Method for determining stress distribution rule of fastener contact area

Abstract

The invention belongs to the field of comprehensive strength design, and relates to a fastener contact area stress distribution rule determination method. The method comprises the following steps: when the connection form of a fastener is lap joint connection and the loading form of the fastener is single shear, determining that the fastener bears an additional bending moment; when the connection form of the fastener is butt joint connection, the loaded form of the fastener is double shear, and it is determined that the fastener does not bear additional bending moment; when the loading form is single shear, the contact stress distribution rule of the fastener is analyzed as follows: the circumferential direction of the periphery of a hole is distributed according to a sine rule, and the thickness direction is distributed according to a linear rule; the position bearing the maximum stress is the midpoint of the upper boundary of the fastener contact area, and the tangent line of the midpoint is perpendicular to the stress direction; the contact stress distribution rule is that the periphery of the hole is annularly distributed according to a sine rule, and the thickness direction is distributed according to a linear rule; when the loading form is double shear, the contact stress distribution rule is that the circumferential direction of the periphery of the hole is distributed according to the sine rule, and the stress in the thickness direction is kept unchanged.

Description

Technical Field

[0001] The invention belongs to the field of comprehensive strength design and relates to a method for determining stress distribution rules in a contact area of ​​a fastener. Background Art

[0002] The fastener connection area is a key region for static and fatigue strength analysis of helicopter structures. As a key parameter characterizing these strengths, the analysis of the stress around the hole has always been of great importance. Determining the stress distribution pattern in the fastener connection hole contact area is crucial. This is achieved by performing theoretical analysis to determine the maximum stress in the contact area, and then applying finite element analysis to the hole edge extrusion stress to determine the maximum principal stress around the hole edge. This allows for subsequent static and fatigue strength analysis.

[0003] Defects of background technology:

[0004] At present, the average contact stress (extrusion stress) is used to characterize the contact stress in the fastener connection area. The above method is used to calculate the average contact stress for both single shear nails and double shear nails. The influence of the additional bending moment of the single shear nail on the average contact stress is not considered. Therefore, this method has limitations. The maximum principal stress at the hole edge is generally obtained by consulting relevant data to obtain the stress concentration factor. For more complex hole edge structures, since there is no appropriate stress concentration factor, only an approximate method can be used to obtain the stress concentration factor for analysis, which has a large error. Summary of the Invention

[0005] Purpose of the invention: To provide a method for determining the stress distribution law of the contact area of ​​a fastener, determine the contact stress distribution law of the fastener, and then obtain the maximum stress in the contact area and the maximum principal stress at the hole edge with higher accuracy.

[0006] Technical solution:

[0007] A method for determining stress distribution law in a fastener contact area is provided, characterized by comprising:

[0008] When the fastener connection is lap joint, the fastener load is simple shear, and the additional bending moment borne by the fastener is determined;

[0009] When the fastener connection is butt connection, the fastener load form is double shear, and it is determined that the fastener does not bear additional bending moment;

[0010] When the loading form is simple shear, the contact stress distribution pattern of the fastener is analyzed as follows: the circumferential direction around the hole follows a sinusoidal distribution pattern, and the thickness direction follows a linear distribution pattern. The location where the fastener is subjected to the maximum stress is the midpoint of the upper boundary of the fastener contact area, and the tangent of this midpoint is perpendicular to the stress direction. The contact stress distribution pattern of the fastener is analyzed as follows: the circumferential direction around the hole follows a sinusoidal distribution pattern, and the thickness direction follows a linear distribution pattern. When the loading form is double shear, the contact stress distribution pattern of the fastener is analyzed as follows: the circumferential direction around the hole follows a sinusoidal distribution pattern, and the thickness direction stress remains unchanged. The location where the fastener is subjected to the maximum stress is the midline of the fastener contact area along the thickness direction.

[0011] Maximum stress at the midpoint for:

[0012] ;

[0013] Where F is the shear load borne by the fastener; h is the thickness of the single-side plate; r is the radius of the fastener hole; and D is the diameter of the fastener hole.

[0014] Furthermore, the maximum stress on the center line for:

[0015] ;

[0016] Where F is the shear load borne by the fastener; h is the thickness of the single-side plate; r is the radius of the fastener hole; and D is the diameter of the fastener hole.

[0017] Furthermore, the maximum stress in the fastener contact area under the single shear condition is four times the maximum stress in the fastener contact area under the double shear condition.

[0018] Beneficial effects:

[0019] The stress distribution law and maximum stress calculation method of the fastener contact area in the present invention have been applied to the design of critical fatigue areas of the structure, effectively solving the problem of difficult determination of the complex stress state of the hole edge, and correcting the average extrusion stress in different situations such as single and double shear, resulting in extremely high economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of a fastener lap joint.

[0021] Figure 2 Schematic diagram of the butt connection of fasteners.

[0022] Figure 3 This is a schematic diagram of the circumferential direction of the fastener's single-side plate hole.

[0023] Figure 4 Schematic diagram of the thickness of the plate hole on one side of the fastener. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the implementation of this application will be described in more detail below in conjunction with the drawings in the implementation of this application. In the drawings, the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions. The described implementation is a part of the implementation of this application, not all of the implementations. The implementation described below with reference to the drawings is exemplary and is intended to be used to explain this application, and should not be understood as a limitation on this application. Based on the implementation in this application, all other implementations obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The implementation of this application is described in detail below in conjunction with the drawings.

[0025] In the description of the present invention, it should be understood that the terms "center", "axial", "vertical", "up", "down", "upper end", "bottom end", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the scope of protection of the present invention.

[0026] The present invention provides a method for determining stress distribution law in a fastener contact area, the specific steps of which are as follows:

[0027] a) According to the different connection forms of fasteners, they are divided into lap connection and butt connection. For specific connection forms, please see the attached Figure 1-2 shown.

[0028] b) In the lap joint form, the fasteners are loaded in single shear mode; in the butt joint form, the fasteners are loaded in double shear mode.

[0029] c) When the loading form is simple shear, the fasteners bear additional bending moment; when the loading form is double shear, the fasteners do not bear additional bending moment.

[0030] d) When the load form is simple shear, the contact stress distribution law of the fastener is: the circumferential direction around the hole is distributed according to the sine law, the thickness direction is distributed according to the linear law, and the circumferential direction and the plate thickness direction are distributed according to the linear law. Figure 3-4 shown.

[0031] e) Under simple shear conditions, the maximum stress calculation formula for the fastener contact area is as follows:

[0032]

[0033]

[0034] In the above formula: F is the shear load borne by the fastener; h is the thickness of the single-side plate; r is the radius of the fastener hole; is the half-hole annular angle of the fastener; D is the fastener hole diameter, and x is the thickness variable from 0 to h.

[0035] f) determining the maximum stress and position of the fastener contact area through step e), and obtaining a complete distribution pattern of stress in the contact area for subsequent calculation of extrusion strength and maximum principal stress at the hole edge;

[0036] g) When the load form is double shear, the contact stress distribution law of the fastener is: the circumferential direction around the hole is distributed according to the sine law, and the stress in the thickness direction remains unchanged;

[0037] h) Under double shear conditions, the maximum stress calculation formula for the fastener contact area is as follows:

[0038]

[0039]

[0040] In the above formula: F is the shear load borne by the fastener; h is the thickness of the single-side plate; r is the radius of the fastener hole; is the half-hole annular angle of the fastener; D is the fastener hole diameter, and x is the thickness variable from 0 to h.

[0041] i) determining the maximum stress and position of the fastener contact area through step h), and obtaining a complete distribution pattern of stress in the contact area for subsequent calculation of extrusion strength and maximum principal stress at the hole edge;

[0042] j) Based on the analysis in steps e) and h), the maximum stress in the fastener contact area under the single shear condition is four times the maximum stress in the fastener contact area under the double shear condition.

[0043] k) Taking a fastener subjected to a 1000N shear load as an example, the maximum stress at the hole edge under single shear and double shear loading conditions is explained respectively.

[0044] l) For the simple shear case, the plate thickness is 5mm, that is, the height h is 5mm, the fastener diameter is 5mm, the plate width meets the fastener edge distance requirements, that is, 4D+2=22mm, and the end distance meets the requirements of 2D+1=11mm. In this case, the maximum stress at the hole edge for:

[0045]

[0046] According to the previous algorithm, the average extrusion stress is used to represent the hole edge stress , the characterization stress is:

[0047]

[0048] According to the algorithm of the present invention, the maximum stress at the hole edge is 4 times that of the previous algorithm. The average extrusion stress used in the previous algorithm is obviously too small, which poses a great risk when performing fatigue strength calculations.

[0049] m) For the double shear case, the middle plate thickness is 5mm, that is, the height h is 5mm, the fastener diameter is 5mm, the plate width meets the fastener edge distance requirement, that is, 4D+2=22mm, and the end distance meets the requirement of 2D+1=11mm. In this case, the maximum stress at the hole edge for:

[0050]

[0051] According to the previous algorithm, the average extrusion stress is used to represent the hole edge stress , the characterization stress is:

[0052]

[0053] In the algorithm of the present invention, the maximum stress at the hole edge is the same as the average extrusion stress, that is, in the absence of additional bending moment, the two stresses are the same. When performing fatigue strength calculations, either algorithm can be used.

[0054] Other embodiments of the present disclosure will readily occur to those skilled in the art after considering the specification and practicing the disclosure herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow the general principles of the present disclosure and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the present disclosure being indicated by the following claims.

[0055] It should be understood that the present disclosure is not limited to the exact structures that have been described above and shown in the drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A method for determining stress distribution law in a fastener contact area, characterized in that: include: When the fastener connection is lap joint, the fastener load is simple shear, and the additional bending moment borne by the fastener is determined; When the fastener connection is butt connection, the fastener load form is double shear, and it is determined that the fastener does not bear additional bending moment; When the load is simple shear, the contact stress distribution pattern of the fastener is analyzed as follows: the distribution follows a sinusoidal law in the circumferential direction around the hole and a linear law in the thickness direction. The location where the fastener is subjected to maximum stress is the midpoint of the upper boundary of the fastener contact area, and the tangent of this midpoint is perpendicular to the stress direction. The contact stress distribution pattern of the fastener is analyzed as follows: the distribution follows a sinusoidal law in the circumferential direction around the hole and a linear law in the thickness direction. When the load form is double shear, the contact stress distribution law of the fastener is analyzed as follows: the circumferential direction around the hole is distributed according to the sine law, and the stress in the thickness direction remains unchanged; The location where the fastener is subjected to maximum stress is the midline of the fastener contact area along the thickness direction; Maximum stress at the midpoint for: ； Where F is the shear load borne by the fastener; h is the thickness of the single-side plate; r is the radius of the fastener hole; and D is the diameter of the fastener hole.

2. The method according to claim 1, characterized in that Maximum stress on the center line for: ； Where F is the shear load borne by the fastener; h is the thickness of the single-side plate; r is the radius of the fastener hole; and D is the diameter of the fastener hole.

3. The method according to claim 2, characterized in that The maximum stress in the fastener contact area under the single shear condition is four times that under the double shear condition.

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