A method for optimizing a continuous fiber-reinforced composite patch based on a crack propagation path

Abstract

The application discloses a kind of continuous fiber reinforced composite patch optimization method based on crack propagation path, specifically for: calculate and extract the stress tensor of patch along crack propagation path;According to the stress component extracted, the crack expansion principal stress is calculated;Then according to the principal stress value, the principal stress value distribution curve along the crack propagation path is established;Combined with the principal stress distribution curve, the displacement vector field for regulating and controlling the distribution density of continuous fiber is constructed, and the fiber is moved according to the vector field, and the principal stress direction on the crack propagation path is calculated again, and on this basis, the fiber distribution direction is optimized, so that all the fibers on the crack propagation path are arranged parallel to the principal stress direction;Finally, the corner is smoothly transitioned;And using 3D printing technology, the patch is prepared, and the aircraft crack is repaired.The application combines 3D printing technology, optimizes and improves the traditional composite patch structure, and further improves the strength of the aircraft repair structure.

Description

Technical Field

[0001] This invention belongs to the field of aircraft maintenance technology. Background Technology

[0002] With the rapid development of the aerospace industry, the upgrading of aircraft maintenance technology has become a challenge. Currently, the maintenance of metal structural components of aircraft still mainly relies on metal patches, but this process significantly increases the weight of the aircraft, affecting payload, thrust-to-weight ratio, and economic costs. Therefore, using composite materials to replace metal patches has become a trend. However, currently, laminated plate structures are still used for composite patches in maintenance. This approach does not fully utilize the mechanical properties of composite materials and lacks customized design for crack propagation paths and main load-bearing directions. Summary of the Invention

[0003] Purpose of the invention: In order to solve the problems existing in the prior art, the present invention provides an optimization method for continuous fiber reinforced composite material patches based on crack propagation path.

[0004] Technical solution: This invention provides an optimization method for continuous fiber reinforced composite material patches based on crack propagation paths, characterized by the following specific methods:

[0005] Step 1: Extract the stress tensor of the composite material repair structure along the crack propagation path;

[0006] Step 2: Based on the stress tensor from Step 1, calculate the principal stress values ​​of the composite material patch and establish the principal stress distribution curve f(x,y) along the crack propagation path;

[0007] Step 3: Calculate the mean value of the principal stress distribution curve and introduce a coefficient 'a' into the mean value to obtain the function ave; establish a three-dimensional rectangular coordinate system, with the xy plane as the plane where the crack is located and the z-axis used to represent the principal stress value; project the principal stress distribution curve onto the yz plane and plot the function ave on the yz plane; set the fiber adjustment range in the composite material patch based on the intersection points of the principal stress distribution curve on the yz plane and the function ave on the yz plane, and uniformly arrange the fibers in each adjustment range;

[0008] Extract the centroid x-coordinate of the graph formed by the principal stress distribution curve in the yz plane and the i-th control interval; and denote it as y i0 According to the distance D between the j-th fiber of the i-th control interval and the centroid of the i-th control interval. ij Establish the displacement equation of the j-th fiber in the i-th control interval; control the distribution density of the fiber based on the fiber displacement equation;

[0009] Step 4: Calculate the principal stress direction of the composite patch and optimize the fiber layout so that the fibers are arranged parallel to the principal stress trace of the composite patch;

[0010] Step 5: Optimize the fiber layout at the mid-angle of the composite patch to ensure a smooth transition of fibers at the angle;

[0011] Step 6: Use 3D printing technology to prepare composite material patches.

[0012] Furthermore, step 1 specifically involves: firstly extracting the discrete coordinate points (x, y) of the crack surface, then generating a continuous curve on the composite material patch based on the position information, and using a post-processing method to extract the stress tensor on the entire curve.

[0013] Furthermore, the principal stress distribution curve f(x,y) in step 2 is shown below:

[0014]

[0015] In the formula, (x,y) are the discrete coordinate points of the crack surface. These are the principal stress values ​​at each coordinate. It is stress parallel to the x-direction. It is the stress parallel to the y-direction. It is shear stress. It is the maximum value of the principal stress at all coordinates.

[0016] Furthermore, the expression for the function `ave` is as follows:

[0017]

[0018] Where k represents the total number of discrete point coordinates on the crack surface.

[0019] Furthermore, the method for setting the control interval is as follows: all intersection points between the function ave and the principal stress distribution curve projection of the yz plane are projected onto the y-axis to obtain several projection points with the z-axis being 0. The interval formed by two projection points is taken as the control interval to obtain several control intervals.

[0020] Furthermore, the displacement equation mov of the j-th fiber in the i-th control interval is... ij It is represented as follows:

[0021]

[0022] Among them, b ij To adjust the direction of fiber movement; y ij A represents the y-coordinate of the j-th fiber in the i-th interval.i Let c be the integral of the area of ​​the graph corresponding to the i-th control interval; c is the coefficient, n is the exponent, and e is the offset distance.

[0023] Furthermore, the principal stress directions of the composite material patch in step 4 are as follows;

[0024]

[0025] Where (x,y) are the crack coordinates. It is stress parallel to the x-direction. It is the stress parallel to the y-direction. It is shear stress.

[0026] Furthermore, in step 6: after 3D printing, a vacuum pump is used to create a vacuum, and an autoclave is used for external curing to cure the composite material patch.

[0027] Beneficial effects: Based on the stress characteristics of the patch at the crack location in the aircraft, this invention designs a continuous fiber-reinforced composite material patch based on the crack propagation path; high-strength design of the composite material patch is achieved by adjusting the fiber distribution density and arrangement direction; and additive manufacturing technology is used for fabrication, reducing the complexity of the fabrication process and simplifying the manufacturing process. This invention improves the mechanical properties of aircraft after repair, and the method disclosed in this invention is applicable to the repair of components in aircraft, automobiles, ships, and other similar applications. Attached Figure Description

[0028] Figure 1 This is a flowchart of the present invention.

[0029] Figure 2 This is a graph showing the distribution of principal stress values.

[0030] Figure 3 This is a control diagram of fiber distribution range.

[0031] Figure 4 Optimize and control the fiber distribution map.

[0032] Figure 5 Optimize the fiber arrangement direction design.

[0033] Figure 6 This is an optimized diagram for the angle. Detailed Implementation

[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 improper limitation of the invention.

[0035] like Figure 1As shown, this invention provides an optimization method for continuous fiber reinforced composite material patches based on crack propagation paths, the method comprising the following steps:

[0036] Step 1: The strength of the patch plays a decisive role in the mechanical properties of the aircraft after repair. By optimizing the design of the continuous fibers constituting the composite patch, the mechanical properties of the patch can be improved, greatly restoring the load-bearing capacity of the aircraft after repair. Therefore, this invention uses simulation methods to simulate the operating conditions of the repaired aircraft components; and calculates and extracts the stress tensor of the patch at the crack propagation path.

[0037] First, the discrete coordinate points (x, y) of the crack surface are extracted. Then, based on the position information, a continuous curve is generated on the patch, and the stress tensor on the entire curve is extracted using post-processing methods.

[0038] Step 2: Based on the extracted stress tensor, calculate the principal stress values ​​of the patch in the crack propagation path region, and establish the principal stress distribution curve, as shown in the figure. Figure 2 As shown,

[0039] The principal stress distribution curve f(x,y) is shown below:

[0040]

[0041] In the formula, (x,y) are the discrete coordinate points of the crack surface. These are the principal stress values ​​at each coordinate. It is stress parallel to the x-direction. It is the stress parallel to the y-direction. It is shear stress. It is the maximum value of the principal stress at all coordinates.

[0042] Step 3: Optimize the fiber distribution density based on the principal stress distribution curve, and fill more continuous fibers in areas with higher principal stress values.

[0043] Calculate the mean value of the principal stress distribution curves, and introduce a coefficient 'a' into the mean value to obtain the function ave:

[0044]

[0045] Where k represents the total number of discrete point coordinates on the crack surface.

[0046] Establish a three-dimensional rectangular coordinate system, with the xy plane representing the crack plane and the z-axis representing the principal stress values. Project the principal stress distribution curve onto the yz plane (a plane perpendicular to the fiber direction), and plot the function ave on the yz plane. Obtain the intersection points of the principal stress distribution curve on the yz plane and the function ave on the yz plane, such as... Figure 3As shown, all intersection points are projected onto the y-axis to obtain several projection points with the z-axis set to 0. The interval formed by two projection points is used as the control interval to obtain several control intervals.

[0047] Extract the centroid x-coordinate of the graph formed by the principal stress distribution curve in the yz plane and the i-th control interval; and denote it as y i0 The graphic is as follows Figure 3 As shown in the shaded area, the distance D between the j-th fiber of the i-th control interval and the centroid of the i-th control interval is... ij Establish the displacement equation for the j-th fiber in the i-th control interval; based on the fiber displacement equation, adjust the fiber distribution density to regulate the fiber distribution pattern, so that the region with larger principal stress values ​​contains more fiber bundles, such as... Figure 4 As stated above.

[0048] The displacement equation mov of the j-th fiber in the i-th control interval ij It is represented as follows:

[0049]

[0050] Among them, b ij To adjust the direction of fiber movement; y ij A represents the y-coordinate of the j-th fiber in the i-th interval. i Let c be the integral of the area of ​​the graph corresponding to the i-th control interval; c is the coefficient, n is the exponent, and e is the offset distance.

[0051] Step 4: As Figure 5 As shown, the principal stress direction is calculated, and the fiber layout is optimized to make it parallel to the principal stress trace.

[0052] The principal stress directions of the composite material patch are shown below;

[0053]

[0054] Where (x,y) are the crack coordinates. It is stress parallel to the x-direction. It is the stress parallel to the y-direction. It is shear stress.

[0055] Step 5: As Figure 6 As shown, the fiber layout method at the bend is optimized to ensure a smooth transition, improve process stability, and prevent stress concentration.

[0056] Step 6: Using the method designed in this invention, design the aircraft repair structure; then, combined with 3D printing technology, print high-strength patches, use a vacuum pump to evacuate the vacuum, and use an autoclave for external curing to cure the composite material patches.

[0057] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

Claims

1. An optimization method for continuous fiber-reinforced composite material patches based on crack propagation paths, characterized in that, Specifically, the methods include the following: Step 1: Extract the stress tensor of the composite material repair structure along the crack propagation path; Step 2: Based on the stress tensor from Step 1, calculate the principal stress values ​​of the composite material patch and establish a principal stress distribution curve along the crack propagation path. ; Step 3: Calculate the mean value of the principal stress distribution curves, and introduce a coefficient 'a' into the mean value to obtain the function. Establish a three-dimensional rectangular coordinate system, with the xy plane representing the plane where the crack is located and the z-axis representing the principal stress values. Project the principal stress distribution curve onto the yz plane and plot the function on the yz plane. Based on the principal stress distribution curves in the yz plane and the function of the yz plane. The intersection points are used to set the fiber control range in the composite material patch; the fibers are evenly distributed in each control range; Extract the centroid x-coordinate of the graph formed by the principal stress distribution curve in the yz plane and the i-th control interval; and denote it as y i0 According to the distance D between the j-th fiber of the i-th control interval and the centroid of the i-th control interval. ij Establish the displacement equation of the j-th fiber in the i-th control interval; control the distribution density of the fiber based on the fiber displacement equation; Step 4: Calculate the principal stress direction of the composite patch and optimize the fiber layout so that the fibers are arranged parallel to the principal stress trace of the composite patch; Step 5: Optimize the fiber layout at the mid-angle of the composite patch to ensure a smooth transition of fibers at the angle; Step 6: Fabricate composite material patches using 3D printing technology; The displacement equation of the j-th fiber in the i-th control interval It is represented as follows: ； Among them, b ij To adjust the direction of fiber movement; , A represents the y-coordinate of the j-th fiber in the i-th interval. i is the value obtained by integrating the area of ​​the graph corresponding to the i-th control interval; c is the coefficient, n is the exponent, and e is the offset distance.

2. The method for optimizing continuous fiber-reinforced composite material patches based on crack propagation paths according to claim 1, characterized in that, Step 1 specifically involves: firstly, extracting the discrete coordinate points of the crack surface. Then, based on the position information, a continuous curve is generated on the composite material patch, and the stress tensor on the entire curve is extracted using a post-processing method.

3. The method for optimizing continuous fiber-reinforced composite material patches based on crack propagation paths according to claim 1, characterized in that, The principal stress distribution curve in step 2 As shown below: ； In the formula, These are the discrete coordinate points of the crack surface. These are the principal stress values ​​at each coordinate. It is stress parallel to the x-direction. It is the stress parallel to the y-direction. It is shear stress. It is the maximum value of the principal stress at all coordinates.

4. The method for optimizing continuous fiber-reinforced composite material patches based on crack propagation paths according to claim 1, characterized in that, function The expression is as follows: ； Where k represents the total number of discrete point coordinates on the crack surface.

5. The method for optimizing continuous fiber-reinforced composite material patches based on crack propagation paths according to claim 1, characterized in that, The specific method for setting the control interval is as follows: [The function is then set to...] All intersection points between the projection of the principal stress distribution curves on the yz plane and the projection of the curves are projected onto the y-axis to obtain several projection points with the z-axis set to 0. The interval formed by two projection points is taken as the control interval to obtain several control intervals.

6. The method for optimizing continuous fiber-reinforced composite material patches based on crack propagation paths according to claim 1, characterized in that, The principal stress directions of the composite material patch in step 4 are shown below; ； in, These are crack coordinates. It is stress parallel to the x-direction. It is the stress parallel to the y-direction. It is shear stress.

7. The method for optimizing continuous fiber-reinforced composite material patches based on crack propagation paths according to claim 1, characterized in that, In step 6: after 3D printing, a vacuum pump is used to create a vacuum, and an autoclave is used for external curing to cure the composite material patch.

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