Numerical simulation method for simulating resin flow in molding process of intelligent composite material with embedded optical fiber

Abstract

The invention discloses a numerical simulation method for simulating resin flow in a molding process of an intelligent composite material with an embedded optical fiber. The method comprises the following steps: generating a fiber bundle model through a Monte Carlo random algorithm; establishing a mesoscopic model for embedding optical fibers inside or outside the fiber bundle; establishing a resin flow control equation based on a phase field method in the finite element model; applying pressure load to an inlet and an outlet of the model, and submitting finite element calculation; the velocity field and the pressure field obtained through simulation are checked, and the influence rule of the optical fiber on the resin infiltration fiber bundle is analyzed. The method has good guiding significance for optimizing the intelligent composite material forming process and reducing forming defects.

Description

Technical Field

[0001] The present invention belongs to the field of process mechanics and relates to a numerical simulation method for simulating resin flow in the forming process of an intelligent composite material with embedded optical fibers. Background Art

[0002] In the field of aerospace, lightweighting of equipment structures is an eternal theme. Lightweighting of structures can increase payload, improve the range or firing range of aircraft, while reducing energy consumption and protecting the environment. The realization of lightweight structures is inseparable from high-performance advanced composite materials. Using advanced composite materials in aerospace structures can reduce the weight by 20%-30%, with extremely significant effects. Under the multi-field coupling action of extreme service environments and complex loads, it is very likely that the material properties will degrade at the macroscopic or microscopic level, resulting in a decrease in the structural load-bearing capacity and causing major accidents during the service of aircraft. Due to the anisotropy and inhomogeneity of composite materials themselves, the damage and failure forms are diverse and difficult to predict, which is one of the hidden dangers during the service of structures. Therefore, it is particularly important to use sensors to conduct synchronous state health monitoring during the service of structures. Optical fiber sensors have the characteristics of small size, light weight, anti-electromagnetic interference, corrosion resistance, wide measurement objects, large information capacity, high sensitivity, good integration, strong multiplexing ability, and suitability for harsh environments. They are commonly used sensing elements in intelligent composite materials and have been widely used in the field of structural health monitoring. Therefore, intelligent composite materials based on optical fiber sensing made by embedding optical fiber sensors in composite materials can meet the dual needs of lightweighting of equipment structures and health monitoring of the internal state of structures, greatly improving the safety and reliability of equipment structures. As a typical composite material manufacturing technology, the liquid composite molding technology has the advantages of low manufacturing cost, high dimensional accuracy, and easy automation. However, some defects may occur during its manufacturing process, such as air bubbles and dry spots. These defects are mainly generated during the process of resin impregnating the fiber preform. At present, the numerical simulation research on resin flow at home and abroad mainly focuses on the macroscopic scale, but the process defects are mainly the concentrated manifestation of micro- and mesoscopic scale problems at the macroscopic scale.

[0003] With the rapid development of computer and numerical simulation technologies, the concept and method of using numerical methods to simulate and predict experiments to improve experimental design have been increasingly valued by people. On the one hand, it can greatly reduce the time and cost of experiments, thereby reducing the cycle and cost of material development; more importantly, it can deeply study the mechanism of defect generation. Summary of the Invention

[0004] In order to understand the resin flow impregnation process and thus guide the design of the intelligent composite material forming process, the present invention proposes a numerical simulation method for simulating resin flow in the forming process of an intelligent composite material with embedded optical fibers.

[0005] The present invention is implemented through the following technical solutions:

[0006] A numerical simulation method for resin flow in the forming process of an intelligent composite material for simulating embedded optical fibers, comprising:

[0007] (1) Construct a fiber bundle model composed of random fibers

[0008] To construct the fiber bundle model, it is first necessary to determine the major and minor axis lengths of the fiber bundle model and the fiber volume fraction of the fiber bundle. These data are obtained through experimental observation and testing; they can also be artificially set, so as to perform parameter analysis and optimization design on the material. The process of generating a random fiber distribution structure using the Monte Carlo method is as follows: First, determine the fiber generation area size, fiber filament radius, and fiber volume fraction, and then sequentially generate the central point coordinates of the fiber filaments within the fiber area. If fiber crossing occurs, regenerate until the fiber volume fraction reaches the expected value and then stop the loop. The algorithm flow chart is as Figure 1 shown.

[0009] (2) Establish a mesoscopic model of the intelligent composite material after embedding the optical fiber

[0010] Considering the influence of optical fibers at different positions on resin flow, embed optical fibers inside or outside the fiber bundle, and determine the fiber radius and the specific position of the optical fiber relative to the fiber bundle. In addition, the influence of optical fibers of different sizes on resin flow can be considered. To simplify the model and improve the calculation efficiency, the fiber filaments and optical fibers are simplified as holes to shorten the calculation time.

[0011] (3) Establish a resin flow control equation in the finite element model

[0012] For the resin flow at the microscale, based on the characteristic that the entire flow region conforms to laminar flow, the tracking of the flow front adopts the phase-field method and obeys the Cahn-Hilliard equation.

[0013] Introduce the Darcy term into the Stokes equation to establish a unified equation for the external flow of the fiber bundle and the seepage flow inside the fiber bundle:

[0014]

[0015] In the formula, μ is the fluid viscosity, P is the pressure, ε is the volume fraction of the porous medium; I is the unit matrix, K is the permeability tensor of the fiber filament bundle; F is the volume force.

[0016] Combining formula (1) with the continuity equation (2) can obtain the velocity field distribution.

[0017]

[0018] For the resin flow at the microscale, based on the characteristic that the entire flow region conforms to laminar flow, the tracking of the flow front adopts the Phase-field method, which obeys the Cahn-Hilliard equation and Equation (4).

[0019]

[0020] In the formula: φ is the phase-field variable; ψ is the transition variable; λ is the mixed energy density; γ and τ are respectively the parameters related to the interface thickness. The surface tension F in the phase-field method st is expressed as:

[0021]

[0022] where G is the chemical potential; is the free energy term.

[0023] (4) Apply loads to the finite element model and submit for analysis

[0024] To simulate the resin flow in the basin, a constant pressure is applied at the basin inlet until the resin completely flows through the entire basin. The upper and lower boundaries of the basin are non-flowable boundaries. The resin flows in from the inlet under the action of pressure, successively flows through the optical fiber and the fiber bundle, and flows out from the outlet. Submit the calculation in the finite element software to simulate the complete resin flow process in the basin.

[0025] (5) Check the analysis results to reveal the wetting situation when the resin flows through the fiber bundle

[0026] After the calculation is completed, by observing the process of the resin flowing and impregnating the fiber bundle under the action of the load, including the resin flow near the optical fiber and the fiber bundle, reveal the mechanism of the resin flow impregnation process.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows: Based on the Phase-field method, the present invention simulates the complete process of the resin flowing from the inlet through the fiber bundle to the outlet under the action of pressure, reveals the influence of the embedded optical fiber on the resin flow process in the intelligent composite material forming process, and has important guiding significance for understanding the resin impregnation preform process and optimizing process parameters to reduce forming defects. Description of the Drawings

[0028] Figure 1 is the flow chart of the Monte Carlo method;

[0029] Figure 2 is the pressure diagram of the flow field without optical fiber;

[0030] Figure 3 is the velocity diagram of the flow field without optical fiber;

[0031] Figure 4 It is the velocity distribution at the center position of the fiber bundle without optical fiber;

[0032] Figure 5 It is the pressure diagram of the flow field when the optical fiber is located inside the fiber bundle;

[0033] Figure 6 It is the velocity diagram of the flow field when the optical fiber is located inside the fiber bundle;

[0034] Figure 7 It is the velocity distribution near the optical fiber when the optical fiber is located inside the fiber bundle;

[0035] Figure 8 It is the pressure diagram of the flow field when the optical fiber is located on the left side of the fiber bundle;

[0036] Figure 9 It is the velocity diagram of the flow field when the optical fiber is located on the left side of the fiber bundle. Specific implementation mode

[0037] The following further describes the specific implementation mode of the present invention in combination with the attached drawings and technical solutions.

[0038] Example 1 (without optical fiber):

[0039] Randomly arranged fiber filaments are generated in the elliptical region through the Monte Carlo random algorithm, where the major semi-axis of the elliptical fiber bundle is 0.4 mm, the minor semi-axis is 0.1 mm, the radius of the fiber filament is 3.5 μm, the number of fiber filaments is 1200, and the inlet pressure is set to 0.5 MPa.

[0040] The calculated pressure distribution of the flow field is as shown in Figure 2 , the resin velocity distribution is as shown in Figure 3 , and the velocity distribution inside the fiber bundle is as shown in Figure 4 . It can be seen from the result diagram that due to the relatively narrow flow channel inside the fiber bundle and the obstruction of the fiber filaments to the resin, the resin flows slowly inside the fiber bundle and fast outside the fiber bundle.

[0041] Example 2 (embedding an optical fiber inside the fiber bundle):

[0042] Embed the optical fiber into the center position of the fiber bundle, with the radius of the optical fiber being 80 μm, and apply a constant pressure of 0.5 MPa at the inlet of the flow domain. Through calculation, the pressure distribution of the flow field can be obtained as shown in Figure 5 , and the velocity cloud diagram of the resin as shown in Figure 6 , and the velocity cloud diagram of the local area near the optical fiber as shown in Figure 7 . Comparing with the velocity cloud diagram at the center position of the fiber bundle without embedding the optical fiber, the resin velocity distribution in the flow domain near the optical fiber has changed significantly, indicating that embedding the optical fiber inside the fiber bundle has a certain impact on the microscopic-scale flow infiltration process of the resin.

[0043] Example 3 (Embedding optical fibers outside the fiber bundle):

[0044] Optical fibers are embedded outside the fiber bundle. The sizes of the fiber bundle and the optical fibers are the same as those in the previous example, and the set inlet constant pressure is 0.5 MPa. The pressure of the flow field obtained by calculation is as Figure 8 , and the velocity contour of the resin is as Figure 9 . The high-speed area outside the fiber bundle increases, the resin flows faster outside the fiber bundle, and it is easier to form a wrap on the right side of the fiber bundle. Moreover, due to the obstruction of the resin flow by the optical fibers, the infiltration of the resin into the inside of the fiber bundle is also affected, resulting in more defects such as air bubbles being more likely to occur inside the fiber bundle.

Claims

1. A numerical simulation method for simulating resin flow in a molding process of an intelligent composite material with embedded optical fiber, characterized in that The following steps are involved: (1) Constructing a fiber bundle model composed of random fibers In order to construct a fiber bundle model, the length of the major and minor semi-axis of the fiber bundle model and the fiber volume fraction of the fiber bundle must be determined first; these data are obtained through experimental observation and testing; or they are set manually, so that parameter analysis and optimization design of the material can be performed; the process of generating a random fiber distribution structure using the Monte Carlo method is to first determine the size of the fiber generation area, the radius of the fiber single fiber, and the fiber volume fraction, and then generate the coordinates of the center point of the fiber single fiber in the fiber area in sequence. If there is a fiber crossing, it will be regenerated until the fiber volume fraction reaches the expected value and the cycle stops; (2) Establish a microscopic model to characterize the smart composite material after embedding optical fiber Consider the effect of optical fibers at different positions on the resin flow, embed optical fibers inside or outside the fiber bundle, and determine the fiber radius and the specific position of the optical fiber relative to the fiber bundle. In addition, consider the effect of optical fibers of different sizes on the resin flow. To simplify the model and improve calculation efficiency, simplify the fiber filaments and optical fibers into holes to shorten the calculation time. (3) Establishing resin flow control equations in the finite element model For the flow of resin at the microscopic scale, based on the laminar characteristics of the entire flow area, the flow front is tracked using the phase-field method, which obeys the Cahn-Hilliard equation. (4) Apply load to the finite element model and submit for analysis In order to simulate the flow of resin in the flow domain, a constant pressure is applied at the inlet of the flow domain until the resin completely flows through the entire flow domain. The upper and lower boundaries of the flow domain are non-flowable boundaries. Under the action of pressure, the resin flows in from the inlet, flows through the optical fiber and fiber bundle in turn, and flows out from the outlet. The calculation is submitted in the finite element software to simulate the complete flow process of the resin in the flow domain. (5) Review the analysis results to reveal the wetting of the resin as it flows through the fiber bundle After the calculation is completed, the mechanism of the resin flow and impregnation process is revealed by observing and studying the process of resin flow and impregnation of the fiber bundle under load, including the flow of resin in the optical fiber and near the fiber bundle.

2. The numerical simulation method for simulating resin flow in a molding process of an intelligent composite material with embedded optical fiber according to claim 1, further comprising: The process of establishing the resin flow control equation is as follows: The Darcy term is introduced into the Stokes equation to establish a unified equation for the flow outside the fiber bundle and the flow inside the fiber bundle: Where μ is the fluid viscosity, P is the pressure, ε is the volume fraction of the porous medium; I is the unit matrix, K is the permeability tensor of the fiber bundle; F is the volume force; Combining formula (1) with the continuity equation (2) will give the velocity field distribution; For the flow of resin at the microscopic scale, based on the laminar characteristics of the entire flow area, the flow front is tracked using the phase-field method, which obeys the Cahn-Hilliard equation and equation (4) Where: φ is the phase field variable; ψ is the transition variable; λ is the mixing energy density; γ and τ are the parameters related to the interface thickness; the surface tension F in the phase field method is st To: Where G is the chemical potential; is the free energy term.

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