A method for calculating leakage at the sealing interface of flared pipe joints

Abstract

The present invention discloses a method for calculating the leakage of the sealing interface of a flared pipe joint. First, the relationship between the axial preload and the friction torque of the sealing interface of the flared pipe joint is obtained; secondly, the joint sealing interface is regarded as a rough interface in contact under the action of a load, and the porosity of the rough interface micro-convex body after contact deformation under the action of the load is introduced into the interface separation calculation formula; thirdly, the relationship between the contact depth and the load of the rough interface under different loads is obtained, and the interface separation of the rough interface under different loads is obtained according to the relationship between the contact depth and the porosity of the rough interface after deformation; finally, the interface separation is introduced into the existing pipe joint leakage calculation formula, and the leakage of the sealing interface of the flared pipe joint calculated under different loads is obtained. The present invention can calculate the interface separation by directly obtaining the relevant parameters of the flared pipe joint, which greatly simplifies the calculation steps of the interface separation when calculating the leakage.

Description

Technical Field

[0001] The invention belongs to the technical field of sealing detection of aviation pipe joints, and in particular relates to a method for calculating leakage of a sealing interface of a flared pipe joint. Background Art

[0002] The aircraft's hydraulic lines, serving as its "nervous system," are located throughout the aircraft. The main lines have diameters ranging from 2 to 40 mm and are typically connected using flared or non-flared joints. Flared joints utilize a bushing that is squeezed by the inner threads of the outer nut and the outer threads of the tapered joint, forming a sealing ring that fits the tapered inner wall of the flared pipe against the outer wall of the tapered joint to ensure sealing performance. During its service life, the oil pressure fluctuates between 4 and 32 MPa. At the same time, the lines are constantly subjected to external aerodynamic loads, vibration loads, temperature loads, and other cyclic effects, making it difficult for them to maintain 10 -6 The tightness requirement of approximately mBarL / s makes joint sealing defects highly susceptible to occurrence. This leads to frequent leaks from pipe joints after landing, seriously impacting service safety and reliability. Furthermore, during aircraft manufacturing and operation, leaks from pipe joints can lead to waste of resources, environmental pollution, and compromise the efficiency of aircraft power systems. In severe cases, they can cause fatal failures and even major flight accidents. Therefore, calculating the leakage rate of aircraft hydraulic pipe joints is crucial.

[0003] Existing leakage calculations for hydraulic flared pipe joints mostly rely on numerical simulations. Theoretically, only the Persson contact mechanics model is used to calculate leakage. However, this method has a complex calculation process, and the stress distribution probability is a statistical quantity, making it difficult to accurately determine the specific value. Furthermore, the influence of the interface tangential load on the contact separation is not considered during the calculation process, which affects the accuracy of the calculation. Summary of the Invention

[0004] In view of the above background technology, the purpose of the present invention is to provide a method for calculating the leakage of the sealing interface of a flared pipe joint, so as to solve the problems existing in the existing method for calculating the leakage of a hydraulic flared pipe joint.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for calculating leakage at a sealing interface of a flared pipe joint comprises the following steps:

[0007] S1. Since the tightening torque of the sealing interface of the flared pipe joint is composed of the friction torque of the contact surface between the internal thread and the external thread and the friction torque of the contact surface between the nut surface and the bushing, the internal friction torque of the flared pipe joint is calculated to obtain the relationship between the axial preload and the friction torque of the sealing interface;

[0008] S2. The sealing interface of the flared pipe joint is regarded as a rough interface in contact under load. Under the load, the micro-convex bodies of the rough interface undergo contact deformation, and the relationship between the porosity and contact depth of the rough interface after deformation is obtained;

[0009] S3. Based on the definition of interface separation, the relationship between the porosity of the rough interface and the contact depth after the contact deformation of the rough interface micro-asperities under load is introduced to obtain the relationship between the interface separation and the contact depth;

[0010] S4. Obtain the relationship between the contact depth and load of the rough interface under different loads, including:

[0011] (1) Under normal load:

[0012] Based on the relationship between the normal load and contact depth of a single asperity in the elastic and elastoplastic stages of a rough interface under normal load, and combined with the number of contact points on the rough interface calculated based on the contact volume probability characterization method, the relationship between the contact depth and load in the elastic and elastoplastic stages of a rough interface under normal load is obtained.

[0013] (2) Under the combined compression and shear action of normal load and tangential load:

[0014] ① Elastic stage:

[0015] Considering the effect of adhesion from an energy perspective, the total energy of the system under normal load and the shear energy under tangential load of the two asperities are combined, and combined with the Hertz formula, the relationship between the total energy of the entire system under the combined action of compression and shear and the normal and tangential loads is obtained. When the entire system is stable under the combined action of compression and shear, the partial derivative of the total energy with respect to the applied load is 0, and the relationship between the contact radius of a single asperity and the load is obtained. Based on the relationship between the contact radius and contact depth and the contact volume probability characterization method, the relationship between the contact depth and load in the elastic stage of the rough interface under the combined action of compression and shear is obtained.

[0016] ② Elastic-plastic stage:

[0017] The effect of adhesion is not considered in the elastic-plastic stage. Based on the von Mises stress yield criterion, the change in the true contact area of ​​a single asperity in the elastic-plastic stage under combined compression and shear is obtained. The calculation formula for the contact depth of a single asperity is derived from the change in the true contact area. Since the total normal load on the rough interface is the product of the normal load on a single asperity and the number of contact points on the rough interface, the relationship between the contact depth and load of the entire rough interface in the elastic-plastic stage under combined compression and shear is obtained.

[0018] S5. Introducing the relationship between the contact depth and load of the rough interface under different loads into the relationship between the interface separation and contact depth, and based on the relationship between the axial preload of the sealing interface and the normal pressure perpendicular to the sealing interface and the tangential force parallel to the sealing interface, replacing the normal load with the normal pressure perpendicular to the sealing interface and replacing the tangential load with the tangential force parallel to the sealing interface, to obtain a calculation formula for the interface separation of the rough interface under different loads;

[0019] S6. Calculate the interface separation value based on the calculation formula of the interface separation of the rough interface under different loads, and substitute it into the existing pipe joint leakage calculation formula to obtain the calculated leakage of the flared pipe joint sealing interface under different loads.

[0020] Furthermore, in step S1, the friction torque is expressed as follows:

[0021] The expression of the friction torque obtained by taking the distance between the internal force of the flared pipe joint and the contact surface of the internal thread and the external thread is:

[0022] ;

[0023] Where, is the friction torque between the internal thread and the external thread contact surface, is the axial preload of the sealing interface, is the thread pitch, is the friction coefficient of the thread surface, is the thread pitch diameter, Half the thread angle;

[0024] The friction torque obtained by taking the distance between the nut surface and the bushing contact surface from all forces inside the flared pipe joint is:

[0025] ;

[0026] Where, is the friction torque between the nut surface and the bushing contact surface, is the friction coefficient between the bushing and the nut, Equivalent radius of contact area;

[0027] Then we have:

[0028] or .

[0029] Furthermore, in step S2, the relationship between the porosity and contact depth of the rough interface after deformation is as follows:

[0030] ;

[0031] Where, is the porosity of the rough interface under load; is the initial void ratio, is the contact depth, It is the distance between the highest point of the upper rough interface and the lowest point of the lower rough interface in contact.

[0032] Furthermore, in step S3, the relationship between the interface separation and the contact depth is:

[0033] ;

[0034] Where, is the interface separation.

[0035] Furthermore, in step S4, the normal load on a single asperity in the elastic stage and the elastic-plastic stage under the action of the normal load is The relationship with contact depth is as follows:

[0036] ;

[0037] Where, is the normal load on a single asperity, is the equivalent Young's modulus, Equivalent asperity radius, is the normal load corresponding to the asperity entering the plastic stage, is the yield strength, is the critical contact depth;

[0038] Number of contact points on the rough interface for:

[0039] ;

[0040] Where, is the total number of asperities on the rough interface, is the normalized height, , and is a constant related to the support curve of the rough surface;

[0041] The total normal load on the rough interface is The expression is:

[0042] ;

[0043] The relationship between the contact depth and load of the rough interface in the elastic stage and the elastic-plastic stage under normal load is obtained as follows:

[0044] .

[0045] Furthermore, in step S4, in the elastic stage under the combined action of compression and shear, the total energy of the system of the two asperities under the normal load includes the elastic energy stored in the asperities, the energy generated by the load, and the adhesive energy. The two asperities generate shear energy under the tangential load. The relationship between the total energy of the system of the two asperities under the normal load and the elastic energy stored in the asperities, the energy generated by the load, and the adhesive energy is: ; Combined with Hertz's formula, we have:

[0046] ;

[0047] ;

[0048] ;

[0049] Where, is the total energy of the system under the normal load of the two asperities, is the elastic energy stored in the asperities, is the energy generated by the load, For adhesion energy; For adhesion, is the external load, For external load The corresponding contact depth, Considering adhesion The external load is unloaded until the adhesion force is maintained while keeping the original contact radius unchanged. The corresponding contact depth, , , 、 are the viscosity coefficients of the two asperities, is the viscosity coefficient of the contact interface between the two asperities, is the contact radius of a single asperity under the combined action of compression and shear, according to Hertz's formula: ;

[0050] The total energy of the system under the normal load of the two asperities is for:

[0051] ;

[0052] Combined with Hertz's formula, the shear energy generated by two asperities under tangential load is for:

[0053] ;

[0054] Where, is the tangential load on a single asperity, is the tangential deformation, is the equivalent shear modulus, , 、 are the Poisson's ratios of the two asperities, 、 are the shear moduli of the two asperities respectively;

[0055] The total energy of the entire system under the combined action of compression and shear is obtained for:

[0056] ;

[0057] According to the stability of the entire system under the combined action of compression and shear, the partial derivative of the total energy with respect to the external load is 0, that is: , then ,because , and then the relationship between the contact radius of a single asperity and the load is obtained as follows:

[0058] ;

[0059] The relationship between the contact radius and contact depth of a single asperity is: , the relationship between the contact depth and load of the rough interface in the elastic stage under the combined action of compression and shear is obtained as follows:

[0060] ;

[0061] Where, is the total tangential load on the rough interface.

[0062] Furthermore, in step S4, in the elastic-plastic stage under the combined action of compression and shear, the change in the actual contact area of ​​a single micro-convex body is:

[0063] ;

[0064] Where, is the actual contact area of ​​a single asperity under the combined action of compression and shear, is the actual contact area of ​​a single asperity under normal load only, is the material parameter;

[0065] in:

[0066] ;

[0067] ;

[0068] ;

[0069] Where, is the contact depth of a single asperity under normal load only;

[0070] The calculation formula of the contact depth of a single micro-convex body obtained from the change of the real contact area is:

[0071] ;

[0072] The relationship between the contact depth and load of the entire rough interface in the elastic-plastic stage under the combined action of compression and shear is obtained as follows:

[0073] .

[0074] Furthermore, in step S5, the relationship between the axial preload force of the sealing interface, the normal pressure perpendicular to the sealing interface, and the tangential force parallel to the sealing interface is as follows:

[0075] ;

[0076] ;

[0077] Where, is the positive pressure perpendicular to the sealing interface, is the tangential force parallel to the sealing interface, It is half the angle of the flare of the tapered joint;

[0078] The calculation formula of the interface separation of the rough interface under normal load is as follows:

[0079] Elasticity stage:

[0080] ;

[0081] Elastic-plastic stage:

[0082] ;

[0083] in, or .

[0084] Furthermore, in step S5, the relationship between the axial preload force of the sealing interface, the normal pressure perpendicular to the sealing interface, and the tangential force parallel to the sealing interface is as follows:

[0085] ;

[0086] ;

[0087] Where, is the positive pressure perpendicular to the sealing interface, is the tangential force parallel to the sealing interface, It is half the angle of the flare of the tapered joint;

[0088] The calculation formula of the interface separation of the rough interface under the combined action of compression and shear is as follows:

[0089] Elasticity stage:

[0090] ;

[0091] Elastic-plastic stage:

[0092] ;

[0093] in, or .

[0094] Compared with the shortcomings and deficiencies of the prior art, the present invention has the following beneficial effects:

[0095] The present invention regards the sealing interface of the flared pipe joint as a rough interface in contact under load, and provides a method for calculating the interface separation of the rough interface under different loads. The interface separation is a key parameter for calculating leakage. The interface separation of the present invention is calculated based on the relevant parameters of the flared pipe joint that can be directly obtained, which greatly simplifies the steps of calculating the interface separation when calculating leakage. Compared with the traditional leakage calculation method that only considers the normal load, the method for calculating leakage under normal load proposed by the present invention can be calculated by directly obtaining the relevant parameters of the pipe joint, and the calculation process is simple. In addition, the present invention also considers the influence of the interface tangential load on the contact separation, and proposes a method for calculating leakage under the combined action of compression and shear. The leakage calculation results are basically consistent with the measured results, thereby verifying the accuracy of the leakage calculation of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0096] Figure 1 is a cross-sectional view along the middle axis of a flared pipe joint provided by an embodiment of the present invention;

[0097] Figure 2 yes Figure 1 Enlarged view of point A in the middle;

[0098] Figure 3 is a schematic diagram of contact between two rough interfaces provided by an embodiment of the present invention;

[0099] Figure 4 Schematic diagram of the change in contact radius of two asperities under the combined action of compression and shear provided by an embodiment of the present invention;

[0100] Figure 5 The relationship between the normal load and the contact depth when the adhesion force is considered and when the adhesion force is not considered is provided in an embodiment of the present invention;

[0101] Figure 6The leakage rate changes with pressure as calculated based on the method of the present invention, provided in an embodiment of the present invention;

[0102] Figure 7 3 is a comparison chart of the leakage rate calculated based on the method of the present invention and the experimental measurement results provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0103] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0104] 1. Mechanical analysis of flared pipe joints

[0105] The flared pipe joint consists of four parts: the outer nut, the bushing, the flared pipe, and the tapered joint. The inner thread of the outer nut and the outer thread of the tapered joint engage and squeeze the bushing, and the tapered inner wall of the flared pipe and the outer wall of the tapered joint fit together to form a sealing ring to ensure sealing performance. The cross-sectional view of the flared pipe joint along the middle axis is as follows: Figure 1 As shown, the tightening torque It consists of two parts, namely the friction torque of the contact surface between the internal thread and the external thread And the friction torque between the nut surface and the bushing contact surface .

[0106] The distance between the contact surface of the internal thread and the external thread of the joint can be obtained by taking the total force inside the joint The expression is:

[0107] ;

[0108] Where, is the axial preload of the sealing interface, is the thread pitch, is the friction coefficient of the thread surface, is the thread pitch diameter, Half the thread angle;

[0109] The distance between the nut surface and the bushing contact surface can be obtained by taking all the forces inside the joint The expression is:

[0110] ;

[0111] Where, is the friction coefficient between the bushing and the nut, is the equivalent radius of the contact area;

[0112] and The expression transformation is:

[0113] or .

[0114] Figure 1 The enlarged image of point A is as follows Figure 2 As shown, the axial preload of the sealing interface Decomposed into the positive pressure perpendicular to the sealing interface and tangential forces parallel to the sealing interface , the calculation formula is:

[0115] ;

[0116] ;

[0117] Where, It is half the flare angle of the tapered connector.

[0118] 2. Calculation of interface separation

[0119] 2.1 Interface separation is the key parameter for calculating leakage. The leakage calculation formula for flared pipe joints is as follows:

[0120] ;

[0121] Where, is the leakage amount, is the pressure difference, is the interface separation, is the fluid viscosity coefficient, is the sealing ring radius, is the sealing ring width.

[0122] 2.2 Schematic diagram of contact between two rough interfaces Figure 3 As shown, the uncontacted area is defined as the void volume V void , the void volume calculation formula is:

[0123] ;

[0124] Where, is the void ratio of the rough interface under no load, which is defined as the void volume With total volume The ratio of is the distance between the highest point of the upper rough interface and the lowest point of the lower rough interface in contact, is the nominal contact area of ​​the rough interface.

[0125] According to the definition of interface separation, the calculation formula of interface separation under no load is:

[0126] .

[0127] 2.3 The sealing interface of the flared pipe joint is regarded as a rough interface in contact under load. Under the action of load, the micro-convex body of the rough interface undergoes contact deformation. The calculation formula of the porosity of the rough interface after deformation is:

[0128] ;

[0129] Where, is the porosity of the rough interface under load, is the initial void ratio, is the contact depth, is the distance between the highest point of the upper rough interface and the lowest point of the lower rough interface in contact;

[0130] Porosity of rough interface after deformation Replace the void ratio of the rough interface under no load , introduced into the calculation formula of interface separation, the calculation formula of interface separation under load is obtained:

[0131] .

[0132] 3. Relationship between rough interface contact depth and load

[0133] Since the parameter of rough interface contact depth exists in the calculation of interface separation under load, and when the sealing interface of the flared pipe joint is regarded as a rough interface in contact under load, the axial preload F of the sealing interface can be directly obtained. Therefore, the relationship between the interface separation under load and the load can be obtained through the relationship between the rough interface contact depth and the load, thereby simplifying the calculation of the interface separation. Next, the contact depth of the rough interface under different loads is analyzed.

[0134] 3.1 Under normal load:

[0135] The relationship between the normal load and contact depth of a single asperity in the elastic and elastoplastic stages under normal load on a rough interface is as follows:

[0136] ;

[0137] Where, is the normal load on a single asperity, is the equivalent Young's modulus, Equivalent asperity radius, is the normal load corresponding to the asperity entering the plastic stage, is the yield strength, is the critical contact depth;

[0138] Calculating the number of contact points on a rough interface based on the contact volume probability representation method :

[0139] ;

[0140] Where, is the total number of asperities on the rough interface, is the normalized height, , and is a constant related to the support curve of the rough surface;

[0141] The total normal load on the rough interface is the product of the normal load on a single asperity and the number of contact points on the rough interface. The total normal load on the rough interface can be obtained as Contact depth The relationship is:

[0142] ;

[0143] The contact depth of the rough interface under normal load can be obtained as The expression:

[0144] .

[0145] 3.2 Under the combined compression and shear action of normal load and tangential load:

[0146] ① Elastic stage:

[0147] First consider the change of contact radius of two asperities under the combined action of compression and shear, such as Figure 4 As shown, the two radii are The viscosity coefficients of the micro-convex bodies are 、 , the viscosity coefficient of the asperity contact interface is , which produces a contact depth of deformation.

[0148] First, the contact radius without considering the adhesion condition can be obtained according to the Hertz formula:

[0149] ,in ;

[0150] Where, is the asperity contact radius.

[0151] Secondly, the surface force is introduced to consider the effect of adhesion from the energy perspective. The total energy of the system under the normal load of the two convex bodies is Including elastic energy stored in asperities , the energy generated by the load and adhesion energy , the following relationship exists:

[0152] ;

[0153] Figure 5 The relationship between normal load and contact depth when adhesion is considered and when adhesion is not considered. When the two convex bodies are under the action of normal load, the load is loaded to The corresponding contact depth is , the contact depth reaches The corresponding external load is ; Then, consider the adhesion When the external load is unloaded, the original contact radius is kept unchanged. When the external load is unloaded to the adhesion The corresponding contact depth is .according to Figure 5 Combined with the above Hertz formula, the elastic energy stored in the micro-convex body can be calculated respectively , the energy generated by the load and adhesion energy , the calculation formula is as follows:

[0154] ;

[0155] ;

[0156] ;

[0157] Where, , is the contact radius of a single asperity under the combined action of compression and shear, according to Hertz's formula: ;

[0158] Then the total energy of the system under normal load is:

[0159] ;

[0160] The calculation formula for the shear energy generated by two micro-convex bodies under the action of tangential load is:

[0161] ;

[0162] Where, is the shear energy generated by the tangential load, is the tangential load on a single asperity, is the tangential deformation, is the equivalent shear modulus, , 、 are the Poisson's ratios of the two asperities, 、 are the shear moduli of the two asperities respectively;

[0163] Combined with the above Hertz formula, the calculation formula for the shear energy generated by two asperities under tangential load can be transformed into:

[0164] ;

[0165] The total energy of the entire system under the combined action of compression and shear of the two convex bodies is obtained The relationship between the total energy of the system under normal load and the shear energy under tangential load is:

[0166] ;

[0167] According to the partial derivative of the total energy of the entire system under the combined action of compression and shear when the entire system is stable, the value of the total energy to the external load is 0, that is, , then ,because , and then the calculation formula of the contact radius of a single asperity under the combined action of compression and shear is obtained as follows:

[0168] ;

[0169] and , based on the contact volume probability characterization method, , , is the total tangential load on the rough interface. From a single asperity to the entire contact interface, the expression of the contact depth of the rough interface in the elastic stage under the combined action of compression and shear can be obtained as follows:

[0170] .

[0171] ② Elastic-plastic stage:

[0172] When entering the elastic-plastic stage, the effect of adhesion is not considered. = 0, based on the von Mises stress yield criterion, the change of the true contact area of ​​a single asperity in the elastic-plastic stage under the combined action of compression and shear is obtained:

[0173] ;

[0174] Where, is the actual contact area of ​​a single asperity under the combined action of compression and shear, is the actual contact area of ​​a single asperity under normal load only, is the material parameter;

[0175] in:

[0176] ;

[0177] ;

[0178] ;

[0179] Where, is the contact depth of a single asperity under normal load only;

[0180] The expression of the contact depth of a single asperity in the elastic-plastic stage under the combined action of compression and shear is obtained from the change of the real contact area:

[0181] ;

[0182] According to the fact that the total normal load on the rough interface is the product of the normal load on a single asperity and the number of contact points on the rough interface, the expression for the contact depth of the entire rough interface in the elastic-plastic stage under the combined action of compression and shear can be obtained:

[0183] .

[0184] 4. The expression of the contact depth of the rough interface under different loads is introduced into the calculation formula of the interface separation under load, and the axial preload of the sealing interface is calculated according to the Positive pressure perpendicular to the sealing interface and tangential forces parallel to the sealing interface The relationship between the positive pressure perpendicular to the sealing interface Instead of a normal load, a tangential force parallel to the sealing interface is used Instead of the tangential load, the calculation formula for the interface separation of the rough interface under different loads is obtained:

[0185] (1) Under normal load:

[0186] Elasticity stage:

[0187] ;

[0188] Elastic-plastic stage:

[0189] ;

[0190] (2) Under the combined action of compression and shear:

[0191] Elasticity stage:

[0192] ;

[0193] Elastic-plastic stage:

[0194] ;

[0195] in, or .

[0196] 5. Calculation of leakage at the sealing interface of flared pipe joints

[0197] When calculating the leakage of the sealing interface of the flared pipe joint, first calculate the axial preload of the sealing interface based on the relevant parameters of the flared pipe joint. , then the axial preload and other parameter values ​​are brought into the interface separation calculation formula of the rough interface under different loads to obtain the corresponding interface separation value, and then the interface separation value is brought into the existing pipe joint leakage calculation formula for calculation, and the calculated leakage of the flared pipe joint sealing interface under different loads is obtained.

[0198] Since the traditional method does not consider the effect of the interface tangential load on the contact separation when calculating the leakage of the flared pipe joint sealing interface, in this case, the method for calculating the leakage of the flared pipe joint sealing interface under the normal load proposed in the present invention can be directly used for calculation. However, if the comprehensive load effect on the flared pipe joint sealing interface is considered, the method for calculating the leakage of the flared pipe joint sealing interface under the combined action of compression and shear proposed in the present invention can be used for calculation. The leakage is calculated using the method for calculating the leakage of the flared pipe joint sealing interface under the combined action of compression and shear proposed in the present invention, and compared with the experimental results. The parameters of the flared pipe joint are shown in Table 1:

[0199] Table 1 Parameters of flared pipe joints

[0200]

[0201] The literature mentioned in Table 1 is Deng L, Luo B, Zhang K, et al. A novel analytic model for sealing performance of static metallic joint considering the yieldhardening effect[J]. The International Journal of Advanced Manufacturing Technology, 2023, 126(5): 1997-2010. The leakage rate of the sealing interface of the flared pipe joint under the combined action of compression and shear proposed in this invention is calculated as follows: Figure 6 As shown in the figure, the comparison between the leakage rate calculated based on the method of the present invention and the experimental measurement results is as follows: Figure 7 As shown, it can be seen that the calculated results of the leakage amount are basically consistent with the experimental measurement results, thereby verifying the accuracy of the leakage amount calculation method of the flared pipe joint sealing interface of the present invention.

[0202] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for calculating the leakage of the sealing interface of a flared pipe joint, characterized in that: The steps include: S1. Since the tightening torque of the sealing interface of the flared pipe joint is composed of the friction torque of the contact surface between the internal thread and the external thread and the friction torque of the contact surface between the nut surface and the bushing, the internal friction torque of the flared pipe joint is calculated to obtain the relationship between the axial preload and the friction torque of the sealing interface; S2. The sealing interface of the flared pipe joint is regarded as a rough interface in contact under load. Under the load, the micro-convex bodies of the rough interface undergo contact deformation, and the relationship between the porosity and contact depth of the rough interface after deformation is obtained; S3. Based on the definition of interface separation, the relationship between the porosity of the rough interface and the contact depth after the contact deformation of the rough interface micro-asperities under load is introduced to obtain the relationship between the interface separation and the contact depth; S4. Obtain the relationship between the contact depth and load of the rough interface under different loads, including: (1) Under normal load: Based on the relationship between the normal load and contact depth of a single asperity in the elastic and elastoplastic stages of a rough interface under normal load, and combined with the number of contact points on the rough interface calculated based on the contact volume probability characterization method, the relationship between the contact depth and load in the elastic and elastoplastic stages of a rough interface under normal load is obtained. (2) Under the combined compression and shear action of normal load and tangential load: ① Elastic stage: Considering the effect of adhesion from an energy perspective, the total energy of the system under normal load and the shear energy under tangential load of the two asperities are combined, and combined with the Hertz formula, the relationship between the total energy of the entire system under the combined action of compression and shear and the normal and tangential loads is obtained. When the entire system is stable under the combined action of compression and shear, the partial derivative of the total energy with respect to the applied load is 0, and the relationship between the contact radius of a single asperity and the load is obtained. Based on the relationship between the contact radius and contact depth and the contact volume probability characterization method, the relationship between the contact depth and load in the elastic stage of the rough interface under the combined action of compression and shear is obtained. ② Elastic-plastic stage: The effect of adhesion is not considered in the elastic-plastic stage. Based on the von Mises stress yield criterion, the change in the true contact area of ​​a single asperity in the elastic-plastic stage under combined compression and shear is obtained. The calculation formula for the contact depth of a single asperity is derived from the change in the true contact area. Since the total normal load on the rough interface is the product of the normal load on a single asperity and the number of contact points on the rough interface, the relationship between the contact depth and load of the entire rough interface in the elastic-plastic stage under combined compression and shear is obtained. S5. Introducing the relationship between the contact depth and load of the rough interface under different loads into the relationship between the interface separation and contact depth, and based on the relationship between the axial preload of the sealing interface and the normal pressure perpendicular to the sealing interface and the tangential force parallel to the sealing interface, replacing the normal load with the normal pressure perpendicular to the sealing interface and replacing the tangential load with the tangential force parallel to the sealing interface, to obtain a calculation formula for the interface separation of the rough interface under different loads; S6. Calculate the interface separation value based on the calculation formula of the interface separation of the rough interface under different loads, and substitute it into the existing pipe joint leakage calculation formula to obtain the calculated leakage of the flared pipe joint sealing interface under different loads.

2. The method for calculating the leakage of the sealing interface of a flared pipe joint according to claim 1, wherein: In step S1, the friction torque is expressed as follows: The expression of the friction torque obtained by taking the distance between the internal force of the flared pipe joint and the contact surface of the internal thread and the external thread is: ； Where, is the friction torque between the internal thread and the external thread contact surface, is the axial preload of the sealing interface, is the thread pitch, is the friction coefficient of the thread surface, is the thread pitch diameter, Half the thread angle; The friction torque obtained by taking the distance between the nut surface and the bushing contact surface from all forces inside the flared pipe joint is: ； Where, is the friction torque between the nut surface and the bushing contact surface, is the friction coefficient between the bushing and the nut, Equivalent radius of contact area; Then we have: or .

3. The method for calculating the leakage of the sealing interface of a flared pipe joint according to claim 2, wherein: In step S2, the relationship between the porosity and contact depth of the rough interface after deformation is as follows: ； Where, is the porosity of the rough interface under load; is the initial void ratio, is the contact depth, It is the distance between the highest point of the upper rough interface and the lowest point of the lower rough interface in contact.

4. The method for calculating the leakage of the sealing interface of a flared pipe joint according to claim 3, wherein: In step S3, the relationship between the interface separation and the contact depth is: ； Where, is the interface separation.

5. The method for calculating the leakage of the sealing interface of a flared pipe joint according to claim 4, wherein: In step S4, the relationship between the normal load and the contact depth of a single asperity in the elastic stage and the elastic-plastic stage under the action of the normal load on the rough interface is as follows: ； Where, is the normal load on a single asperity, is the equivalent Young's modulus, Equivalent asperity radius, is the normal load corresponding to the asperity entering the plastic stage, is the yield strength, is the critical contact depth; Number of contact points on the rough interface for: ； Where, is the total number of asperities on the rough interface, is the normalized height, , and is a constant related to the support curve of the rough surface; The total normal load on the rough interface is The expression is: ； The relationship between the contact depth and load of the rough interface in the elastic stage and the elastic-plastic stage under normal load is obtained as follows: 。 6. The method for calculating the leakage of the sealing interface of a flared pipe joint according to claim 4, wherein: In step S4, in the elastic stage under the combined action of compression and shear, the total energy of the system under the normal load of the two asperities includes the elastic energy stored in the asperities, the energy generated by the load, and the adhesive energy. The two asperities generate shear energy under the tangential load. The relationship between the total energy of the system under the normal load and the elastic energy stored in the asperities, the energy generated by the load, and the adhesive energy is: ; Combined with Hertz's formula, we have: ； ； ； Where, is the total energy of the system under the normal load of the two asperities, is the elastic energy stored in the asperities, is the energy generated by the load, For adhesion energy; For adhesion, is the external load, For external load The corresponding contact depth, Considering adhesion The external load is unloaded until the adhesion force is maintained while keeping the original contact radius unchanged. The corresponding contact depth, is the normal load on a single asperity, Equivalent asperity radius, , is the equivalent Young's modulus, , 、 are the viscosity coefficients of the two asperities, is the viscosity coefficient of the contact interface between the two asperities, is the contact radius of a single asperity under the combined action of compression and shear, according to Hertz's formula: ; The total energy of the system under the normal load of the two asperities is for: ； Combined with Hertz's formula, the shear energy generated by two asperities under tangential load is for: ； Where, is the tangential load on a single asperity, is the tangential deformation, is the equivalent shear modulus, , 、 are the Poisson's ratios of the two asperities, 、 are the shear moduli of the two asperities respectively; The total energy of the entire system under the combined action of compression and shear is obtained for: ； According to the stability of the entire system under the combined action of compression and shear, the partial derivative of the total energy with respect to the external load is 0, that is: , then ,because , and then the relationship between the contact radius of a single asperity and the load is obtained as follows: ； The relationship between the contact radius and contact depth of a single asperity is: , the relationship between the contact depth and load of the rough interface in the elastic stage under the combined action of compression and shear is obtained as follows: ； Where, is the total number of asperities on the rough interface, is the normalized height, , and is a constant related to the support curve of the rough surface; is the total normal load on the rough interface, is the total tangential load on the rough interface.

7. The method for calculating the leakage of the sealing interface of a flared pipe joint according to claim 6, wherein: In step S4, in the elastic-plastic stage under the combined action of compression and shear, the change in the actual contact area of ​​a single micro-convex body is: ； Where, is the actual contact area of ​​a single asperity under the combined action of compression and shear, is the actual contact area of ​​a single asperity under normal load only, is the material parameter; in: ； ； ； Where, is the contact depth of a single asperity under normal load only, is the normal load corresponding to the asperity entering the plastic stage, is the yield strength, is the critical contact depth; The calculation formula of the contact depth of a single micro-convex body obtained from the change of the real contact area is: ； The relationship between the contact depth and load of the entire rough interface in the elastic-plastic stage under the combined action of compression and shear is obtained as follows: 。 8. The method for calculating the leakage of the sealing interface of a flared pipe joint according to claim 5, wherein: In step S5, the relationship between the axial preload force of the sealing interface, the normal pressure perpendicular to the sealing interface, and the tangential force parallel to the sealing interface is as follows: ； ； Where, is the positive pressure perpendicular to the sealing interface, is the tangential force parallel to the sealing interface, It is half the angle of the flare of the tapered joint; The calculation formula of the interface separation of the rough interface under normal load is as follows: Elasticity stage: ； Elastic-plastic stage: 。 9. The method for calculating the leakage of the sealing interface of a flared pipe joint according to claim 7, wherein: In step S5, the relationship between the axial preload force of the sealing interface, the normal pressure perpendicular to the sealing interface, and the tangential force parallel to the sealing interface is as follows: ； ； Where, is the positive pressure perpendicular to the sealing interface, is the tangential force parallel to the sealing interface, It is half the angle of the flare of the tapered joint; The calculation formula of the interface separation of the rough interface under the combined action of compression and shear is as follows: Elasticity stage: ； Elastic-plastic stage: 。

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