A closed-cell metal foam with controllable relative density distribution and a method for preparing the same
By using Voronoi modeling and additive manufacturing technology to prepare closed-cell foam metal with controllable relative density distribution, the problem of the inability to adjust the density distribution of closed-cell foam in metal substrates in the prior art is solved, and the control of specific stress-strain curves is achieved, which is applicable to a variety of metal materials.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NORTHWESTERN POLYTECHNICAL UNIV
- Filing Date
- 2023-10-11
- Publication Date
- 2026-06-02
AI Technical Summary
Existing technologies cannot produce closed-cell foam metals with controllable relative density distribution, especially closed-cell foams with metal substrates, which cannot meet specific impact protection requirements.
A sheet geometry model was established using the Voronoi modeling method. A solid model was formed by punching holes and imparting cell wall thickness. Closed-cell foam metal with controllable relative density distribution was then prepared using additive manufacturing technology.
The preparation of closed-cell foam metal has been realized, and the stress-strain curve can be adjusted according to the pre-designed density distribution function. It is applicable to a variety of metal matrix materials and improves the impact protection performance.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention relates to the field of impact-resistant energy-absorbing material preparation technology, specifically to a closed-cell foam metal with controllable relative density distribution and its preparation method. Background Technology
[0002] Impact-resistant energy-absorbing materials can reduce the amplitude of impact loads and prolong their duration, effectively protecting the structure and occupants of transportation vehicles. Therefore, they are widely used in impact protection and energy absorption. Foam materials, as the most widely used representative of impact-resistant energy-absorbing materials, are favored by engineers and researchers. Foam materials can be divided into open-cell foams and closed-cell foams. Closed-cell foams exhibit more complex deformation modes under impact loads, thus finding wider application in energy absorption. The most important material parameter affecting the mechanical properties of closed-cell foam is its relative density, which is the ratio of the closed-cell foam density to the density of the matrix material forming the foam. Traditional melt foaming methods produce closed-cell foams with a uniform relative density distribution. However, under impact loads, the mechanical responses of the impact and support ends of such uniform foams cannot be specifically adjusted according to specific impact protection requirements. Therefore, researchers have designed gradient foams with continuously changing relative density distributions by adjusting the solidification sequence. However, gradient foams prepared using melt foaming methods can only achieve a gradient change in trend and cannot be prepared according to a pre-designed distribution function. A recently developed method combining Voronoi foam modeling with additive manufacturing technology can overcome this problem and achieve the preparation of closed-cell foam with controllable distribution function. However, this method uses additive manufacturing technology based on melt filamentation, which can only produce closed-cell foam with polymer substrate. The specific strength and specific stiffness of polymers are generally lower than those of metal materials. Therefore, such samples are more suitable for basic research on the mechanical problems of closed-cell foam. For practical engineering problems involving impact protection, closed-cell foam metal with controllable relative density distribution is essential. Summary of the Invention
[0003] To address the aforementioned technical problems, the present invention aims to provide a closed-cell foam metal with controllable relative density distribution and its preparation method, thereby solving the problem that the additive manufacturing process in the prior art cannot prepare closed-cell foam metal with controllable relative density distribution.
[0004] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A method for preparing closed-cell foam metal with controllable relative density distribution is provided, comprising the following steps:
[0005] (1) Establish a sheet geometric model of closed-cell foam with a relative density that conforms to a specific distribution function;
[0006] (2) Drill holes at the centroid of each cell wall in the sheet geometry model obtained in step (1);
[0007] (3) Determine the diameter of the hole in step (2) by microscopic finite element simulation;
[0008] (4) Assign a specific thickness to each cell wall in the sheet geometry model to form a solid geometry model;
[0009] (5) The solid geometric model obtained in step (4) is sliced and additive manufacturing sample is prepared to obtain a sample, namely a closed-cell foam metal with controllable relative density distribution.
[0010] Based on the above technical solution, the present invention can be further improved as follows:
[0011] Furthermore, in step (1), a specific distribution function is established using the Voronoi modeling method.
[0012] Furthermore, the Voronoi modeling method includes the following steps:
[0013] (1.1) Set a three-dimensional space of a certain volume, and add cell core points to the three-dimensional space one by one, while satisfying that the distance between the newly added core point and all existing core points is greater than or equal to a set value. Let the set value be a function of the three-dimensional coordinates so that the distribution of core points conforms to a specific distribution function.
[0014] (1.2) When it is impossible to add more core points in the above three-dimensional space, all core points expand outward at the same expansion rate. The expansion process ends after the cell walls of all adjacent core points overlap.
[0015] (1.3) Extract the required three-dimensional volume from the three-dimensional space where the expansion has ended to obtain the sheet geometry model of the closed-cell foam.
[0016] Furthermore, in step (1.1), the three-dimensional space is a cube of 150mm×150mm×300mm.
[0017] Furthermore, in step (1.1), the specific distribution function is a gradient function in which the cell size changes linearly from 8 mm to 16 mm along the height direction in three-dimensional space.
[0018] Furthermore, in step (1.1), the specific distribution function is s = 8 + 8 × h / H; where s is the cell size, h is the coordinate value along the height direction, and H is the total height of the cube.
[0019] Furthermore, in step (1.3), the sheet geometry of the closed-cell foam is a cylinder with a diameter of 80 mm and a height of 120 mm.
[0020] Furthermore, in step (2), holes are punched by the following method: the centroid position of each cell wall in the sheet geometry model of the closed-cell foam is counted, and holes are punched at the centroid positions of all cell walls with the centroid as the center and D as the diameter.
[0021] Further, in step (3), the diameter of the hole is determined by the following method: the sheet geometry model in step (1) and the perforated sheet geometry model in step (2) are divided into two-dimensional meshes respectively. The mesh model of the closed-cell foam is imported into the finite element software. The mesh model of the closed-cell foam is placed between two parallel rigid bodies. The finite element model is submitted and a micro-finite element simulation calculation is performed. The stress-strain curves of the closed-cell foam before and after the hole are statistically analyzed. The specific energy absorption corresponding to the curve is further calculated. When the specific energy absorption ratio between the perforated model and the complete model is >98%, the corresponding hole diameter is acceptable. Otherwise, steps (2) and (3) are repeated to adjust the hole diameter D.
[0022] Furthermore, in step (3), the diameter of the hole is 0.8 mm.
[0023] Furthermore, in step (4), each cell wall in the sheet geometry model is given a specific thickness by stretching the thickness of the cell wall by a specified distance along the normal of the cell wall plane.
[0024] Furthermore, in step (4), the thickness is 0.5 mm.
[0025] Furthermore, in step (5), the solid geometric model formed in step (4) is imported into the additive manufacturing slicing software, the model is sliced layer by layer, the sliced model is exported, and the sample is imported into the metal additive manufacturing equipment to prepare the sample, thereby obtaining closed-cell foam metal with controllable relative density distribution.
[0026] Furthermore, the matrix material for sample preparation is AlSi10Mg aluminum alloy, titanium alloy, aluminum alloy, copper alloy, tungsten alloy, stainless steel, high-strength steel, or high-temperature alloy of mold steel.
[0027] Furthermore, the matrix material for sample preparation was AlSi10Mg aluminum alloy.
[0028] Furthermore, step (6) is included after step (5) to test the mechanical properties of the sample prepared in step (5) and verify that the mechanical response meets the design requirements.
[0029] Furthermore, in step (6), the sample prepared by additive manufacturing is subjected to a quasi-static mechanical loading experiment to obtain the corresponding mechanical response. Through data processing, the stress-strain curve is obtained and compared with the results of micro-finite element simulation to perform mechanical property testing.
[0030] The present invention also provides closed-cell foam metal with controllable relative density distribution obtained by the above method.
[0031] The present invention has the following beneficial effects:
[0032] 1. Due to the layer-by-layer molding characteristic of additive manufacturing, the previous method of combining additive manufacturing with foam models could only realize the preparation of closed-cell foam non-metals and open-cell foam metals. This invention can realize the preparation of closed-cell foam metals, overcoming the current limitations.
[0033] 2. In the traditional melt foaming process for preparing foam materials, it is impossible to quantitatively control the relative density distribution. The relative density distribution of the closed-cell foam metal prepared by this invention can conform to a pre-given distribution function, thereby obtaining the desired stress-strain curve.
[0034] 3. The closed-cell foam metal prepared by the present invention is not limited to a specific type of metal matrix material. Any metal material that can be used in selective laser melting additive manufacturing process can be applied to the present invention. Attached Figure Description
[0035] Figure 1 A complete sheet geometry model for closed-cell foam that meets a specific relative density distribution;
[0036] Figure 2 A geometric model of a perforated sheet of closed-cell foam to meet a specific relative density distribution;
[0037] Figure 3 A comparison of the stress-strain curves of the complete sheet geometry model and the perforated sheet geometry model calculated by finite element simulation.
[0038] Figure 4 A geometric model of a perforated solid for closed-cell foam that meets a specific relative density distribution;
[0039] Figure 5 Closed-cell foam metal to meet specific relative density distribution;
[0040] Figure 6 Comparison of micro-finite element simulation results and quasi-static experimental results for closed-cell foam metals that meet specific relative density distributions. Detailed Implementation
[0041] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.
[0042] Example 1:
[0043] A method for preparing closed-cell metal foam with controllable relative density distribution, comprising the following steps:
[0044] (1) Establish a sheet geometric model of closed-cell foam that conforms to a specific relative density distribution function.
[0045] The Voronoi modeling method can be used to ensure that the relative density distribution of closed-cell foam satisfies a specific distribution function. The steps of the Voronoi algorithm are as follows:
[0046] The first step is to set up a three-dimensional space of a certain volume (in this example, the three-dimensional space is a cube with length, width, and height of 150mm × 150mm × 300mm). Cell core points are added to this three-dimensional space one by one, while ensuring that the distance between the newly added core point and all existing core points is greater than or equal to a set value. Let the set value be a function of the three-dimensional coordinates so that the distribution of core points conforms to a specific distribution function (in this example, the distribution function is a gradient function in which the cell size changes linearly from 8mm to 16mm along the height direction, s = 8 + 8 × h / H, where s is the cell size, h is the coordinate value along the height direction, and H is the total height of the cube. In fact, this gradient function can be set arbitrarily so that the sample meets the desired mechanical response).
[0047] The second step is that when it is impossible to add more core points in the given three-dimensional space (that is, the newly added core point cannot satisfy the requirement that the distance between it and all existing core points is greater than or equal to the set value, which is the value of s in the formula in the first step), all core points expand outward at the same expansion rate. The expansion process ends after the cell walls of all adjacent core points overlap.
[0048] The third step is to extract the required three-dimensional volume from the expanded three-dimensional space to create the final foam model. In this example, the final model size is a cylinder with a diameter of 80mm and a height of 120mm, as shown below. Figure 1 As shown.
[0049] (2) Drill holes at the centroid of each cell wall in the sheet geometry model.
[0050] When fabricating a closed-cavity model using selective laser melting additive manufacturing, the powder inside the cavity may become trapped. Therefore, it is necessary to drill holes in the walls of the closed cavity to allow the powder to flow out. The centroid position of each cell wall in the sheet geometry model of the closed-cell foam is determined. Using the centroid as the center and D as the diameter (the final value needs to be determined through micro-finite element simulation in step three), holes are drilled at the centroid positions of all cell walls. (See...) Figure 2 As shown.
[0051] (3) Determine the diameter of the hole through microscopic finite element simulation.
[0052] Making holes in the wall of a closed cavity will inevitably reduce the load-bearing capacity of the entire model. However, since the size of additive manufacturing powder is three orders of magnitude smaller than that of the closed-cell foam sample model, by selecting an appropriate hole diameter, it is possible to ensure the normal outflow of printing powder and to ensure that the overall mechanical properties of the closed-cell foam change only slightly. To achieve this goal, it is necessary to determine the appropriate hole diameter through finite element simulation.
[0053] Two-dimensional meshes were generated for the complete sheet geometry model in step (1) and the perforated sheet geometry model in step (2), with an average mesh size of 0.5 mm. After meshing, mesh element properties were assigned. All mesh elements of the model were defined as a hybrid mesh of linear, finite film strain, reduced integral, quadrilateral shell element (S4R) and linear, finite film strain, reduced integral, triangular shell element (S3R). The mesh model of closed-cell foam was imported into the finite element software, and the matrix material property was defined as AlSi10Mg. Based on the article published in the Journal of Alloys and Compounds, Volume 897, No. 162933 in 2022, the Johnson-Cook elastoplastic constitutive model and damage criterion were used to describe the mechanical properties of the matrix material. The material parameters are shown in Tables 1-2.
[0054] Table 1. Johnson-Cook Elastoplastic Constitutive Material Parameters
[0055]
[0056] Table 2. Material parameters for the Johnson-Cook damage criterion:
[0057]
[0058] The closed-cell foam mesh model is placed between two parallel rigid bodies. The contact properties between all models are defined as normal hard contact, tangential frictional contact, and a friction coefficient of 0.1. The lower rigid body has six degrees of freedom fixed, and the upper rigid body has five degrees of freedom fixed except for the foam's axial translation. The closed-cell foam mesh model is then compressed downwards at a speed of 1 m / s. The finite element model is submitted for mesoscopic finite element simulation calculations. The stress-strain curves of the calculated closed-cell foam are shown below. Figure 3 As shown, the stress-strain curves of closed-cell foam before and after perforation are very close. Further calculation of the specific energy absorption (i.e. the amount of energy absorbed per unit mass) corresponding to the curves is performed. When the ratio of the specific energy absorption of the perforated model to that of the complete model is greater than 98%, it is considered that the effect of perforation on the mechanical properties of closed-cell foam is negligible. At this time, the corresponding perforation diameter is acceptable. Otherwise, adjust the perforation diameter D and repeat steps (2) and (3). The perforation diameter finally determined in this invention example is 0.8 mm.
[0059] (4) Assign a specific thickness to each cell wall in the sheet geometry model to form a solid geometry model.
[0060] Additive manufacturing technology cannot operate on sheet models directly; therefore, it is necessary to assign thickness to the sheet to form a solid. For a perforated sheet geometry model verified by mesoscopic finite element simulation, a specified thickness is assigned to all cell walls in the model. That is, the thickness of the cell walls is stretched by a specified distance along the normal direction of the cell wall plane. In this example, the thickness is set to 0.5 mm, ultimately forming a solid geometry model, such as... Figure 4 As shown.
[0061] (5) Slice the solid geometric model for additive manufacturing preparation.
[0062] The solid geometric model formed in step (4) is imported into the additive manufacturing slicing software. The model is sliced layer by layer. After the slicing is completed, the sliced model is exported and imported into the metal additive manufacturing equipment for sample preparation, thus obtaining closed-cell foam metal with controllable relative density distribution. Figure 5 As shown.
[0063] The matrix material used in this example is AlSi10Mg aluminum alloy. In fact, other metals using selective laser melting additive manufacturing processes, such as titanium alloys, aluminum alloys, copper alloys, tungsten alloys, stainless steel, high-strength steel, mold steel, and high-temperature alloys, can also be used in this invention.
[0064] (6) The additively manufactured specimens were subjected to quasi-static mechanical loading experiments to obtain the corresponding mechanical responses. Through data processing, stress-strain curves were obtained and compared with the results of micro-finite element simulations (see...). Figure 6 The results showed that the stress level in the experimental results was slightly lower than that in the finite element simulation curve. This is because the simulation model does not have forming defects such as micropores inside the material. Micro-defects in the actual sample will lead to a reduction in stress level. However, overall, the simulation results are in good agreement with the experimental results. Moreover, compared with the stress-strain curve of the single plateau stress of conventional homogeneous foam, the closed-cell foam metal prepared by the method of this invention can achieve the desired stress-strain curve distribution.
[0065] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A method for preparing closed-cell foam metal with controllable relative density distribution, characterized in that, The steps are as follows: (1) Establish a sheet geometric model of closed-cell foam with a relative density that conforms to a specific distribution function; (2) Drill holes at the centroid of each cell wall in the sheet geometry model obtained in step (1); (3) Determine the diameter of the hole in step (2) by microscopic finite element simulation; (4) Assign a specific thickness to each cell wall in the sheet geometry model to form a solid geometry model; (5) The solid geometric model obtained in step (4) is sliced and additive manufacturing sample is prepared to obtain a sample, namely a closed-cell foam metal with controllable relative density distribution.
2. The method for preparing closed-cell foam metal with controllable relative density distribution according to claim 1, characterized in that, In step (1), a specific distribution function is established using the Voronoi modeling method.
3. The method for preparing closed-cell foam metal with controllable relative density distribution according to claim 2, characterized in that, The Voronoi modeling method includes the following steps: (1.1) Set a three-dimensional space of a certain volume, and add cell core points to the three-dimensional space one by one, while satisfying that the distance between the newly added core point and all existing core points is greater than or equal to a set value. Let the set value be a function of the three-dimensional coordinates so that the distribution of core points conforms to a specific distribution function. (1.2) When it is impossible to add more core points in the above three-dimensional space, all core points expand outward at the same expansion rate. The expansion process ends after the cell walls of all adjacent core points overlap. (1.3) Extract the required three-dimensional volume from the three-dimensional space where the expansion has ended to obtain the sheet geometry model of the closed-cell foam.
4. The method for preparing closed-cell foam metal with controllable relative density distribution according to claim 3, characterized in that, In step (1.1), the three-dimensional space is a cube of 150mm×150mm×300mm.
5. The method for preparing closed-cell foam metal with controllable relative density distribution according to claim 3, characterized in that, In step (1.1), the specific distribution function is a gradient function in which the cell size changes linearly from 8 mm to 16 mm along the height direction in three-dimensional space.
6. The method for preparing closed-cell foam metal with controllable relative density distribution according to claim 1, characterized in that, In step (1.3), the sheet geometry of the closed-cell foam is a cylinder with a diameter of 80 mm and a height of 120 mm.
7. The method for preparing closed-cell foam metal with controllable relative density distribution according to claim 1, characterized in that, In step (3), the diameter of the hole is determined by the following method: the sheet geometry model in step (1) and the perforated sheet geometry model in step (2) are divided into two-dimensional meshes respectively. The mesh model of the closed-cell foam is imported into the finite element software. The mesh model of the closed-cell foam is placed between two parallel rigid bodies. The finite element model is submitted and the micro-finite element simulation calculation is performed. The stress-strain curves of the closed-cell foam before and after the hole are statistically analyzed. The specific energy absorption corresponding to the curve is further calculated. When the specific energy absorption ratio between the perforated model and the complete model is >98%, the corresponding hole diameter is acceptable. Otherwise, steps (2) and (3) are repeated to adjust the hole diameter D.
8. The method for preparing closed-cell foam metal with controllable relative density distribution according to claim 1, characterized in that, In step (4), each cell wall in the sheet geometry model is given a specific thickness by stretching the thickness of the cell wall by a specified distance along the normal of the cell wall plane.
9. The method for preparing closed-cell foam metal with controllable relative density distribution according to claim 1, characterized in that, Step (5) is followed by step (6), which tests the mechanical properties of the sample prepared in step (5) to verify that the mechanical response meets the design requirements.
10. The closed-cell foam metal with controllable relative density distribution prepared by the method of any one of claims 1-9.