Complex model 4D printing method based on carbon fiber reinforced SMP composite material self-folding technology

Abstract

The invention provides a complex model 4D printing method based on a shape memory polymer self-folding technology, which comprises the following steps: performing triangular skin covering on a complex model to enable the surface to be subjected to surface patch treatment, and performing surface patch simplification; unfolding the simplified complex model into a two-dimensional plane, and recording an included angle between every two planes; parameter design is carried out on the self-folding unit structures with different bending angles, so that the self-folding unit structures replace folding lines unfolded on a two-dimensional plane, and a self-folding two-dimensional plane is obtained; the SMP / carbon fiber powder composite material and the thermoplastic polyurethane elastomer are used for 3D printing of a self-folded two-dimensional plane; and putting the printed self-folded two-dimensional plane into a constant-temperature heat source, automatically bending the printed self-folded two-dimensional plane into a three-dimensional complex model, and then cooling the three-dimensional complex model at room temperature. According to the method, a complex three-dimensional model can be unfolded into a two-dimensional plane, and self-folding of the complex model is achieved by accurately designing the folding marks and the folding angle.

Description

Technical Field

[0001] This invention belongs to the field of composite materials and their processing technology, and in particular relates to a 4D printing method for complex models based on carbon fiber reinforced SMP composite material self-folding technology. Background Technology

[0002] In modern manufacturing, the demand for composite materials with shape memory properties and good mechanical properties is constantly growing, especially in aerospace, medical devices, and intelligent robotics. Traditional composite materials have limitations in shape memory and mechanical properties, making it difficult to meet the requirements of complex structures and high-precision applications. Furthermore, traditional folding methods are inefficient and inaccurate in the manufacturing of complex models, hindering automation and limiting the production and development of complex structures. 4D printing technology, as an emerging manufacturing technology, can realize shape changes in materials in time and space, providing new ideas and methods for manufacturing complex models. However, current applications of 4D printing technology in the self-folding of complex models still face some challenges, such as insufficient material properties, low folding accuracy, and inaccurate simulation analysis. Therefore, developing an SMP / carbon fiber powder composite material suitable for 4D printing and its self-folding technology is of significant practical importance. Summary of the Invention

[0003] The primary objective of this invention is to provide a carbon fiber reinforced SMP composite material suitable for 4D printing, comprising thermoplastic shape memory polymer (SMP) and carbon fiber powder, wherein the carbon fiber powder accounts for 3-5% by mass.

[0004] This composite material possesses both excellent shape memory and mechanical properties, enabling stable and reliable deformation recovery under external stimuli, thus meeting the application requirements of self-folding and intelligent actuation of complex three-dimensional structures.

[0005] In some embodiments of the present invention, the carbon fiber powder accounts for 5% by mass.

[0006] A second objective of this invention is to provide a method for preparing the above-mentioned carbon fiber reinforced SMP composite material, comprising the following steps:

[0007] SMP and carbon fiber powder are dried separately and then mixed to obtain a mixture. The mixture is then fed into a twin-screw extruder, and after melting, extrusion, and cooling, carbon fiber reinforced SMP composite material is finally obtained.

[0008] A third objective of this invention is to provide a self-folding unit structure, which includes a 3D-printed shrinkage layer and a confinement layer. The shrinkage layer is made of carbon fiber reinforced SMP composite material, and the confinement layer is made of thermoplastic polyurethane elastomer (TPU).

[0009] The structure is automatically folded by superimposing carbon fiber reinforced SMP composite material and elastic material TPU through printing. The stress difference and shape memory effect between the two under heat conditions are used to achieve the automatic folding of the structure.

[0010] The fourth objective of this invention is to provide a finite element simulation method based on a viscoelastic constitutive model for predicting the folding behavior of self-folding element structures under different loading conditions, comprising the following steps:

[0011] S1: Conduct mechanical property characterization experiments on carbon fiber reinforced SMP composites, obtain material parameters, and fit the viscoelastic constitutive equation;

[0012] S2: Input material parameters into the finite element model, establish a simulation model of the self-folding unit structure, and conduct simulation experiments to simulate the bending process of the self-folding unit structure;

[0013] S3: Verify the accuracy of the simulation model of the self-folding unit structure by comparing the simulation results with the actual experimental results.

[0014] In some embodiments of the present invention, the mechanical property characterization experiments include dynamic mechanical analysis experiments, variable-temperature uniaxial tensile experiments, and variable-temperature relaxation experiments.

[0015] In some embodiments of the present invention, the material parameters include printing speed, thickness, and length.

[0016] In some embodiments of the present invention, the viscoelastic constitutive equations include equations (1) to (8), as follows:

[0017]

[0018] Where, σ (t) Let E be the stress at the current time t, ε0 be the initial strain of the material, and E be the stress at the current time t. (t) Let ξ represent the relaxation modulus at time t, where t is the current time, and ξ be the integral variable over time. E (t) E is represented by equation (2); ∞ Let E be the relaxation modulus as time approaches infinity. i Let τ be the relaxation modulus of the i-th Maxwell element. i =ξ i / E iLet t = 0 be the relaxation time for the i-th unit to reach thermal equilibrium. Substituting t = 0 into equation (2) yields equation (3): E0 is the initial elastic modulus, which is also the relaxation modulus at t = 0. Dividing both sides of the equation by the initial modulus, we obtain the dimensionless relaxation modulus formula, as shown in equation (4); e (t) That is, the dimensionless relaxation modulus, e i Let e ​​be the dimensionless modulus of the i-th unit. ∞ The dimensionless residual modulus, the Prony series, is expressed by equation (6); G (t) G0 is the shear stress relaxation modulus at a specific time t, where G0 represents the initial shear relaxation modulus of the material, and τ is the shear stress relaxation modulus. i g represents the time required for the relaxation process. i is a dimensionless material constant representing a normalized parameter related to relaxation behavior; E is the relaxation modulus; t corresponds to time; T represents temperature, with T1 as the reference temperature and T2 as the actual temperature; a r C1 represents the time-temperature conversion factor, which is the scaling factor for converting time t at temperature T1 to the equivalent time at temperature T2; C1 and C2 are obtained by fitting the experimental results with equation (8), and T g It is the glass transition temperature.

[0019] The aforementioned finite element simulation method is used to simulate the folding process of self-folding structures under different loading conditions and is verified through experiments. The influence of parameters such as printing speed, thickness and length on bending behavior is obtained, and precise control of the folding angle from 0° to 360° is achieved, thereby providing theoretical guidance and technical support for the design and optimization of self-folding technology.

[0020] The fourth objective of this invention is to provide a 4D printing method for complex models based on SMP / carbon fiber powder composite material self-folding technology, comprising the following steps:

[0021] 1) Triangular skinning is applied to complex models to make the surfaces into patches, and the patches are then simplified.

[0022] 2) Unfold the simplified complex model into a two-dimensional plane and record the angle between each face;

[0023] 3) By using the bending law of the self-folding unit structure, the parameters of the self-folding unit structure with different bending angles are designed so that the self-folding unit structure replaces the crease line of the two-dimensional plane and obtains a self-folding two-dimensional plane.

[0024] 4) Based on the obtained self-folding two-dimensional plane, 3D printing of the self-folding two-dimensional plane is carried out using SMP / carbon fiber powder composite material and thermoplastic polyurethane elastomer.

[0025] 5) Place the printed self-folding 2D plane into a constant temperature heat source, where it will automatically bend into a complex 3D model, and then cool at room temperature.

[0026] The above 4D printing methods, combined with finite element simulation, optimize and adjust local parameters of the model, thereby achieving automated, high-precision self-folding forming of complex structures, significantly improving the efficiency and quality of intelligent structure manufacturing. These methods, through comprehensive design of printing paths, material distribution, and simulation predictions, enable automated, high-precision self-folding of complex structures, expanding the application scope of 4D printing in the field of intelligent structure manufacturing.

[0027] In some embodiments of the present invention, the 3D printing is performed using dual-nozzle printing with the following parameters: nozzle diameter 0.4-0.6 mm, printed layer thickness 0.2 mm, nozzle temperature 210-230°C, heated bed temperature 30°C, and fill density 100%.

[0028] In some embodiments of the present invention, the constant temperature heat source is a water bath.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] (1) This invention significantly improves shape memory performance and mechanical properties by using SMP / carbon fiber powder composite material. Compared with traditional materials, this composite material can recover to the preset shape more quickly and accurately under external stimuli, exhibiting a higher shape recovery rate and shape fixation rate. At the same time, the addition of carbon fiber enhances the mechanical strength and toughness of the material, enabling it to better withstand complex mechanical environments, thereby extending the service life of the product.

[0031] (2) This invention can unfold complex three-dimensional models into two-dimensional planes and achieve self-folding of complex models by precisely designing creases and folding angles, thus broadening the application scope of 4D printing technology. At the same time, through simulation and experimentation, this invention analyzes and determines the key parameters affecting the folding angle, such as printing speed and layer thickness, and establishes the corresponding bending rules, realizing precise angle self-folding and further improving the accuracy and repeatability of folding.

[0032] (3) This invention demonstrates significant advantages in artistic creation and applications in space-constrained environments. In the art field, this invention enables the self-folding of complex structures, providing artists with entirely new creative means. It can precisely fold artworks of various complex shapes according to design requirements, greatly enriching artistic expression. In confined environments or situations where transportation space is limited, the self-folding technology of this invention allows models to be folded and unfolded in a smaller space, thereby facilitating transportation and storage, saving space, and improving the flexibility and convenience of use.

[0033] (4) This invention also has good economic and environmental benefits. By optimizing material formulation and process parameters, it improves product performance while reducing production costs. 4D printing technology has a high material utilization rate, reduces material waste, and is more environmentally friendly. Attached Figure Description

[0034] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0035] Figure 1 A schematic diagram illustrating the macroscopic shape memory programming process of a rectangular spline printed from a carbon fiber reinforced SMP composite filament / TPU assembly;

[0036] Figure 2 The diagram shows the dynamic mechanical properties of carbon fiber reinforced SMP composites.

[0037] Figure 3 The stress-strain curves of the specimens are shown for six different temperatures.

[0038] Figure 4 Stress-time curves at different temperatures;

[0039] Figure 5 The relaxation modulus master curve is shown at a reference temperature of 70℃.

[0040] Figure 6 To fit the curve of WLF parameters;

[0041] Figure 7 The curve is the result of fitting the Maxwell viscoelastic constitutive model.

[0042] Figure 8 The simulation diagram of the self-folding of a rectangular spline;

[0043] Figure 9 The bending pattern of rectangular splines printed from carbon fiber reinforced SMP composite / TPU combination is shown in the figure (a is the printing length-bending angle curve; b is the printing speed-bending angle curve; c is the printing thickness-bending angle curve).

[0044] Figure 10 This is a schematic diagram of the self-folding of a complex model. Detailed Implementation

[0045] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0046] Embodiments of this disclosure are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this disclosure, and should not be construed as limiting this disclosure.

[0047] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0048] Example 1

[0049] The steps for preparing carbon fiber reinforced SMP composites are as follows:

[0050] Step 1: Place the SMP particles into powder and carbon fiber powder in a vacuum drying oven at 50-100℃ for 10 hours.

[0051] Step 2: Mix the shape memory polymer SMP and carbon fiber powder, with the carbon fiber powder accounting for 5% of the total mass.

[0052] The powder mixture is added to the feed inlet of the filament extruder and melted into a plastic form at high temperature. It is then cooled and solidified by a water-cooling device in the middle, passes through the pulley system on the left, and is finally wound into the filament material spool on the left end to obtain a carbon fiber reinforced SMP composite material with a theoretical diameter of 1.75 mm.

[0053] Example 2

[0054] A self-folding unit structure includes a 3D-printed shrinkage layer and a confinement layer. The shrinkage layer is obtained by 3D printing the carbon fiber reinforced SMP composite material prepared in Example 1, and the confinement layer is obtained by 3D printing TPU. Its design is as follows: Figure 1 As shown, when the self-folding unit structure is heated in hot water at 70°C, the carbon fiber reinforced SMP layer softens, releases residual stress, and shrinks, while TPU, being an elastomer, does not shrink. This mismatch in shrinkage between the two causes the bending phenomenon.

[0055] Example 3

[0056] Establishment of viscoelastic constitutive equations and finite element simulation method for self-folding elements:

[0057] The generalized Maxwell model is a classic viscoelastic theory model that describes this property of materials through a mechanical structure of multiple springs and viscous dampers connected in series. This model not only expresses the mechanical behavior of carbon fiber reinforced SMP composites under different stress and temperature conditions, but also provides theoretical support for further in-depth research into the properties of these materials.

[0058] The generalized Maxwell model is shown in equation (1):

[0059]

[0060] Where σ (t) Let E be the stress at the current time t, ε0 be the initial strain of the material, and E be the stress at the current time t. (t) Let ξ represent the relaxation modulus at time t, where t is the current time, and ξ be the integral variable over time. E (t) It can be expressed by equation (2):

[0061]

[0062] In the formula E ∞ Let E be the relaxation modulus as time approaches infinity. i Let τ be the relaxation modulus of the i-th Maxwell element. i =ξ i / E i Let t = 0 be the relaxation time for the i-th unit to reach thermal equilibrium, and substitute it into equation (2):

[0063]

[0064] E0 is the initial elastic modulus, which is also the relaxation modulus at t=0. Dividing both sides of the equation by the initial modulus yields the dimensionless relaxation modulus formula:

[0065]

[0066] In the formula e (t) That is, the dimensionless relaxation modulus, e i Let be the dimensionless modulus of the i-th element. The expression for the Prony series is:

[0067]

[0068] Among them G (t) G0 is the shear stress relaxation modulus at a specific time t, where G0 represents the initial shear relaxation modulus of the material, and τ is the shear stress relaxation modulus. i g represents the time required for the relaxation process. i is a dimensionless material constant, representing a normalized parameter related to relaxation behavior. After making the shear stress relaxation modulus dimensionless, a more intuitive and easier-to-analyze relationship between the modulus and time can be obtained. Furthermore, in order to more clearly reveal the mechanical properties of the material and its time-dependent behavior, it is necessary to fit the obtained Prony series.

[0069] Because time and temperature both affect the modulus of a material, this invention introduces the Williams–Landel–Ferry displacement function (WLF) to construct a time-temperature equivalent equation in order to describe the relationship among these three factors during the definition of time-domain viscoelasticity using Prony series expansion. This allows the relaxation process at different temperatures to be analyzed under the same reference temperature. This method simplifies the material modeling process and enables the prediction of material mechanical properties at different temperatures, thereby describing viscoelastic behavior.

[0070] E(T1, t) = E(T2, t / a) r (7)

[0071] Where E is the relaxation modulus, t corresponds to time, and the reference temperature is T1 while the actual temperature is represented by T2. It is generally assumed that when T1 = T... g At that time, the movement factor satisfies the WLF equation:

[0072]

[0073] C1 and C2 in the formula need to be obtained by fitting the experimental results with formula (8), T g It is the glass transition temperature.

[0074] By combining the time-temperature equivalence principle with the WLF equation, the relationship between time and temperature was established, which allows for a better fit to the material's performance parameters.

[0075] To fit the constitutive model parameters, the carbon fiber reinforced SMP composite material obtained in Example 1 was printed into standard tensile test specimens and subjected to the following tests:

[0076] (1) Dynamic Mechanics Analysis (DMA)

[0077] The material was analyzed using a Metravib 450+ dynamic thermomechanical analyzer to study the material response of the specimens under different dynamic loads and temperatures. Using tensile mode, at a frequency of 1 Hz and a strain of 0.18%, parameters such as storage modulus, loss modulus, loss factor (tanδ), and glass transition temperature (Tg) were measured at a heating rate of 2 °C / min.

[0078] like Figure 2As shown, the modulus change of this material can be divided into three stages. The first stage, from 25 to 60℃, is a low-temperature stage, characterized by a large storage modulus and a relatively small but stable loss modulus. During this stage, the material is in a glassy state, and the loss factor, representing the ratio of loss modulus to storage modulus, is relatively stable. The second stage, from 75℃ onwards, is a high-temperature stage, where both storage modulus and loss modulus are small, and the material exhibits a rubbery state. The loss factor is also relatively stable. The third stage, from 60 to 75℃, is a stage of rapid temperature change. During this range, both storage modulus and loss modulus decrease rapidly, indicating a transition from a glassy to a rubbery state. The loss factor fluctuates significantly during this transition. The temperature corresponding to the peak value of the material's loss factor is the glass transition temperature (Tg), which is 68.5℃.

[0079] (2) Variable temperature uniaxial tensile test

[0080] The experiment was conducted according to ASTM D638 standard. Tensile specimens were placed in an environmental chamber in a universal testing machine, with the temperature set between 25°C and 75°C, and uniaxial tensile tests were performed at different temperatures. This allowed for the measurement of the force-displacement curves of carbon fiber reinforced SMP composites at different temperatures, preparing for subsequent calculations of the elastic modulus.

[0081] To reduce errors and improve the accuracy of experimental data, three uniaxial tensile tests were performed at each temperature, and the average value of the results was taken. The specimen was fixed in the testing machine fixture, and the ambient temperature was adjusted to the corresponding temperature and maintained for 5 minutes to ensure the temperature inside the ambient chamber was stable and to keep the specimen temperature as close to the ambient temperature as possible. After the temperature stabilized, the tensile machine applied a uniaxial tensile load to the specimen at a speed of 2 mm / min, thus completing the variable-temperature uniaxial tensile test.

[0082] The stress-strain curves of the specimens under six temperature conditions are as follows: Figure 3 As shown in the figure, it can be seen that the stress-strain response of the material at different temperatures exhibits certain regularities during the tensile test. As the specimen is continuously stretched, the stress gradually increases and then slowly tends to stabilize. This change corresponds to the material gradually transitioning from the elastic stage to the plastic stage. In comparison, it can be found that temperature also affects the mechanical properties of the material. When the temperature increases, the critical stress level corresponding to plastic deformation of the material gradually decreases, especially after the temperature exceeds 65℃, the stress value shows a significant decrease. This change indicates that the material stiffness weakens significantly with increasing temperature, and the mechanical properties shift towards a more flexible direction. Subsequently, after statistical calculation of the experimental results, the elastic modulus of the carbon fiber reinforced SMP composite material prepared in Example 1 at different temperatures can be obtained. The elastic modulus at the corresponding temperatures is shown in Table 1.

[0083] Table 1 Elastic modulus at different temperatures

[0084]

[0085] (3) Temperature relaxation experiment

[0086] Under constant strain, carbon fiber reinforced SMP composites exhibit stress relaxation due to their viscoelastic properties, where stress gradually decreases over time. To further refine the parameters of carbon fiber reinforced SMP composites, relaxation experiments at different temperatures are necessary. This experiment uses the same equipment as the tensile test and is conducted within the same temperature range. After the specimen is clamped and fixed, the ambient chamber is first heated to the set temperature and maintained for 5 minutes to ensure temperature stability. Then, the specimen is stretched at a rate of 2 mm / min to 2% of the strain (corresponding to an elongation of 1 mm) and held at this stretching distance for 15 minutes. The relaxation curves of the material at different temperatures are recorded. The stress-time curves at different temperatures are shown below. Figure 4 As shown, the material exhibits higher stiffness at lower temperatures and lower stiffness at higher temperatures. Especially above 60℃, the relaxation curve shows a slower decrease in stress, and the material's modulus decreases significantly.

[0087] Based on the time-temperature equivalence principle, the time and temperature effects of viscoelastic materials are considered equivalent. By taking the logarithm of the relaxation modulus and relaxation time data of carbon fiber reinforced SMP composites at different temperatures obtained experimentally, the time-temperature equivalence principle can be satisfied, allowing the plotting of relaxation curves at different temperatures, i.e., LogE(t)-Logt curves. By determining a translation factor, these curves are moved to the same reference temperature (70℃ in this example), thus constructing the master curve at that reference temperature. Using this master curve, the temperature-dependent modulus evolution relationship can be transformed into a time-scale modulus change, achieving a unified modeling of the modulus-time relationship. This allows for a clear explanation of the relationship between time, temperature, and modulus, described by a single curve without the need for multiple curves, such as... Figure 5 As shown. And by fitting the main curve to equation (8), the values ​​of parameters C1 and C2 in the WLF equation can be obtained, as shown. Figure 7 The fitted modulus curve shows that C1 = 29.26 and C2 = 81.35. This method allows us to express the thermodynamic behavior of materials at different temperatures and reveal their viscoelastic properties more deeply.

[0088] After obtaining the improved WLF equation, the translated relaxation modulus principal curve can be derived from experimental data, such as... Figure 7 By fitting it with equation (2), the relaxation modulus of the material can be obtained.

[0089] Maxwell's viscoelastic constitutive model is one of the classic models used to describe the viscoelastic behavior of materials. In its generalized form, the Prony series is used to characterize the change of the material's relaxation modulus or creep compliance over time, and is an important mathematical tool in characterizing viscoelastic materials. To obtain the corresponding Prony series describing the material's relationship with time, normalization is required. The Prony series are shown in Table 2.

[0090] Table 2 Prony series

[0091]

[0092]

[0093] A finite element model of the self-folding unit structure was established and meshed, with appropriate mesh sizes selected to ensure the accuracy and stability of the simulation calculations. Simultaneously, reasonable boundary and loading conditions were set to accurately simulate the external forces and constraints experienced during the folding process. In the simulation, the relationship between bending behavior and printing speed, thickness, and length was considered. Following the self-folding principle, TPU and carbon fiber reinforced SMP composite materials were superimposed and printed. The TPU formed a confinement layer, and the carbon fiber reinforced SMP composite material formed a shrinkage layer. The printed model was a plane. The simulation simulated the thermal bending process of the planar model. First, a temperature field was applied to the material to simulate the internal stress accumulation process during printing. A displacement load was set in the temperature field to represent the internal stress. After the model was given internal stress, the temperature field was changed to room temperature to solidify the model and store the internal stress. When the model was placed in hot water, it softened, stimulating the model to self-fold. The simulation results are as follows. Figure 8 As shown in the figure, w is the length of the model, and ts is the thickness of the carbon fiber reinforced SMP composite material. First, we simulated models of different lengths. The results showed that the longer the model, the larger the bending angle. This is because thermal bending occurs at each unit length of the model, thus the longer the model, the larger the bending angle. Second, we simulated the thickness. As shown in the figure, the thicker the shrinkage layer, the smaller the bending angle. This is because a larger thickness increases the cross-sectional rigidity of the model, making it less prone to bending.

[0094] To verify the reliability of the simulation analysis, corresponding experiments were conducted, and the changes in bending angle under different parameters were tested and recorded. The experimental results were highly consistent with the simulation predictions, verifying the effectiveness of the model. Furthermore, a graph illustrating the influence of various factors on the bending angle was plotted through comparative analysis. Figure 9 The results show that the self-folding unit structure can achieve the expected arbitrary angle folding and maintain the final bent state stably after cooling, demonstrating good controllability and repeatability.

[0095] Example 4

[0096] This embodiment designs a self-folding rabbit model. The component is printed using carbon fiber reinforced SMP composite filament and TPU filament. Ordinary complex models (rabbits) have smooth surfaces that cannot be unfolded into a plane. Therefore, the model is covered with triangular skinning to create a patch-like surface, which is then simplified to retain the original local features while reducing the number of skinning patches. It is then unfolded into a two-dimensional plane, and the angles between each face are recorded. By using bending rules, the parameters of self-folding units with different bending angles are designed to replace the crease lines of the unfolded two-dimensional plane, resulting in a self-folding two-dimensional plane. The design of the model component is as follows: Figure 10 As shown, the printed rabbit flat surface is placed in a 70°C constant temperature water bath, where it will automatically bend into a three-dimensional rabbit shape, and then be fixed into a rabbit shape after cooling at room temperature.

[0097] The collection, storage, use, processing, transmission, provision, and disclosure of user personal information disclosed in this invention comply with relevant laws and regulations and do not violate public order and good morals.

[0098] It should be noted that personal information collected from users should be used for legitimate and reasonable purposes and should not be shared or sold outside of these legitimate uses. Furthermore, such collection / sharing should only be conducted after receiving the user's informed consent, including but not limited to notifying the user to read the user agreement / user notice and sign an agreement / authorization that includes authorization of relevant user information before the user uses the function. In addition, any necessary steps must be taken to protect and safeguard access to such personal information data and ensure that others with access to personal information data comply with their privacy policies and procedures.

[0099] This invention is intended to provide implementation schemes for users to selectively prevent the use or access to personal information data. That is, this disclosure is intended to provide hardware and / or software to prevent or block access to such personal information data. Once personal information data is no longer needed, risks can be minimized by restricting data collection and deleting data. Furthermore, where applicable, such personal information can be de-identified to protect user privacy.

[0100] The acquisition, transmission, storage, use, and processing of data in the technical solution of this invention all comply with the relevant provisions of national laws and regulations.

[0101] It should be noted that in the embodiments of the present invention, certain software, components, models and other existing solutions in the industry may be mentioned. These should be regarded as exemplary and are only intended to illustrate the feasibility of implementing the technical solution of this application. However, they do not mean that the applicant has used or necessarily used the solution.

[0102] In the foregoing descriptions of the embodiments, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this disclosure. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0103] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this disclosure, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0104] Any process or method description in the flowchart or otherwise herein can be understood as representing a module, segment, or portion of code comprising one or more executable instructions for implementing custom logic functions or processes, and the scope of preferred embodiments of this disclosure includes additional implementations in which functions may be performed not in the order shown or discussed, including substantially simultaneously or in reverse order depending on the functions involved, as will be understood by those skilled in the art to which embodiments of this disclosure pertain.

[0105] The logic and / or steps represented in the flowchart or otherwise described herein, for example, can be considered as a sequenced list of executable instructions for implementing logical functions, and can be embodied in any computer-readable medium for use by, or in conjunction with, an instruction execution system, apparatus, or device (such as a computer-based system, a processor-included system, or other system that can fetch and execute instructions from, an instruction execution system, apparatus, or device). For the purposes of this specification, "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transmit programs for use by, or in conjunction with, an instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of computer-readable media include: an electrical connection having one or more wires (electronic device), a portable computer disk drive (magnetic device), random access memory (RAM), read-only memory (ROM), erasable and editable read-only memory (EPROM or flash memory), fiber optic devices, and portable optical disc read-only memory (CDROM). Furthermore, computer-readable media can even be paper or other suitable media on which programs can be printed, because programs can be obtained electronically, for example, by optically scanning the paper or other media, followed by editing, interpreting, or otherwise processing as necessary, and then stored in computer memory.

[0106] It should be understood that various parts of this disclosure can be implemented using hardware, software, firmware, or a combination thereof. In the above embodiments, multiple steps or methods can be implemented using software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware as in another embodiment, it can be implemented using any one or a combination of the following techniques known in the art: discrete logic circuits having logic gates for implementing logical functions on data signals, application-specific integrated circuits (ASICs) having suitable combinational logic gates, programmable gate arrays (PGAs), field-programmable gate arrays (FPGAs), etc.

[0107] Those skilled in the art will understand that all or part of the steps of the methods described in the above embodiments can be implemented by a program instructing related hardware, and the program can be stored in a computer-readable storage medium. When executed, the program includes one or a combination of the steps of the method embodiments.

[0108] Furthermore, the functional units in the various embodiments of this disclosure can be integrated into a processing module, or each unit can exist physically separately, or two or more units can be integrated into a module. The integrated module can be implemented in hardware or as a software functional module. If the integrated module is implemented as a software functional module and sold or used as an independent product, it can also be stored in a computer-readable storage medium.

[0109] The storage medium mentioned above can be a read-only memory, a disk, or an optical disk, etc. Although embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present disclosure. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present disclosure.

Claims

1. A carbon fiber reinforced SMP composite material suitable for 4D printing, characterized in that: It includes thermoplastic shape memory polymers and carbon fiber powder, with carbon fiber powder accounting for 3-5% by mass.

2. The carbon fiber reinforced SMP composite material for 4D printing according to claim 1, characterized in that: The carbon fiber powder accounts for 5% of the total mass.

3. A method for preparing the carbon fiber reinforced SMP composite material according to claim 1 or 2, comprising the following steps: SMP and carbon fiber powder are dried separately and then mixed to obtain a mixture. The mixture is then fed into a twin-screw extruder, and after melting, extrusion, and cooling, carbon fiber reinforced SMP composite material is finally obtained.

4. A self-folding unit structure, characterized in that: The self-folding unit structure includes a 3D-printed shrinkage layer and a confinement layer. The shrinkage layer is made of carbon fiber reinforced SMP composite material, and the confinement layer is made of thermoplastic polyurethane elastomer.

5. A finite element simulation method based on a viscoelastic constitutive model, characterized in that: Includes the following steps: S1: Conduct mechanical property characterization experiments on carbon fiber reinforced SMP composites, obtain material parameters, and fit the viscoelastic constitutive equation; S2: Input material parameters into the finite element model, establish a simulation model of the self-folding unit structure, and conduct simulation experiments to simulate the bending process of the self-folding unit structure; S3: Verify the accuracy of the simulation model of the self-folding unit structure by comparing the simulation results with the actual experimental results.

6. The finite element simulation method based on a viscoelastic constitutive model according to claim 5, characterized in that: The mechanical property characterization experiments include dynamic mechanical analysis experiments, variable-temperature uniaxial tensile experiments, and variable-temperature relaxation experiments.

7. The finite element simulation method based on a viscoelastic constitutive model according to claim 5, characterized in that: The material parameters include printing speed, thickness, and length.

8. The finite element simulation method based on a viscoelastic constitutive model according to claim 5, characterized in that: The viscoelastic constitutive equations include equations (1) to (8), as follows: E(T1,t)=E(T2,t / a r ) (7) Where, σ (t) Let E be the stress at the current time t, ε0 be the initial strain of the material, and E be the stress at the current time t. (t) Let ξ represent the relaxation modulus at time t, where t is the current time, and ξ be the integral variable over time. E (t) E is represented by equation (2); ∞ Let E be the relaxation modulus as time approaches infinity. i Let τ be the relaxation modulus of the i-th Maxwell element. i =ξ i / E i Let t = 0 be the relaxation time for the i-th unit to reach thermal equilibrium. Substituting t = 0 into equation (2) yields equation (3): E0 is the initial elastic modulus, which is also the relaxation modulus at t = 0. Dividing both sides of the equation by the initial modulus, we obtain the dimensionless relaxation modulus formula, as shown in equation (4); e (t) That is, the dimensionless relaxation modulus, e i Let e ​​be the dimensionless modulus of the i-th element. ∞ The dimensionless residual modulus is represented by the expression for the Prony series, which is given by equation (6); G (t) G0 is the shear stress relaxation modulus at a specific time t, where G0 represents the initial shear relaxation modulus of the material, and τ is the shear stress relaxation modulus. i g represents the time required for the relaxation process. i is a dimensionless material constant representing a normalized parameter related to relaxation behavior; E is the relaxation modulus; t corresponds to time; T represents the heating temperature, with T1 as the reference temperature and T2 as the actual temperature; a r C1 represents the time-temperature conversion factor, which is the scaling factor for converting time t at temperature T1 to the equivalent time at temperature T2; C1 and C2 are obtained by fitting the experimental results with equation (8), and T g It is the glass transition temperature.

9. A method for 4D printing complex models based on SMP / carbon fiber powder composite material self-folding technology, characterized in that: Includes the following steps: 1) Triangular skinning is applied to complex models to make the surfaces into patches, and the patches are then simplified. 2) Unfold the simplified complex model into a two-dimensional plane and record the angle between each face; 3) By using the bending law of the self-folding unit structure, the parameters of the self-folding unit structure with different bending angles are designed so that the self-folding unit structure replaces the crease line of the two-dimensional plane and obtains a self-folding two-dimensional plane. 4) Based on the obtained self-folding two-dimensional plane, 3D printing of the self-folding two-dimensional plane is carried out using SMP / carbon fiber powder composite material and thermoplastic polyurethane elastomer. 5) Place the printed self-folding 2D plane into a constant temperature heat source, where it will automatically bend into a complex 3D model, and then cool at room temperature.

10. The method for 4D printing complex models based on SMP / carbon fiber powder composite material self-folding technology according to claim 9, characterized in that: The 3D printing uses a dual-nozzle printing method with the following parameters: nozzle diameter 0.4-0.6 mm, printed layer thickness 0.2 mm, nozzle temperature 210-230℃, heated bed temperature 30℃, and infill density 100%.

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