Design method for allowable value of static connection strength of aircraft countersunk head rivet in aluminum alloy plate

Abstract

The invention relates to the field of countersunk head fastener connection, in particular to a design method for a static connection strength allowable value of an aircraft countersunk head rivet in an aluminum alloy plate. The method comprises the following steps: (1) determining an extrusion bearing strength line of static connection of a countersunk head rivet in an aluminum plate; (2) determining a mixed failure allowable value curve of static connection of the countersunk head rivets in the aluminum plate; (3) determining a shearing cut-off line of static connection of the countersunk head rivet in the aluminum plate; and (4) calculating an allowable value curve of static connection of the countersunk head rivet in the aluminum plate. Different failure modes of the countersunk head rivet in the aluminum alloy plates with different thicknesses are distinguished, the allowable value of the static connection strength of the countersunk head rivet in the extrusion and shear mixed failure mode is obtained through fitting and derivation of assembly extrusion test data, and the accuracy and effectiveness of analysis of the allowable value of the static connection strength of the typical airplane countersunk head rivet and the aluminum plate are improved.

Description

Technical Field

[0001] This invention relates to the field of countersunk fastener connections, and to a design method for the allowable value of static connection strength of aircraft countersunk rivets within aluminum alloy plates. Background Technology

[0002] The most common source of failure in aircraft and other structures is the connection structure. Many factors contribute to its failure, and accurate evaluation is difficult. Unlike convex fasteners, the connection between countersunk fasteners and thin plates involves complex contact patterns and more diverse failure modes. The allowable value for the connection under mixed failure modes cannot be simply expressed by the allowable value for fastener shear failure or thin plate crush failure; it must be determined through relevant experimental data. The book "Practical Aircraft Structural Stress Analysis and Dimensional Design" also states that the allowable load for the combination of countersunk fasteners and thin plates can only be determined based on experimental data. Summary of the Invention

[0003] Purpose of the invention This invention provides a design method for the allowable static connection strength of countersunk rivets in aluminum alloy plates. The allowable static connection strength of countersunk rivets under the combined failure mode of extrusion and shear is derived by fitting data from assembly extrusion test.

[0004] Technical solution A design method for the allowable static connection strength of countersunk rivets in aluminum alloy plates is proposed. This method distinguishes different failure modes of countersunk rivets in aluminum alloy plates of different thicknesses and derives the allowable static connection strength of countersunk rivets under the combined failure mode of extrusion and shear by fitting and deducing the data from the extrusion test of the assembly.

[0005] Furthermore, this includes the following steps: Step (1) Determine the extrusion bearing strength line of the countersunk rivet in the static connection within the aluminum plate; Step (2) Determine the mixed failure allowable value curve of the countersunk rivet in the static connection within the aluminum plate; Step (3) Determine the shear cut-off line of the countersunk rivet in the static connection within the aluminum plate; Step (4) Calculate the allowable value curve of the countersunk rivet in the static connection of the aluminum plate.

[0006] Furthermore, in step (1), determining the compressive strength line of the countersunk rivet in the static connection within the aluminum plate includes: The extrusion bearing strength line is a line with a slope of The oblique line of (psi) / (π / 4) terminates at point A:

[0007] in: —Extrusion breaking strength A value of aluminum alloy sheet; —The x-axis of the allowable value curve; —Thickness of aluminum alloy sheet; —Diameter of countersunk fastener; —The extrusion reduction coefficient is related to the extrusion strength of the aluminum plate holes.

[0008] Further, step (2), determining the mixed failure allowable value curve of the countersunk rivet in the static connection within the aluminum plate includes: The assembly is in a mixed failure state of hole extrusion and fastener shear. The allowable value curve for mixed failure starts at point A and ends at point B. Furthermore, the calculation formula is derived by fitting the extrusion test data of the assembly as follows:

[0009] in: —Combined failure allowable value curve; A0, A1, A2 — Curve coefficients for mixed failure allowable values.

[0010] Furthermore, step (3) determines the shear cutoff line of the countersunk rivet in the static connection within the aluminum alloy plate, including: The shear cutoff value is a horizontal line starting from point B:

[0011] in: — Allowable shearing value for countersunk rivets.

[0012] Furthermore, in one embodiment of the present invention, step (4) of calculating the allowable value curve of the countersunk rivet in the static connection within the aluminum plate includes: The x-coordinates of points A and B in the allowable extrusion value curve of countersunk rivets t / d Value and coefficient of linear descent of compressive bearing strength The calculation equation is shown below, unit: ksi, calculation parameters for the allowable extrusion value curve of countersunk rivets: ;

[0013]

[0014] A t / d Let A be the x-coordinate of point A. t / d Value; B t / d Let B be the x-coordinate. t / d value; Furthermore, combining the above parameter A t / d 、 B t / d Then, based on steps (1) to (3), determine the coordinates of points A and B, the extrusion bearing line and the shear cutoff line, and the mixed failure allowable value curve. P AB Point A is tangent to the extrusion bearing line; the coordinates of points A and B can then be used to determine the location.

[0015] Furthermore, the allowable design value curve equation for countersunk fasteners was finally established. The following is an example, with the unit being psi;

[0016]

[0017] .

[0019] The beneficial effects of this application are as follows: The method for calculating the allowable value of countersunk rivets under extrusion in aluminum plates according to the embodiments of the present invention distinguishes different failure modes of countersunk rivets in aluminum alloy plates of different thicknesses. By fitting and deducing the extrusion test data of the assembly, the allowable value of static connection strength of countersunk rivets under the mixed extrusion and shear failure mode is obtained, which improves the accuracy and effectiveness of the analysis of the allowable value of static connection strength between typical aircraft countersunk rivets and aluminum plates. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] The features and illustrative embodiments of various aspects of the present invention will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention may be practiced without requiring some of these specific details. The following description of embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The invention is by no means limited to any specific setup and method set forth below, but covers any improvements, substitutions, and modifications to the structures, methods, and devices without departing from the spirit of the invention. In the following description, well-known structures and techniques are not shown to avoid unnecessarily obscuring the invention.

[0022] In the description of this invention, it should be noted that the directions or positional relationships indicated by terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer" are based on the stated directions or positional relationships and are only for the convenience of describing and simplifying the invention, and should not be construed as limiting the invention. Furthermore, the use of ordinal numbers (e.g., "first and second," etc.) is for distinguishing objects and is not limited to this order, and should not be construed as indicating or implying relative importance.

[0023] The following detailed description is based on embodiments of the present invention.

[0024] A method for calculating the allowable extrusion value of countersunk rivets within an aluminum alloy plate includes the following steps: (1) Determine the extrusion bearing strength line of the countersunk rivet in the static connection of the aluminum plate; (2) Determine the allowable failure curve of the countersunk rivet in the static connection of the aluminum plate; (3) Determine the shear cut-off line of the countersunk rivet in the static connection of the aluminum plate; (4) Calculate the allowable value curve of countersunk rivets in static connection within aluminum plate.

[0025] In one embodiment of the present invention, determining the compressive strength line of the countersunk rivet in the static connection within the aluminum plate includes: The extrusion bearing strength line is a line with a slope of The oblique line of (psi) / (π / 4) terminates at point A:

[0026] in: —Extrusion breaking strength A value of aluminum alloy sheet; —The x-axis of the allowable value curve; —Thickness of aluminum alloy sheet; —Diameter of countersunk fastener; —The extrusion reduction coefficient is related to the extrusion strength of the aluminum plate holes.

[0027] In one embodiment of the present invention, determining the mixed failure allowable value curve of a countersunk rivet in a static connection within an aluminum plate includes: The assembly is under a mixed failure state of hole extrusion and fastener shear. The allowable value curve for mixed failure starts at point A and ends at point B. The calculation formula is derived from fitting the extrusion test data of the assembly:

[0028] in: —Combined failure allowable value curve; A0, A1, A2 — Curve coefficients for mixed failure allowable values.

[0029] In one embodiment of the present invention, determining the shear cutoff line of the countersunk rivet in the static connection within the aluminum alloy plate includes: The shear cutoff value is a horizontal line starting from point B:

[0030] in: — Allowable shearing value for countersunk rivets.

[0031] In one embodiment of the present invention, calculating the allowable value curve for a countersunk rivet in a static connection within an aluminum plate includes: The x-coordinate t / d values ​​of points A and B in the allowable extrusion value curve of countersunk rivets and the coefficient of linear descent of extrusion bearing strength. The calculation equations are shown in Table 1.

[0032] Table 1. Calculation parameters for the allowable extrusion value curve of countersunk rivets.

[0033] Based on the above parameters, and according to steps (1) to (3), determine the coordinates of points A and B, the extrusion bearing line and the shear cutoff line, and the mixed failure allowable value curve. P AB Point A is tangent to the extrusion bearing line. By combining the coordinates of points A and B, the allowable design value curve equation for the countersunk fastener can be determined. The following (unit: psi).

[0034]

[0035]

[0036]

[0037] The invention will be further illustrated below with specific examples.

[0038] Example: Taking the assembly of NAS1097AD6 rivets and 2024 (clad aluminum)-T3-AMS4462 test plate as an example, calculate its allowable design value.

[0039] According to relevant material handbooks, the single shear breaking strength of NAS1097AD6 rivets is 30 Ksi; the hole extrusion strength (A) of the 2024 (aluminum clad)-T3-AMS4462 test plate is 121 Ksi. The abscissas of points A and B and the coefficient of descent of the extrusion bearing strength are calculated based on the hole extrusion performance of the test plate and the single shear performance of the fasteners. As shown in Table 2.

[0040] Table 2 Calculation parameters for the allowable value curve of countersunk rivets

[0041] Based on the above parameters, and according to steps (1) to (3), determine the coordinates of points A and B, the extrusion bearing line and the shear cutoff line, and the mixed failure allowable value curve. P AB Point A is tangent to the extrusion bearing line. Combining the coordinates of points A and B, the final design allowable value curve formula for the NAS1097AD6 rivet and the 2024 (clad aluminum)-T3-AMS4462 test plate assembly can be determined as follows (unit: psi):

[0042]

[0043]

[0044] Example of design allowable value lookup: If the diameter of the rivet shank in this assembly is 0.195in (4.953mm) and the plate thickness is 0.1in (2.54mm), then t / d=0.513. The allowable value obtained by calculation is 28548psi (196.83MPa). Multiplying by the cross-sectional area of ​​the fastener shank, the allowable load of this assembly is 852.58lbs (3792.43N).

[0045] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly, encompassing both direct connection and indirect connection via an intermediate medium. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances.

[0046] It should be noted that, unless otherwise specified, the embodiments of the present invention and the features thereof can be combined with each other, and the various embodiments can be referenced and cited in each other. The present invention will now be described in detail with reference to and in conjunction with the embodiments.

[0047] The above detailed embodiments are a description of the present invention. It should not be considered that the specific embodiments of the present invention are limited to these descriptions. For those skilled in the art, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the protection scope of the present invention.

Claims

1. A method for designing the allowable value of static connection strength of aircraft countersunk rivets in aluminum alloy plates, characterized in that, Different failure modes of countersunk rivets in aluminum alloy plates of different thicknesses are distinguished, and the allowable static connection strength of countersunk rivets under the mixed failure mode of extrusion and shear is derived by fitting the extrusion test data of the assembly.

2. The method as described in claim 1, characterized in that, Includes the following steps: Step (1) Determine the extrusion bearing strength line of the countersunk rivet in the static connection within the aluminum plate; Step (2) Determine the mixed failure allowable value curve of the countersunk rivet in the static connection within the aluminum plate; Step (3) Determine the shear cut-off line of the countersunk rivet in the static connection within the aluminum plate; Step (4) Calculate the allowable value curve of the countersunk rivet in the static connection of the aluminum plate.

3. The method as described in claim 2, characterized in that, In step (1), determining the compressive bearing strength line of the countersunk rivet in the static connection within the aluminum plate includes: The extrusion bearing strength line is a line with a slope of The oblique line of (psi) / (π / 4) terminates at point A: in: —A value of the extrusion breaking strength of aluminum alloy sheet; —The x-axis of the allowable value curve; —Thickness of aluminum alloy sheet; —Diameter of countersunk fastener; —The extrusion reduction coefficient is related to the extrusion strength of the aluminum plate holes.

4. The method as described in claim 2, characterized in that, Step (2), determining the mixed failure allowable value curve of the countersunk rivet in the static connection within the aluminum plate includes: The assembly is in a mixed failure state of hole extrusion and fastener shear. The allowable value curve for mixed failure starts at point A and ends at point B.

5. The method as described in claim 4, characterized in that, The calculation formula is derived from the fitting of the extrusion test data of the assembly: in: — Hybrid failure allowable value curve; A0, A1, A2 — Curve coefficients for mixed failure allowable values.

6. The method as described in claim 2, characterized in that, Step (3) Determines the shear cutoff line of the countersunk rivet in the static connection within the aluminum alloy plate, including: The shear cutoff value is a horizontal line starting from point B: in: — Allowable shearing value for countersunk rivets.

7. The method as described in claim 2, characterized in that, Step (4) Calculating the allowable value curve for countersunk rivets in static connections within aluminum plates includes: The x-coordinates of points A and B in the allowable extrusion value curve of countersunk rivets t / d Value and coefficient of linear descent of compressive bearing strength The calculation equation is shown below, unit: ksi, calculation parameters for the allowable extrusion value curve of countersunk rivets: ； A t / d Let A be the x-coordinate of point A. t / d Value; B t / d Let B be the x-coordinate. t / d value.

8. The method as described in claim 7, characterized in that, Combining the above parameter A t / d 、 B t / d Then, based on steps (1) to (3), determine the coordinates of points A and B, the extrusion bearing line and the shear cutoff line, and the mixed failure allowable value curve. P AB Point A is tangent to the extrusion bearing line; the coordinates of points A and B can then be used to determine the location.

9. The method as described in claim 8, characterized in that, Finally, the allowable value curve equation for countersunk fastener design was established. The following is an example, with the unit being psi; 。

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