A method for predicting thermal deformation in service for laser sintered composites

Abstract

The present invention discloses a service thermal deformation prediction method for laser sintered composites, comprising the steps of: reconstructing the microstructure according to the fiber direction arrangement and fiber content to obtain the reconstruction model in different fiber directions; constructing the constitutive model of glass fiber and PEEK matrix; establishing the thermal deformation prediction model of laser sintered PEEK composites based on the microscale reconstruction algorithm; adopting the laser sintering process to carry out the laser sintering manufacturing of glass fiber reinforced PEEK composites, calibrating and verifying the thermal deformation prediction model of laser sintered PEEK composites for composites with specific content and fiber arrangement; and predicting the thermal deformation of laser sintered composites based on the verified thermal deformation prediction model of laser sintered PEEK composites. Its significant effect is that it can accurately predict thermal deformation, improve the reliability of laser sintered composite material structure design, reduce the risk of failure in practical applications, and help promote the development of this material in the field of high-performance applications.

Description

Technical Field

[0001] The invention relates to the technical field of safe service of laser sintered composites, and in particular to a service thermal deformation prediction method for laser sintered composites. Background Art

[0002] Laser powder bed sintering technology is a processing method that uses laser as a heat source to sinter materials layer by layer through a powder bed to manufacture three-dimensional objects. Compared with conventional molding and injection molding of composite materials, this technology has unique advantages. Since the laser powder bed does not require a mold, is integrated and has no processing freedom restrictions, it can manufacture complex integrated structures.

[0003] The principle of laser sintering technology is to spread the powder material evenly on the substrate, and then scan it according to the predetermined three-dimensional model trajectory under the control of a laser beam. The powder material irradiated by the laser beam will quickly absorb energy and melt or sinter, and bond with the solidified material in the lower layer to form a layer of cross section. Subsequently, the substrate drops to a certain height, and a new powder layer is spread on the solidified layer. The laser beam scans and sinters again, and the cycle repeats until the entire three-dimensional object is completely manufactured. Compared with other rapid prototyping composite materials technologies (fused deposition modeling, light curing), parts prepared by laser sintering have the characteristics of good interlayer performance and high processing accuracy. With the continuous advancement and development of technology, laser sintering technology is expected to be widely used in more fields and bring more innovations and breakthroughs to the manufacturing industry.

[0004] Laser sintering composite technology can be applied to the aerospace field. In terms of the space service of laser sintering composite technology, the impact of extremely harsh environments is a key issue that researchers focus on. Due to the extreme uneven temperature (-150 degrees to 150 degrees) and temperature changes (one extreme cycle every 60 to 90 minutes) in the low-Earth orbit, under the overall constraints of the satellite, the laser sintering composite structure will experience thermal deformation during the service process. How to reasonably design process parameters in the manufacturing process to suppress thermal deformation during the service stage is a bottleneck problem that needs to be overcome in the research on the service of satellite laser sintering composite structures.

[0005] Therefore, in order to solve the problem that traditional service analysis methods cannot effectively predict the service thermal deformation of laser sintered composites, it is necessary to propose a service thermal deformation prediction method for laser sintered composites to solve the above problem. Summary of the invention

[0006] In view of the deficiencies in the prior art, an object of the present invention is to provide a method for predicting service thermal deformation of laser sintered composites to solve the problems existing in the above-mentioned background technology.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for predicting service thermal deformation of laser sintered composites includes the following steps:

[0009] Step 1: Reconstruct the microstructure according to the fiber direction arrangement and fiber content to obtain the reconstructed models in different fiber directions;

[0010] Step 2, construct the constitutive model of glass fiber and PEEK matrix;

[0011] Step 3: Based on the microscale reconstruction algorithm, a thermal deformation prediction model for laser sintering PEEK composites is established;

[0012] Step 4: Use laser sintering technology to carry out laser sintering manufacturing of glass fiber reinforced PEEK composites, and calibrate and verify the thermal deformation prediction model of laser sintered PEEK composites with specific content and fiber arrangement;

[0013] Step 5: Based on the verified thermal deformation prediction model of laser sintered PEEK composites, thermal deformation prediction of laser sintered composites is performed.

[0014] Furthermore, the steps for constructing the constitutive model of glass fiber and PEEK matrix in step 2 are as follows:

[0015] The constitutive model of glass fiber and PEEK matrix was established by using yield criterion and flow criterion, and the thermodynamic simulation of laser sintered PEEK composite was carried out.

[0016] The Kriging surrogate model is used to describe the effect of temperature on the elastic modulus and tensile and compressive yield stress of PEEK material.

[0017] Furthermore, in step 3, the steps of establishing a thermal deformation prediction model for laser sintering PEEK composites are as follows:

[0018] Based on the microscale reconstruction algorithm, the finite element model of thermal deformation simulation of laser sintered PEEK composites was established by using the finite element method.

[0019] The thermal deformation of glass fiber reinforced PEEK composites with different fiber orientation distribution and different fiber content was analyzed, and the thermal deformation results of laser sintered composites with different fiber orientation distribution and different fiber content were obtained;

[0020] The fiber direction tensor is used to control the fiber arrangement, and the voxel-based fiber filling achieves a high filling volume fraction.

[0021] The Python-based mesh generation method is used to generate a thermal deformation prediction model for laser sintering PEEK composites.

[0022] Furthermore, the steps of establishing a finite element model for thermal deformation simulation of laser sintered PEEK composites using a finite element method based on a microscale reconstruction algorithm are as follows:

[0023] Based on the voxel-based fiber filling algorithm and the improved random order adsorption algorithm, the RVE model of laser sintered PEEK composites is established in a three-dimensional voxel cube space composed of a set of ordered voxels.

[0024] The remaining voxels in the three-dimensional voxel cube space are used as the matrix material to obtain the finite element model of thermal deformation simulation of laser sintered PEEK composites.

[0025] Furthermore, the establishment process of the RVE model of the laser sintered PEEK composite is as follows:

[0026] The fiber length set is obtained by a normalized distribution random algorithm, and the fiber orientation set is generated by sampling the probability distribution function recovered from the second-order and fourth-order three-dimensional fiber orientation tensors;

[0027] The core line of the fiber can be calculated according to the center point, length and orientation of the fiber, and the voxels along the core line are selected to establish a voxelized core line set;

[0028] For each voxel in the core line set, the neighboring voxels within the fiber radius are collected to reconstruct the fiber;

[0029] An improved random sequential adsorption algorithm was used to fill each reconstructed fiber into the centrifugal space one by one until the RVE model of the reconstructed laser sintered PEEK composite was obtained.

[0030] Furthermore, in step 4, the steps of model calibration and verification for composite materials with specific content and fiber arrangement are as follows:

[0031] Select typical fiber content, printing parameters, and sample orientation;

[0032] The laser sintering process is adopted to obtain the laser sintered PEEK composite sample;

[0033] Thermal deformation tests were performed on laser sintered PEEK composite samples to calibrate and verify the thermal deformation prediction model for laser sintered PEEK composites.

[0034] Furthermore, the steps for predicting thermal deformation of laser sintered composites in step 5 are as follows:

[0035] Based on the verified thermal deformation prediction model of laser sintered PEEK composites, the deflection is used to describe the thermal warpage of laser sintered PEEK composites at different sizes, and the thermal deformation of laser sintered composites is predicted to obtain the prediction results.

[0036] The remarkable effects of the present invention are:

[0037] 1) By constructing a constitutive model of the constituent materials including glass fiber and PEEK matrix, the asymmetry, hydrostatic pressure effect, and temperature effect of laser sintered PEEK under tension and compression can be described, and the stress-strain behavior of the material at different temperatures can be accurately predicted, which improves the applicability and prediction accuracy of the model and can accurately simulate the response of laser sintered PEEK composites under thermal loads;

[0038] 2) In the process of establishing the model in steps 1 and 3, by parameterizing the material, the model can be applied to different process parameter conditions, thereby improving the versatility and flexibility of the model;

[0039] 3) In step 2, when establishing the constitutive model, the constructed constitutive model is encoded into the Abaqus user subroutine VUMAT, so that the model can be directly applied to complex finite element analysis, which is convenient for engineering applications;

[0040] 4) The calibrated and verified thermal deformation prediction model of laser sintered PEEK composites can accurately predict the service thermal deformation behavior of laser sintered composites, which is crucial for designing and evaluating the performance of laser sintered composite structures in practical applications;

[0041] 5) Through accurate prediction of thermal deformation, the reliability of laser sintered composite material structure design can be improved and the failure risk in practical applications can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a flow chart of the method.

[0043] Figure 2 The measured and predicted stress-strain curves of laser sintered PEEK at different temperatures in the present invention.

[0044] Figure 3 Schematic diagram of the thermal deformation prediction model of laser sintered PEEK composites in the present invention.

[0045] Figure 4 The thermal deformation of laser sintered PEEK composites with different fiber contents and fiber orientation distributions was simulated in the present invention.

[0046] Figure 5 The figures are the deformation shapes of the laser sintered glass fiber reinforced PEEK composite material with a fiber mass fraction of 30% at different temperatures in the present invention. DETAILED DESCRIPTION

[0047] The specific implementation manner and working principle of the present invention are further described in detail below with reference to the accompanying drawings.

[0048] like Figure 1As shown, the embodiment of the present invention proposes a method for predicting service thermal deformation of laser sintered composites, and the specific steps are as follows:

[0049] Step 1: Reconstruct the microstructure according to the fiber direction arrangement and fiber content to obtain the reconstructed models in different fiber directions;

[0050] Step 2, construct the constitutive model of glass fiber and PEEK matrix;

[0051] The steps for constructing the constitutive model are as follows:

[0052] Considering the asymmetry of the component, the influence of hydrostatic pressure and thermal environment, the glass fiber was treated as isotropic and linear elastic. The constitutive model of glass fiber and PEEK matrix was established using the Tschogel yield criterion and flow criterion, and the thermodynamic simulation of laser sintered PEEK composites was carried out.

[0053] The Kriging surrogate model is used to describe the effect of temperature on the elastic modulus and tensile and compressive yield stress of PEEK material.

[0054] Through the study of the mechanical degradation of glass fibers at high temperatures, it was found that the effect of temperature changes on the stiffness of glass fibers in space environments is negligible, and no obvious plastic deformation is observed in the stress-strain relationship. Therefore, the glass fibers are regarded as isotropic and linear elastic, and the material parameters are set to be independent of temperature.

[0055] The tensile stress-strain relationship of laser sintered PEEK material at different temperatures is shown in Figure 2. Figure 2 As shown. The Green-Lagrangian strain tensor E of laser sintered PEEK material is calculated using the deformation gradient tensor F, which consists of the thermal, elastic, and plastic parts of the deformation. The expression is:

[0056]

[0057] Here, I is the unit tensor.

[0058] The thermal characteristic strain α is:

[0059] α=α o (TT 0 )I

[0060] Where α 0 is the thermal expansion coefficient, T is the current temperature, T 0 is the reference temperature. The calculation formula of the second Piola-Kirchhoff stress S is:

[0061] S=C T (E-α-E p )

[0062] Among them, C T is the elastic modulus tensor at temperature T.

[0063] The yield criterion for laser sintered PEEK is:

[0064]

[0065] Among them, σ t,T and σ c,T is the yield stress of laser sintered PEEK under uniaxial tension and compression at temperature T, J 2 is the second invariant of the deviatoric stress tensor, I 1 is the first invariant of the stress tensor. The non-associated flow law proposed by Melro is used to describe the plastic evolution of laser sintered PEEK, and its expression is:

[0066]

[0067] In the formula, is the strain tensor rate, is the plasticity ratio, σ vm is the von Mises equivalent stress, p is the hydrostatic pressure, and β is the material parameter.

[0068] The effect of temperature on the elastic modulus and tensile and compressive yield stresses of laser sintered PEEK was characterized using the Kriging proxy model.

[0069] When establishing the constitutive model, this embodiment encodes the constructed constitutive model into the Abaqus user subroutine VUMAT, so that the model can be directly applied to complex finite element analysis, which is convenient for engineering application.

[0070] Step 3: Based on the microscale reconstruction algorithm, a finite element model for thermal deformation simulation of laser sintered PEEK composites is established. The steps are as follows:

[0071] Step 31: Based on a microscale reconstruction algorithm, a finite element model for thermal deformation simulation of laser sintered PEEK composites is established using a finite element method;

[0072] In this embodiment, the steps of establishing a finite element model for thermal deformation simulation of laser sintered PEEK composites are as follows:

[0073] Based on the voxel-based fiber filling algorithm and the improved random order adsorption algorithm, the RVE model of laser sintered PEEK composites is established in a three-dimensional voxel cube space composed of a set of ordered voxels.

[0074] The establishment process of the RVE model of the laser sintered PEEK composite is as follows:

[0075] S1. The fiber length set is obtained by a normalized distribution random algorithm, and the fiber orientation set is generated by sampling the probability distribution function recovered from the second-order and fourth-order three-dimensional fiber orientation tensors; the second-order tensor is the state variable of the input direction, and the fourth-order tensor is predicted by the best fit method based on the invariant; when the initial point (0,0,0) is set as the fiber center, the spatial position of the fiber can be determined according to the given length and direction.

[0076] The expression of the second-order three-dimensional fiber orientation tensor is:

[0077]

[0078] Where Φ is the fiber angle in Cartesian coordinates and ψ(Φ) is the probability distribution function (PDF). The PDF can also be recovered from the fiber orientation tensor.

[0079] The expression of the fourth-order three-dimensional fiber orientation tensor is:

[0080]

[0081] Where b ij and b ijkl is the deviation form of the direction tensor; f ij and f ijkl is a tensor basis function.

[0082] S2, the core line of the fiber can be calculated according to the center point, length and orientation of the fiber, and the voxels along the core line are selected to establish a voxelized core line set;

[0083] S3, for each voxel in the core line set, collect neighboring voxels within the fiber radius to reconstruct the fiber;

[0084] S4. An improved random sequential adsorption algorithm is used to fill each reconstructed fiber into the centrifugal space one by one until the RVE model of the reconstructed laser sintered PEEK composite is obtained, as well as the position, length and direction of the filling fiber.

[0085] In the filling process, this embodiment uses a spatial search algorithm to find feasible filling positions. When the position of the newly added fiber is randomly generated in the three-dimensional space, the translation vector is applied to all voxels stored in the fiber. Then, the corresponding elements in the three-dimensional space are checked to detect overlap with existing fibers. If overlap occurs, the potential fiber will be abandoned. If not, the corresponding element in the three-dimensional space is assigned a new value to represent the added fiber.

[0086] In addition, in the later stage of fiber filling, long fibers are difficult to be filled into the three-dimensional space, which will affect the acquisition and reconstruction efficiency of fiber length distribution. Therefore, the fiber volume fraction, fiber length, and fiber filling direction can be adjusted to improve the efficiency of fiber length reconstruction and ensure that the reconstructed RVE model accurately matches the target tensor.

[0087] S5. The remaining voxels in the three-dimensional voxel cube space are used as matrix materials to obtain a finite element model for thermal deformation simulation of laser sintered PEEK composites.

[0088] Step 32, analyzing the thermal deformation of the glass fiber reinforced PEEK composite material under different fiber direction distributions and different fiber contents, and obtaining the thermal deformation results of the laser sintered composite material under different fiber direction distributions and different fiber contents;

[0089] Step 33, using the fiber direction tensor to control the fiber arrangement, and achieving a high filling volume fraction based on voxel-based fiber filling;

[0090] Step 34: Generate a thermal deformation prediction model for laser sintered PEEK composites using a Python-based mesh generation method.

[0091] This embodiment establishes a finite element model for thermal deformation simulation of laser sintered PEEK composites in service based on a microscale reconstruction algorithm. A voxel-based fiber filling method is used to achieve a high filling volume fraction, and a Python-based mesh generation method is used to generate a finite element model.

[0092] In order to reduce the computational cost, a finite element model with the size of 1000 μm × 200 μm × 25 μm was established for the laser sintered glass fiber reinforced PEEK composite material, and the proportions consistent with the experimental design were maintained. Figure 3 As shown, the fiber volume fractions in the finite element model of the laser sintered glass fiber reinforced PEEK composite are 2.56%, 5.26%, 11.11% and 17.65%, respectively, and the fiber orientation tensor a is used to adjust the fiber distribution in the finite element model. In the material coordinate system, X-ray computed tomography (XCT) was used for measurement. The finite element model in the X direction is The finite element model in the Y direction is:

[0093] When simulating the thermal deformation of laser sintered PEEK composites, linear tetrahedron (C3D4), triangular prism (C3D6) and reduced integral hexahedron (C3D8R) elements were used in the grid. The two ends of the finite element model were fixed. It should be pointed out that the actual laser sintered PEEK composite specimens were not completely straight in the experiment, and the initial curvature of the specimens was small, which was conducive to thermal deformation. Before the thermal load, a very small load was applied along the thickness direction of the center of the FEA model. The small warping deformation caused by the initial load characterizes the small curvature of the sample. Subsequently, the temperature field was applied to the finite element model, and the temperature field was increased from 23°C to 150°C.

[0094] Step 4: Use laser sintering technology to carry out laser sintering manufacturing of glass fiber reinforced PEEK composites, and perform model calibration and verification on composites with specific content and fiber arrangement;

[0095] In the embodiment of the present invention, the steps of model calibration and verification are as follows:

[0096] Select typical fiber content, printing parameters, and sample orientation;

[0097] The laser sintering process is adopted to obtain the laser sintered PEEK composite sample;

[0098] Thermal deformation tests were performed on laser sintered PEEK composite samples to calibrate and verify the thermal deformation prediction model for laser sintered PEEK composites.

[0099] Step 5: Based on the verified thermal deformation prediction model of laser sintered PEEK composites, thermal deformation prediction of laser sintered composites is performed.

[0100] In this embodiment, when predicting thermal deformation, deflection is used to describe the thermal warpage of laser sintered PEEK composites at different sizes. An initial preload is used to achieve small deformation and better simulate the thermal expansion process.

[0101] In the specific implementation process, based on the results of thermal deformation prediction, the thermal deformation prediction of laser sintering composites can be carried out with fiber orientation and fiber variables as variables and thermal deformation resistance as the goal, so as to optimize the process parameters of laser sintering composites. The process is as follows:

[0102] The microstructure is reconstructed according to the fiber direction arrangement to obtain the reconstructed model in different fiber directions. Through the orthogonal parameter setting, the thermal deformation disturbance under different fiber directions and fiber contents is obtained by simulation, the optimal process parameters are screened, and the thermal deformation deflection is given.

[0103] Figure 4 Comparison of simulated thermal warpage deformation and experimental results of laser sintered glass fiber reinforced PEEK composites with different fiber contents and fiber orientation distributions. Figure 5The deformation shapes of laser sintered glass fiber reinforced PEEK composites with a fiber weight fraction of 30% at different temperatures.

[0104] Depend on Figure 4 and Figure 5 It can be seen that with the addition of glass fiber, the simulated warping deformation of the laser sintered PEEK composite is reduced, and the finite element model along the X direction has good resistance to thermal deformation.

[0105] In summary, the thermal deformation prediction method for laser sintered composites proposed in the present invention provides a scientific and accurate tool for the design and application of laser sintered composite materials. It can predict the stress-strain behavior of materials at different temperatures, which is crucial for designing and evaluating the performance of laser sintered composite structures in practical applications. Through accurate thermal deformation prediction, the reliability of laser sintered composite structure design can be improved, the failure risk in practical applications can be reduced, and it is helpful to promote the development of this material in the field of high-performance applications.

[0106] The above only describes in detail the preferred embodiments of the present invention, which is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

[0107] It should be understood that, although each step in the flow chart of the embodiment of the present invention is shown in sequence according to the indication of the arrow, these steps are not necessarily performed in sequence according to the order indicated by the arrow. Unless there is a clear explanation in this article, the execution of these steps does not have strict order restrictions, and these steps can be performed in other orders. Moreover, at least a portion of the steps in each embodiment may include a plurality of sub-steps or a plurality of stages, and these sub-steps or stages are not necessarily performed at the same time, but can be performed at different times, and the execution order of these sub-steps or stages is not necessarily performed in sequence, but can be performed in turn or alternately with at least a portion of other steps or sub-steps or stages of other steps.

[0108] Those skilled in the art will readily appreciate other embodiments of the present disclosure after considering the disclosure in the specification and examples. This application is intended to cover any variations, uses or adaptations of the present disclosure, which follow the general principles of the present disclosure and include common knowledge or customary techniques in the art that are not disclosed in the present disclosure. The specification and examples are intended to be exemplary only, and the true scope and spirit of the present disclosure are indicated by the claims.

Claims

1. A method for predicting service thermal deformation of laser sintered composites, characterized in that: The steps include: Step 1: Reconstruct the microstructure according to the fiber direction arrangement and fiber content to obtain the reconstructed models in different fiber directions; Step 2, construct the constitutive model of glass fiber and PEEK matrix; Step 3: Based on the microscale reconstruction algorithm, a thermal deformation prediction model for laser sintering PEEK composites is established; Step 4: Use laser sintering technology to carry out laser sintering manufacturing of glass fiber reinforced PEEK composites, and calibrate and verify the thermal deformation prediction model of laser sintered PEEK composites with specific content and fiber arrangement; Step 5: Based on the verified thermal deformation prediction model of laser sintered PEEK composites, thermal deformation prediction of laser sintered composites is performed; In step 3, the steps to establish the thermal deformation prediction model of laser sintering PEEK composites are as follows: Based on the microscale reconstruction algorithm, the finite element model of thermal deformation simulation of laser sintered PEEK composites was established by using the finite element method. The thermal deformation of glass fiber reinforced PEEK composites with different fiber orientation distribution and different fiber content was analyzed, and the thermal deformation results of laser sintered composites with different fiber orientation distribution and different fiber content were obtained; The fiber direction tensor is used to control the fiber arrangement, and the voxel-based fiber filling achieves a high filling volume fraction. A Python-based mesh generation method was used to generate a thermal deformation prediction model for laser sintered PEEK composites. The steps of establishing a finite element model for thermal deformation simulation of laser sintered PEEK composites using the finite element method based on a microscale reconstruction algorithm are as follows: Based on the voxel-based fiber filling algorithm and the improved random order adsorption algorithm, the RVE model of laser sintered PEEK composites is established in a three-dimensional voxel cube space composed of a set of ordered voxels. The remaining voxels in the three-dimensional voxel cube space are used as the matrix material to obtain a finite element model for thermal deformation simulation of laser sintered PEEK composites; The establishment process of the RVE model of the laser sintered PEEK composite is as follows: The fiber length set is obtained by a normalized distribution random algorithm, and the fiber orientation set is generated by sampling the probability distribution function recovered from the second-order and fourth-order three-dimensional fiber orientation tensors; The core line of the fiber can be calculated according to the center point, length and orientation of the fiber, and the voxels along the core line are selected to establish a voxelized core line set; For each voxel in the core line set, the neighboring voxels within the fiber radius are collected to reconstruct the fiber; An improved random sequential adsorption algorithm was used to fill each reconstructed fiber into the centrifugal space one by one until the RVE model of the reconstructed laser sintered PEEK composite was obtained.

2. The method for predicting service thermal deformation of laser sintered composites according to claim 1, characterized in that: The steps to construct the constitutive model of glass fiber and PEEK matrix in step 2 are as follows: The constitutive model of glass fiber and PEEK matrix was established by using yield criterion and flow criterion, and the thermodynamic simulation of laser sintered PEEK composite was carried out. The Kriging surrogate model is used to describe the effect of temperature on the elastic modulus and tensile and compressive yield stress of PEEK material.

3. The method for predicting service thermal deformation of laser sintered composites according to claim 1, characterized in that: In step 4, the steps for model calibration and verification of composite materials with specific content and fiber arrangement are as follows: Select typical fiber content, printing parameters, and sample orientation; The laser sintering process is adopted to obtain the laser sintered PEEK composite sample; Thermal deformation tests were performed on laser sintered PEEK composite samples to calibrate and verify the thermal deformation prediction model for laser sintered PEEK composites.

4. The method for predicting service thermal deformation of laser sintered composites according to claim 1, characterized in that: The steps for predicting thermal deformation of laser sintered composites in step 5 are as follows: Based on the verified thermal deformation prediction model of laser sintered PEEK composites, the deflection is used to describe the thermal warpage of laser sintered PEEK composites at different sizes, and the thermal deformation of laser sintered composites is predicted to obtain the prediction results.

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