Calculation method for average force of continuous gradual change corrugated pipe

Abstract

The invention discloses a method for calculating the average force of a continuous gradually-changing corrugated pipe, and the method comprises the steps: 1, building a continuous gradually-changing corrugated pipe model, enabling the outer contour line of the continuous gradually-changing corrugated pipe model to be a sine curve, and enabling the amplitude and wavelength of the outer contour line to be continuously changed in the axial direction; 2, the average force of the traditional circular energy absorption box of the circular pipe with the outer contour being a straight line is expressed, and an average force expression of the traditional circular energy absorption box is obtained. And 3, cutting the continuous gradual change corrugated pipe model into a plurality of cutting blocks by taking each outwards convex corrugation as a unit according to the cross section angle and the axial direction, and calculating the average force of each cutting block based on an average force expression of a traditional circular energy absorption box. The invention relates to the technical field of corrugated pipes, and particularly provides a method for calculating the average force of a continuous gradual change corrugated pipe.

Description

Technical Field

[0001] The present invention relates to the technical field of corrugated pipes, and particularly to a calculation method for the average force of a continuously variable corrugated pipe. Background Art

[0002] The energy absorption box is a tubular structure and an important part of the vehicle passive safety system, playing a key protective role during vehicle collisions. In the process of the energy absorption box being impacted during a vehicle collision, the traditional circular cross-section energy absorption box has the problem of excessive initial peak force. The excessive peak force will increase the risk of injury to vehicle occupants.

[0003] According to research, by using a roller press to roll a circular cross-section energy absorption box, a corrugated pipe with concave and convex fold characteristics can be obtained. Further research shows that the corrugated pipe has a lower initial peak force, thereby reducing the risk of injury to vehicle occupants and improving the protective effect of the energy absorption box. Based on the above conclusions, a sine corrugated pipe with a sine wave profile characteristic has been proposed, and the sine corrugated pipe has the characteristic of regular distribution of concave and convex folds.

[0004] Although this is an advantage of the sine corrugated pipe, on the one hand, subsequent research shows that the amplitude and wavelength of the corrugated pipe have an important impact on the average force of the energy absorption box, and changes in the amplitude and wavelength will cause changes in the average force of the energy absorption box. In other words, there is still the possibility and necessity for further optimization of the ordinary sine corrugated pipe. On the other hand, the ideal situation of the energy absorption box is that the average force can gradually increase from the top to the bottom, which helps to provide a lower average force in the early stage of the collision, avoiding excessive changes in the instantaneous impact force before and after the collision, resulting in injury to vehicle occupants; it also helps the energy absorption box absorb more impact energy in the later stage of the collision, reducing the risk of the collision force being transmitted into the occupant compartment and causing the occupant compartment to be squeezed and deformed. However, for the existing sine corrugated pipe, its contour line is distributed according to the sine wave law, and it is impossible to achieve the situation where the average force of the ideal energy absorption box can gradually increase from the top to the bottom. Therefore, based on the conclusion that "the amplitude and wavelength of the corrugated pipe have an important impact on the average force of the energy absorption box, and changes in the amplitude and wavelength will cause changes in the average force of the energy absorption box", the present invention designs a new type of continuously variable corrugated pipe with gradually changing amplitude and wavelength, and proposes a calculation method for its average force. Summary of the Invention

[0005] The technical problem to be solved by the present invention is that for the existing sine corrugated pipe, its contour line is distributed according to the sine wave law, and it is impossible to achieve the situation where the average force of the ideal energy absorption box can gradually increase from the top to the bottom.

[0006] The present invention provides the following technical invention: A calculation method for the average force of a continuously variable corrugated pipe proposed by the present invention includes:

[0007] Step 1: Construct a continuously variable corrugated pipe model. The outer contour line of the continuously variable corrugated pipe model is a sine curve, and the amplitude and wavelength of the outer contour line vary continuously along the axial direction.

[0008] Step 2: Express the average force of a traditional circular energy absorber box with a circular pipe whose outer contour is a straight line, and obtain the average force expression of the traditional circular energy absorber box.

[0009] Step 3: Cut the continuously variable corrugated pipe model into multiple pieces at the cross-sectional angle and along the axial direction, with each outwardly protruding corrugation as a unit, and calculate the average force of each piece based on the average force expression of the traditional circular energy absorber box.

[0010] Step 4: Calculate the overall average force of the continuously variable corrugated pipe model through the number of pieces and the total sum of the average forces of all pieces.

[0011] Step 5: Verify the overall average force of the continuously variable corrugated pipe model.

[0012] (1) First, establish a finite element simulation model;

[0013] (2) Use physical tests to correct the accuracy of the finite element simulation model;

[0014] (3) Verify by comparing the differences between the calculation results of the present invention and the results of the verified finite element model.

[0015] The beneficial effects obtained by adopting the above scheme for a calculation method of the average force of a continuously variable corrugated pipe proposed by the present invention are as follows:

[0016] (1) In the present invention, by constructing a continuously variable corrugated pipe model and discretizing the corrugated pipe into several parts, analyzing one part of the corrugated pipe, and thus generalizing the analysis results to all components, the calculation of the average force of the continuously variable corrugated pipe is realized. The calculation method is simple and fast, with high calculation accuracy, and the error is much lower than the existing theory.

[0017] (2) The error of the proposed calculation method for the average force of the continuously variable corrugated pipe is increased from -45.84% of the existing method to -2.95%, greatly reducing the error. Description of the Drawings

[0018] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation to the present invention. In the drawings:

[0019] Figure 1 : Schematic diagram of the continuously variable corrugated pipe in the embodiment of the present invention Figure 1 ;

[0020] Figure 2: Analysis diagram of the shape collapse process of the energy absorption box under axial compression in the embodiment of the present invention;

[0021] Figure 3 : Comparison diagram of the shape of the small Ci block before and after being impacted in the embodiment of the present invention;

[0022] Figure 4 : Schematic diagram of the continuously variable corrugated pipe model in the embodiment of the present invention Figure 2 ;

[0023] Figure 5 : Schematic diagram of the force-displacement curve of the finite element model and the physical test curve in the embodiment of the present invention;

[0024] Figure 6 : Comparative analysis diagram of amplitude change, only wavelength change, and both amplitude and wavelength change in the embodiment of the present invention. Detailed implementation manners

[0025] Next, the technologies in the embodiments of the present invention will be described clearly and completely in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0026] Embodiment 1

[0027] A calculation method for the average force of a continuously variable corrugated pipe, comprising:

[0028] Step 1: Construct a continuously variable corrugated pipe model, wherein the outer contour line of the continuously variable corrugated pipe model is a sine curve, and the amplitude and wavelength of the outer contour line change continuously along the axial direction.

[0029] As Figure 1 The constructed continuously variable corrugated pipe has a radius of 40 mm, a length of 80 mm, and a wall thickness of 1.5 mm. Among them, the axial outer contour line is a continuously variable sine wave that changes according to the following formula:

[0030] y = A × sin(Bx)

[0031] Where x is the distance from the bottom of the continuously variable corrugated pipe model to the point where it is located, A is the amplitude of the sine wave A = mx + C1; B is the frequency of the sine wave, B = nx + C2, where m, n, C1, and C2 are constants. By changing these constants, continuously variable corrugated pipes with different shapes can be designed. The change in the amplitude of the continuously variable corrugated pipe model can be achieved by the values of m and C1, and the change in the wavelength of the continuously variable corrugated pipe model can be achieved by the values of n and C2.

[0032] Step 2: Express the average force of the traditional circular energy absorber with a circular tube having a straight outer contour, and obtain the expression for the average force of the traditional circular energy absorber.

[0033] Previous studies have concluded that the external work required for the complete collapse of a circular tube is dissipated through bending and membrane energy: Zhang Xiong et al. proposed that when a pipe with a circular cross-section is subjected to axial impact, the external work required for the complete collapse of the circular tube is dissipated through bending energy and membrane energy, that is:

[0034] 2HP m k = W bending +W membrane (1)

[0035] where H is the half-wavelength, P m is the average force of the energy absorber, W benging is the energy consumed by the bending of the circular tube, W membrane is the membrane energy, k is a constant, and the calculation formula for k is as follows:

[0036]

[0037] where d max represents the maximum compression distance, and l is the original length of the energy absorber.

[0038] Analyze the shape collapse process of the energy absorber under axial compression, as Figure 2 shown:

[0039] When the side wall rotates around three plastic hinge lines, the calculation formula for the bending energy is:

[0040]

[0041] where L i = 2πR is the average circumference of the traditional circular tube, where R is the average radius of the tube. M 0 = σ 0 t 2 / 4 is the collapse moment, θ 0 = (π - α) is the bending angle at the plastic hinge line (bending angle, as shown in the bending angle), σ 0 is the yield stress of the material.

[0042] α is the bending angle of strand 1, β is the bending angle of strand 2. Note: This figure here is a schematic diagram of the shape of the pipe fitting after being impacted and deformed. Before the pipe fitting is impacted, the bending angle α 前 = 180° of strand 1, and the bending angle β 前 = 0° of strand 2,

[0043] Membrane energy dissipated by the metal stretched at three plastic hinge lines:

[0044]

[0045] where t is the wall thickness, S is the area of the membrane element at the plastic hinge line, and it is assumed that S = γH 2 , and the coefficient γ is the tensile membrane area coefficient at the plastic hinge line, and γ ∈ [1.2, 3].

[0046] Step 3: Cut the continuously tapered bellows model into multiple segments with each outward convex corrugation as a unit from the cross-sectional angle and along the axial direction, and calculate the average force of each segment based on the average force expression of the traditional circular energy absorber box.

[0047] Cut the continuously tapered bellows into many small pieces with each outward convex corrugation as a unit, such as C in the right figure i and C i-1 are the i-th and (i - 1)-th two independent small pieces respectively. Since the outer contour lines of each small piece are the same in the radial direction, therefore, one of the line segments can be selected for analysis, and the wall deformation of the C i small piece is analyzed as Figure 3 .

[0048] From Figure 3 it can be known that the bending energy of the continuously tapered bellows is obtained by the rotation of the wall around the plastic line, where the angular change (θ c2 ) that occurs at the plastic hinge line 2 during the impact can be calculated as: θ c2 = α c′ -(π - α c ), and the angular changes at the plastic hinge lines 1 and 3 are expressed as: θ c1 = θ c3 = β c′ - β c .

[0049] Therefore, the bending energy of the Ci segment of the continuously tapered bellows can be defined as:

[0050]

[0051] where, R Ci is the average radius of the Ci segment, α ci is the bending angle of the strand 1 of the Ci segment of the bellows before impact, and β ci is the bending angle of the strand 2 of the Ci segment of the bellows before impact.

[0052] The membrane energy of the Ci segment can be calculated according to the area of the membrane element at the plastic hinge line:

[0053] (where H ci is the half wavelength of the Ci block)

[0054] Furthermore, substituting formulas (5) and (6) into (1), it can be known that the expression of the average force of the Ci small block is:

[0055] where P m_ci is the average force of the Ci small block, t ci is the wall thickness of the Ci small block, γ ci is the tensile membrane area coefficient at the plastic hinge line of the Ci small block

[0056] Then substituting M 0 = σ 0 t 2 / 4 (in the present invention, the thickness of the continuously tapered corrugated pipe is constant, so t = t ci ) into formula (7), the following can be obtained:

[0057]

[0058] Step 4: Calculate the overall average force of the continuously tapered corrugated pipe model through the number of blocks and the sum of the average forces of all blocks.

[0059] Since the i-segment is a part of the entire energy absorption box and also any part; therefore, for the entire energy absorption box, summing up all the blocks can obtain the overall average force of the energy absorption box, that is, formula (8) can be written as:

[0060]

[0061] where f is the number of corrugation folds of the entire energy absorption box. In formula (9), is variable. The reason is that the amplitude and wavelength in the continuously tapered corrugated pipe are gradually changing and not fixed. In other words, as Figure 4 shown, α i1 ≠ α i2 , β i1 ≠ β i2 , H i1 ≠ H i2 . Therefore, there is no way to directly obtain

[0062] In the present invention, the following formula is used for calculation

[0063]

[0064] Example 2

[0065] Based on Embodiment 1, a method for calculating the average force of a continuously variable corrugated pipe. In order to verify the average force calculation method proposed by the present invention,

[0066] (1) We first established a finite element simulation model;

[0067] (2) Use physical tests to correct the accuracy of the finite element simulation model;

[0068] (3) Verify by comparing the differences between the calculation results of the present invention and the results of the verified finite element model.

[0069] Comparison between the simulation results of the finite element model and the physical test results is as Figure 5 .

[0070] As Figure 5 shown, the force-displacement curve of the finite element model is basically the same as that of the physical test. The error of the initial peak force compared with the physical test is only 2.06%. The error of the integral of the force-displacement curve of the finite element model (energy = force × displacement, so the integral of the force-displacement curve is actually the value of the energy absorbed by the energy absorption box after being impacted) is -3.17%. Therefore, the error of the finite element model is very small. This also proves that the finite element model can effectively reflect the force and displacement conditions of the corrugated pipe during impact overshoot and can be used to verify the accuracy of the calculation method proposed by the present invention.

[0071] Supplementally, the calculation formula for the average force of the energy absorption box:

[0072]

[0073] where F(x) is the impact force of the energy absorption box at the x displacement, d is the impact distance, and EA is the energy absorbed by the energy absorption box after being impacted. MCF is the average force.

[0074] The calculation formula for the average force of the sine corrugated pipe is:

[0075]

[0076] The following formula (15) is referred to as the "existing formula" and is used to calculate the average force of the continuously variable corrugated pipe.

[0077] Considering that the sine equation is: Y = Asin(Bx), in other words, both the amplitude A and the wavelength B can vary. A and B can vary independently or together. To comprehensively verify the superiority of the average force calculation method proposed by the present invention compared with the existing method, the following comparative analyses are carried out for three cases: only the amplitude changes, only the wavelength changes, and both the amplitude and the wavelength change:

[0078] From Figure 6It can be known that when the existing formula is used for calculating the average force of a continuously variable corrugated pipe, the average error is: -45.84%, and the error of the calculation formula proposed by the present invention is: -2.95%, and the error is much lower than the existing theory.

[0079] Therefore, the present invention has great superiority over the existing technologies.

[0080] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, material or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, material or device.

[0081] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for calculating the average force of a continuously gradient bellows, characterized in that: include: Step 1: construct a continuous gradient bellows model, wherein the outer contour of the continuous gradient bellows model is a sine curve, and the amplitude and wavelength of the outer contour continuously change along the axial direction; Step 2: Express the average force of a traditional circular crash box of a circular tube with a straight outer contour to obtain an average force expression of the traditional circular crash box; Step 3: Cut the continuous gradient bellows model into multiple blocks according to the cross-sectional angle and along the axial direction according to each outwardly protruding corrugation, and calculate the average force of each block based on the average force expression of the traditional circular energy absorbing box; Step 4: The overall average force of the continuous gradient bellows model is calculated by the number of cuts and the sum of the average forces of all cuts.

2. The method for calculating the average force of a continuously gradient bellows according to claim 1, characterized in that: The verification methods for the global average force of the continuous gradient bellows model include: (1) A finite element simulation model was first established; (2) Use physical tests to calibrate the accuracy of the finite element simulation model; (3) The results are verified by comparing the calculation results of the present invention with the results of the verified finite element model.

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