| Sandwich structure is composed of low-density core material and thin panel,which is widely used because of its light weight and high strength.Among many sandwich structures,wood sandwich structure can effectively reduce the pollution to the environment at the end of its service life because it reduces the use of plastic panels and filled foam.In addition,the combination of sandwich structure and wood can not only save wood resources,but also take advantage of the high strength to weight ratio of wood itself to give full play to the advantages of sandwich structure.However,the mechanical properties of sandwich panels made of poor wood such as fast-growing wood need to be improved.Therefore,it is very necessary to study the reinforcement of wood sandwich panels,which is of great significance to expand the application range of wood sandwich panels.In addition,the use of all wood materials will increase the flammability of sandwich panels,which limits the application of wood sandwich structures in transportation,construction and other industries.Therefore,how to improve the flame retardant performance of wood sandwich panels is also an important issue.In this paper,poplar veneer is used to prepare wood corrugations by direct hot pressing,and then the corrugations and panels are assembled to obtain wood corrugation core sandwich panels.The resin reinforcement,equivalent model construction and flame retardant performance of the corrugated sandwich structures are studied.The main results are as follows:(1)The relationship between hot pressing time and corrugated water content was studied.The results show that when the hot pressing time is 60 s/mm,the ripple moisture content is(8±2)%and meets the standard moisture content value.As the hot pressing time continues to increase,the ripple reaches absolute dry,so the hot pressing time of the ripple is determined to be60 s/mm.(2)The resin reinforced corrugated board was prepared by molding and curing the phenolic resin impregnated veneer.The results show that compared with ordinary corrugations,the flat compression modulus and strength of reinforced corrugations are increased by 56%and 67%,respectively;at the same time,the bending and shear properties of the reinforced corrugated sandwich plates are also greatly improved.The flexural stiffness,flexural elastic modulus,shear stiffness and core shear elastic modulus of the reinforced corrugated sandwich plate increased by39.3%,40.1%,9.5%and 132%,respectively.In addition,the density of the reinforced corrugated sandwich panel has increased from 0.2 g/cm~3 to 0.22 g/cm~3,which is only 1.1 times that of the ordinary corrugated sandwich panel,indicating that the resin impregnation reinforcement treatment has little effect on the quality of the sandwich panel.The resin impregnation process further improves the mechanical properties of corrugated sandwich panels and expands the application range of wood sandwich structures.(3)Using the equivalent model,the equivalent elastic properties of the corrugated core layer are calculated.According to the laminated board theory,after calculating the stiffness matrix of each single-layer board,the overall stiffness matrix of the sandwich board is further calculated to obtain the elastic constant of the laminated board.Comparing the theoretical values calculated by the model with the experimental results,the results show that the errors between the theoretical calculated values of the shear modulus of the core layer and the elastic modulus of the sandwich panel and the experimental values are 6.76%and 8.36%,respectively,and the errors are small,indicating that The corrugated equivalent model and the sandwich panel stiffness calculation method used in this paper have high accuracy,and the mechanical properties of the sandwich structure can be accurately predicted by using this method.By adjusting the corrugated geometric parameters,the results show that the change of the thickness of the corrugated core has the greatest influence on the elastic properties of the sandwich panel,and the performance of the sandwich panel is also the most sensitive to it.By adjusting the grain direction of the veneer and the number of veneer layers,the results show that the 0°corrugated sandwich panel has better elastic properties than the 90°and 45°corrugations;The increase of,will lead to the decrease of the elastic properties of the sandwich panel.In addition,the increase of the number of panel layers can significantly improve the elastic properties of the sandwich panel.Finally,the model calculation results show that the elastic modulus of the single-layer reinforced corrugated sandwich panel is 2659 MPa,and the value measured by the experiment is(3048±136)MPa.The error between the two is 12.76%,and the error is small.The calculation method is also applicable to the stiffness prediction of reinforced corrugated sandwich panels.(4)The flame-retardant veneer was prepared by layer-by-layer self-assembly technology,and the flame-retardant veneer was prepared by using the flame-retardant veneer and the composite adhesive added with the two-dimensional layered materialα-zirconium phosphate(α-Zr P).The results of flame retardant properties of plywood showed that compared with the untreated plywood,the peak heat release rate(p HRR)and total heat release(THR)of the plywood prepared by using ordinary veneer and the composite adhesive added withα-Zr P were respectively decreased by 31.2%and 9.9%.The p HRR and THR were reduced by 5.9%and 8.4%for plywood prepared with flame-retardant veneer and adhesive withoutα-Zr P addition,respectively.The p HRR and THR of the plywood(P-Z/UF)prepared with flame retardant veneer andα-Zr P-added composite adhesive decreased by 41.8%and 22.9%,respectively,indicating that the P-Z/UF plywood has excellent flame retardant properties,which can It is used as a panel of a wooden sandwich structure. |
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