent units,the degree of automation of the preparation process was low,and the amount of sizing is large,resulting in high cost.The replacement of small-sized bamboo strips with large-section specifications can reduce the preparation process and cut down the amount of adhesive used,thereby improving the utilization rate,automation level of bamboo,and reducing production cost.At the same time,the normalized,standardized and serialized bamboo dimension flattening panels can produce bamboo products with stable quality and performance design,and are also convenient for storage and transportation,which provides guarantee for the large-scale development of the bamboo industry.Therefore,the Moso bamboo(Phyllostachs heterocycla)was used as the research object in this study,the research on the size and hardness modulus of bamboo was carried out,and developed the new equipment and new technology of bamboo exhibition,proposed the concept of bamboo specification material,and explored the bamboo specification material.The preparation process,bonding performance and finger joint performance were investigated,and the stress-strain evolution process of the bonding interface was analyzed.The main conclusions through research are as follows:(1)By measuring the size of 200 Moso bamboo stalks,it was concluded that the total height,the height under branches,the diameter under branches and the diameter at breast height of Moso bamboo stalks were normal distribution trend,and the diameter at breast height has a good positive correlation with the other three indicators.According to the wall thickness and diameter measurement of the cut 1400 circular round bamboo,the wall thickness distribution of the bamboo was 5-13mm,with 1mm as a classification module,the round bamboo can be divided into 8 levels and different walls.There were significantly different among different wall thickness groups.(2)Based on the wood hardness test method and the gradient variation of the cross-section shape and radial performance of Moso bamboo,a grading method for the indentation strength of the longitudinal end face of the bamboo was proposed,and the grading index-hardness modulus of the round bamboo was defined.It is found that the hardness modulus of the longitudinal end of the round bamboo ranges from 35.8 to 64.5 MPa through the measurement and statistics of the hardness modulus of 200 round bamboos,demonstrating a normal distribution trend.According to the classification interval of 5 MPa,the hardness modulus of bamboo can be divided into 6 grades,mainly distributed in the interval of 45-55 MPa.According to the statistics of the hardness modulus of large samples of Moso bamboo,the hardness modulus and density,the compressive strength of the grain and the modulus of rupture(MOR)and the modulus of elasticity(MOE)are in a good linear relationship.The hardness modulus can be used to characterize the mechanical properties of Moso bamboo,the V-type hardness modulus grading method can be used as a reference for the classification of bamboo.(3)The density and mechanical properties of the bamboo flattening panels corresponding to the round bamboo with different hardness modulus grades increased with increasing the hardness modulus of the round bamboo.Meanwhile,in addition to the compressive strength of the grain and the tensile strength of the grain,the physical and mechanical properties of the corresponding grades of round bamboo flattening panels were higher than those of the round bamboos,and the performance of the flattening panels with different indentation levels was significant,but there were overlapping regions,so the hardness modulus classification can help to roughly classify the later materials to a certain extent.But there are limitations to the performance of the flattening panels.(4)Compared with the traditional flattening process,the new bamboo flattening technology can not only improve the surface quality and mechanical properties of bamboo flattening panels,but also increase productivity and reduce production costs.According to the actual use,the bamboo flattening panels was standardized,and the intermediate products of specification,serialization and standardization are provided for the processing of bamboo products,laying a foundation for large-scale production.(5)According to the results of shear strength of bamboo flattening adhesive layer,the shear strength of the bamboo outer-outer surface was the largest,followed by the bamboo outer-inner surface,and the bamboo inner-inner surface has the lowest shear strength.The optimum bonding process for different bonding surfaces is different.The preferred process of bamboo inner-inner surface is hot pressing pressure of 2 MPa and sizing amount of 210 g/m~2.The digital speckle analysis was employed to analyze the stress-strain distribution of different gluing interfaces,the relative shifting and single-point displacement analysis of the three gluing interfaces exhibited that under different gluing conditions,the relative shifting of two sides will be turned when loaded to a certain stage,and the glue interface will be different,and the degree of turning will vary with the bonding interface.The bonding effect of bamboo inner-inner surface is the best when the same material is bonded,and the bonding effect is the best in the middle position of the bonding surface is along the direction of the glue line.When different materials are bonded(bamboo outer-inner surface),the bonding effect is poor,and the displacement along the direction of the glue line(from moving end to fixed end)increases gradually.According to the shear stress formula of Volkersen theory,the shear stress of bamboo surface in the process of tensile shear is calculated.The comparison between the average shear stress of bamboo inner surface calculated by the theory and the measured value shows that the model has excellent applicability and accuracy for the shear stress of bamboo specification material.(5)By comparing the finger-joined materials of the same tenon type,the mechanical properties of the V-tenon type were better than those of the H-tenon type.Comparing the mechanical properties of finger-joined materials with different chimerism and different tenon parameters,it was considered that the type II finger-finger finger-jointed tool with short finger length was used without affecting the material strength.The optimum fingering parameter is0.1.By comparing the mechanical properties of finger-bonded bamboo dimension lumber with those of non-finger-bonded bamboo dimension lumber,it was found that the MOR,MOE,tensile strength and impact toughness of finger-bonded bamboo dimension lumbers were59.2%,88.9%,47.7%and 37.2%of those of non-finger-bonded bamboo dimension lumbers respectively,which maintained the flexural and tensile properties of raw materials and met the requirements of M_E16(flexural strength 63.0 MPa)and the highest M_E18(tensile strength 42.5MPa).It is with great application prospects as structural materials. |
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