Method for predicting bearing capacity of carbon fiber reinforced composite reinforced load-holding pipe node

Abstract

The invention provides a method for predicting the bearing capacity of a carbon fiber reinforced composite reinforced holding pipe joint, and belongs to the field of application of high-performance composites.The method comprises the steps that first pressure is applied to a main pipe of a pipe joint through a test press, and second pressure is provided for the main pipe through a screw when the test press stops applying the first pressure; wherein in the process that the screw rod provides the second pressure for the main pipe, the pipe joint is reinforced by adopting a carbon fiber reinforced composite material so as to obtain a reinforced carrying pipe joint, third pressure is applied to the branch pipe of the reinforced carrying pipe joint, and a relational expression is established based on the first pressure and the second pressure; establishing a finite element model based on the relational expression; and performing parameter analysis on the finite element model, and determining the target bearing capacity of the reinforced load-holding pipe node based on a parameter analysis result. According to the method provided by the invention, the target bearing capacity of the carbon fiber reinforced composite reinforced bearing pipe joint can be accurately predicted.

Description

Technical Field

[0001] The present invention belongs to the field of application of high-performance composite materials, and particularly relates to a method for predicting the bearing capacity of a carbon fiber reinforced composite material strengthened load-bearing tubular joint. Background Art

[0002] With the in-depth development of offshore oil and gas resource development, the safety and reliability of offshore jacket platforms are facing severe challenges. As the main load-bearing area of offshore jacket platforms, tubular joints play a decisive role in the mechanical properties of the platforms. However, factors such as harsh environmental exposure, material corrosion, and cracks will lead to a decline in the performance of tubular joints, further threatening the safety of the platforms. In order to ensure the safe operation of the platforms, it is necessary to reinforce and repair the tubular joints. Carbon fiber reinforced composite materials are regarded as an ideal choice for strengthening offshore jacket platforms due to their high tensile strength, excellent fatigue performance, and corrosion resistance. A large number of practices have proved that by fully impregnating it with epoxy resin and wrapping it on the surface of the structure to be strengthened, the mechanical properties of the structure can be greatly improved.

[0003] Currently, there are insufficient methods for predicting the mechanical properties of tubular joints after strengthening, and the lack of prediction methods limits the wide application of carbon fiber reinforced composite materials in the field of tubular joint strengthening. Therefore, when using it for the strengthening of tubular joints in actual engineering, a method for predicting the bearing capacity of the strengthened tubular joints is essential. This method can be used to determine the quantitative relationship between the bearing capacity, tubular joint parameters, and carbon fiber reinforced composite material parameters, so as to guide the strengthening design of tubular joints (such as the selection of the number of layers of carbon fiber reinforced composite materials for strengthening) and the evaluation of mechanical properties after strengthening.

[0004] For the strengthening of in-service offshore jacket platforms, it is necessary to consider the adverse effects of the load-bearing of the tubular joints (i.e., the main pipe continuously bears the load) on the bearing capacity after strengthening. Traditional bearing capacity prediction formulas, such as the national standard "Code for Design of Steel Structures (GB50017-2017)", can only predict the bearing capacity of unstrengthened tubular joints. On the other hand, traditional prediction models for the bearing capacity of strengthened joints are based on the premise that the structure does not bear the load, which means that the model can only be used under the condition of structural unloading, which is often difficult to achieve in actual engineering. Therefore, there is an urgent need for an effective method for evaluating the bearing capacity of carbon fiber reinforced composite material strengthened load-bearing tubular joints to guide the strengthening design of tubular joints under the condition of continuous load. Summary of the Invention

[0005] In view of the above problems, the embodiments of the present application provide a method for predicting the bearing capacity of a carbon fiber reinforced composite material strengthened load-bearing tubular joint to overcome or at least partially solve the above problems.

[0006] An embodiment of the present application provides a method for predicting the bearing capacity of a load-bearing pipe joint reinforced with carbon fiber reinforced composite materials, including: Applying a first pressure to the main pipe of the pipe joint through a test press, and when the test press stops applying the first pressure, providing a second pressure to the main pipe through a screw; wherein, during the process of the screw providing the second pressure to the main pipe, reinforcing the pipe joint with carbon fiber reinforced composite materials to obtain a reinforced load-bearing pipe joint, and applying a third pressure to the branch pipe of the reinforced load-bearing pipe joint; Based on the first pressure and the second pressure, establishing a relationship expression; wherein, the relationship expression characterizes the correlation between the first pressure and the second pressure; Based on the relationship expression, establishing a finite element model; wherein, the finite element model is used to simulate the mechanical behavior during the process of applying the third pressure to the branch pipe of the reinforced load-bearing pipe joint; Conducting parameter analysis on the finite element model to determine the target bearing capacity of the reinforced load-bearing pipe joint.

[0007] Furthermore, the step of providing the second pressure to the main pipe through the screw includes: Passing the screw through a reserved hole in the main pipe end plate, and tightening and connecting with the main pipe end plate with a nut at the end of the screw, so that the screw provides the second pressure to the main pipe; wherein, the main pipe end plate is perpendicular to the end of the main pipe.

[0008] Furthermore, the included angle between the branch pipe and the main pipe is 90 degrees.

[0009] Furthermore, through the following expression, the step of applying the first pressure to the main pipe of the pipe joint through the test press is realized: ; wherein, is the first pressure; is the compression amount of the main pipe when bearing the first pressure applied by the test press; is the length of the main pipe; is the cross-sectional area of the main pipe; is the elastic modulus of the main pipe.

[0010] Furthermore, through the following expression, the step of providing the second pressure to the main pipe through the screw is realized: ; wherein, is the second pressure; is the number of screws; is the elongation amount of the screw or the rebound deformation amount of the main pipe; is the length of the screw; is the cross-sectional area of the minor diameter of a single screw rod; is the elastic modulus of the screw rod.

[0011] Further, through the following expression, the step of establishing a relational expression based on the first pressure and the second pressure is realized: ; where, is the first pressure; is the length of the main pipe of the tubular joint; is the cross-sectional area of the main pipe; is the elastic modulus of the main pipe; is the second pressure; is the number of screw rods; is the length of the screw rod; is the cross-sectional area of the minor diameter of a single screw rod; is the elastic modulus of the screw rod.

[0012] Further, the establishing of the finite element model based on the relational expression includes: Determining the force boundary conditions based on the relational expression; wherein, the force boundary conditions characterize the stress condition of the main pipe in the loaded state in the finite element model; Obtaining the geometric parameters and reinforcement parameters of the reinforced and loaded tubular joint; wherein, the geometric parameters include: the diameter of the main pipe, the wall thickness of the main pipe, the diameter of the branch pipe, the wall thickness of the branch pipe, the length of the main pipe and the length of the branch pipe, and the reinforcement parameters include the number of reinforcement layers of the carbon fiber reinforced composite material; Based on the geometric parameters and the reinforcement parameters, applying the force boundary conditions to establish the finite element model.

[0013] Further, the performing of parameter analysis on the finite element model to determine the target bearing capacity of the reinforced and loaded tubular joint includes: Obtaining the bearing capacity when the tubular joint undergoes plastic failure; wherein, the bearing capacity is respectively related to the diameter ratio of the branch pipe to the main pipe, the diameter-thickness ratio of the main pipe, the included angle between the branch pipe and the main pipe, and the magnitude of the axial compressive stress on both sides of the main pipe; Performing parameter analysis on the finite element model, and based on the results of the parameter analysis and the bearing capacity, determining the influence coefficient of the target bearing capacity of the reinforced and loaded tubular joint; Performing multiple regression linearization processing on the influence coefficient of the target bearing capacity to determine the target bearing capacity.

[0014] Further, through the following expression, the step of performing multiple regression linearization processing on the influence coefficient of the target bearing capacity to determine the target bearing capacity is realized: ; Wherein, is the target bearing capacity; is the diameter ratio of the branch pipe to the main pipe; is the diameter-thickness ratio of the main pipe; is the initial load-holding rate; is the ratio of the thickness of the carbon fiber reinforced composite material to the thickness of the main pipe; is the wall thickness of the main pipe, is the yield strength of the steel of the main pipe.

[0015] Therefore, through a method for predicting the bearing capacity of a load-holding pipe joint reinforced with carbon fiber reinforced composite materials provided in this embodiment, first, a first pressure is applied to the main pipe of the pipe joint by using a test press. When the test press stops applying the first pressure, a second pressure is provided to the main pipe by a screw rod to maintain the bearing state of the pipe joint. During the process of the screw rod providing the second pressure to the main pipe, a carbon fiber reinforced composite material can also be wrapped around the pipe joint to complete the reinforcement of the load-holding pipe joint, and then a reinforced load-holding pipe joint is obtained. Then, a third pressure is applied to the branch pipe of the reinforced load-holding pipe joint. Next, based on the first pressure and the second pressure, a relationship expression representing the correlation between the two is established to determine the magnitude of the second pressure provided by the screw rod to the main pipe. A finite element model is established based on this relationship expression. The finite element model can simulate the mechanical behavior during the process of applying the third pressure to the branch pipe of the reinforced load-holding pipe joint. Finally, parameter analysis is performed on the finite element model, and based on the results of the parameter analysis, the target bearing capacity of the reinforced load-holding pipe joint is predicted. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for the description of the embodiments of the present application will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can also be obtained based on these drawings without creative efforts.

[0017] Figure 1 is a flowchart of the steps of a method for predicting the bearing capacity of a load-holding pipe joint reinforced with carbon fiber reinforced composite materials provided by an embodiment of the present application; Figure 2 is a schematic diagram of the manufacturing process of a load-holding pipe joint provided by an embodiment of the present application; Figure 3 is a schematic diagram of a finite element model provided by an embodiment of the present application; Figure 4 is a schematic diagram of the comparison of the load-displacement curves of the pipe joint test and the finite element provided by an embodiment of the present application; Figure 5 is a schematic diagram of the comparison of the bearing capacity fitting formula with the finite element simulation and the test measured results provided by an embodiment of the present application. Detailed implementation manners

[0018] The exemplary embodiments of the present application will be described in more detail below with reference to the accompanying drawings in the embodiments of the present application. Although the exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided so that the present application can be more thoroughly understood and the scope of the present application can be fully conveyed to those skilled in the art.

[0019] Refer to Figure 1 , Figure 1 which is a flowchart of the steps of a method for predicting the bearing capacity of a fiber-reinforced composite material-reinforced load-bearing pipe joint provided by an embodiment of the present application. It can be seen from Figure 1 that this step includes: Step S101: Apply a first pressure to the main pipe of the pipe joint through a test press, and when the test press stops applying the first pressure, provide a second pressure to the main pipe through a screw; wherein, during the process of the screw providing the second pressure to the main pipe, reinforce the pipe joint with a carbon fiber-reinforced composite material to obtain a reinforced load-bearing pipe joint, and apply a third pressure to the branch pipe of the reinforced load-bearing pipe joint.

[0020] In this embodiment, in order to facilitate the prediction of the bearing capacity of the reinforced load-bearing pipe joint, it is necessary to manufacture the reinforced load-bearing pipe joint. Refer to Figure 2 , Figure 2 which is a schematic diagram of the manufacturing process of a reinforced load-bearing pipe joint provided by an embodiment of the present application. It can be seen from Figure 2 (a) that the pipe joint includes a main pipe and a branch pipe, and main pipe end plates are respectively arranged at both ends of the main pipe, and branch pipe end plates are respectively arranged at both ends of the branch pipe. Regarding the process of manufacturing the reinforced load-bearing pipe joint, it can be elaborated in detail with reference to Figure 2 in (b)-(e): First, a first pressure can be applied to the main pipe of the pipe joint through a test press, that is Figure 2 in . The first pressure is the pressure directly applied to the main pipe of the pipe joint by the test press. The value of the first pressure is not limited in this embodiment and can be set according to actual test requirements. Secondly, in order to maintain the pipe joint in a bearing state, after the test press applies the first pressure to the main pipe of the pipe joint, a second pressure is provided to the main pipe through the screws installed at both ends of the main pipe, that is Figure 2 in , to ensure that after the test press unloads, that is, stops applying the first pressure to the main pipe, the main pipe can still be in a bearing state through the second pressure provided by the screws. At the same time, during the process of the screws providing the second pressure to the main pipe, the fiber-reinforced composite material can be wrapped around the pipe joint to obtain a reinforced load-bearing pipe joint, that is Figure 2(e), the reinforcement method of the load-bearing pipe joint can be to wrap or attach the carbon fiber reinforced composite material on the load-bearing pipe joint, so as to obtain the reinforced load-bearing pipe joint. In addition, after obtaining the reinforced load-bearing pipe joint, from Figure 2 (f), it can be seen that it is also necessary to apply a third pressure to the branch pipe of the reinforced load-bearing pipe joint, that is, Figure 2 in , the third pressure can be provided by a test press. In this embodiment, the number and size of the screws are not limited, as long as a stable second pressure can be provided to the main pipe. The pipe joint in this embodiment is a pipe joint not reinforced with carbon fiber reinforced composite material, and the reinforced load-bearing pipe joint is a carbon fiber reinforced composite material reinforced pipe joint that bears the second pressure.

[0021] Step S102: Based on the first pressure and the second pressure, establish a relationship expression; wherein, the relationship expression characterizes the correlation between the first pressure and the second pressure.

[0022] In this embodiment, in order to ensure that the main pipe is in a load-bearing state during the process of bearing the third pressure, specifically, the second pressure is used to replace the first pressure to provide axial pressure to the main pipe. The first pressure is applied to the main pipe of the pipe joint by a test press, and the second pressure is applied to the main pipe of the pipe joint by screws after the test press is unloaded. After the test press is unloaded, the screws maintain the main pipe in a load-bearing state. However, during the unloading process of the test press, the main pipe of the pipe joint in the load-bearing state will rebound, and the screws will elongate under the influence of the rebound of the main pipe of the pipe joint. Therefore, the first pressure and the second pressure are not equal, but there is a correlation. This correlation can be quantified by establishing a mathematical model or experimental calibration to ensure that the screws can effectively maintain the axial pressure of the main pipe after the test press is unloaded.

[0023] Step S103: Based on the relationship expression, establish a finite element model; wherein, the finite element model is used to simulate the mechanical behavior during the process of applying the third pressure to the branch pipe of the reinforced load-bearing pipe joint.

[0024] In this embodiment, since the relationship expression correlates the first pressure applied by the test press and the second pressure applied by the screws, reflecting the mechanical relationship between the first pressure and the second pressure, this relationship can be incorporated into the finite element model to facilitate setting accurate force boundary conditions, so that the finite element model can be used to simulate the mechanical behavior of the reinforced load-bearing pipe joint. In order to determine the bearing capacity of the reinforced load-bearing pipe joint, from Figure 2As can be seen from (f), a third pressure can be applied to the branch pipe of the reinforced load-bearing pipe joint. The third pressure can be provided by a test press or other equipment capable of providing the third pressure. The third pressure can be a continuously changing force. During the process of applying the third pressure to the branch pipe of the reinforced load-bearing pipe joint, a relationship curve of the third pressure with respect to the displacement of the branch pipe end plate can be obtained. The peak value of this curve is the test value of the bearing capacity. A finite element model can be used to simulate the mechanical behavior of this process, and the finite element model can be verified by comparing the relationship curve and the bearing capacity.

[0025] Step S104: Perform parameter analysis on the finite element model to determine the target bearing capacity of the reinforced load-bearing pipe joint.

[0026] In this embodiment, parameter analysis can be performed on the verified finite element model. Specifically, the parameter analysis is carried out by changing the numerical values of different parameters in the finite element model, running the finite element model, and finally jointly determining the target bearing capacity of the reinforced load-bearing pipe joint based on the results of the analysis of different parameter numerical values.

[0027] Therefore, through a method for predicting the bearing capacity of a reinforced load-bearing pipe joint using carbon fiber reinforced composite materials provided in this embodiment, first, a first pressure is applied to the main pipe of the pipe joint using a test press. When the test press stops applying the first pressure, a second pressure is provided to the main pipe by a screw to maintain the load-bearing state of the pipe joint. During the process of the screw providing the second pressure to the main pipe, carbon fiber reinforced composite materials can also be wrapped around the pipe joint to complete the reinforcement of the load-bearing pipe joint, thereby obtaining the reinforced load-bearing pipe joint. Then, a third pressure is applied to the branch pipe of the reinforced load-bearing pipe joint. Next, based on the first pressure and the second pressure, a relationship expression representing the correlation between the two is established to determine the magnitude of the second pressure provided by the screw to the main pipe. A finite element model is established based on this relationship expression to simulate the mechanical behavior during the process of applying the third pressure to the branch pipe of the reinforced load-bearing pipe joint. Finally, parameter analysis is performed on the finite element model, and based on the results of the parameter analysis, the target bearing capacity of the reinforced load-bearing pipe joint is accurately predicted.

[0028] In a specific embodiment, the step of providing the second pressure to the main pipe by the screw includes: passing the screw through a reserved hole in the main pipe end plate and tightening the nut at the end of the screw to connect with the main pipe end plate, so that the screw provides the second pressure to the main pipe; wherein, the main pipe end plate is perpendicular to the end of the main pipe.

[0029] In this embodiment, the second pressure provided by the screw to the main pipe is specifically achieved in the following manner. Combining Figure 2 , from Figure 2As can be seen from (a) and (d), the main pipe end plates are arranged at both ends of the main pipe. The screw passes through the reserved holes in the main pipe end plates, and nuts are tightened at the ends of the screws to connect with the main pipe end plates. When the testing press is unloaded, the pressure provided by the screws continuously increases. After the testing press is completely unloaded, the pressure provided by the screws for the main pipe reaches the second pressure, which is the sum of the loads applied by all the screws to the main pipe of the pipe joint.

[0030] Exemplarily, the process of establishing the relational expression for this embodiment will be elaborated in detail below in conjunction with Figure 2 : When the first pressure is applied to the main pipe of the pipe joint by the testing press, compression deformation will occur to the main pipe. If the pipe joint is an X-type joint, the step of applying the first pressure to the main pipe of the pipe joint by the testing press is achieved through formula (1): Formula (1); Wherein, is the first pressure; is the compression amount when the main pipe bears the first pressure applied by the testing press; is the length of the main pipe; is the cross-sectional area of the main pipe; is the elastic modulus of the main pipe.

[0031] In addition, since the testing press needs to be unloaded and the screws need to provide pre-loaded axial pressure for the main pipe in the pipe joint, as the pressure applied by the testing press decreases, rebound will occur to the main pipe of the pipe joint. When the value of the testing press decreases to 0, the rebound deformation amount of the main pipe of the pipe joint is . The screws are in a relaxed state when the testing press provides the first pressure for the main pipe. When the testing press is unloaded, the screws will elongate due to the influence of the rebound of the main pipe of the pipe joint. The elongation amount of the screws is equal to the rebound deformation amount of the main pipe of the pipe joint, both of which are .

[0032] Therefore, through formula (2), the step of providing the second pressure for the main pipe by the screws can be achieved: Formula (2); Wherein, is the second pressure; is the number of screws; is the elongation amount of the screws and the rebound deformation amount of the main pipe; is the length of the screws; is the cross-sectional area of the minor diameter of a single screw; is the elastic modulus of the screws.

[0033] The final compression deformation amount of the main pipe of the X-type pipe joint is , the final axial pressure it receives is the second pressure provided by the screw to the X-type pipe joint, and thus the formula (3) can be obtained as follows: Formula (3); Among them, is the compression amount when the main pipe bears the first pressure applied by the test press; is the elongation amount of the screw and the rebound deformation amount of the main pipe; is the screw length; is the cross-sectional area of the minor diameter of a single screw; is the elastic modulus of the screw; is the main pipe length; is the cross-sectional area of the main pipe; is the elastic modulus of the main pipe.

[0034] According to formula (3), it can be deduced that the rebound deformation amount of the main pipe of the pipe joint and the compression deformation amount of the pipe joint after the test press applies the first pressure have the relationship of formula (4) as follows: Formula (4); Among them, is the compression amount when the main pipe bears the first pressure applied by the test press; is the elongation amount of the screw and the rebound deformation amount of the main pipe; is the screw length; is the cross-sectional area of the minor diameter of a single screw; is the elastic modulus of the screw; is the main pipe length; is the cross-sectional area of the main pipe; is the elastic modulus of the main pipe.

[0035] In a specific embodiment, by combining formula (1), formula (2) and formula (4), the relationship between the second pressure borne by the main pipe of the pipe joint and the first pressure is established as formula (5): Formula (5); Among them, is the first pressure; is the length of the main pipe of the pipe joint; is the cross-sectional area of the main pipe; is the elastic modulus of the main pipe; is the second pressure; is the number of screws; is the screw length; is the cross-sectional area of the minor diameter of a single screw; is the elastic modulus of the screw.

[0036] In a specific embodiment, the included angle between the branch pipe and the main pipe is 90 degrees.

[0037] In this embodiment, a branch pipe is provided on the pipe joint. The branch pipe can be connected to the main pipe by welding, and the included angle between the branch pipe and the main pipe is 90°. Then, this pipe joint can be an X-type joint.

[0038] In a specific embodiment, establishing a finite element model based on the relationship expression includes: determining force boundary conditions based on the relationship expression, where the force boundary conditions characterize the stress condition of the main pipe in the holding state in the finite element model; obtaining the geometric parameters and reinforcement parameters of the reinforced holding pipe joint, where the geometric parameters include: main pipe diameter, main pipe wall thickness, branch pipe diameter, branch pipe wall thickness, main pipe length, and branch pipe length, and the reinforcement parameters include the number of reinforcement layers of carbon fiber reinforced composite materials; applying the force boundary conditions based on the geometric parameters and the reinforcement parameters to establish the finite element model.

[0039] In this embodiment, a third pressure is applied to the branch pipe of the reinforced holding pipe joint, and force boundary conditions are determined based on the relationship expression. Since the force boundary conditions characterize the stress condition of the main pipe in the holding state in the finite element model, the stress condition of the main pipe in the holding state can be reflected by the initial holding rate of the main pipe. In this embodiment, determining the holding boundary conditions of the main pipe in the finite element model can refer to Figure 3 , Figure 3 is a schematic diagram of a finite element model provided by an embodiment of the present application. As can be seen from Figure 3 , one reference point is set on each of the upper and lower branch pipe end plates of the finite element model. The reference points are bound to the branch pipe end plates. The reference point of the lower branch pipe end plate is completely fixed, which can restrict displacements and rotations in all directions. The upper end plate of the pipe joint is the loading end, and the displacement in the Z-axis direction of the reference point of the upper end plate is released. In addition, the relationship expression is the correlation relationship between the first pressure applied by the test press and the second pressure applied by the screw. Through this correlation relationship, the magnitude of the second pressure provided by the screw, that is, the holding magnitude borne by the main pipe, can be known. Then, the geometric parameters and reinforcement parameters of the reinforced holding pipe joint are obtained. Among them, the geometric parameters include: main pipe diameter, main pipe wall thickness, branch pipe diameter, branch pipe wall thickness, main pipe length, and branch pipe length, and the reinforcement parameters include the number of reinforcement layers of carbon fiber reinforced composite materials. Obtaining geometric parameters such as the main pipe diameter, wall thickness, and length, as well as parameters such as the number of reinforcement layers of carbon fiber reinforced composite materials, can restore the actual size and reinforcement design of the pipe joint, and can make the geometric shape, size, and number of reinforcement layers of the finite element model consistent with the pipe joint in the actual project, improving the accuracy of the finite element model simulation.

[0040] Since the force boundary conditions characterize the force-bearing conditions of the main pipe in the finite element model under the load-bearing state, the force boundary conditions can be applied based on the geometric parameters and reinforcement parameters to establish a finite element model.

[0041] The finite element model established above is verified as follows. First, run the established finite element model, and then obtain the load-displacement curve of the simulated tubular joint of the finite element model. Refer to Figure 4 , Figure 4 which is a schematic diagram of the comparison between the tubular joint test and the finite element load-displacement curve provided by the embodiment of the present application. Figure 4 In , is the ultimate load calculated by the finite element model, and Figure 4 is the ultimate load obtained from the direct test of the tubular joint. It can be seen from Figure 4 that the finite element simulation curve and the test curve fit well before the specimen reaches its bearing capacity. When the specimen reaches its bearing capacity, the finite element result is slightly larger than the test result. However, the load-displacement curves obtained from both the finite element result and the test result show a decreasing trend, indicating that the finite element model accurately captures the key mechanical behavior that the reinforced load-bearing tubular joint loses its ability to resist load after the carbon fiber reinforced composite material in the intersection area fractures and fails. Therefore, the bearing capacity of the reinforced load-bearing tubular joint simulated by the finite element model decreases slowly. Therefore, through the above comparison of the load-displacement curve and the bearing capacity, it is shown that the finite element model established in this embodiment can more accurately simulate the mechanical behavior of the reinforced load-bearing tubular joint under the third pressure on the branch pipe.

[0042] In a specific embodiment, the parameter analysis of the finite element model to determine the target bearing capacity of the reinforced load-bearing tubular joint includes: obtaining the bearing capacity when the tubular joint undergoes plastic failure; wherein the bearing capacity is respectively related to the diameter ratio of the branch pipe to the main pipe, the diameter-thickness ratio of the main pipe, the included angle between the branch pipe and the main pipe, and the magnitude of the axial compressive stress on both sides of the main pipe; performing parameter analysis on the finite element model, and based on the results of the parameter analysis and the bearing capacity, determining the influence coefficient of the target bearing capacity of the reinforced load-bearing tubular joint; performing multiple regression linearization processing on the influence coefficient of the target bearing capacity to determine the target bearing capacity.

[0043] In this embodiment, the bearing capacity when the tubular joint undergoes plastic failure can be obtained according to the "Code for Design of Steel Structures", and specifically, reference can be made to formula (6): Formula (6); Wherein, is the influence parameter of the axial stress of the main pipe, , when the main pipe on both sides or one side of the tubular joint is in tension, take , is the wall thickness of the main pipe; is the design value of the tensile, compressive, and flexural strengths of the main pipe steel; is the angle less than a right angle between the axes of the main and branch pipes; is the bearing capacity at the time of plastic failure of the pipe joint; is the yield strength of the main pipe steel; is the smaller absolute value of the axial compressive stresses in the main pipes on both sides of the pipe joint.

[0044] As can be seen from formula (6), the bearing capacity is related to the diameter ratio of the branch pipe to the main pipe, the diameter-thickness ratio of the main pipe, the angle between the branch pipe and the main pipe, and the magnitude of the axial compressive stresses on both sides of the main pipe; without considering the influence of the angle between the branch pipe and the main pipe, the bearing capacity of the X-type pipe joint strengthened with carbon fiber reinforced composite materials when the main pipe undergoes plastic failure is given in combination with the specification formula as shown in formula (7).

[0045] Formula (7); wherein, is the influence coefficient of the bearing capacity of the pipe joint, and its value is related to the geometric parameters of the X-type pipe joint (diameter ratio of the branch pipe to the main pipe , diameter-thickness ratio of the main pipe ), the strengthening parameters of the carbon fiber reinforced composite materials (number of layers of carbon fiber reinforced composite materials ), and the initial stress state (initial load-bearing ratio ). The wall thickness of the main pipe is used to normalize the number of layers of carbon fiber reinforced composite materials , and the ratio of the thickness of the carbon fiber reinforced composite material to the thickness of the main pipe ( ) is used to represent the influence of the number of layers of carbon fiber reinforced composite materials on the bearing capacity of the pipe joint.

[0046] It should be noted here that in formula (7), the yield strength of the main pipe steel can be used to replace the design values of the tensile, compressive, and flexural strengths of the main pipe steel because the design value of the steel strength is less than the yield strength of the steel, and in order to improve the accuracy of the bearing capacity prediction formula, it is closer to the measured bearing capacity of the pipe joint to calculate using the yield strength of the steel.

[0047] In addition, parametric analysis of the finite element model is also required. The process of parametric analysis of the finite element model is as follows: First, different parameter ranges are set to determine the influence on the bearing capacity of the pipe joint. The initial load-bearing ratio parameter can consider the influence of the magnitude of the initial axial force applied to the main pipe on the bearing capacity of the pipe joint. Therefore, the initial load-bearing ratio is expressed as the ratio of the axial stress generated by the initial axial force on the main pipe to the yield strength of the steel ; , where is the second pressure and the cross-sectional area of the main pipe The ratio of, i.e., . The considered range is 0 - 80%.

[0048] Geometric parameters of the tubular joint: The influence of the geometric dimensions of the tubular joint on the bearing capacity of the tubular joint can be considered. The diameter ratio of the branch pipe to the main pipe and the diameter-to-thickness ratio of the main pipe are used to represent. Among them, the diameter ratio of the branch pipe to the main pipe , the considered range is 0.4 - 0.8, and the diameter-to-thickness ratio of the main pipe , the considered range is 10 - 20. The diameter of the main pipe , the considered range is 0 - 300. is the reinforcement parameter of the carbon fiber reinforced composite material. The influence of different layers of carbon fiber reinforced composite materials on the bearing capacity of the reinforced and load-bearing tubular joint can be considered, and the considered range is 0 - 20.

[0049] Specifically, Table 1 can be referred to. Table 1 shows the specific values of the research parameters, as follows: Table 1 - Specific Values of Research Parameters ; During the process of carrying out parameter analysis on the reinforced and load-bearing tubular joint, it is assumed that the included angle between the main pipe and the branch pipe is 90°; the basic parameters of the specimen are as follows: the diameter of the main pipe = 114 mm, the length of the main pipe = 1400 mm, the tensile elastic modulus of the carbon fiber reinforced composite material = 238000 MPa, the fiber tensile strength of the carbon fiber reinforced composite material = 2549 MPa, the thickness of a single layer of carbon fiber reinforced composite material = 0.167 mm, the number of layers of carbon fiber reinforced composite material for reinforcement = 4, the length of the carbon fiber reinforced composite material for reinforcing the main pipe = 500 mm, and the length of the carbon fiber reinforced composite material for reinforcing the branch pipe = 140 mm. In addition, considering the influencing factor of the size of the main pipe diameter of the tubular joint, parameter analysis is carried out on the large-size main pipe diameter model, and the diameter of the main pipe of the large-size tubular joint used in the calculation is 300 mm.

[0050] The change in the diameter ratio of the branch pipe to the main pipe and the diameter-to-thickness ratio of the main pipe is achieved by changing the diameter of the branch pipe and the wall thickness of the main pipe . In addition, the wall thickness ratio of the branch pipe to the main pipe The influence of such parameter changes on the bearing capacity of tubular joints, the wall thickness ratio of the branch pipe to the main pipe change may cause the failure of the component earlier than that of the tubular joint, that is, when the wall thickness ratio of the branch pipe to the main pipe is small, the branch pipe fails first. The bearing capacity obtained from this failure mode is not the bearing capacity considered in the design of the tubular joint. The true bearing capacity of the tubular joint is the radial bearing capacity of the main pipe when plastic failure of the main pipe occurs under the axial compression of the branch pipe under the condition of certain geometric dimensions. Therefore, in the parametric analysis research, the wall thickness ratio of the branch pipe to the main pipe is set to 1, that is, the wall thickness of the branch pipe is designed to be equal to that of the main pipe to ensure that the branch pipe does not fail before the main pipe.

[0051] According to the above parametric analysis results, the diameter ratio of the branch pipe to the main pipe , the diameter-thickness ratio of the main pipe , the initial load-bearing rate and the thickness ratio of the carbon fiber reinforced composite material to the main pipe thickness , the four dimensionless parameters are the key parameters affecting the bearing capacity of the X-type tubular joint strengthened with carbon fiber reinforced composite material under the axial force of the main pipe. Therefore, the expression of the influence coefficient of the tubular joint bearing capacity can be written as formula (8).

[0052] Formula (8); In addition, the linearization method of multiple regression is used to convert formula (8) into a linear form, and taking the logarithm of both sides of formula (8) gives formula (9), as follows:[[]] Formula (9); Finally, according to a large number of results of the parametric analysis and combined with the multiple linear regression analysis method, the multiple regression linearization process of the influence coefficient of the target bearing capacity is realized through formula (9), and the value of can be obtained, where are all fitting constants, and the steps to determine the target bearing capacity are as follows:[[]] Formula (10); Among them, is the target bearing capacity; is the diameter ratio of the branch pipe to the main pipe; is the diameter-thickness ratio of the main pipe; is the initial load-bearing rate; is the thickness ratio of the carbon fiber reinforced composite material to the main pipe thickness; is the wall thickness of the main pipe, is the yield strength of the steel of the main pipe.

[0053] To verify the accuracy of the fitting formula for the bearing capacity of tubular joints, the results of finite element parametric analysis and the measured values of the X-type tubular joints with carbon fiber reinforced composite material strengthened main pipes under axial force in the experimental study are compared with the calculation results of formula (10). The comparison results are as follows Figure 5 . Figure 5 FIG. Figure 5 is a schematic diagram comparing the fitting formula for bearing capacity provided in the embodiment of the present application with the finite element simulation and experimental measured results. The abscissa is the calculation results of the finite element model and the experimental measured values in the parametric analysis N uc,η , and the ordinate is the predicted result of the fitting formula of formula (10) N cX,η . N cX,η / N uc,η The average value of N / N is 1.0014, and the standard deviation is 0.0516. As can be seen from Figure 5 , the error between the bearing capacity results of the tubular joints predicted by the fitting formula and the bearing capacity results of the finite element simulation and experimental measurement in the parametric analysis is within 10%. The above results indicate that the formula (10) proposed in this embodiment can accurately predict the target bearing capacity of the strengthened load-bearing tubular joints.

[0054] In addition, the range of use parameters of the formula (10) proposed in this embodiment is: , , and .

[0055] Each embodiment in this specification is described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other.

[0056] The embodiments of the present invention are described with reference to the flowcharts and / or block diagrams of methods and devices according to the embodiments of the present invention. It should be understood that each process and / or block in the flowchart and / or block diagram can be implemented by computer program instructions, and the combination of the processes and / or blocks in the flowchart and / or block diagram can also be implemented by computer program instructions. These computer program instructions can be provided to the processor of a general computer, a special computer, an embedded processor or other programmable data processing terminal devices to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing terminal devices generate a device for implementing the functions specified in one Figure 1 process or multiple processes and / or blocks Figure 1 block or multiple blocks.

[0057] These computer program instructions can also be stored in a computer-readable memory that can direct a computer or other programmable data processing terminal device to work in a specific manner, such that the instructions stored in the computer-readable memory produce a manufactured article including an instruction device that implements the functions specified in one process Figure 1 one process or multiple processes and / or blocks Figure 1 specified in one block or multiple blocks.

[0058] These computer program instructions can also be loaded onto a computer or other programmable data processing terminal device, such that a series of operational steps are performed on the computer or other programmable terminal device to produce a computer-implemented process, thereby providing steps for implementing the functions specified in one process Figure 1 one process or multiple processes and / or blocks Figure 1 specified in one block or multiple blocks.

[0059] Although the preferred embodiments of the embodiments of the present invention have been described, those skilled in the art can make additional changes and modifications once they learn the basic creative concept. Therefore, the appended claims are intended to be construed to include the preferred embodiments as well as all changes and modifications that fall within the scope of the embodiments of the present invention.

[0060] Finally, it should also be noted that in this document, 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 such 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, such that a process, method, article or terminal device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article or terminal device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or terminal device comprising the element.

[0061] The above has introduced in detail a method for predicting the bearing capacity of a carbon fiber-reinforced composite material-reinforced load-bearing pipe joint. In this article, specific examples are used to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for predicting the bearing capacity of a load-bearing pipe joint strengthened with carbon fiber reinforced composite materials, characterized in that, Including: Applying a first pressure to the main pipe of the pipe joint by a testing press, and when the testing press stops applying the first pressure, providing a second pressure to the main pipe by a screw; wherein, during the process of the screw providing the second pressure to the main pipe, reinforcing the pipe joint with a carbon fiber reinforced composite material to obtain a reinforced load-bearing pipe joint, and applying a third pressure to the branch pipe of the reinforced load-bearing pipe joint; Based on the first pressure and the second pressure, establishing a relationship expression; wherein, the relationship expression characterizes the correlation between the first pressure and the second pressure; Based on the relationship expression, establishing a finite element model; wherein, the finite element model is used to simulate the mechanical behavior during the process of applying the third pressure to the branch pipe of the reinforced load-bearing pipe joint; Conducting parameter analysis on the finite element model to determine the target bearing capacity of the reinforced load-bearing pipe joint.

2. The prediction method according to claim 1, wherein The step of providing a second pressure to the main pipe by the screw includes: Passing the screw through a reserved hole in the main pipe end plate, and tightening and connecting the end of the screw with the main pipe end plate by a nut, so that the screw provides the second pressure to the main pipe; wherein, the main pipe end plate is perpendicular to the end of the main pipe.

3. The prediction method according to claim 1, wherein The included angle between the branch pipe and the main pipe is 90 degrees.

4. The method according to claim 1, characterized in that, The step of applying a first pressure to the main pipe of the pipe joint by a testing press is realized through the following expression: ； Wherein, is the first pressure; is the compression amount when the main pipe bears the first pressure applied by the test press; is the length of the main pipe; is the cross-sectional area of the main pipe; is the elastic modulus of the main pipe.

5. The method according to claim 1, wherein The step of providing a second pressure to the main pipe by the screw is realized through the following expression: ； Among them, is the second pressure; is the number of screws; is the elongation of the screw or the rebound deformation of the main pipe; is the screw length; is the cross-sectional area of the minor diameter of a single screw; is the elastic modulus of the screw.

6. The method according to claim 1, characterized in that, The step of establishing a relationship expression based on the first pressure and the second pressure is realized through the following expression: ； Wherein, is the first pressure; is the length of the main pipe of the pipe joint; is the cross-sectional area of the main pipe; is the elastic modulus of the main pipe; is the second pressure; is the number of screws; is the length of the screw; is the cross-sectional area of the minor diameter of a single screw; is the elastic modulus of the screw.

7. The method according to claim 3, wherein The step of establishing a finite element model based on the relationship expression includes: Based on the relationship expression, determining the force boundary conditions; wherein, the force boundary conditions characterize the stress situation of the main pipe in the load-bearing state in the finite element model; Obtaining the geometric parameters and reinforcement parameters of the reinforced load-bearing pipe joint; wherein, the geometric parameters include: main pipe diameter, main pipe wall thickness, branch pipe diameter, branch pipe wall thickness, main pipe length and branch pipe length, and the reinforcement parameters include the number of reinforcement layers of the carbon fiber reinforced composite material; Based on the geometric parameters and the reinforcement parameters, applying the force boundary conditions to establish the finite element model.

8. The method according to claim 7, wherein The step of conducting parameter analysis on the finite element model to determine the target bearing capacity of the reinforced load-bearing pipe joint includes: Obtaining the bearing capacity when the pipe joint undergoes plastic failure; wherein, the bearing capacity is respectively related to the diameter ratio of the branch pipe to the main pipe, the diameter-thickness ratio of the main pipe, the included angle between the branch pipe and the main pipe, and the magnitude of the axial compressive stress on both sides of the main pipe; Conducting parameter analysis on the finite element model, and based on the results of the parameter analysis and the bearing capacity, determining the influence coefficient of the target bearing capacity of the reinforced load-bearing pipe joint; Conducting multiple regression linearization processing on the influence coefficient of the target bearing capacity to determine the target bearing capacity.

9. The method according to claim 8, wherein The step of conducting multiple regression linearization processing on the influence coefficient of the target bearing capacity to determine the target bearing capacity is realized through the following expression: ； Among them, is the target bearing capacity; is the diameter ratio of the branch pipe to the main pipe; is the diameter-thickness ratio of the main pipe; is the initial load holding rate; is the ratio of the thickness of the carbon fiber reinforced composite material to the thickness of the main pipe; is the wall thickness of the main pipe, is the yield strength of the steel of the main pipe.

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