Circular arc curve honeycomb core structure with negative Poisson ratio characteristic
Technical Field
The invention relates to the field of negative Poisson ratio mechanical metamaterials, in particular to an arc curve honeycomb core structure with a negative Poisson ratio characteristic.
Background
Typically, a material undergoes shrinkage in its axial direction when it is longitudinally stretched, whereas it undergoes expansion in its axial direction when it is longitudinally compressed. The poisson ratio of the traditional material is a positive value, only few materials in nature can have the property of negative poisson ratio, but due to the rise of mechanical metamaterials, the negative poisson ratio mechanical metamaterials become a research hotspot at home and abroad.
The poisson ratio (v) is formulated as follows:
v=-εx/εy
wherein epsilonxDenotes the transverse shrinkage strain, ε, of the materialyRepresenting the strain of elongation in the machine direction of the material. The material with the negative Poisson's ratio has the characteristics different from the common material, and the mechanical properties of the material are superior to those of the common material under many conditions, including the characteristics of impact resistance, fracture resistance, resilience toughness, shear modulus and the like, so that the material has wide application prospects in the fields of aerospace, medical equipment, national defense engineering and the like.
The patent No. CN103214728A relates to a bionic negative Poisson's ratio material and a preparation method thereof, and the material is designed and prepared based on the microporous structure of natural foam and the principle of generating negative Poisson's ratio. The material is a porous foam structure material prepared from thermoplastic plastics through a screw extruder, the pores are elongated cellular micropores, and the long axes of the cellular micropores are arranged in a manner of diverging symmetrically outwards from the central axis layer by layer along the radial direction. Although the material disclosed in the patent has a negative poisson's ratio characteristic, stress concentration inevitably occurs due to sharp corners in the microporous structure, so that the impact resistance and the pressure resistance are greatly reduced, and the material is easy to crush and deform when being impacted by a large load, and the problem of crushing and deformation of the material when being impacted by the large load is not solved in the patent.
The patent number CN106541568A relates to a three-dimensional negative Poisson's ratio periodic porous material and a manufacturing method thereof, wherein the material is formed by alternately splicing two rotating modules; the projection shapes in the horizontal X direction and the horizontal Y direction are consistent, the projection in the vertical direction is an orthogonal square grid, the negative Poisson ratio property of a three-dimensional space is realized, and when the material is pulled in the vertical direction, the material is expanded in the horizontal two directions; and when the vertical direction is pressed, the horizontal direction shrinks inwards. However, due to the characteristics of the orthogonal square grids in the vertical projection, when the structure is subjected to a force acting in the vertical direction, if the direction of the force is deviated, the structure is easy to generate relative displacement in the horizontal direction to cause lateral bending of the material, so that the structure is unstable or the square structures which are vertically intersected are crushed to be changed into rhombuses, and an ideal deformation effect is not achieved.
Disclosure of Invention
The invention aims to provide an arc curve honeycomb core structure with a negative Poisson ratio characteristic, which improves the performance and stability of the conventional negative Poisson ratio mechanical metamaterial and has good application prospects in the fields of impact resistance, shock absorption and the like.
The technical solution adopted by the invention to achieve the above purpose is as follows: the honeycomb core structure with negative Poisson's ratio characteristic is formed by arranging arc curve rods in three horizontal 60-degree directions at equal intervals and continuously symmetrically in the vertical direction, and finally continuously connecting two farthest points on the arc curve through the vertical rods.
The arc curve is formed by periodically arranging arcs with alternate concave and convex parts and equal diameters and lengths.
The arc angle of the arc curve can be changed, so that the structure has the mechanical properties such as Poisson's ratio, equivalent elastic modulus and the like required by specific application occasions.
The vertical rod can adjust the length of the rod under the condition that the upper arc curve rod and the lower arc curve rod do not interfere with each other, the length of the rod is increased, so that the structure has a larger deformation space, and the length of the rod is reduced, so that the structure has better stability and a larger negative Poisson ratio effect.
The cross section shapes of the arc curve rod and the vertical rod can be circular, square, rectangle and other geometric shapes.
The increase of the cross-sectional area of the composition rods in the circular arc curve honeycomb core structure with the negative poisson ratio characteristic under the same cross-sectional shape can increase the bearing capacity of the structure, but can weaken the negative poisson ratio effect of the structure.
The microstructure of the circular arc curve honeycomb core structure with the negative Poisson ratio characteristic can be integrally formed through 3D printing, and can also be formed into various macroscopic shapes and sizes through a method of quickly producing single cells and then overlapping, so that the effect of quick production is achieved.
The invention has the following beneficial effects:
(1) the material of the present invention has a negative poisson's ratio characteristic, and expands in the XY plane when stretched in the Z direction and contracts in the XY plane when compressed in the Z direction. (2) According to the invention, the arc curved rod is used as a core rod for generating the negative Poisson ratio effect instead of a linear rod used by a plurality of negative Poisson ratio mechanical metamaterials, so that the stress concentration phenomenon of the traditional straight rod structure at the joint is relieved, and the elastic straight rod structure has better elasticity. (3) Compared with the traditional lapping mode, the three-dimensional lapping mode has higher stability and can resist load in a non-ideal direction.
Drawings
The invention is shown in the attached figure 5, wherein:
FIG. 1 is a schematic view of a circular arc curve honeycomb core structure having a negative Poisson's ratio characteristic.
Fig. 2 is a top view of a circular arc curved honeycomb core structure having a negative poisson's ratio characteristic.
Fig. 3 is a two-dimensional cross-section of its three-dimensional structure in one of its directions.
FIG. 4 is a method for dividing and dimensioning a two-dimensional unit of the structure.
Fig. 5 is a method of dividing a cell body when rapid manufacturing is performed.
Detailed Description
The following describes the present invention with reference to the accompanying drawings.
As shown in fig. 1 to 3, the invention provides a circular arc curve honeycomb core structure with negative poisson's ratio characteristic, wherein circular arc curve rods in a three-dimensional structure are circumferentially arranged in three horizontal directions of 60 degrees and are continuously and symmetrically arranged in the vertical direction, and then two farthest points of the circular arc curve are continuously connected through a vertical rod, and the three-dimensional building mode expands in each direction of an XY plane when being stretched in a Z direction; when compressed in the Z direction, it contracts in each direction in the XY plane and the unique three-dimensional lap joint provides it with good resistance to lateral loads.
As shown in fig. 2, the triangle formed by the three-dimensional lap joint mode in the transverse section endows the structure with better stability when being subjected to transverse load compared with the vertical lap joint mode.
As shown in fig. 3, the deformation mechanism of the two-dimensional unit body is the source of the negative poisson's ratio property of the three-dimensional structure, and the three-dimensional structure can also be understood as being formed by overlapping two-dimensional negative poisson's ratio structures which are equidistantly arranged in three directions.
As shown in FIG. 4, the dimensional parameters of the two-dimensional structure can be varied within a reasonable range, and the figure only takes a circular section as an example, and the height of the unit body is 2LyLength is LxThe radian corresponding to the arc line is theta, and the Poisson ratio v of the two-dimensional structure under the longitudinal load is obtained by calculating by using an energy method under the condition of neglecting the influence of the shear stress and the normal stressyComprises the following steps:
besides the structure, the arc angle corresponding to the arc curve of the structure can be changed, and the geometric dimensions of other structures, such as the thickness and the arrangement number of the rods, can be optimized in a reasonable range without influencing the deformation mechanism of the structure.
Due to the lap joint mode of the three-dimensional structure triangle, the poisson ratios of the three transverse directions arranged on the two-dimensional plane are the same as those of the two-dimensional plane when bearing uniform load, and due to the equal ratio property of the triangle when changing, the poisson ratios of all directions are the same as those of the two-dimensional plane, so that the poisson ratios are the same as those of the two-dimensional structure when bearing longitudinal load.
The mechanical metamaterial has excellent performance and needs a rapid preparation method, and many mechanical metamaterials are prepared by a 3D printing method, so that the speed is low and the cost is high. The three-dimensional structure can be connected by a welding method through mold mass production unit cells to form macroscopic structures with different quantities and shapes, and a dividing method of unit bodies is shown in fig. 5.