A method and apparatus for determining the size of a debonded zone in a honeycomb sandwich structure after impact

Abstract

The application provides a method and device for determining the debonding size of a honeycomb sandwich structure after impact, the method comprising: completing an impact test of a test piece according to multiple impact energy levels; performing data fitting according to the least square method with the average value of the bearing capacity of the test piece, the average bearing capacity value at each energy level as the dependent variable, and the corresponding energy level data as the variable; and according to the data fitting result, if the correlation coefficient is greater than or equal to 0.95, the mechanical properties of the honeycomb sandwich structure material, the honeycomb height and the panel thickness are not changed before and after the impact, and the panel wrinkling critical stress σ qzcr is equal; when the panel working stress reaches the panel wrinkling critical stress, the panel buckles, at this time, the external load applied is the bearing capacity of the honeycomb sandwich structure; the wrinkling section bending moment M is valued for different impact energy values; and the debonding size corresponding to the impact energy is obtained according to the equal panel wrinkling critical stress.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of comprehensive strength design, and particularly relates to a method and device for determining the debonding area size of a honeycomb sandwich structure after impact. BACKGROUND

[0002] The bearing capacity of a honeycomb sandwich structure test piece is generally characterized by the panel wrinkling critical stress. In order to verify and correct the panel wrinkling critical stress calculation formula, a four-point bending test of a small test piece under impact load is one of the verification tests.

[0003] After the honeycomb sandwich structure bears the impact load, the panel and the honeycomb are prone to debonding. At present, there is no clear method for determining the debonding area size, but the debonding area size has a great influence on the bearing capacity of the structure. Therefore, how to determine the debonding area size is of great significance. SUMMARY

[0004] The purpose of the application is that the application can determine the debonding area size of the four-point bending test piece of the honeycomb sandwich structure after impact, and provide a basis for the bearing capacity analysis of the structure after impact.

[0005] In a first aspect, the application provides a method for determining the debonding area size of a honeycomb sandwich structure after impact, which comprises:

[0006] performing an impact test on the four-point bending test piece of the honeycomb sandwich structure according to multiple impact energy levels;

[0007] using the average value of the bearing capacity of the test piece and the average bearing capacity value at each energy level as the dependent variable, and using the corresponding energy level data as the variable, data fitting is performed according to the least square method;

[0008] According to the data fitting result, if the correlation coefficient is greater than or equal to 0.95, the mechanical properties of the honeycomb sandwich structure material, the honeycomb height and the panel thickness do not change before and after impact, and the panel wrinkling critical stress σ qzcr is the same according to the panel wrinkling allowable stress calculation method;

[0009] When the panel working stress reaches the panel wrinkling critical stress, the panel buckles, and at this time, the applied external load is the bearing capacity of the honeycomb sandwich structure;

[0010] The wrinkling cross-section bending moment M is valued, and the values of different impact energies are taken;

[0011] According to the equal panel wrinkling critical stress, the debonding size corresponding to the impact energy is obtained.

[0012] Preferably, before the impact test on the four-point bending test piece of the honeycomb sandwich structure according to multiple impact energy levels, the method further comprises:

[0013] Determine the honeycomb sandwich structure test piece and the average value of the test piece bearing capacity.

[0014] Preferably, the honeycomb sandwich structure test piece is determined, comprising:

[0015] The test piece length is a, the width is b, the test area length is d, the area boundary is arc-shaped, the arc radius is R, and the minimum distance of the test area in the width direction is c.

[0016] Preferably, the average value of the test piece bearing capacity is determined, comprising:

[0017] The number of un-impacted intact test pieces is n1, n1≥5, and the corresponding bearing capacity values are x1, x2, x3…x n , and the average value is

[0018] Preferably, the panel working stress calculation formula is

[0019]

[0020] In the formula, M is the bending moment of the wrinkled profile, h is the honeycomb height, E is the panel elastic modulus, f is the wrinkled profile width, the un-impacted profile is c, the impacted profile is c-e, and e is the assumed debonding area size in the width direction.

[0021] Preferably, the test piece impact test is completed according to the 6-level impact energy, and the number of test pieces required for each impact energy is greater than or equal to 5, comprising:

[0022] The un-impacted test piece is considered as an impacted test piece with an impact energy of 0, and the energy level is the 0th level.

[0023] Preferably, the impact position is located at the center position of the test piece, and the number of test pieces required for each impact energy is greater than or equal to 5.

[0024] In the second aspect, the application also provides a device for determining the debonding area size of the honeycomb sandwich structure after impact, comprising:

[0025] The impact module is used to complete the impact test of the honeycomb sandwich structure four-point bending test piece according to the multi-level impact energy;

[0026] The fitting module is used to perform data fitting according to the least square method with the average value of the test piece bearing capacity, the average bearing capacity value under each energy level as the dependent variable, and the corresponding energy level data as the variable;

[0027] The processing module is configured to, according to a data fitting result, if a correlation coefficient is greater than or equal to 0.95, the mechanical properties of the honeycomb sandwich structure material, the honeycomb height and the panel thickness do not change before and after the impact, and according to a panel wrinkling allowable stress calculation method, a panel wrinkling critical stress σ qzcr is the same as before the impact.

[0028] The processing module is further configured to, when the panel working stress reaches the panel wrinkling critical stress, the panel buckles, and the external load applied at this time is the load bearing capacity of the honeycomb sandwich structure.

[0029] The processing module is further configured to, when the panel working stress reaches the panel wrinkling critical stress, the panel buckles, and the external load applied at this time is the load bearing capacity of the honeycomb sandwich structure.

[0030] The determining module is configured to obtain the debonding size corresponding to the impact energy according to the panel wrinkling critical stress.

[0031] The beneficial technical effects of the present application are as follows:

[0032] The method provided by the present application is applied to the analysis of the load bearing capacity of a helicopter honeycomb sandwich structure after the impact, effectively controls the design risk, and brings great economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 The debonding size of the test piece provided by the embodiment of the present application is shown in the figure.

[0034] Figure 2 The impact of the test piece provided by the embodiment of the present application is shown in the figure. DETAILED DESCRIPTION

[0035] It should be noted that the composite material structure, especially the honeycomb sandwich structure, has the characteristics of poor impact resistance. At present, the honeycomb sandwich structure is used in the whole machine structure with a high proportion. In the field, it is difficult to discover and handle the structure debonding caused by accidental impact damage in the first time, but the debonding has caused the decrease of the load bearing capacity of the structure. Since the debonding size is related to the load bearing capacity, the debonding size that may occur in the field is determined in the structure design, and then the decrease ratio of the load bearing capacity is analyzed to eliminate the hidden danger in the field.

[0036] Therefore, it is of great practical value to determine the debonding size of the honeycomb sandwich structure. The core idea of the present application is that, after the impact, although the honeycomb sandwich structure has a debonding area, the panel wrinkling critical stress representing the load bearing capacity of the honeycomb sandwich structure does not change. Based on this, the debonding size of the test piece is obtained by analyzing the load bearing capacity of the test piece before and after the impact.

[0037] Please refer to Figures 1-2 , the specific steps are as follows:

[0038] Step 1, the honeycomb sandwich structure test piece is shown in the attached Figure 1 , wherein the test piece length is a, the width is b, the evaluation area length is d, the area boundary is arc-shaped, the arc radius is R, and the minimum distance of the evaluation area in the width direction is c;

[0039] Step 2, the number of un-impacted intact test pieces is n1 (n1≥5), and the corresponding bearing capacity values are x1, x2, x3…x n , and the average value is , that is

[0040] Step 3, the test piece impact test is completed according to the 6th impact energy, and the number of test pieces required for each impact energy is greater than or equal to 5. The impact position is located at the center of the test piece, as shown in the attached Figure 2 .

[0041] The test pieces are arranged from small to large according to the impact energy, and the test pieces corresponding to different energies are shown in the table below. After impact at each corresponding impact energy, the bearing capacity test is performed, and after the test is completed, new un-impacted test pieces are selected to carry out the impact test of the next level of impact energy, and then the bearing capacity test is performed. The corresponding bearing capacity of each level of impact energy is shown in Table 1, and the corresponding values of the test pieces are shown in Table 1.

[0042] Table 1

[0043]

[0044] Step 4, the un-impacted test pieces in step 2 are considered as impacted test pieces with impact energy of 0, and the energy level is the 0th level;

[0045] Step 5, according to the corresponding average bearing capacity values in steps 2, 3, and 4 as the dependent variable, and the corresponding energy level data as the variable, data fitting is performed according to the least squares method;

[0046] Step 6, according to the data fitting results of step 5, if the correlation coefficient is greater than or equal to 0.95, the subsequent steps can continue, otherwise the method cannot be applied;

[0047] Step 7, the mechanical properties of the un-impacted and impacted honeycomb sandwich structure materials, the honeycomb height, and the panel thickness do not change, and the panel wrinkling critical stress σ qzcr is the same according to the panel wrinkling allowable stress calculation method.

[0048] Step 8, when the panel working stress reaches the panel wrinkling critical stress, the panel buckles, and the external load applied at this time is the bearing capacity of the honeycomb sandwich structure;

[0049] Step 9, the panel working stress calculation formula is

[0050] In the formula, M is the bending moment of the profile subjected to wrinkling (appendix Figure 1 The middle distance is c profile); h is the honeycomb height; E is the panel elastic modulus; f is the wrinkling profile width (the profile not subjected to impact is c, the profile subjected to impact is c-e, e is the assumed debonding area size along the width direction);

[0051] Step 10, the wrinkling profile bending moment M value, for different impact energy values are shown in Table 2, the wrinkling profile bending moment values corresponding to different impact energies.

[0052] Table 2

[0053]

[0054]

[0055] Step 10, taking the non-impacted, first-level impact energy test piece as an example, according to the wrinkling critical stress equivalence, the following can be obtained:

[0056]

[0057] Wherein, e1 is the debonding size corresponding to the first-level impact energy.

[0058] From the above formula, the following can be obtained:

[0059]

[0060] Step 11, according to the processing method of step 10, the debonding size corresponding to the gth-level (g≤6) impact energy is e f , and the corresponding average bearing capacity is The calculation formula is:

[0061]

[0062] From the above formula, the following can be obtained:

[0063]

[0064] Step 12, according to formula (4), the honeycomb debonding area size under the corresponding impact energy can be determined.

[0065] The present application is based on the bearing capacity of the test pieces subjected to impact and not subjected to impact, and the corresponding size of the debonding area is obtained by analysis and processing. Since the debonding area size is related to the bearing capacity, the corresponding bearing capacity reduction factor under the non-impact state can be obtained through the size.

[0066] Therefore, the application has important practical value. Whether the damage tolerance analysis of the size of the debonding area is considered in the design stage or the reduction analysis of the carrying capacity after the debonding area is obtained according to the corresponding impact energy when the external field problem is handled, the design and use risks can be reduced through the determination of the size of the debonding area.

Claims

1. A method of determining the size of a debond zone in a honeycomb sandwich structure after impact, characterized by, The method comprises: The impact test of the four-point bending test piece of the honeycomb sandwich structure is completed according to multi-level impact energy; The data fitting is performed according to the least square method, with the average bearing capacity of the test piece and the average bearing capacity value at each energy level as the dependent variables, and with the corresponding energy level data as the variables; According to the data fitting results, the correlation coefficient , the mechanical properties of the honeycomb sandwich structure material, the honeycomb height, and the panel thickness did not change before and after the impact, and according to the panel wrinkling allowable stress calculation method, the panel wrinkling critical stress was the same. When the working stress of the panel reaches the panel wrinkling critical stress, the panel buckles, and at this time, the external load applied is the bearing capacity of the honeycomb sandwich structure; The wrinkling profile bending moment M is valued, and the values are different for different impact energies; According to the equality of the panel wrinkling critical stress, the debonding size corresponding to the impact energy is obtained.

2. The method of claim 1, wherein, Before the impact test of the four-point bending test piece of the honeycomb sandwich structure is completed according to multi-level impact energy, the method further comprises: Determine the honeycomb sandwich structure test piece and the average bearing capacity of the test piece.

3. The method of claim 2, wherein, The determination of the honeycomb sandwich structure test piece comprises: Determine the length a of the test piece, the width b, and the length d of the test area, the boundary of the test area is arc-shaped, the arc radius is R, and the minimum distance c of the test area in the width direction.

4. The method of claim 3, wherein, Determine the average bearing capacity of the test piece, comprising: The number of non-impacted intact test pieces is 4 , The corresponding bearing capacity value is 1.5 , and the average value is 1.5 .

5. The method of claim 4, wherein, The panel working stress calculation formula is In the formula, M is the bending moment of the wrinkling profile; h is the honeycomb height; E is the elastic modulus of the panel; f is the wrinkling profile width, the unimpacted profile is c, the impacted profile is c-e, and e is the assumed debonding size in the width direction.

6. The method of claim 5, wherein, The test piece impact test is completed according to 6 levels of impact energy, and the number of test pieces required for each impact energy is greater than or equal to 5, comprising: The unimpacted test piece is considered as an impacted test piece with an impact energy of 0, and the energy level is the 0th level.

7. The method of claim 1, wherein, The impact position is located at the center of the test piece, and the number of test pieces required for each impact energy is greater than or equal to 5.

8. An apparatus for determining the size of a debonded zone of a honeycomb sandwich structure after impact, comprising: The device comprises: An impact module for completing the impact test of the four-point bending test piece of the honeycomb sandwich structure according to multi-level impact energy; A fitting module for performing data fitting according to the least square method, with the average bearing capacity of the test piece and the average bearing capacity value at each energy level as the dependent variables, and with the corresponding energy level data as the variables; The processing module is configured to determine, according to a result of data fitting being performed, whether a correlation coefficient The mechanical properties, the honeycomb height and the panel thickness of the honeycomb sandwich structure material before and after the impact do not change, and the panel wrinkling critical stress is the same according to a panel wrinkling allowable stress calculation method. The processing module is further configured to determine the bearing capacity of the honeycomb sandwich structure when the working stress of the panel reaches the panel wrinkling critical stress, and the panel buckles; The processing module is further configured to value the wrinkling profile bending moment M, and the values are different for different impact energies; A determination module for obtaining the debonding size corresponding to the impact energy according to the equality of the panel wrinkling critical stress.

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