A method for designing a groove depth of an axial extrusion pipe joint based on preventing pull-out

Abstract

The application provides a kind of axial extrusion pipe joint groove depth design method based on preventing pull-out, and relates to the technical field of metal conduit connection.The steps of the application are as follows: (1) calculating the tangential stress σ of the conduit when pull-out θ ; (2) calculating the unit pressure q on the surface of the conduit; (3) calculating the pull-out force F on the conduit; (4) calculating the groove depth H of the pipe joint.The groove depth design method is suitable for the design of the minimum groove diameter of the axial extrusion pipe joint, so that the pipe joint can meet the connection strength standard in structure, provides a theoretical basis for the research of such joints in China, and is conducive to promoting the domestic research progress.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of metal pipe connection, in particular to a groove depth design method of axial extrusion pipe joint based on preventing pull-out. BACKGROUND

[0002] Pipe system as the link of aircraft flight control system has become one of the important factors affecting the safety and reliability of the aircraft. In the aircraft hydraulic system, the number of hydraulic pipe joints is large and widely distributed. The leakage of any pipe joint can cause the failure of the aircraft hydraulic system and even a major flight accident. In order to control the aircraft to complete reliable and accurate actions, a high-reliability hydraulic pipe system must be provided to ensure the realization of these actions. Therefore, selecting a safe and reliable connection method, designing the connection strength, sealing performance and service cycle of the pipe joint is a very important link in the pipe system.

[0003] The axial extrusion connection technology is a new pipe connection technology in recent years. The axial extrusion pipe joint is composed of an outer ring and a pipe sleeve. The outer ring is pushed along the axial direction of the joint by external force to extrude the pipe sleeve, thereby forming a mechanical connection and a metal seal. The connection has the advantages of light weight, simple structure, simple process, short working hours and high efficiency.

[0004] However, there is little research on the axial extrusion pipe joint in China, and no one has proposed a reliable scheme for the design of the pipe joint, especially the design method of the connection strength of the axial extrusion pipe joint corresponding to the domestic standard. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a groove depth design method of axial extrusion pipe joint based on preventing pull-out.

[0006] A groove depth design method of axial extrusion pipe joint based on preventing pull-out, comprising the following steps:

[0007] Step 1: Calculate the tangential stress σ of the pipe when pulled out θ ;

[0008] The Lame yield equation in absolute value is

[0009]

[0010] In the formula, β is the intermediate principal stress influence coefficient, and β = 1.1 is taken for the plane stress problem; is the actual deformation resistance of the material.

[0011] The tangential strain ε θ is the maximum compression principal strain, which is equal to the equivalent strain in the stress-strain relationship, so there is the following formula:

[0012]

[0013]

[0014]

[0015] where σ0 is the initial yield stress of the material; B2 is the strain stiffness modulus of the material; Y b , ε b are the true stress and the corresponding logarithmic strain at the necking point b, respectively; σ s is the yield strength of the material; R is the outer diameter of the pipe at the location where the pipe resists the pull-off force; R0 is the groove diameter of the pipe.

[0016] Since plastic flow occurs in the deformation zone, take σ0 = σ s , the tangential stress σ θ of the pipe is

[0017]

[0018] Step 2: Calculate the unit pressure q on the pipe surface;

[0019] Take a base element in the deformation zone with two intersecting radial planes and two parallel planes perpendicular to the conical surface, where θ is the included angle of the base element between the two intersecting radial planes, β is the included angle of the base element on the plane perpendicular to the conical surface, is the included angle of the base element on the plane perpendicular to the axis.

[0020] Where:

[0021] The equilibrium equation of the base element along the normal direction N is:

[0022]

[0023] where f1, f2 are the areas of the corresponding faces on the base element, t is the wall thickness of the pipe; α is the half-cone angle of the pipe deformation zone.

[0024] Therefore, the unit pressure q on the pipe surface is:

[0025]

[0026] Step 3: Calculate the pull-off force F on the pipe;

[0027] The force F required for the pipe to be pulled off from the pipe joint is equal to the product of the compressive stress, the area of the pipe being contacted, and the friction coefficient between the pipe joint and the pipe contact surface, i.e.:

[0028]

[0029] Wherein, F is the pull-off force; μ is the friction coefficient of the contact surface; R is the diameter of the contact circumference of the sleeve and the pipe; L is the contact length of the sleeve and the pipe; P is the pressure on the surface of the pipe.

[0030] Wherein, μ, t, π, L, cos α are constants, and the setting parameter C = 4.4 μtπ 2 L 2 cos α, so

[0031]

[0032] Step 4: calculating the groove depth H of the sleeve;

[0033] The pull-off force of the pipe joint shall meet the minimum connection strength [F] of the test standard, and when the sleeve has a groove, that is,

[0034] F ≥ [F]

[0035] When R = r, r is the minimum diameter of the deformed zone of the pipe when the sleeve extrudes the pipe, the pull-off force F is the minimum, and therefore the groove diameter R0 of the sleeve meets

[0036]

[0037] Therefore, the groove depth H of the sleeve needs to meet

[0038]

[0039] In step 4, if the sleeve has n grooves of the same size, the pull-off force F shall meet

[0040] nF ≥ [F]

[0041] Wherein, n is the number of grooves.

[0042] The beneficial effects generated by the above technical solution are:

[0043] The application provides a groove depth design method of an axial extrusion type pipe joint based on prevention of pull-off, the minimum groove depth of the axial extrusion type pipe joint is obtained through theoretical calculation, domestic standards are combined, the axial extrusion type pipe joint suitable for domestic connection strength is designed, a theoretical basis is provided for research of the domestic joint, and domestic research progress is promoted. DETAILED DESCRIPTION

[0044] Figure 1 Fig. 1 is a schematic diagram of the connection state of the axial extrusion type pipe joint in the embodiment of the application;

[0045] In the figure, 1 is a sleeve; 101 is a sleeve groove; 2 is a pipe; and 3 is an outer ring.

[0046] Figure 2Figure 1 is a schematic view of a base element of a catheter in a pipe sleeve groove according to an embodiment of the present application; DETAILED DESCRIPTION

[0047] The specific embodiments of the present application will be further described in conjunction with the accompanying drawings and examples. The following examples are used to illustrate the present application but are not intended to limit the scope of the present application.

[0048] A design method for axial extrusion pipe joint groove depth based on preventing pull-out, comprising the following steps:

[0049] Step 1: Calculate the tangential stress σ θ of the catheter when pulled out;

[0050] When pulled out, the pipe diameter of the deformation zone of the catheter is reduced and elongated in the axial direction. At this time, the tangential stress σ θ and the axial stress σ r are both compressive stresses, but the absolute value of σ θ must be greater than the absolute value of σ r . The absolute value of the Lame yield equation is

[0051]

[0052] In the formula, β is the intermediate principal stress influence coefficient, and β = 1.1 is taken for the plane stress problem; is the actual deformation resistance of the material.

[0053] The tangential strain ε θ is the maximum compressive principal strain, which is equal to the equivalent strain in the stress-strain relationship, so the following formula is obtained:

[0054]

[0055]

[0056]

[0057] In the formula, σ0 is the initial yield stress of the material; B2 is the strain stiffness modulus of the material; Y b , ε b are the true stress and the corresponding logarithmic strain at the necking point b, respectively; σ s is the yield strength of the material; R is the outer diameter size of the catheter at the pull-out resistance position; and R0 is the diameter of the pipe sleeve groove.

[0058] Since plastic flow occurs in the deformation zone, σ0 = σ s , the tangential stress σ θ of the catheter is

[0059]

[0060] Step 2: Calculate the unit pressure q on the surface of the conduit;

[0061] Take a base element in the deformation zone with two intersecting radial planes and two parallel planes perpendicular to the conical surface, wherein θ is the included angle of the base element between the two intersecting radial planes, and β is the included angle of the base element on the plane perpendicular to the conical surface, is the included angle of the base element on the plane perpendicular to the axis.

[0062] Wherein:

[0063] The column base element is balanced along the law phase N equation:

[0064]

[0065] In the formula, f1, f2 are the areas of the corresponding faces of the base element, t is the wall thickness of the conduit; α is the half cone angle of the deformation zone of the conduit.

[0066] Therefore, the unit pressure q on the surface of the conduit is:

[0067]

[0068] Step 3: Calculate the pull-out force F of the conduit; when calculating the pull-out force F of the conduit, only the force resisting the protrusion of the conduit at the groove and the straight angle edge of the sleeve groove is taken as the main pull-out force, and the remaining resistance is ignored in this step.

[0069] The force F required for the conduit to be pulled out from the pipe joint is equal to the product of the compressive stress, the area of the pipe to be connected, and the friction coefficient between the pipe joint and the conduit contact surface, that is:

[0070]

[0071] In the formula, F is the pull-out force; μ is the friction coefficient of the contact surface; R is the diameter of the contact circumference of the sleeve and the pipe to be connected; L is the contact length of the sleeve and the pipe to be connected; P is the pressure on the surface of the conduit.

[0072] Wherein, μ, t, π, L, cosα are constants, and the parameter C is set as C=4.4μtπ 2 L 2 cosα, so

[0073]

[0074] Step 4: Calculate the groove depth H of the sleeve; when calculating the groove depth H of the sleeve, due to the wall thickness of the sleeve, the groove diameter is generally taken as 1-1.1 times the minimum groove depth H, to prevent the groove from being too deep and affecting the metal flowability of the sleeve during connection, thereby reducing the connection strength.

[0075] The pull-off force of the pipe joint shall meet the minimum connection strength [F] of the test standard. When there is a groove on the pipe sleeve, i.e.

[0076] F≥[F]

[0077] When R=r, r is the minimum diameter of the deformed zone of the pipe sleeve when the pipe sleeve is extruded on the pipe, the pull-off force F is the minimum, and therefore the groove diameter R0 of the pipe sleeve meets

[0078]

[0079] Therefore, the groove depth H of the pipe sleeve needs to meet

[0080]

[0081] In step 4, if there are n grooves of the same size on the pipe sleeve, the pull-off force F shall meet

[0082] nF≥[F]

[0083] Wherein, n is the number of grooves.

[0084] The material properties of the pipe affect the groove depth H of the pipe sleeve. The higher the initial yield strength σ s of the pipe material, the higher the tensile strength σ b , and the smaller the groove depth H.

[0085] The contact area between the pipe and the pipe sleeve during pull-off affects the groove depth H of the pipe sleeve. The larger the contact area, the smaller the groove depth H.

[0086] The friction coefficient between the pipe sleeve and the pipe affects the groove depth H of the pipe sleeve. The larger the friction coefficient, the smaller the groove depth H.

[0087] In this embodiment, as shown in Figure 1 , Figure 2 the pipe material is TA18, the outer diameter is 12 mm, the wall thickness t is 1 mm, the yield stress σ s is 566 MPa, the true stress Y b at the necking point b is 902 MPa, the corresponding logarithmic strain ε b is 0.223, R=r is 5.65 mm, the friction coefficient μ is 0.2, the contact length L is 0.8 mm, the groove width of the pipe sleeve is 3 mm, cos α is 0.97, and the minimum connection strength [F] is 19 kN. The groove depth H of the pipe sleeve is calculated as follows

[0088] Step 1: Calculate the tangential stress σ θ of the pipe 2 during pull-off.

[0089]

[0090]

[0091] Step two: calculate the unit pressure q on the surface of the pipe 2.

[0092]

[0093] Step three: calculate the pull-off force F on the pipe 2.

[0094] C = 4.4 μt π 2 L 2 cos α = 4.4 x 0.2 x 1 x π 2 x 0.8 2 x 0.97 = 5.39

[0095]

[0096] Step four: calculate the groove depth H of the pipe sleeve groove 101.

[0097] The pull-off force of the pipe joint shall meet the minimum connection strength [F] of the test standard, i.e.

[0098] F ≥ [F]

[0099] When R = r, the pull-off force F is the smallest, so the diameter R0 of the pipe sleeve groove 101 needs to meet

[0100]

[0101] Therefore, the groove depth H of the pipe sleeve groove needs to meet:

[0102] H ≥ R0 - r = 5.88 - 5.65 = 0.23 mm

[0103] The above description is only the preferred embodiment of the present disclosure and the explanation of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in the embodiments of the present disclosure is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the above inventive concept. For example, the above features are replaced with the technical features disclosed in the embodiments of the present disclosure (but not limited to) having similar functions to form technical solutions.

Claims

1. A method for designing a groove depth of an axial compression pipe joint based on prevention of pullout, characterized by, The method comprises the following steps: Step 1 : Calculate tangential stress σ of the catheter at pull-off θ ; The step 1 is specifically as follows: the absolute value column Mises yield equation is as follows: ； In the formula, β is the intermediate principal stress influence coefficient, and β = 1.1 for a plane stress problem; is the actual deformation resistance of the material; tangential strain ε θ The maximum compressive principal strain is equal to the equivalent strain in the stress-strain relationship, so there is the following formula: ； ； ； where σ0 is the initial yield stress of the material; B2 is the strain stiffness modulus of the material; Y b , ε b are the true stress and the corresponding logarithmic strain at the point of necking b, respectively; σ s is the yield strength of the material; R is the outer diameter dimension of the conduit at the point of resistance to the sleeve during pull-off; R0 is the diameter of the sleeve groove; Due to the plastic flow in the deformation zone, take σ0=σ s , the tangential stress σ θ of the pipe is: ； Step 2: calculate the unit pressure q on the surface of the conduit; The step 2 is specifically as follows: a base element is taken in the deformation zone with two intersecting radial planes and two parallel planes perpendicular to the conical surface, wherein θ is the included angle of the base element between the two intersecting radial planes, β is the included angle of the base element on the plane perpendicular to the conical surface, and φ is the included angle of the base element on the plane perpendicular to the axis; wherein: , ; , ; The column base element is obtained along the law phase N balance equation: ； In the formula, f1, f2 are the areas of the corresponding faces on the elementary body, ; t is the wall thickness of the conduit; a is the half-cone angle of the conduit deformation zone; Therefore, the unit pressure q on the surface of the conduit is as follows: ； Step 3: calculate the pull-off force F of the conduit; The step 3 is specifically as follows: the pull-off force F required for the conduit to be pulled off from the pipe joint is equal to the product of the compressive stress, the area of the pipe to be connected and the friction coefficient between the pipe joint and the conduit contact surface, that is: ； In the formula, F is the pull-off force; μ is the friction coefficient of the contact surface; R is the diameter of the pipe sleeve and the pipe to be connected contact circumference; L is the length of the pipe sleeve and the pipe to be connected contact; and P is the pressure on the surface of the conduit; Wherein, μ, t, π, L, cosα are constants, set parameters Therefore: ； Step 4: calculate the groove depth H of the pipe sleeve, and complete the groove depth design of the axial extrusion type pipe joint; The step 4 is specifically as follows: the pull-off force of the pipe joint meets the minimum connection strength [F] of the test standard, and when the pipe sleeve has a groove, that is: F≥ [F]; When R=r, r is the minimum diameter of the conduit in the deformation zone when the pipe sleeve extrudes the conduit, the pull-off force F is minimum, and therefore the groove diameter R0 of the pipe sleeve meets: ； Therefore, the groove depth H of the pipe sleeve meets: ； In step 4, if the pipe sleeve has n grooves with the same size, the pull-off force F meets: nF≥ [F]; Wherein, n is the number of grooves.

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