| Wood resource has always been the main raw material for human survival.Compared with raw materials such as steel,cement and plastics,wood resource is the only renewable biomass material.It is of great practical significance and wide application needs to make rational use of the natural properties of wood,improve the utilization value and application field of wood materials,and carry out the research and optimization design of wood engineering materials.Lattice sandwich structure integrates material design,structural design and functional design.It is a light,strong and ductile material with great application prospect.From the perspective of the design of new wood-based engineering materials,this paper used low-carbon and environmentally friendly wood resources as raw materials,combined with the characteristics of light weight,high specific strength/stiffness and multifunctional design of lattice sandwich structure,carried out the design and optimization of wood-based lattice core sandwich structure.Using solid wood and plywood as panels and birch dowels as core,pyramidal,improved pyramidal,hybrid and two-layer improved lattice sandwich structures were prepared respectively,and the mechanical properties were tested and analyzed.Simulation models were also established in ABAQUS for the sandwich structures.This paper provided theoretical basis and experimental data support for the research and application of wood-based lattice core sandwich structure in practical buildings and structures.The main research work of this paper are as follows:Firstly,the preparation process of wood-based lattice core sandwich structure was studied,and the slotting and adhesive bonding approach was improved.According to the performance characteristics of wood materials,the automatic positioning drilling device was independently developed to ensure the drilling accuracy in the preparation.The wood-based lattice sandwich structure was designed and prepared with larch sawn timber and spruce finger board as the face sheet and birch dowel as the core.The theoretical formula of mechanical properties of pyramidal lattice structure under flatwise compression and bending loads was deduced.According to the characteristics of the panel failure in the flatwise compression,the panel reinforcement design was carried out to improve the compressive stability of the sandwich structure,and the flatwise compressive failure modes were analyzed.The sandwich structure with three-layer panel reinforcement design had more stable performance,and the experimental and theoretical errors of compressive strength and elastic modulus were 4.47%and 11.37%.According to the failure mode of the core,the reinforcement design of at the ends of the core was carried out.The results showed that the compressive strength and elastic modulus of the structure were increased by 15.61%and 10.43%respectively.Combined with the characteristics of wood-based materials,the three-point bending tests and failure mode analysis of short beam and long beam of sandwich structures with different panel materials were carried out.Secondly,in order to further improve the mechanical properties and stability of the structure,plywood was selected as the panel material,and the improved pyramidal lattice sandwich structures were designed and prepared,which shorten the distance between individual cores in the pyramidal configuration and effectively improve the mechanical properties of the sandwich structure.Flatwise compression,edgewise compression,bending and low-velocity impact tests were conducted,and the mechanical properties and failure modes of the structure were deeply analyzed.The results showed that relative density had big influence on the compressive failure modes,and was positively correlated with strength,stiffness,and the load-to-mass ratio.At relative densities from 1.87%to 6.33%,the load-to-mass ratio of the structure increased by 77.70%,114.01%,160.66%,246.16%,404.05%from 36.55N/g,respectively.Combined with the characteristics of wood materials,the edgewise compression failure mechanism was studied.The results indicated that the stiffness and strength of the face sheet played a dominant role in the edgewise compressive behavior.The mechanical properties of the core and the degree of damage of the face sheet induced by drilling had a substantial effect on the endwise compressive properties.The edgewise compressive strength of sandwich structure with core diameter of 6mm was the largest.The bending test results showed that the flexural strength and elastic modulus of the structure were improved after carbon fiber reinforcement.The impact test adopted face impact to study the low-velocity impact performance of sandwich structure under different impact energies.The ABAQUS simulation models of wood-based lattice core sandwich structure were established and analyzed under the flatwise and edgewise compression,which provided a simulative basis for evaluating the mechanical properties of wood-based sandwich structure.Then,from the perspective of improving the flatwise compression mechanical properties of the sandwich structure,two hybridal lattice sandwich structures of "pyramid+straight column"and "improved+straight column" were designed,and the flatwise compression theoretical model was deduced.The bearing capacity of the hybrid structure was significantly increased,and the compressive strength,elastic modulus and load-to-mass ratio were greatly improved under the compressive tests.The compressive strength and elastic modulus of HB hybridal structure were 3.39MPa ? 200.98MPa,respectively,which were 1.22 and 2.12 times higher than those of B8 improved structure.The compressive strength and elastic modulus of JC hybridal structure were 2.48MPa? 153.96MPa,respectively,which were 4.16 and 1.53 times higher than those of PA2 pyramidal lattice structure.Compared with the lattice structure made of metal and carbon fiber composites,the wood-based hybridal lattice structure had certain advantages in load-to-mass ratio,specific strength/stiffness and so on.Finally,in order to improve the energy absorption characteristics of sandwich structure,according to the compressive failure mode,a two-layer improved lattice sandwich structure was designed.The flatwise compression and three-point bending tests were carried out.The results showed that the intermediate plate shortened the distance between the upper and lower panels,increased the compressive performance of the structure,and the impact of the thickness of the intermediate plate of 5mm and 9mm on the flatwise compressive mechanical properties of the structure was analyzed in detail.The two-layer structure specimens B and D with 9mm intermediate plate were selected for simulation modeling,and the simulation results were compared with the test results.Compared with the single-layer structure of the same size,the two-layer structure greatly improved the energy absorption characteristics of the structure.The specific energy absorption characteristics of samples A and B were twice higher than those of single-layer structure REF1.Compared with single-layer structure REF2,the specific energy absorption characteristics of samples C and D were increased by 125%and 118%.It is of great significance for the safety of structures.Through the three-point bending test,the shear capacity of the two-layer sandwich structure was tested and compared with single-layer sandwich structure. |
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