A fractal-stacked design approach for programmable deformable superstructures

Abstract

The invention relates to a fractal-stacking design method for a programmable deformable superstructure, belonging to the technical field of structures and mechanisms; the composition of the deformable superstructure is designed, and the deformable superstructure comprises n cores, an electric heating plate, a front end cover, a rear end cover, a front fastening head, a rear fastening head, screws and nuts; n is a positive integer; the materials of the cores, the front end cover, the rear end cover, the front fastening head, the rear fastening head, the screws and nuts are designed; according to the NiTi shape memory alloy material of the cores, the constitutive model of the shape memory alloy is determined; the stress-strain relationship curve of the loading-unloading section of the equivalent shape memory alloy material is approximated by the elastic-plastic constitutive method; the cores are manufactured; the electric heating plates are designed; and the deformable superstructures are stacked and assembled; the invention can realize that the output deformation of the cores can be designed and customized through the distribution optimization of phase change strain, the output force can be programmably customized through stacking and assembly, and the thermally induced phase change of the cores can be realized through temperature control design.

Description

Technical Field

[0001] The invention belongs to the technical field of structures and mechanisms, and relates to a fractal-stack design method for programmable deformable superstructures. Background Art

[0002] Deformable systems represented by morphing aircraft and dexterous shape-changing robots have become an important development area for industrial transformation in the world's powerful countries. As the common core key components of the deformation system, the deformation drive component needs to achieve flexible and reliable large-scale deformation under limited installation space and harsh and variable load conditions. However, the traditional motor drive system has many heterogeneous components and complex mechanical connections, which makes it difficult to meet the future development needs of further miniaturization, lightweight, high load and high reliability.

[0003] The use of shape memory materials with thermally induced phase change capabilities is an important technical approach to achieve the above needs. At present, there are two major material systems that are widely used in the industrial sector, namely shape memory alloys and shape memory polymers. Shape memory alloys have the characteristics of large recovery force and rapid response, but the deformation rate is generally less than 8%, which is not suitable for large deformation scenarios. Shape memory polymers have the advantages of large deformation and low density, but the recovery force is 2 orders of magnitude smaller than that of shape memory alloys, and are not suitable for high-load scenarios. In summary, the current shape memory materials have a technical bottleneck that is difficult to balance large deformation and high output force.

[0004] Fractals are a common structural form in nature. Their characteristics are that at any scale, the topological form of the structure is similar and the deformation mode is the same. The advantage of this structural form is that it can maximize the deformation of the structure under small strain constraints. It has been applied in the fields of flexible circuits and high-strength and tough materials. Inspired by the fractal structure, the shape memory alloy fractal structure is prepared by 4D printing process, which can significantly increase the deformation rate of the shape memory alloy structure. However, the shape memory alloy structure based on fractal design still has the following problems: (1) Due to the small cross-sectional area of ​​the fractal structure, the restoring force is seriously reduced and it does not have the bearing capacity; (2) The spatial morphology of the fractal structure is complex, uniform heating is difficult, and it is difficult for the structure to undergo uniform phase change at the same time.

[0005] In summary, the existing design methods cannot take into account large deformation, large deformation force and convenient heating. Summary of the invention

[0006] The technical problem solved by the present invention is: to overcome the shortcomings of the prior art and propose a fractal-stacking design method for programmable deformable superstructures, which can achieve the design and customization of the output deformation of the core through the distribution optimization of phase change strain, achieve programmable customization of the output force through stacking assembly, and achieve thermally induced phase change of the core through temperature control design.

[0007] The solution of the present invention is:

[0008] A fractal-stacked design method for programmable deformable superstructures, comprising:

[0009] Design the composition of the deformable superstructure, the deformable superstructure comprising n cores, an electric heating plate, a front cover, a rear cover, a front fastening head, a rear fastening head, screws and nuts; n is a positive integer;

[0010] Design the materials of the core, front cover, rear cover, front fastening head, rear fastening head, screws and nuts;

[0011] According to the NiTi shape memory alloy material of the core, the constitutive model of the shape memory alloy is determined; the stress-strain relationship curve of the loading-unloading section of the equivalent shape memory alloy material is approximated by the elastic-plastic constitutive model;

[0012] Making tablet cores;

[0013] Design electric heating sheet;

[0014] Stacking and assembling deformable superstructures.

[0015] In the above-mentioned fractal-stacking design method for programmable deformable superstructures, the n cores and the electric heating plate are coaxially spaced to form a middle column structure; the front end cover is coaxially installed at the axial front end of the middle column structure; the front fastening head is coaxially installed at the axial front end of the front end cover; the rear end cover is coaxially installed at the axial rear end of the middle column structure; the rear fastening head is coaxially installed at the axial rear end of the rear end cover; and the assembly of the core, the electric heating plate, the front end cover, the rear end cover, the front fastening head, and the rear fastening head is achieved by screws and nuts.

[0016] In the above-mentioned fractal-stacking design method for programmable deformable superstructures, the core is made of NiTi shape memory alloy with a phase transition temperature of C; the front end cover, the rear end cover, the front fastening head, and the rear fastening head are made of aluminum alloy or stainless steel metal materials; the screws and nuts are standard screws and nuts.

[0017] In the above-mentioned fractal-stacked design method for programmable deformable superstructure, the chip manufacturing method is:

[0018] A matrix material with a complex cross-section is prepared by 4D printing; the matrix material is a cylindrical structure; the cross-sectional shape of the matrix material is the optimized core shape; the core thickness is selected as h, a cross-sectional shape parametric model is constructed at a key deformation position of the core, m control parameters are designed in the cross-sectional shape parametric model to achieve control of the cross-sectional shape change, and the number of cores n is obtained; the matrix material is cut into n thin sheets of equal thickness by wire cutting to form a core; n is a positive integer not less than 6; the axial length of the matrix material is n×h.

[0019] In the above-mentioned fractal-stacking design method for programmable deformable superstructures, the resistance of the electric heating sheet is Ω; the cross-sectional shape of the electric heating sheet is consistent with the cross-sectional shape of the sheet core; the electric heating sheet and the sheet core are stacked alternately, and all the heating sheets are arranged in parallel; when the temperature of the electric heating sheet is higher than K1, the circuit is short-circuited, and when the temperature is lower than K2, the circuit is open, and the power supply is a kV DC power supply; K1 and K2 are set temperature thresholds respectively; K1≥K2≥C.

[0020] In the above-mentioned fractal-stacking design method for programmable deformable superstructure, the method of stacking and assembling the deformable superstructure is:

[0021] The front end cover and the rear end cover are used to encapsulate the core and the electric heating plate; the front fastening head and the rear fastening head are used to constrain the deformation of the core to ensure that all cores uniformly output single-degree-of-freedom deformation; the programmable deformable superstructure is fastened together by fasteners such as screws and nuts.

[0022] In the above-mentioned fractal-stacking design method for programmable deformable superstructures, the constitutive model of the shape memory alloy is similar to the elastic-plastic constitutive model in the loading-unloading section; the slope k1, k2 and turning point p of the elastic-plastic constitutive relationship are used to approximately replace the elastic modulus E1 before the phase transition, the elastic modulus E2 during the phase transition and the phase transition point of the shape memory alloy; the constitutive model of the shape memory alloy is equivalent to the elastic-plastic constitutive model, thereby reducing the consumption of simulation analysis and calculation of the shape memory alloy structure.

[0023] In the above-mentioned fractal-stacking design method for programmable deformable superstructures, the core includes an inner ring, an outer ring and special-shaped corrugated strips; the outer ring is coaxially mounted on the outside of the inner ring; between the inner ring and the outer ring, special-shaped corrugated strips are evenly distributed along the circumferential direction; by designing m control parameters in the parametric model of the core cross-sectional shape, the shape of the special-shaped corrugated strips is determined.

[0024] In the above-mentioned fractal-stacked design method for programmable deformable superstructures, the value of m is positively correlated with the complexity of the cross-sectional shape of the core; when the cross-sectional shape of the core is complex, the value of m is large; otherwise, the value of m is small; m is a positive integer not less than 3;

[0025] The loading-unloading section of the core structure is established for finite element simulation analysis. The finite element division adopts structural grid, and the grid scale is uniformly defined as l. The simulation results are post-processed to extract the number of units A whose Von-Mises plastic strain is greater than 0.05 and less than 0.06 after the core is unloaded. The distribution level of the high strain area of ​​the core is defined as A / B. B is the total number of core structure units, and the cross-sectional shape of the core is optimized. The optimization variable is the spline curve control parameter, and the optimization target is max A / B. The constraint condition is the maximum plastic strain ε of the core after unloading. max≤0.06; through optimized design, the core cross-sectional shape with the highest level of high strain distribution under the same deformation is obtained.

[0026] In the above-mentioned fractal-stacking design method for programmable deformable superstructures, the deformation q of each core is the same as the output force / torque f; through parallel stacking design, the total output deformation of the deformable superstructure is q, and the total output force / torque is m×f; wherein m is the number of core stacks, and the parallel stacking is constrained by the deformation output component; the front end cover, the rear end cover, the front fastening head, and the rear fastening head are used to constrain the deformation of all cores to one-dimensional deformation, torsional deformation or telescopic deformation.

[0027] The beneficial effects of the present invention compared with the prior art are:

[0028] (1) The fractal-stacked design method for programmable deformable superstructures of the present invention can achieve customizable output deformation of the die by optimizing the distribution of phase change strain;

[0029] (2) The present invention realizes programmable customization of output force through stacking assembly and realizes thermally induced phase change of the core through temperature control design;

[0030] (3) The present invention expands the deformation rate of the shape memory alloy structure through fractal design, and the angle can be designed and defined. The output force of the deformable superstructure is linearly customized through discrete stacking. By adopting an alternating stacking method of sheet cores and electric heating sheets, all sheet cores are uniformly heated and a uniform phase change is produced by controlling electric energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A fractal-stacked design flow chart for a programmable deformable superstructure of the present invention;

[0032] Figure 2 It is a schematic diagram of the composition of the deformed superstructure of the present invention;

[0033] Figure 3 It is a schematic diagram of the core structure of the present invention;

[0034] Figure 4 This is a schematic diagram of the stacked assembled deformed superstructure of the present invention. DETAILED DESCRIPTION

[0035] The present invention will be further described below in conjunction with the embodiments.

[0036] The present invention provides a fractal-stacking design method for programmable deformable superstructures. Through fractal design, the deformation rate of shape memory alloy structures is expanded, and the angle can be designed and defined. The output force of the deformable superstructure is linearly customized through discrete stacking. By adopting an alternating stacking method of sheet cores and electric heating sheets, uniform heating of all sheet cores and uniform phase change can be achieved through electric energy control.

[0037] A fractal-stacked design approach for programmable deformable superstructures, such as Figure 1 As shown, the specific steps include:

[0038] The composition of the deformable superstructure is designed, and the deformable superstructure includes n cores, an electric heating plate, a front cover, a rear cover, a front fastening head, a rear fastening head, screws and nuts; n is a positive integer.

[0039] like Figure 2 As shown, n cores and electric heating plates are coaxially spaced to form a middle column structure; the front end cover is coaxially installed at the axial front end of the middle column structure; the front fastening head is coaxially installed at the axial front end of the front end cover; the rear end cover is coaxially installed at the axial rear end of the middle column structure; the rear fastening head is coaxially installed at the axial rear end of the rear end cover; the assembly of the core, electric heating plate, front end cover, rear end cover, front fastening head and rear fastening head is achieved by screws and nuts.

[0040] Design the materials of the core, front end cover, rear end cover, front fastening head, rear fastening head, screws and nuts; the core adopts NiTi shape memory alloy with a phase change temperature of C; the front end cover, rear end cover, front fastening head and rear fastening head are made of aluminum alloy or stainless steel metal materials; the screws and nuts are standard screws and nuts.

[0041] According to the NiTi shape memory alloy material of the core, the constitutive model of the shape memory alloy is determined; the stress-strain relationship curve of the loading-unloading section of the equivalent shape memory alloy material is approximated by the elastic-plastic constitutive model.

[0042] The constitutive model of shape memory alloy is similar to the elastic-plastic constitutive model in the loading-unloading section; the slope k1, k2 and turning point p of the elastic-plastic constitutive relationship are used to approximately replace the elastic modulus E1 before the phase transformation, the elastic modulus E2 during the phase transformation and the phase transformation point of the shape memory alloy; the elastic-plastic constitutive model is used to equate the constitutive model of shape memory alloy, thereby reducing the consumption of simulation analysis and calculation of the shape memory alloy structure.

[0043] The method for making the tablet core is as follows:

[0044] A matrix material with a complex cross-section is prepared by 4D printing; the matrix material is a cylindrical structure; the cross-sectional shape of the matrix material is the optimized core shape; the core thickness is selected as h, a cross-sectional shape parametric model is constructed at a key deformation position of the core, m control parameters are designed in the cross-sectional shape parametric model to achieve control of the cross-sectional shape change, and the number of cores n is obtained; the matrix material is cut into n thin sheets of equal thickness by wire cutting to form a core; n is a positive integer not less than 6; the axial length of the matrix material is n×h.

[0045] like Figure 3 As shown, the core includes an inner ring, an outer ring and a special-shaped corrugated strip; the outer ring is coaxially mounted on the outer side of the inner ring; between the inner ring and the outer ring, the special-shaped corrugated strips are evenly distributed along the circumference; by designing m control parameters in the parametric model of the core cross-sectional shape, the shape of the special-shaped corrugated strip is determined. The value of m is positively correlated with the complexity of the core cross-sectional shape; when the core cross-sectional shape is complex, the value of m is large; otherwise, the value of m is small; m is a positive integer not less than 3.

[0046] Design electric heating plate.

[0047] The resistance of the electric heating sheet is Ω; the cross-sectional shape of the electric heating sheet is consistent with the cross-sectional shape of the sheet core; the electric heating sheets and the sheet core are stacked alternately, and all the heating sheets are arranged in parallel; when the temperature of the electric heating sheet is higher than K1, the circuit is short-circuited, and when the temperature is lower than K2, the circuit is connected, and the power supply is a kV DC power supply; K1 and K2 are set temperature thresholds respectively; K1≥K2≥C.

[0048] Stacking and assembling deformable superstructures.

[0049] The method of stacking and assembling the deformable superstructure is:

[0050] The front cover and the rear cover are used to encapsulate the core and the electric heating plate; the front fastening head and the rear fastening head are used to constrain the core deformation to ensure that all cores uniformly output single-degree-of-freedom deformation; the programmable deformable superstructure is fastened together by screws and nuts, such as Figure 4 shown.

[0051] The loading-unloading section of the core structure is established for finite element simulation analysis. The finite element division adopts structural grid, and the grid scale is uniformly defined as l. The simulation results are post-processed to extract the number of units A whose Von-Mises plastic strain is greater than 0.05 and less than 0.06 after the core is unloaded. The distribution level of the high strain area of ​​the core is defined as A / B. B is the total number of core structure units, and the cross-sectional shape of the core is optimized. The optimization variable is the spline curve control parameter, and the optimization target is max A / B. The constraint condition is the maximum plastic strain ε of the core after unloading. max ≤0.06; through optimized design, the core cross-sectional shape with the highest level of high strain distribution under the same deformation is obtained.

[0052] The deformation q of each core is the same as the output force / torque f; through the parallel stacking design, the total output deformation of the deformable superstructure is q, and the total output force / torque is m×f; where m is the number of core stacks, and the parallel stacking is constrained by the deformation output component; the front cover, the rear cover, the front fastening head, and the rear fastening head are used to constrain the deformation of all cores to one-dimensional deformation, torsional deformation or telescopic deformation.

[0053] The fractal-stacking design method for programmable deformable superstructures of the present invention can achieve customizable output deformation of the chip core by optimizing the distribution of phase change strain.

[0054] The present invention realizes programmable customization of output force through stacking assembly and realizes thermally induced phase change of the core through temperature control design.

[0055] The present invention expands the deformation rate of the shape memory alloy structure through fractal design, and the angle can be designed and defined. The output force of the deformable superstructure is linearly customized through discrete stacking. By adopting an alternating stacking method of sheet cores and electric heating sheets, all sheet cores are uniformly heated and a uniform phase change is produced by controlling electric energy.

[0056] Although the present invention has been disclosed as above in the form of a preferred embodiment, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope of the technical solution of the present invention.

Claims

1. A fractal-stacked design method for programmable deformable superstructures, characterized by: include: Designing the composition of the deformable superstructure, the deformable superstructure includes n cores, an electric heating plate, a front cover, a rear cover, a front fastening head, a rear fastening head, screws and nuts; n is a positive integer; Design the materials of the core, front cover, rear cover, front fastening head, rear fastening head, screws and nuts; According to the NiTi shape memory alloy material of the core, the constitutive model of the shape memory alloy is determined; the stress-strain relationship curve of the loading-unloading section of the equivalent shape memory alloy material is approximated by the elastic-plastic constitutive model; Making tablet cores; Design electric heating sheet; Stacking and assembling deformable superstructures.

2. A fractal-stacked design method for programmable deformable superstructures according to claim 1, characterized in that: The n cores and the electric heating plate are coaxially arranged at intervals to form a middle column structure; the front end cover is coaxially installed at the axial front end of the middle column structure; the front fastening head is coaxially installed at the axial front end of the front end cover; the rear end cover is coaxially installed at the axial rear end of the middle column structure; the rear fastening head is coaxially installed at the axial rear end of the rear end cover; the cores, the electric heating plate, the front end cover, the rear end cover, the front fastening head and the rear fastening head are assembled by screws and nuts.

3. The fractal-stacked design method for programmable deformable superstructures according to claim 2, characterized in that: The core is made of NiTi shape memory alloy with a phase change temperature of C; the front end cover, the rear end cover, the front fastening head and the rear fastening head are made of aluminum alloy or stainless steel metal materials; the screws and nuts are standard screws and nuts.

4. The fractal-stacked design method for programmable deformable superstructures according to claim 3, characterized in that: The method for making the core is as follows: A matrix material with a complex cross-section is prepared by 4D printing; the matrix material is a cylindrical structure; the cross-sectional shape of the matrix material is the optimized core shape; the core thickness is selected as h, a cross-sectional shape parametric model is constructed at a key deformation position of the core, m control parameters are designed in the cross-sectional shape parametric model to achieve control of the cross-sectional shape change, and the number of cores n is obtained; the matrix material is cut into n thin sheets of equal thickness by wire cutting to form a core; n is a positive integer not less than 6; the axial length of the matrix material is n×h.

5. The fractal-stacked design method for programmable deformable superstructures according to claim 4, characterized in that: The resistance of the electric heating sheet is Ω; the cross-sectional shape of the electric heating sheet is consistent with the cross-sectional shape of the sheet core; The electric heating plates and the cores are stacked alternately, and all the heating plates are set in parallel; when the temperature of the electric heating plate is higher than K1, the circuit is short-circuited, and when the temperature is lower than K2, the circuit is open, and the power supply is a kV DC power supply; K1 and K2 are set temperature thresholds respectively; K1≥K2≥C.

6. The fractal-stacked design method for programmable deformable superstructures according to claim 2, characterized in that: The method of stacking and assembling the deformable superstructure is: The front end cover and the rear end cover are used to encapsulate the core and the electric heating plate; the front fastening head and the rear fastening head are used to constrain the deformation of the core to ensure that all cores uniformly output single-degree-of-freedom deformation; the programmable deformable superstructure is fastened together by fasteners such as screws and nuts.

7. The fractal-stacked design method for programmable deformable superstructures according to claim 2, characterized in that: The constitutive model of the shape memory alloy is similar to the elastic-plastic constitutive model in the loading-unloading section; the elastic modulus E1 before the phase transformation, the elastic modulus E2 during the phase transformation and the phase transformation point of the shape memory alloy are approximately replaced by the slope k1, k2 and the turning point p of the elastic-plastic constitutive relationship; the constitutive model of the shape memory alloy is equivalent to the elastic-plastic constitutive model, thereby reducing the consumption of simulation analysis and calculation of the shape memory alloy structure.

8. The fractal-stacked design method for programmable deformable superstructures according to claim 4, characterized in that: The core comprises an inner ring, an outer ring and a special-shaped corrugated strip; the outer ring is coaxially mounted on the outer side of the inner ring; the special-shaped corrugated strips are evenly distributed along the circumferential direction between the inner ring and the outer ring; and the shape of the special-shaped corrugated strips is determined by designing m control parameters in a parametric model of the cross-sectional shape of the core.

9. The fractal-stacked design method for programmable deformable superstructures according to claim 8, characterized in that: The value of m is positively correlated with the complexity of the cross-sectional shape of the core; when the cross-sectional shape of the core is complex, the value of m is large; Otherwise, m takes a small value; m is a positive integer not less than 3; Establish the loading-unloading section of the core structure for finite element simulation analysis; The finite element division adopts structural grid, and the grid scale is uniformly defined as l. The simulation results are post-processed to extract the number of units A whose Von-Mises plastic strain is greater than 0.05 and less than 0.06 after the core is unloaded; the distribution level of the high strain area of ​​the core is defined as A / B; where B is the total number of core structural units, the cross-sectional shape of the core is optimized; the optimization variable is the spline curve control parameter, and the optimization target is max A / B; the constraint condition is the maximum plastic strain ε of the core after unloading max ≤0.06; through optimized design, the core cross-sectional shape with the highest level of high strain distribution under the same deformation is obtained.

10. The fractal-stacked design method for programmable deformable superstructures according to claim 9, characterized in that: The deformation amount q of each core is the same as the output force / torque f; Through the parallel stacking design, the total output deformation of the deformable superstructure is q, and the total output force / torque is m×f; Where m is the number of core stacks, and the parallel stacking is constrained by the deformation output component; the front cover, the rear cover, the front fastening head, and the rear fastening head constrain the deformation of all cores to one-dimensional deformation, torsional deformation or telescopic deformation.

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