A method and device for treating shear wrinkling in a composite load-bearing honeycomb sandwich structure

Abstract

The application provides a honeycomb sandwich structure shear wrinkle processing method based on a composite load, comprising the following steps: classifying the honeycomb sandwich structure to obtain a panel of a metal material and a panel of a composite material; performing shear wrinkle instability processing on the panel of the metal material to obtain a first shear wrinkle critical stress; judging whether the structure meets the strength design requirement based on the first shear wrinkle critical stress; performing shear wrinkle instability processing on the panel of the composite material to obtain a second shear wrinkle critical stress; and judging whether the structure meets the strength design requirement based on the second shear wrinkle critical stress. Meanwhile, the application also provides a honeycomb sandwich structure shear wrinkle processing device based on a composite load. The application solves the shear wrinkle calculation problem of the honeycomb sandwich structure under the composite load by proposing a principal stress method.

Description

Technical Field

[0001] This application belongs to the field of comprehensive strength design technology, specifically relating to a method and apparatus for treating shear wrinkles in honeycomb sandwich structures under composite loads. Background Technology

[0002] Honeycomb sandwich structures are widely used in the aerospace field due to their excellent bending stiffness and weight advantages. Shear wrinkling in honeycomb sandwich structures, as a failure mode of local instability, has attracted considerable attention, and its algorithms have been a focus of research. This paper primarily provides calculation formulas for the upper panel under unidirectional compression and pure shear conditions, but does not offer corresponding methods for handling combined loads. Summary of the Invention

[0003] The purpose of this invention is to address the shear and wrinkling problem of honeycomb sandwich structures under composite loads, as honeycomb sandwich structures are generally subjected to composite loads. To expand the application range of this algorithm under composite loads, the principal stress method is proposed to solve the shear and wrinkling problem of honeycomb sandwich structures under composite loads.

[0004] In a first aspect, this application provides a method for shear wrinkling treatment of a honeycomb sandwich structure based on composite load, wherein the honeycomb sandwich structure includes an upper panel, a lower panel, and a honeycomb sandwich layer disposed between the upper panel and the lower panel; the method includes:

[0005] The honeycomb sandwich structure is classified into metal panels and composite material panels;

[0006] The metal panel is subjected to shearing and wrinkling instability treatment to obtain the first shearing and wrinkling critical stress. Based on the first shearing and wrinkling critical stress, it is determined whether the structure meets the strength design requirements.

[0007] The composite material panel is subjected to shear wrinkling instability treatment to obtain the second shear wrinkling critical stress. Based on the second shear wrinkling critical stress, it is determined whether the structure meets the strength design requirements.

[0008] Preferably, both the upper panel and the lower panel bear a combined load, the combined load including bearing an X-direction stress of σ. x The stress in the Y direction is σ y The shear load is τ xy .

[0009] Preferably, the step of determining whether the structure meets the strength design requirements based on the first shear wrinkle critical stress includes:

[0010] If the critical stress of the first shear wrinkle is greater than or equal to the first threshold, the strength design requirements are met.

[0011] If the critical stress of the first shear wrinkle is less than the first threshold, the strength design requirements are not met.

[0012] Preferably, the step of determining whether the structure meets the strength design requirements based on the second shear wrinkle critical stress includes:

[0013] If the critical stress of the second shear wrinkle is greater than or equal to the second threshold, the strength design requirements are met.

[0014] If the critical stress of the second shear wrinkle is less than the second threshold, the strength design requirements are not met.

[0015] Preferably, the first threshold is different from the second threshold.

[0016] Preferably, the treatment of the metal panel to induce shear wrinkling instability and obtain the first critical shear wrinkling stress includes:

[0017] Calculate the principal stress and maximum shear stress under the combined load of the inner and outer panels, and determine the elastic modulus in the direction of the principal stress and the direction of the maximum shear stress. Since the metal panel is an isotropic structure, the elastic modulus is equal in all directions. Calculate the critical shear stress under the principal stress state and the critical shear stress under the maximum shear stress state for the inner and outer panels respectively.

[0018] Preferably, the treatment of the composite material panel to induce shear wrinkling instability and obtain the second critical shear wrinkling stress includes:

[0019] Calculate the principal stress and maximum shear stress under the combined load of the inner and outer panels, and determine the elastic modulus in the directions of principal stress and maximum shear stress. Since the composite material panel is an orthotropic structure, the elastic modulus is different in each direction. Calculate the critical shear stress under the principal stress state and the critical shear stress under the maximum shear stress state for the inner and outer panels respectively.

[0020] Secondly, this application also provides a shearing and wrinkling treatment device based on a composite load honeycomb sandwich structure, wherein the honeycomb sandwich structure includes an upper panel, a lower panel, and a honeycomb sandwich layer disposed between the upper panel and the lower panel; the device includes:

[0021] The classification module is used to classify the honeycomb sandwich structure to obtain the panels made of metal materials and the panels made of composite materials;

[0022] The first processing module is used to process the shearing and wrinkling instability of the metal material panel, obtain the first shearing and wrinkling critical stress, and determine whether the structure meets the strength design requirements based on the first shearing and wrinkling critical stress.

[0023] The second processing module is used to treat the shear wrinkle instability of the composite material panel, obtain the second shear wrinkle critical stress, and determine whether the structure meets the strength design requirements based on the second shear wrinkle critical stress.

[0024] The beneficial technical effects of this application are as follows:

[0025] This invention provides methods for treating shear wrinkles in metal panels and composite material panels under combined loads. Based on principal stress and maximum shear stress, this method fully considers the stress state characteristics under combined loads, and comprehensively solves the calculation problem of shear wrinkles in honeycomb sandwich structure panels under combined loads.

[0026] This method has been widely used in strength design for shear wrinkling failure of helicopter cellular sandwich structures. By fully considering the influence of composite loads, it effectively controls design risks and improves the accuracy of analysis. Attached Figure Description

[0027] Figure 1 A schematic diagram of a honeycomb sandwich structure panel subjected to composite loads provided in an embodiment of this application;

[0028] Figure 2 This is a schematic diagram of shearing wrinkles provided in an embodiment of this application. Detailed Implementation

[0029] It should be noted that honeycomb sandwich structures have been widely used in airframe structures, and their usage ratio is even used as an important indicator of whether an aircraft design is advanced.

[0030] Shear wrinkling, as an important failure mode of honeycomb sandwich structures, has received widespread attention in structural design and strength analysis. However, the algorithms currently presented only consider the action of unidirectional loads and do not provide algorithms for shear wrinkling under combined loads. Since composite material panels are mainly subjected to combined loads, the above algorithms cannot solve this problem.

[0031] Please see Figure 1 and Figure 2 The specific steps of the method provided in this application embodiment are as follows:

[0032] Step 1: The honeycomb sandwich structure panel bears an X-direction stress of σ. x The stress in the Y direction is σ y The shear load is τ xy This situation is what we call being subjected to a combined load, see Appendix Figure 1 As shown;

[0033] Step 2: According to the calculation method of critical shear stress of honeycomb sandwich structure plate on page 549 of "Aircraft Design Handbook, Volume 9: Loads, Strength and Stiffness", the following is the method:

[0034] 1) When the panel is subjected to a uniform compressive load in a single direction:

[0035]

[0036] 2) Panel withstands pure shear

[0037]

[0038] In formulas (1) and (2): G xz G yz —The shear modulus of the core in the xz and yz planes, where h is the thickness of the honeycomb core, t1 is the thickness of the upper panel, t2 is the thickness of the lower panel, E1 is the elastic modulus of the upper panel, and E2 is the elastic modulus of the lower panel. The above elastic moduli are explained as follows: when subjected to X-direction load, the modulus of the upper and lower panels refers to the X-direction modulus; when subjected to Y-direction load, the modulus of the upper and lower panels refers to the Y-direction modulus.

[0039] See attached document for shear wrinkling instability modes. Figure 2 As shown.

[0040] Step 3: Divide the panel into two material types: metal and composite materials, and provide different processing methods for each;

[0041] Step 4: When the panel is made of metal, it is an isotropic material. The elastic modulus of the inner and outer panels is the same in all directions. Assume that the inner and outer panels are made of the same material, i.e., E1 = E2 = E, where E is the elastic modulus of the material.

[0042] Step 5: Under the premise of step 4, the process for handling shear wrinkle instability is as follows:

[0043] 1. Select the panel for shear and wrinkle calculation, that is, select the panel with surrounding structural supports such as frames, beams, and horizontal members as the whole analysis panel;

[0044] 2. Conservatively, the X-direction normal stress, Y-direction normal stress, and shear stress of the upper and lower panels according to the finite element mesh size are selected in the entire analysis panel.

[0045] 3. Determine the principal stress and maximum shear stress (τ1) of the outer panel under the stress state corresponding to step 2, and calculate τ using formula (2). wr1 Residual strength modulus (this value is less than 1 to meet design requirements): R1=τ1 / τ wr1 ;

[0046] 4. Calculate the principal stress and maximum shear stress (τ2) of the inner panel under the stress state corresponding to step 2, and calculate τ using formula (2). wr2 Residual strength modulus (this value is less than 1 to meet design requirements): R² = τ² / τ wr2 ;

[0047] 5. Calculate the critical shear wrinkle stress σ of the outer panel according to formula (1). wr1 The residual strength modulus (this value is less than 1, which meets the design requirements) R1 = σ 2w / σ wr1 (where σ is in the formula) 2w (This refers to the maximum compressive principal stress of the outer panel);

[0048] 6. Calculate the critical shear stress σ of the inner panel according to formula (1). wr2 The residual strength modulus (this value is less than 1, which meets the design requirements) R² = σ 2n / σ wr2 (where σ is in the formula) 2n (This represents the maximum compressive principal stress of the inner panel).

[0049] Step 6: When both the inner and outer panels are made of composite materials, assume that they are orthotropic and that the elastic modulus is different in the X and Y directions.

[0050] Step 7: Assume the elastic modulus E in the X direction. x With the elastic modulus E in the Y direction y The existence relation is: E x >E y ;

[0051] Step 8: Select the panel for shear and wrinkle calculation, that is, select the panel with surrounding structural supports such as frames, beams, and horizontal members as the whole analysis panel.

[0052] Step 9. Conservatively, select the X-direction normal stress, Y-direction normal stress, and shear stress of each layer of the upper and lower panels according to the finite element mesh size in the entire analysis panel.

[0053] Step 10: Treat the inner and outer panels as equivalent to metal panels.

[0054] The three plane stress values ​​(average stress) of the inner and outer panels of this "equivalent metal panel" are calculated using the following formula:

[0055]

[0056] In the formula, σ i For the stress of the i-th layer of the inner or outer panel (note: the stress of a single layer must be output in the same direction), t i The thickness of the i-th layer of the inner or outer panel.

[0057] Step 11, under the premise of steps 6, 7, 8, 9, and 10, the method for handling shear wrinkle instability is as follows:

[0058] 1. Calculate the average stress of the inner and outer panels according to formula (3);

[0059] 2. Determine the maximum and minimum principal stresses and the principal stress direction angles of the outer panel. The elastic modulus corresponding to the above angle is Perform calculations. Range of angle values E xw This refers to the X-direction elastic modulus corresponding to the upper panel;

[0060] 3. Determine the maximum and minimum principal stresses and the direction angles of the principal stresses in the inner panel. The elastic modulus corresponding to the above angle is Perform calculations. Range of angle values E xn This refers to the X-direction elastic modulus corresponding to the upper panel;

[0061] 4. In Formula 1, let The critical shear stress σ corresponding to the outer panel is calculated according to formula (1). wr1 ,

[0062] The residual strength modulus (a value less than 1 satisfies design requirements) is: R1 = σ 2w / σ wr1 (where σ is in the formula) 2w (This refers to the maximum compressive principal stress of the outer panel);

[0063] 5. In Formula 1, let The critical shear stress σ corresponding to the outer panel is calculated according to formula (1). wr2 ,

[0064] Residual strength modulus (this value is less than 1 to meet design requirements): R² = σ 2n / σ wr2 (where σ is in the formula) 2n (This refers to the maximum compressive principal stress of the outer panel);

[0065] 6. Determine the maximum and minimum stresses and principal stress direction angles of the outer panel. Next, determine the maximum shear stress (τ1) and the direction of principal stress rotation at 45°. The elastic modulus of the outer panel, the elastic modulus corresponding to the above angles according to... Perform calculations. Range of angle values

[0066] 7. Determine the maximum and minimum stresses and principal stress direction angles of the inner panel. Next, determine the maximum shear stress (τ2) and the direction of principal stress rotation at 45°. The elastic modulus of the outer panel, the elastic modulus corresponding to the above angles according to... Perform calculations. Range of angle values

[0067] 8. In Formula 2, let The critical shear stress τ corresponding to the outer panel is calculated according to formula (2). wr1 Residual strength modulus (this value is less than 1 to meet design requirements): R1=τ1 / τ wr1 (where τ1 is the maximum shear stress of the outer panel);

[0068] 9. In Formula 2, let The critical shear stress τ corresponding to the outer panel is calculated according to formula (2). wr2 Residual strength modulus (this value is less than 1 to meet design requirements): R² = τ² / τ wr2 (where σ is in the formula) 2n (This refers to the maximum compressive principal stress of the outer panel);

[0069] Step 12: For cases where the inner and outer panels are made of metal or composite materials, this paper will not consider such cases for the time being.

Claims

1. A method for treating shear wrinkles in a honeycomb sandwich structure under composite load, characterized in that, The honeycomb sandwich structure includes a top panel, a bottom panel, and a honeycomb sandwich layer disposed between the top panel and the bottom panel; the method includes: The honeycomb sandwich structure is classified into metal panels and composite material panels; The metal panel is subjected to shearing and wrinkling instability treatment to obtain the first shearing and wrinkling critical stress. Based on the first shearing and wrinkling critical stress, it is determined whether the structure meets the strength design requirements. The composite material panel is subjected to shear wrinkling instability treatment to obtain the second shear wrinkling critical stress. Based on the second shear wrinkling critical stress, it is determined whether the structure meets the strength design requirements. The process of treating the metal panel to induce shear wrinkling instability and obtaining the first critical shear wrinkling stress includes: Calculate the principal stress and maximum shear stress under the combined load of the inner and outer panels, and determine the elastic modulus in the direction of the principal stress and the direction of the maximum shear stress. Since the metal panel is an isotropic structure with equal elastic modulus in all directions, calculate the critical shear stress under the principal stress state and the critical shear stress under the maximum shear stress state for the inner and outer panels respectively. The process of treating the composite material panel for shear wrinkling instability to obtain the second critical shear wrinkling stress includes: Calculate the principal stress and maximum shear stress under the combined load of the inner and outer panels, and determine the elastic modulus in the directions of principal stress and maximum shear stress. Since the composite material panel is an orthotropic structure, the elastic modulus is different in each direction. Calculate the critical shear stress under the principal stress state and the critical shear stress under the maximum shear stress state for the inner and outer panels respectively.

2. The method according to claim 1, characterized in that, Both the upper panel and the lower panel are subjected to a combined load, which includes bearing X-direction stress. Bearing Y-direction stress Bearing shear load .

3. The method according to claim 2, characterized in that, The step of determining whether a structure meets strength design requirements based on the first shear wrinkle critical stress includes: If the critical stress of the first shear wrinkle is greater than or equal to the first threshold, the strength design requirements are met; If the critical stress of the first shear wrinkle is less than the first threshold, the strength design requirements are not met.

4. The method according to claim 3, characterized in that, The step of determining whether a structure meets strength design requirements based on the second shear wrinkle critical stress includes: If the critical stress of the second shear wrinkle is greater than or equal to the second threshold, the strength design requirements are met. If the critical stress of the second shear wrinkle is less than the second threshold, the strength design requirements are not met.

5. The method according to claim 4, characterized in that, The first threshold is different from the second threshold.

6. A device for treating shearing and wrinkling of a honeycomb sandwich structure under composite load, characterized in that, The honeycomb sandwich structure includes a top panel, a bottom panel, and a honeycomb sandwich layer disposed between the top panel and the bottom panel; the device includes: The classification module is used to classify the honeycomb sandwich structure to obtain the panels made of metal materials and the panels made of composite materials; The first processing module is used to process the shearing and wrinkling instability of the metal material panel, obtain the first shearing and wrinkling critical stress, and determine whether the structure meets the strength design requirements based on the first shearing and wrinkling critical stress. The second processing module is used to treat the shear wrinkle instability of the composite material panel, obtain the second shear wrinkle critical stress, and determine whether the structure meets the strength design requirements based on the second shear wrinkle critical stress. The first processing module is also used to calculate the principal stress and maximum shear stress under the combined load of the inner and outer panels, and to determine the elastic modulus in the direction of the principal stress and the direction of the maximum shear stress. Since the metal panel is an isotropic structure with equal elastic modulus in all directions, the critical shear stress under the principal stress state and the critical shear stress under the maximum shear stress state of the inner and outer panels are calculated respectively. The second processing module is also used to calculate the principal stress and maximum shear stress under the combined load of the inner and outer panels, and to determine the elastic modulus in the direction of the principal stress and the direction of the maximum shear stress. Since the composite material panel is an orthotropic structure, the elastic modulus is different in each direction. The critical shear stress under the principal stress state and the critical shear stress under the maximum shear stress state of the inner and outer panels are calculated respectively.

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