RU2771391C1 - Method for producing a three-dimensional auxetic with a cellular structure (variants) - Google Patents

Abstract

FIELD: additive technology.SUBSTANCE: group of inventions relates to the field of formation by methods of 3D printing in the form of a three-dimensional (3D) cellular structure of complex geometry with a negative Poisson's ratio, to be used in various applications, including sports and medicine, as elements of personal protective equipment, as well as in implantology and orthopedics. Described are methods for producing a three-dimensional auxetic with a cellular structure (variants), including building a 20×20×10 mm unit cell, with the lateral edge inclined at an angle of 60 degrees to the horizontal edge, based on various materials: thermoplastic polyurethane (TPU) elastomer, or based on AlSi11Cu. The unit cell is created using solid-state modelling in computer-aided design systems. A three-dimensional auxetic based on a thermoplastic polyurethane elastomer is formed by 3D printing by the fused deposition modelling method with a layer of 300 mcm in thickness at a printing speed of 15 mm/s, at an extrusion temperature of 225°C. A three-dimensional auxetic based on AlSi11Cu is formed by 3D printing by the selective laser melting method with a layer of 30 mcm in thickness, with a scanning speed of 1,650 mm/s, with a power of the laser of 370 W.EFFECT: creation of a cellular structure with a negative Poisson's ratio, characterised by a complex three-dimensional geometry, with a periodic structure, the possibility of manufacturing by methods of 3D printing from various materials, including polymers and metal alloys, as well as the capacity for absorbing (dampening) and evenly distributing mechanical energy throughout the entire volume of the structure due to the auxetic effect (uniform compression); the value of location of the lateral edge to the horizontal edge used herein creates an optimal Poisson's ratio/mechanical properties ratio.2 cl, 11 dwg, 2 ex

Description

The invention relates to the field of formation by 3D printing methods in the form of a three-dimensional (3D) honeycomb structure of complex geometry with a negative Poisson's ratio, which can be used in various fields, including the fields of sports and medicine, as elements of personal protective equipment, as well as in implantology and orthopedics.

Due to the geometric features of the construction, auxetics show a negative Poisson ratio, i.e. they increase in volume when stretched and vice versa decrease in volume when compressed.

An invention is known (US 8652602 B1 published on February 18, 2014), which is a three-dimensional, cylindrical and spherical (polar coordinate system) auxetics with a honeycomb structure, which can potentially be used in the aerospace and biomedical industries.

The disadvantage of the mentioned invention is that this auxetic structure is not adapted to the main existing production technologies, such as forming, subtractive and additive production, due to the structure and arrangement of elementary cells in the structure.

An invention is known (US 7910193 B2 published on March 22, 2011), which is a description of a three-dimensional auxetic with an elementary cell in the form of a pyramid, which can potentially be used as a mechanical energy damper.

The disadvantage of the mentioned invention is that the auxetic structure is not adapted to the main production technologies.

An invention is known (US 9908295 B2 publ. 03/06/18), which is a description of the process of digital preparation of three-dimensional auxetics for 3D printing.

The disadvantage of the mentioned invention is that, based on the description, this process is aimed at preparing three-dimensional auxetics for the 3D printing method with several materials at once, in particular, the FDM method (Fusion Deposition Modeling). The multi-material printing method has a narrow set of materials, since the materials require physical and chemical interaction, therefore this significantly narrows the printing temperature range.

The prototype is an invention (EP 2702884 A1 publ. 08/02/13), which is a two-dimensional auxetic with a honeycomb structure for use in clothing and sports equipment, obtained by hot pressing.

The disadvantage of the mentioned invention is the limited production technology.

The technical result of the claimed invention is to create a complex three-dimensional geometry with a periodic structure with the possibility of manufacturing it from various types of materials, including polymers and metals and the possibility of producing a three-dimensional auxetic using additive technologies, in particular 3D printing with high mechanical properties in compression ( metals): ultimate strength of the auxetic structure is more than 150 MPa; resistance to long-term cyclic compressive loads (elastomers, metals): up to 500 cycles (elastomers) and up to 2000 cycles (metals).

The technical result in the first object of the invention is achieved as follows.

A method for producing a three-dimensional auxetic with a honeycomb structure includes building a unit cell based on polymers or elastomers of a given size from 20 × 20 × 10 to 250 × 250 × 150 mm with a rotation angle between the ribs equal to 60 using solid modeling in computer-aided design systems and further formation of a three-dimensional auxetic by 3D printing by layer-by-layer deposition of a filament in the layer thickness range of 100–1000 µm at a printing speed of 15–50 mm/s at an extrusion temperature of 195–225°C.

The technical result in the second object of the invention is achieved as follows.

A method for producing a three-dimensional auxetic with a honeycomb structure includes building a unit cell based on metal alloys of a given size from 20 × 20 × 10 to 250 × 250 × 150 mm with a rotation angle between the ribs equal to 60 degrees using solid modeling in computer-aided design systems and further formation of a three-dimensional auxetic by 3D printing by selective laser fusion with a layer thickness of 30–100 μm at a scanning speed of 400–1700 mm/s at a laser power of 300–400 W.

In the proposed three-dimensional auxetic structure ("Auxetic - 90" and "Auxetic - 45"), these characteristics are achieved due to the geometric structure of the elementary cell. In particular, due to the cross section of the ribs, as well as the location of the side rib to the horizontal at an angle of 60 degrees, then the turning angle. Such an arrangement of the ribs creates an auxetic effect, i.e. all-round compression and tension of the structure. Aligning the side ribs along the horizontal direction (in the direction of application of the load) causes them to shift along the vertical direction, thereby leading to an auxetic effect. The bending of edges in one unit cell equally leads to auxetic behavior in the entire structure. The turning angle used creates the optimum Poisson's ratio/mechanical properties.

The invention is illustrated by the drawing, where figure 1 schematically shows a three-dimensional cell "Auxetics - 90" with a honeycomb structure, figure 2 shows the appearance of a 3D model of a three-dimensional cell "Auxetics - 90". Figure 3 shows a schematic three-dimensional elementary cell "Auxetic - 45" with a honeycomb structure. Figure 4 shows the appearance of a 3D model of a three-dimensional elementary cell "Auxetics - 45". Figure 5 shows a photograph of a three-dimensional "Auxetic - 90" with a honeycomb structure, obtained by 3D printing by layer-by-layer deposition of a thread with a layer thickness of 300 μm, with a print speed of 15 mm / s at an extrusion temperature of 225 ° C based on thermoplastic polyurethane (TPU ). Figure 6 shows a diagram of cyclic compression tests of a three-dimensional "Auxetic - 90" with a honeycomb structure based on TPU. Figure 7 shows micrographs of sections of the three-dimensional "Auxetic - 90" based on TPU during cyclic compression tests. Figure 8 shows a photograph of a three-dimensional "Auxetic - 45" with a honeycomb structure, obtained by 3D printing by selective laser melting based on aluminum alloy AlSi ₁₁ Cu. Figures 9 and 10 show diagrams of deformation of the three-dimensional "Auxetic - 45" based on aluminum alloy AlSi ₁₁ Cu under compression. Figure 11 shows a diagram of cyclic compression tests of a three-dimensional "Auxetic - 45" with a honeycomb structure based on aluminum alloy AlSi ₁₁ Cu.

Figure 1 schematically shows views 1 2 3 4 5 6 7 three-dimensional cell "Auxetics - 90" "top", "left", "front" "right", "isometric" "bottom" "isometric". Figure 5 schematically shows views 8 9 10 11 12 13 14 three-dimensional cell "Auxetics - 45" "top", "left", "front" "right", "isometric" "bottom" "isometric". Figure 10 shows micrographs 15 16 17 sections of the three-dimensional "Auxetic - 90" during cyclic compression tests before testing - 0 cycles, in the middle of testing - 250 cycles and after testing - 500 cycles, respectively.

From the diagram of cyclic compression tests of the three-dimensional "Auxetic - 90" in Fig.6 it follows that after 500 cycles the maximum stress value is 14 MPa, with a deformation of 0.5%. According to the micrographs in Fig.7, it can be judged that during the test no structural damage is observed. Figure 8 shows a photograph of a three-dimensional "Auxetic - 45" with a honeycomb structure, obtained by 3D printing by selective laser melting with a layer thickness of 30 μm, with a scanning speed of 1650 mm / s at a laser power of 370 W based on aluminum alloy AlSi ₁₁ Cu . From the diagrams in Fig.9 and 10 it follows that the tensile strength of the auxetic is more than 150 MPa. From the diagram in Fig.11 it follows that after 2000 cycles the maximum stress value is 100 MPa, with a deformation of 8%, respectively, the complete destruction of the structure occurs at 12 kN.

The applicability of the proposed auxetic and evaluation of its mechanical properties is confirmed by the following examples.

Example 1

Thermoplastic polyurethane (TPU) brand (REC 3D, Russia) was used as starting materials. A three-dimensional "Auxetic - 90" with a honeycomb structure in the amount of 5 pieces with a layer thickness of 300 μm was formed by layer-by-layer fusing of a thread with a printing speed of 15 mm/s at an extrusion temperature of 225°C. Three-dimensional auxetics were made in the form of cubes measuring 39×39×35 mm (Fig. 5).

To assess the mechanical properties of the three-dimensional "Auxetic - 90" based on TPU, 5 samples were subjected to low-cycle (up to 500 cycles) compression tests. For testing, a Zwick/Roell Z020 universal testing machine (Zwick GmbH & Co. KG, Germany) was used at a testing speed of 10 mm/min, with a fixed offset value of 5 mm ("hard" testing mode). The samples were cut after cyclic compression tests to obtain photomicrographs of the nodes using a scanning electron microscope Hitachi TM 1000 (Fig. 7). Also, for a qualitative assessment and comparison of the results, samples of a three-dimensional non-auxetic with a honeycomb structure were additionally designed and formed. After 500 cycles, the 3D auxetic specimens buckled at 14 MPa stress and 0.4% strain, which is consistent with non-auxetic specimens (14 MPa stress, 0.5% strain).

Example 2

AlSi ₁₁ Cu aluminum alloy powder was used as starting materials; the particle size was 40 μm. A three-dimensional "Auxetic - 45" with a honeycomb structure in the amount of 5 pieces with a layer thickness of 30 μm was formed by selective laser fusion with a scanning speed of 1650 mm/s and a laser power of 370 W. Three-dimensional auxetics were made in the form of rectangular bars measuring 10 × 10 × 35 mm (Fig. 8).

To evaluate the mechanical properties of a three-dimensional auxetic based on AlSi ₁₁ Cu 5 , the samples were subjected to stepwise cyclic compression tests. One test stage included 500 cycles, the increase in the number of cycles continued until the complete destruction of the samples. For testing, a Zwick/Roell Z020 universal testing machine (Zwick GmbH & Co. KG, Germany) was used at a testing speed of 10 mm/min (corresponding to 0.2 Hz), with a fixed load value ("soft" testing mode). The choice of the load value for the first stage of testing was made taking into account the result of static tests (Fig. 9), in the areas of buckling and the appearance of plastic flow of the material. The minimum effective cross-sectional area of metallic elements was used to estimate the magnitude of the stresses, since the maximum stresses occur in local areas where the cross-sectional area is minimal. Also, for a qualitative assessment and comparison of the results, samples of a three-dimensional non-auxetic with a honeycomb structure were additionally designed and formed. The auxetic shows buckling at a load of 12 kN (after 2000 cycles) and a deformation of 8% at a nominal stress of 110 MPa (Fig. 11). In turn, non-auxetic with a honeycomb structure showed buckling under a load of 8 kN (after 1000 cycles) and a deformation of 2-4% at a nominal stress of 70 MPa.

Claims (2)

1. A method for obtaining a three-dimensional auxetic with a honeycomb structure, including the construction of an elementary cell based on a thermoplastic polyurethane (TPU) elastomer of a given size 20 × 20 × 10 mm with the location of the side edge to the horizontal edge at an angle of 60 degrees, the elementary cell is created using solid modeling in computer-aided design systems, and further formation of a three-dimensional auxetic by 3D printing by layer-by-layer deposition of a filament with a layer thickness of 300 microns at a printing speed of 15 mm/s, at an extrusion temperature of 225°C. 2. A method for producing a three-dimensional auxetic with a honeycomb structure based on AlSi ₁₁ Cu, including the construction of a unit cell based on AlSi ₁₁ Cu of a given size 20×20×10 mm with the location of the side rib to the horizontal rib at an angle of 60 degrees, the unit cell is created using solid modeling in computer-aided design systems, and further formation of a three-dimensional auxetic by 3D printing by selective laser fusion with a layer thickness of 30 μm, with a scanning speed of 1650 mm/s at a laser power of 370 W.

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