Research on the flexibility coefficient of fasteners in fastener connection structure by science and technology and engineering instrument technology Tang Zhaotian (Institute of Strength Design, Shanghai Aircraft Design and Research Institute, Shanghai 200232). The method of determining the flexibility coefficient of the fastener is usually based on experiments, and the human and material resources are expensive. It is hoped that the softness coefficient of the fastener can be studied by theoretical methods, and a new method for calculating the flexibility coefficient of the fastener can be obtained to save the material and time. Based on the knowledge of material mechanics and elasticity theory, the formula for calculating the flexibility coefficient of fasteners is derived. Comparing this method with the well-known companies and NACA report NACATN1051 and other methods, not only the calculation results are in good agreement with them, but also the consideration of the influencing factors is more comprehensive. Therefore, the calculation method of the fastener flexibility coefficient provided has certain use. value.
In the double-shear structure, the classification method is TH131; the mark code A is generally used in the engineering structure to connect the structure. When the fatigue strength of the fastener connection structure is analyzed, the flexibility coefficient of the fastener is calculated and fastened. The necessary parameters for the transfer of the load. After consulting a large amount of data, the methods commonly used at home and abroad to calculate the flexibility coefficient of fasteners come from: engineering empirical formula, which is not conducive to accurate calculation; Second, the fitting of test data requires a large number of tests. Moreover, these methods are only applicable to single-shear structures and symmetric double-shear structures. There is no calculation method for the asymmetric double-shear structures commonly used in engineering. On the other hand, based on the consideration of intellectual property protection, the calculation methods proposed by companies are not conducive to Project promotion and application.
From the perspective of theoretical derivation, this paper studies the flexibility coefficient of fasteners of single shear structure, symmetric double shear structure and asymmetric double shear structure to obtain the calculation method which has application value and can be popularized and applied.
1 Some factors affecting the calculation of the flexibility coefficient of the fastener In the actual application, the deformation state and the stress state near the fastener and its hole edge are extremely complicated, and it is difficult to fully describe it with a simple mathematical expression, and it is necessary to exclude the secondary influence factor. Civil engineering structures have low stress levels, deformations are completely within the linear elastic range, and assembly according to appropriate process requirements, can be received on January 6, 2012: fatigue and damage tolerance design. E-nail:tangzhaotian comac.cn. The effects of friction and assembly stress are reduced to negligible levels.
In order to meet the fatigue strength requirements, it is generally required that the total laminated thickness is not more than twice the diameter of the fastener, and the thickness of the plate is relatively thin, and it can be considered that all the plates are in a plane stress state. In this paper, the factors affecting the flexibility coefficient of the fastener are: the geometrical dimensions of the fastener, the stiffness of the fastener material, the geometry of the substrate (relatively thicker plate) and the strip (thinner plate), and the substrate. And the stiffness of the material with the plate.
2 The method of calculating the flexibility coefficient proposed in this paper This paper proposes a method to calculate the flexibility coefficient of the fastener from the perspective of theoretical analysis. In order to simplify the derivation and calculation process, combined with the engineering practice, the following preconditions are proposed: the extrusion stress along the thickness direction Uniform distribution, as shown; the axis of the fastener is always parallel to the normal plane of the plate; based on the assumptions a),), it is considered to be constrained by the simple support at the centroid of the fastener, as shown, the bending moment is at the centroid Balance, ie M=0. The basic formula of the flexibility coefficient is C=4. In the actual structure, the ratio of the fastener diameter to the effective length d/l=1~2, is a very “thick†short beam, shear stress It has a great influence on its deformation. In this paper, it is considered that the deformation amount of the fastener flexibility coefficient should include at least: in the formula (1): Ay is the deformation caused by the bending moment, Ask is the deformation caused by the shear stress, and A' is the lateral displacement.
The axis of the clamping member (7) and the 0e tightness of the centroid of the Pr fastener are loaded and constrained. The calculation of Abmd and Asl should be based on the theory of ironwood sinco beam, and the derivation process is as follows.
The distribution of the compressive stress on the upper side: due to the symmetry and according to the needs of the actual application, only the component in the z-axis direction is considered. The above formula is derived by taking the unit thickness, so the thickness is t: the compressive stress is transformed as shown. Processing, taking the plane at point C parallel to the x-axis and the y-axis, the projection of BCB' on this plane is the shadow portion in the middle.
On the surface from O' is s, the force acting on the micro-dds of thickness t can be considered as the concentrated force of the value p(s)tds acting perpendicularly on the surface: 4 This method and a well-known aviation The stress generated by the comparison between the method proposed by the enterprise and the NACA report is 0: (The following method compares the method provided in this paper with the method for calculating the flexibility coefficient of the fastener proposed by a well-known aviation company and the NACA report. A well-known aviation company proposed Formula 0 for calculating the compliance coefficient of the fastener: According to the figure, the formula 1 for calculating the flexibility coefficient of the fastener proposed by x' NACA is calculated according to the formula (9). The stress is along the x-axis. The distribution tends to be uniform, then the width of the effective influence zone of the fastener load on the plate when calculating the lateral displacement 4' is W = fastener spacing, as shown.
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