Method for evaluating the connection strength of an axial extruded pipe joint

Abstract

This invention discloses a method for evaluating the connection strength of axially compressed pipe joints, and the minimum connection strength of the pipe joint. F min This invention allows for the assessment of the minimum connection strength of pipe fittings through dimensional measurement and working pressure calculation, and can be used to calculate the connection strength of axially compressed fittings of different sizes. This invention reduces testing costs, shortens the design cycle, effectively improves design efficiency, and has good practicality.

Description

Technical Field

[0001] This invention belongs to the technical field of aircraft piping system assembly, and specifically relates to a method for evaluating the connection strength of axially compressed pipe joints. Background Technology

[0002] Pipe fittings are crucial components in piping systems, directly impacting the overall sealing, strength, and durability of the system. Pipe fitting testing involves multiple aspects, including mechanical properties, sealing performance, corrosion resistance, and pressure resistance, to ensure safe and reliable operation under various environments. Mechanical property testing aims to evaluate the pipe fitting's tensile strength, yield strength, hardness, and other mechanical properties to ensure it won't break or deform during use. Tensile strength testing involves applying tension using a tensile testing machine to determine the material's maximum tensile strength. Yield strength testing assesses the maximum stress the material can withstand before permanent deformation begins. Hardness testing uses methods such as Rockwell hardness and Brinell hardness to evaluate the joint material's hardness, ensuring sufficient wear and compressive strength. The connection strength of pipe fittings is one of the design indicators, evaluating whether the structural connection force meets requirements under axial loads. Currently, in China, the connection strength of pipe fittings is generally verified through physical testing, which increases the design cycle and cost. Methods for accurately predicting the connection strength of fittings in advance using theoretical calculations are still lacking in China. Summary of the Invention

[0003] The purpose of this invention is to provide a method for evaluating the connection strength of axially compressed pipe joints, thereby addressing the aforementioned problems.

[0004] This invention is mainly achieved through the following technical solutions:

[0005] A method for evaluating the connection strength of axially compressed pipe joints, wherein the minimum connection strength F of the pipe joint is... min for:

[0006] F min ≥K3(F Z +F f (6)

[0007] Where: K3 is the safety factor;

[0008] F Z This refers to the axial force between the inner ring of the pipe joint and the conduit at the sealing position of the pipe joint;

[0009] F f This refers to the frictional force generated by the radial force of the conduit.

[0010] To better realize the present invention, further, F Z The calculation formula is:

[0011]

[0012] Where: K1 is a constant term;

[0013] R is the diameter of the catheter;

[0014] μ1 is the frictional force between the groove of the inner ring of the connector and the conduit;

[0015] P0 is the working pressure of the pipeline;

[0016] h is the contact depth between the groove of the inner ring of the connector and the conduit;

[0017] H represents the groove depth of the inner ring of the connector.

[0018] To better realize the present invention, further, F f The calculation formula is:

[0019]

[0020] Where: L is the contact length between the groove of the inner ring of the connector and the conduit;

[0021] F(x) is the contact surface pressure;

[0022] μ2 represents the frictional force between the inner ring of the connector (excluding the groove) and the conduit.

[0023] To better realize the present invention, further, the minimum connection strength F of the pipe joint is... min for:

[0024]

[0025] To better realize the present invention, the following steps are further included:

[0026] Step S1: Determine the sealing position dimensions and working pressure P0 of the pipe joint based on its structure and operating conditions; the sealing position dimensions include the conduit diameter R, the contact depth h between the groove of the inner ring of the joint and the conduit, and the groove depth H of the inner ring of the joint.

[0027] Step S2: Calculate the axial force F between the inner ring of the pipe joint and the conduit at the sealing position of the pipe joint. Z for:

[0028]

[0029] Where: K1 is a constant term;

[0030] μ1 is the frictional force between the groove of the inner ring of the connector and the conduit;

[0031] Step S3: Calculate the radial force F between the inner ring of the connector and the conduit. j The contact area between the inner ring of the connector and the conduit is equivalent to a region with an equivalent elastic modulus E. * The contact between an elastic cylinder and a rigid plane, with the contact center as the origin, and the contact pressure F on the contact surface. j (x) is:

[0032]

[0033] Where: K2 is the correction factor;

[0034] L is the contact length between the groove of the inner ring of the connector and the conduit;

[0035] x is the contact length between the groove of the inner ring of the connector and the conduit;

[0036] Step S4: Calculate the radial force F j The frictional force F generated f :

[0037]

[0038] Where: μ2 is the frictional force between the inner ring of the connector (excluding the groove) and the conduit;

[0039] Step S5: Calculate the minimum connection strength F of the pipe fitting. min :

[0040]

[0041] Where: K3 is the safety factor.

[0042] To better realize the present invention, further, in step S3, the equivalent elastic modulus E * The calculation formula is as follows:

[0043]

[0044] Then the contact pressure F at the contact surface j (x) is:

[0045]

[0046] Among them: E S The elastic modulus of the inner ring of the joint (MPa);

[0047] E c The elastic modulus of the catheter (MPa);

[0048] Vs is the Poisson's ratio of the material of the inner ring of the joint;

[0049] Vc is the Poisson's ratio of the conduit material.

[0050] The beneficial effects of this invention are as follows:

[0051] This invention allows for the assessment of the minimum connection strength of pipe fittings through dimensional measurement and working pressure calculation, and can be used to calculate the connection strength of axially compressed fittings of different sizes. This invention reduces testing costs, shortens the design cycle, effectively improves design efficiency, and has good practicality. Attached Figure Description

[0052] Figure 1 This is a schematic diagram of the axial extrusion pipe joint of the present invention;

[0053] Figure 2 This is a schematic diagram of the force applied to the axially compressed pipe joint of the present invention.

[0054] Wherein: 1-outer ring of connector, 2-inner ring of connector, 3-catheter. Detailed Implementation

[0055] Example 1:

[0056] A method for evaluating the connection strength of axially extruded pipe joints, which accurately predicts the connection strength of axially extruded joints in advance, includes the following steps:

[0057] Step 1: Determine the structural dimensions and working pressure of the pipe fitting: Based on the structure and working conditions of the pipe fitting, determine the sealing position dimensions and working pressure of the pipe fitting.

[0058] Step 2: Calculate the axial force F between the inner ring 2 of the connector and the conduit 3. Z Based on the structure and assembly relationship of the pipe joint, and considering the elastic-plastic deformation of the material during the connection process, the axial force at the sealing position of the pipe joint is calculated using methods including but not limited to theoretical and numerical calculations.

[0059]

[0060] in:

[0061] P0 is the pipeline working pressure (MPa);

[0062] h is the contact depth (mm) between the groove of the inner ring 2 of the connector and the conduit 3;

[0063] H is the groove depth (mm) of the inner ring 2 of the connector;

[0064] R is the diameter of catheter 3 (mm);

[0065] μ1 is the frictional force between the groove of the inner ring 2 of the connector and the conduit 3;

[0066] K1 is a constant term.

[0067] Step 3: Calculate the radial force F between the inner ring 2 of the connector and the conduit 3. j The contact area between the inner ring 2 of the connector and the conduit 3 is equivalent to the contact between an elastic cylinder with an equivalent elastic modulus E and a rigid plane. With the contact center as the origin, the contact pressure F on the contact surface... j (x) is:

[0068]

[0069] in:

[0070] R is the diameter of catheter 3 (mm);

[0071] L is the contact length (mm) between the groove of the inner ring 2 of the connector and the conduit 3;

[0072] K2 is the correction factor, which is a constant term;

[0073] x is the contact length between the groove of the inner ring 2 of the connector and the conduit 3; both can be set directly.

[0074] E * This is the equivalent elastic modulus. The calculation formula is:

[0075]

[0076] in:

[0077] E * It is the equivalent elastic modulus (MPa);

[0078] E S The elastic modulus of the inner ring 2 of the joint (MPa);

[0079] E c The elastic modulus of the catheter (MPa) is 3.

[0080] Vs is the Poisson's ratio of the material of the inner ring 2 of the joint;

[0081] Vc is the Poisson's ratio of the material of catheter 3.

[0082] Step 4: Calculate the frictional force F generated by the radial force. f :

[0083]

[0084] in:

[0085] L is half the width of the contact surface between the inner ring 2 of the connector and the conduit 3;

[0086] F(x) is the contact surface pressure; F(x) is simply F j (x) is a part of it;

[0087] μ1 is the frictional force between the groove of the inner ring 2 of the connector and the conduit 3.

[0088] μ2 is the frictional force between the inner ring 2 of the connector and the conduit 3, excluding the groove.

[0089] Step 5: Calculate the minimum pull-out resistance of the pipe joint:

[0090] F min ≥K3(F Z +F f (6)

[0091] Right now:

[0092]

[0093] Where: K3 is the safety factor, which can be set directly;

[0094] The minimum pull-out resistance value is the minimum connection strength value of the pipe joint.

[0095] Example 2:

[0096] A method for evaluating the connection strength of axially extruded pipe joints, specifically for aircraft axially extruded joints, such as... Figure 1 As shown, the axial compression fitting includes, from top to bottom, an outer ring 1, an inner ring 2, and a conduit 3. The process includes the following steps:

[0097] Step 1, such as Figure 2 As shown, determine the structural dimensions and working pressure of the pipe fitting, where the working pressure is 35 MPa;

[0098] Step 2: Calculate the axial force F between the inner ring 2 of the connector and the conduit 3. Z :

[0099]

[0100] in:

[0101] μ1 is 0.3; p is 35 MPa; h is 0.12 mm; H is 0.16 mm; R is 6 mm; K1 is 8; by including but not limited to formula (2) and finite element method, the axial force Fz at the sealing area position can be calculated to be 1560 N.

[0102] Step 3: Calculate the radial force F in the contact area. j :

[0103]

[0104] in:

[0105] E S 110000MPa; E cThe pressure is 108000 MPa; Vs is 0.33; V C The value is 0.33; L is 0.4 mm; R is 6 mm. The radial force F at the sealing area can be calculated using methods including but not limited to formula (8) and the finite element method. j for:

[0106]

[0107] Step 4: Calculate the frictional force F generated by the radial force. f

[0108]

[0109] The frictional force F generated by the radial force can be calculated using methods including, but not limited to, formula (5) and the finite element method. f It is 2395N.

[0110] Step 5: Calculate the minimum pull-out resistance of the pipe joint:

[0111] F min ≥K3(F Z +F f ) = 1.1 × (1560 + 2395) = 4350 N

[0112] The actual measured value is 4556N. The error between the calculated value and the measured value in this embodiment is within 5%. Therefore, the evaluation method of the present invention has high reliability, reduces test costs, shortens the design cycle, effectively improves design efficiency, and has good practicality.

[0113] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method of evaluating the connection strength of an axial extrusion pipe joint, characterized by, Includes the following steps: Step S1: according to the structure and working condition of the pipe joint, determine the sealing position size of the pipe joint and the working pressure of the pipe joint P 0 ; the sealing position size includes the conduit diameter R , the contact depth of the groove of the inner ring of the joint with the conduit h、 the groove depth of the inner ring of the joint H； Step S2: Calculate the axial force between the inner joint ring of the pipe joint sealing position and the conduit F Z = 0. （2） wherein: K 1 is a constant term; μ 1 This refers to the frictional force between the groove of the inner ring of the connector and the conduit. Step S3: Calculate the radial force between the inner ring of the connector and the conduit. F j The contact area between the inner ring of the connector and the conduit is equivalent to a region with an equivalent elastic modulus E. * The contact between an elastic cylinder and a rigid plane, with the contact center as the origin, and the contact pressure of the contact surface. F j ( x )for: (-L≤x≤L,0<2L≤R)(3) in: K 2 is the correction factor; L This refers to the contact length between the groove of the inner ring of the connector and the conduit; x The contact length between the groove of the inner ring of the connector and the conduit; Step S4: Calculate radial force F j The frictional force generated F f : （5） Where: μ2 is the frictional force between the inner ring of the connector (excluding the groove) and the conduit; Step S5: Calculate the minimum connection strength of the pipe fitting. F min : （6） （7） Where: K3 is the safety factor; F Z This refers to the axial force between the inner ring of the pipe joint and the conduit at the sealing position of the pipe joint; F f This refers to the frictional force generated by the radial force of the conduit.

2. The method for evaluating the connection strength of an axially compressed pipe joint according to claim 1, characterized in that, The equivalent elastic modulus E in the step S3 * The calculation formula is as follows: （4） Then the contact pressure of the contact surface F j ( x )for: ； wherein: E S is the inner loop modulus of elasticity of the joint (MPa); E c Elastic modulus of the conduit (MPa); Vs is the Poisson's ratio of the material of the inner ring of the joint; Vc is the Poisson's ratio of the conduit material.

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