| With the development of science and technology and the continuous emergence of emerging technologies and industries,especially since the 21 century,with the rapid rise of aerospace,navigation and other high-tech fields,people have higher and more stringent requirements for the properties of composite materials.The composite materials should not only meet the performance requirements,but also have a lightweight structure to meet the design requirements of light weight and high strength.Due to the diversity of structure and complex process,the structural design of composite materials is relatively simple.The natural composite structure formed by natural biology over hundreds of millions of years,these biomaterials provide a new idea for the design of artificial materials.Phyllostachys pubescens is a natural structural composite material with high elasticity,high strength and toughness in nature,which has formed the structural characteristics of light weight and high strength in the long process of evolution.Because of its special internode hollow structure and internal gradient distribution,it has a good overall structure,which can provide more inspiration for the design of bionic materials.In this paper,taking phyllostachys pubescens as the research object,the characteristics of microstructure of phyllostachys pubescens were studied by X-ray three-dimensional microscope.Combined with the structural characteristics,the relationship between microstructure and mechanical properties of bamboo was analyzed.It was found that in the cross section of phyllostachys pubescens,the gradient distribution structure composed of vascular bundles and parenchyma cells made a great contribution to the bending and compressive strength of phyllostachys pubescens,and their alternating parallel arrangement greatly increased the partial pressure of phyllostachys pubescens.Based on this,the gradient distribution structure of imitation bamboo and the alternating structure of imitation bamboo are extracted as the design elements of imitation bamboo sandwich board.Combined with the design principle of sandwich composites,single-layer and double-layer bamboo-like sandwich panels are obtained by design and optimization.In order to explore the influence of process parameters on the sandwich panel,firstly,the processing process parameters(temperature,time,pressure)of the sandwich panel were studied,combined with the change of the density of the core layer.the effects of four factors on the bending and impact properties of the sandwich panel were analyzed by orthogonal test,and the best process parameters were obtained.According to the optimized bamboo structure and process parameters,bamboo-like sandwich panels were prepared by molding process using glass fiber,epoxy resin and PVC foaming materials as raw materials.Then,according to the pore structure of phyllostachys pubescens parenchyma cells,corresponding to the changes of core pores,the effects of core pore structure and thickness on the properties of sandwich panels were studied.Finally,aiming at the gradient distribution structure and alternating structure,the influence of the change of core density and the addition of bionic layer on the double-layer sandwich panel structure is analyzed,and the bending and impact action mode and failure mode of each group of sandwich panels are analyzed in detail.prove the advantages of bionic structure.The main conclusions of this paper are as follows:(1)The vascular bundle shape in the cross section of phyllostachys pubescens tends to be stable gradually from the outer to the inner vascular bundle,and the volume fraction of the vascular bundle gradually decreases from the outer to the inner vascular bundle.the area of fiber phase and the distance between the central axis of adjacent vascular bundles increased,and the area of single parenchyma cell of phyllostachys pubescens increased gradually from outside to inside.In the longitudinal section of Phyllostachys pubescens,the vascular bundle structure,fiber cells and parenchyma cells are arranged in parallel with each other in the axial direction,which is characterized by the circular arrangement of fiber cells and parenchyma cells,and the mechanics is characterized by load-bearing structure-buffer structure.Fiber cells are usually located between two parenchyma cells.(2)The bending process and radial compression process of phyllostachys pubescens are the destruction of its laminated structure,when bamboo green or bamboo yellow is upward,the bending strength of bamboo is 131.4 MPa,which is higher than that of ordinary wood,and the radial compression strength of bamboo is 155 MPa,which is 105.5 MPa higher than that along grain,which is mainly caused by the different arrangement direction of vascular bundles and parenchyma cells and the direction of stress.(3)In the single-layer sandwich panel,when the thickness of the core layer is the same,the bending strength and impact strength of the sandwich panel increase with the increase of the density of the core layer.In this paper,when the preparation process parameters of sandwich panel are 180?,5 min and 1.5 MPa,the bending and impact strength of sandwich panel are the best.(4)When the core density is the same,the bending load of,h(core pore structure is larger than that of w(core compression),but because of the small thickness of w,the bending strength of w is larger;when the core density is the same,the impact strength of h is larger than w because h has complete void structure without compression.(5)In the double-layer sandwich panel,the addition of the bionic layer increases the bending strength of the corresponding sandwich panel by 29.5%,3.4%and 21.9%,respectively,and increases the impact strength of the corresponding sandwich panel by106.0%,77.1%and 60.7%.Considering the lightweight and impact and bending strength,the mechanical properties are the best when the density distribution of the core layer is(350 kg/m~3,500 kg/m~3).It is proved that the density gradient distribution can promote the impact and bending properties to a certain extent. |
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