A composite honeycomb sandwich panel pallet nut mounting structure analysis method based on probability analysis

Abstract

The present application belongs to the field of composite honeycomb sandwich panel analysis, and relates to a composite honeycomb sandwich panel support plate nut mounting structure analysis method based on probability analysis. First, a distribution rate equation is determined according to the position deviation and distribution characteristics of the center line of the support plate nut main bolt relative to the center line of the fastener hole, the confidence interval of the panel structure is calculated, and the upper and lower limit positions of the support plate nut mounting are determined. It is assumed that the support plate nut is only installed at the upper limit or lower limit position, and a detailed finite element model is established for different installation conditions. According to the loading conditions of the upper and lower limit positions, the displacement of each support plate nut is corrected, the actual displacement is loaded, and the overall stability coefficient and the local peak stress and strain of the panel are obtained. In the most severe state, the strength of the structure is analyzed, the structural margin is obtained, and it is judged whether the target panel structure meets the design requirements. The present application introduces probability statistical analysis, considers various deviations, truly simulates the limit state, and ensures the safety of the structure design.

Description

Technical Field

[0001] This invention belongs to the field of composite honeycomb sandwich panel analysis, and relates to a method for analyzing the installation structure of the support plate nut of composite honeycomb sandwich panel based on probability analysis. Background Technology

[0002] Since composite honeycomb sandwich structures are often connected to the body structure using tray nuts, a typical tray nut structure is as follows: Figure 1 The movable nature of the pallet nut can lead to installation deviations, resulting in localized non-uniform load distribution on the structure. Current analyses of such structures often rely on uniform load distribution, leading to insufficiently conservative results and an inability to guarantee structural safety during service. Furthermore, the final position of the pallet nut is affected by factors such as installation deviations, fastener diameter deviations, drilling deviations, and the number of fasteners. Extensive testing is required to ensure structural safety, imposing significant resource costs on project implementation. Summary of the Invention

[0003] To address the aforementioned issues, this invention proposes a probabilistic analysis-based method for analyzing the installation structure of a composite honeycomb sandwich panel support plate nut. By introducing probabilistic statistical analysis, various deviations during the assembly process of the support plate nut can be considered simultaneously, providing various extreme position conditions. Furthermore, detailed finite element models are used to assist in the analysis, ensuring that the panel structure meets design requirements (i.e., a strength safety margin greater than 0) under various extreme conditions, thus achieving structural design safety. This method can also be applied to structural test planning, effectively reducing the number of test specimens and significantly lowering verification costs.

[0004] This invention is achieved through the following technical solution:

[0005] A probabilistic analysis-based method for analyzing the installation structure of a composite honeycomb sandwich panel support plate nut is proposed. This method uses probabilistic analysis of the assembly deviation between the centerline of the support plate nut main bolt and the centerline of the bolt hole to obtain the limiting distribution position of the main bolt during assembly. Finite element simulation is then used to obtain the critical strength margin of the panel structure, thereby optimizing the structure to ensure structural design safety. The analysis method includes the following steps:

[0006] Step 1: Perform physical measurement and analysis of the centerline positions of the main bolts of the support plate nuts installed in the target wall panel structure relative to the centerlines of the fastener holes. Obtain the positional deviation and distribution characteristics of the main bolt centerline relative to the centerline of the fastener holes, and determine the distribution rate equation it conforms to. Generally, the positional deviation conforms to a normal distribution, and the equation is as follows:

[0007]

[0008] In the formula, denoted by , where S represents the mean of the location deviation, n represents the number of location deviation samples, t represents the t-distribution characteristic value, and α represents the confidence level correction coefficient.

[0009] Step 2: Determine the required confidence level based on the importance of the target wall panel structure (the confidence level of the main load-bearing structure is selected as 99%, and the confidence level of the secondary structure is selected as 95%), calculate its confidence interval in combination with the distribution rate equation determined in Step 1, and determine the upper and lower limit positions of the main bolt of the support plate nut in the fastener hole based on the confidence interval.

[0010] Step 3: Take the critical case. Assume that the main bolt of the pallet nut in the middle of the target wall panel structure is installed at the upper limit of the confidence interval, and the other main bolts of the pallet nut are installed at the lower limit. Based on this installation case, establish a detailed finite element model, and apply differentiated displacements to the main bolts of the pallet nut at different installation positions to simulate the actual structural constraints and load conditions of each main bolt of the pallet nut. Based on the finite element solver, perform overall stability and static strength analysis to obtain the overall stability coefficient of the target wall panel and the local peak stress and strain of the wall panel under the current installation condition.

[0011] Specifically, assuming that the main bolts of the pallet nut are only located at the upper and lower limits, we first assume that one main bolt of the pallet nut in the middle is located at the upper limit and the rest are located at the lower limit. Based on this installation situation, we establish a detailed finite element model. Combining the influence of the load on the main bolts of the pallet nut at different installation positions on their displacement, we use the confidence interval obtained in step 2 to correct the actual displacement of each main bolt of the pallet nut. We then load the corrected actual displacement in the detailed finite element model and perform overall stability and static strength analysis to obtain the overall stability coefficient of the target wall panel and the local peak stress and strain of the wall panel under the current installation situation.

[0012] The correction method for the actual displacement is as follows: for the main bolt of the pallet nut located at the upper limit position, the upper deviation of the confidence interval is added based on the known average displacement, while for the main bolt of the pallet nut located at the lower limit position, the lower deviation of the confidence interval is reduced based on the known average displacement.

[0013] Step 4: Using the main bolt of the pallet nut installed at the upper limit position in Step 3 as the center, gradually increase the number of main bolts of the pallet nut installed at the upper limit position on both sides until all main bolts of the pallet nut are installed at the upper limit position. Based on each installation case, establish a detailed finite element model one by one, and use the same method as in Step 3 to solve for the overall stability coefficient of the target wall panel structure and the local peak stress and strain of the wall panel under different installation conditions.

[0014] Step 5: Based on the overall stability coefficient and local peak stress and strain of the target wall panel structure obtained in Steps 3 and 4, select the most severe state (minimum overall stability coefficient and maximum local peak stress and strain) to perform strength analysis on the structure and obtain the structural margin to determine whether the target wall panel structure meets the design requirements. The structural margin includes overall instability margin, local instability margin and structural static strength margin.

[0015] Specifically, if the strength analysis results show that the overall instability margin, local instability margin, and static strength margin of the target wall panel are all greater than 0, then the structure meets the design requirements; otherwise, the structure needs to be optimized until all structural margins are greater than 0.

[0016] The beneficial effects of this invention are as follows:

[0017] This invention obtains the limit distribution position of the main bolt of the nut during the assembly process by probabilistic analysis of the assembly deviation between the center line of the main bolt of the pallet nut and the center line of the bolt hole. The critical strength margin of the structure is obtained through finite element simulation, and then the structure is optimized to ensure the safety of the structural design. At the same time, this method can also be applied to structural test planning, effectively reducing the number of test specimens and greatly reducing the verification cost. Attached Figure Description

[0018] Figure 1 A schematic diagram of a typical pallet nut structure, where (a) is the front view and (b) is the side view.

[0019] Figure 2 Typical composite honeycomb sandwich panel support plate and nut installation structure.

[0020] Figure 3 Diagram showing the relative positions of the fastener and the fastener hole when installing the plate nut.

[0021] Figure 4 Comparison of critical coefficients for overall structural instability at different bolt installation positions.

[0022] Figure 5 Comparison of local peak strain in structures with different bolt installation positions.

[0023] Figure 6 Comparison of local peak stress in structures with different bolt installation positions. Detailed Implementation

[0024] The technical solution of the present invention will now be clearly and completely described. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments. All other embodiments derived by those skilled in the art based on the embodiments of the present invention through modifications or adjustments are within the protection scope of the present invention.

[0025] Example:

[0026] It is known that a certain composite honeycomb wall panel is assembled along its long side using 12 support nuts, see... Figure 2 The main bolt diameter of the support plate nut is 5.08mm, the mounting hole diameter is 6.86mm, and the main bolt spacing is 50mm. The analysis method for the installation structure of the support plate nut for this wall panel includes the following steps:

[0027] Step 1: Randomly select 9 pallet nuts and measure and collect the positional deviations of the main bolt centerline of each pallet nut relative to the fastener hole centerline. The data are 0.089mm, 0.065mm, -0.088mm, -0.068mm, 0.046mm, -0.043mm, -0.022mm, 0.020mm, and 0.010mm, respectively. The positional accuracy of the main bolt of the pallet nut generally conforms to a normal distribution; therefore, a distribution equation is introduced:

[0028]

[0029] In the formula, denoted by , where S represents the mean of the location deviation, n represents the number of location deviation samples, t represents the t-distribution characteristic value, and α represents the confidence level correction coefficient.

[0030] Step 2: Since this type of structure is a secondary structure, a confidence level of 95% is chosen. Therefore:

[0031] α / 2 = 0.025

[0032] t 0.025 (n-1)=t 0.025 (9-1)=2.3060

[0033] Simultaneously, based on the position deviation data obtained in step 1, the mean position deviation and the variance of the position deviation are calculated respectively:

[0034]

[0035] S = 0.089 2 +0.065 2 +(-0.088) 2 +(-0.068) 2 +0.046 2 +(-0.043) 2 +(-0.022) 2 +0.020 2 +0.010 2 =0.0295. Based on the distribution equation in step 1, the confidence interval is (-0.022 mm, 0.024 mm):

[0036]

[0037] Furthermore, the upper and lower limit positions for the installation of the main bolt of the pallet nut are obtained, corresponding to... Figure 3 Fastener position A and fastener position B.

[0038] Step 3: Conservatively assuming that the main bolt of the pallet nut is located only at fastener position A or fastener position B, in this embodiment, we first assume that the main bolt of the pallet nut is located in the middle (i.e., Figure 2 Fastener 6) is located at fastener position A, and the remaining main bolts of the pallet nut are located at fastener position B. Because the load conditions of the main bolts of the pallet nut differ at different installation positions, the actual load conditions of each main bolt of the pallet nut are simulated. It is known that under typical compression conditions, the average displacement generated by the compression edge of the wall panel is 0.327 mm. Combining the confidence interval (-0.022 mm, 0.024 mm) obtained in step 2, the actual displacements of the main bolts of the pallet nut at different positions are corrected. Specifically, the main bolt of the pallet nut located at fastener position A participates in the load earlier due to its higher installation position. The total displacement of the wall panel compression edge area affected by this main bolt needs to be increased by the upper deviation of the confidence interval based on the average displacement. Conversely, the main bolt of the pallet nut located at fastener position B participates in the load later due to its lower installation position. The total displacement of the wall panel compression edge area affected by this main bolt needs to be reduced by the lower deviation of the confidence interval based on the average displacement. After correction, the actual displacements of the main bolts of the pallet nut located at fastener positions A and B are as follows:

[0039] D A =0.327 + 0.024 = 0.351

[0040] D B =0.327 - 0.022 = 0.305

[0041] Based on this installation condition, a detailed finite element model was established, and the corrected actual displacement was loaded. The overall stability and static strength of the structure were analyzed using a finite element solver to obtain the overall stability coefficient of the wall panel and the local peak stress and strain of the wall panel under this installation condition.

[0042] Step 4: Centered on fastener 6, gradually increase the number of main bolts for the plate nut located at fastener position A on both sides. Use the same method as in Step 3 to correct the actual displacement of the main bolts for the plate nut at different positions in each installation case. Establish a detailed finite element model for each installation case and load the corresponding actual displacement to obtain the overall stability coefficient of the wall panel and the local peak stress and strain state of the wall panel under different installation cases. See... Figures 4 to 6 .

[0043] Step 5: Select the overall stability coefficient of the wall panel and the local peak stress and strain of the wall panel under the most severe condition, and perform a strength analysis on the structure to obtain the structural margins, including the overall instability margin, the local instability margin, and the static strength margin of the structure. Specifically:

[0044] based on Figure 4 It can be seen that the overall stability coefficient of the wall panel structure first decreases and then increases with the increase of the number of main bolts of the support plate nut at fastener position A. It drops to the lowest value of 1.02 when the number reaches 6. Therefore, the overall instability margin of the structure is 0.02, which is greater than zero, and meets the structural design requirements.

[0045] based on Figure 5 It can be seen that the maximum compressive strain of the structure (corresponding to the local peak strain state of the wall panel) first decreases and then increases with the increase of the number of main bolts of the bracket nut at fastener position A, and reaches the lowest point of -3500μ when the number reaches 4. Given that the allowable compressive strain of the structure is -3300μ, the local compressive margin of the structure in the static strength margin is:

[0046]

[0047] The local compression margin of the structure is -0.06, which is less than zero and does not meet the requirements, so local structural optimization is required.

[0048] based on Figure 6 It can be seen that the maximum compressive stress of the structure (corresponding to the local peak stress state of the wall panel) first decreases and then increases with the increase of the number of main bolts of the support plate nut at fastener position A, and reaches its lowest point of -110MPa when the number reaches 4 or 5. The allowable compressive stress is calculated to be -95MPa according to the inter-lattice buckling formula. Then, the inter-lattice buckling margin in the local instability margin is calculated according to the inter-lattice buckling formula for honeycomb panels.

[0049]

[0050] The inter-lattice buckling margin is -0.14, which is less than zero and does not meet the requirements, so structural optimization is needed.

[0051] The above-described embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A method for analyzing the installation structure of a composite honeycomb sandwich panel support plate nut based on probabilistic analysis, characterized in that, The analytical method includes the following steps: Step 1: Perform physical measurement and analysis on the position of the center line of the main bolt of the bracket nut installed in the target wall panel structure and the position of the center line of the fastener hole to obtain the positional deviation and distribution characteristics of the center line of the main bolt of the bracket nut relative to the center line of the fastener hole, and determine the distribution rate equation that it conforms to. Step 2: Determine the required confidence level based on the importance of the target wall panel structure, calculate its confidence interval using the distribution rate equation determined in Step 1, and determine the upper and lower limit positions of the main bolt of the support plate nut in the fastener hole based on the confidence interval; Step 3: Assume that the main bolt of the pallet nut in the middle of the target wall panel structure is installed at the upper limit of the confidence interval, and the other main bolts of the pallet nut are installed at the lower limit. Based on this installation, a detailed finite element model is established, and differential displacements are applied to the main bolts of the pallet nut at different installation positions to simulate the actual structural constraints and load conditions of each main bolt of the pallet nut. Based on the finite element solver, the overall stability and static strength analysis of the structure are performed to obtain the overall stability coefficient of the target wall panel and the local peak stress and strain of the wall panel under the current installation condition. Step 4: Taking the main bolt of the pallet nut installed at the upper limit position in Step 3 as the center, gradually increase the number of main bolts of the pallet nut installed at the upper limit position to both sides until all the main bolts of the pallet nut are installed at the upper limit position; based on each installation case, establish a detailed finite element model one by one, and use the same method in Step 3 to solve for the overall stability coefficient of the target wall panel structure and the local peak stress and strain of the wall panel under different installation conditions. Step 5: Based on the overall stability coefficient of the target wall panel structure and the local peak stress and strain of the wall panel obtained in Steps 3 and 4, select the most severe state and perform a strength analysis on the structure to obtain the structural margin, so as to determine whether the target wall panel structure meets the design requirements.

2. The method for analyzing the installation structure of a composite honeycomb sandwich panel support plate nut based on probabilistic analysis according to claim 1, characterized in that, In step 1, the positional deviation follows a normal distribution, and the distribution equation is as follows: In the formula, X represents the mean of the positional deviation, S represents the variance of the positional deviation, n represents the number of positional deviation samples, t represents the t-distribution characteristic value, and α represents the confidence level correction coefficient.

3. The method for analyzing the installation structure of a composite honeycomb sandwich panel support plate nut based on probabilistic analysis according to claim 1, characterized in that, Step 3 specifically involves assuming that the main bolts of the pallet nut are only located at the upper and lower limits. First, it is assumed that one main bolt of the pallet nut in the middle is located at the upper limit, and the remaining main bolts of the pallet nut are located at the lower limit. Based on this installation situation, a detailed finite element model is established. Combining the influence of the load on the main bolts of the pallet nut at different installation positions on their displacement, the actual displacement of each main bolt of the pallet nut is corrected using the confidence interval obtained in step 2. The corrected actual displacement is loaded into the detailed finite element model, and the overall stability and static strength analysis are performed to obtain the overall stability coefficient of the target wall panel and the local peak stress and strain of the wall panel under the current installation situation.

4. The method for analyzing the installation structure of a composite honeycomb sandwich panel support plate nut based on probabilistic analysis according to claim 3, characterized in that, The correction method for the actual displacement is as follows: for the main bolt of the pallet nut located at the upper limit position, the upper deviation of the confidence interval is added based on the known average displacement, while for the main bolt of the pallet nut located at the lower limit position, the lower deviation of the confidence interval is reduced based on the known average displacement.

5. The method for analyzing the installation structure of a composite honeycomb sandwich panel support plate nut based on probabilistic analysis according to claim 1, characterized in that, In step 5, the most severe state refers to the minimum overall stability coefficient and the maximum local peak stress and strain.

6. The method for analyzing the installation structure of a composite honeycomb sandwich panel support plate nut based on probabilistic analysis according to claim 1, characterized in that, In step 5, the structural margin includes the overall instability margin, the local instability margin, and the structural static strength margin.

7. The method for analyzing the installation structure of a composite honeycomb sandwich panel support plate nut based on probabilistic analysis according to claim 6, characterized in that, In step 5, the criterion for judging whether the target wall panel structure meets the design requirements is as follows: if the strength analysis results show that the overall instability margin, local instability margin, and static strength margin of the target wall panel are all greater than 0, then the structure meets the design requirements; otherwise, the structure needs to be optimized until all structural margins are greater than 0.

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