Optimization design method for metal-composite material mixed drill rod

Abstract

The invention provides an optimization design method for a metal-composite material mixed drill rod. The optimization design method comprises the steps that S1, a three-dimensional elastic mechanical model of the metal-composite material mixed drill rod is established; s2, setting initial structure parameters of the metal-composite material mixed drill rod, and setting reference load parameters; s3, based on the three-dimensional elastic mechanical model of the metal-composite material mixed drill rod and a multi-mode failure analysis method, maximum load prediction is carried out by considering an increment control strategy of multiple loads, and a critical load proportionality coefficient is determined; and S4, constructing a load capacity map according to the critical load proportionality coefficient and the structure parameters, and determining optimal structure parameters according to the load capacity map. According to the method, accurate and efficient optimization of the metal-composite material mixing drill rod is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of downhole drill tool design, and particularly to an optimized design method for hybrid drill pipes. Background Art

[0002] Traditional drill pipes are mainly made of high-strength alloy steel, such as materials like X95 and G105 specified by the API standard. Such drill pipes have the following characteristics: simple structure, mature manufacturing process, and good strength and toughness. However, metal drill pipes have inherent defects such as high weight and poor corrosion resistance. Taking a drill pipe with a diameter of 5 inches and a length of 6.1 m as an example, the weight of a single pipe can reach more than 175 kg, which will generate a large hanging weight during deep well operations, restricting its application depth. In addition, in an environment containing corrosive media such as H2S and CO2, metal drill pipes are prone to stress corrosion cracking, seriously affecting their service life.

[0003] Traditional drill pipes are mainly made of high-strength alloy steel, such as materials like X95 and G105 specified by the API standard. Such drill pipes have the following characteristics: simple structure, mature manufacturing process, and good strength and toughness. However, metal drill pipes have inherent defects such as high weight and poor corrosion resistance, and in an environment containing corrosive media such as H2S and CO2, metal drill pipes are prone to stress corrosion cracking, seriously affecting their service life. To address the deficiencies of metal drill pipes, research institutions such as the National Energy Technology Laboratory of the US Department of Energy have carried out research on composite drill pipes. Such drill pipes are made of composite materials such as carbon fiber / epoxy resin and carbon fiber / PEEK through a winding process. Their main advantages are: light weight (only about 1 / 5 of that of metal drill pipes) and good corrosion resistance. However, due to the significant anisotropic characteristics of composite materials, local failure is likely to occur under complex stress states. Especially in the downhole high-temperature and high-pressure environment, damage modes such as interlayer delamination and matrix cracking will cause a sharp decline in the strength of the drill pipe.

[0004] In recent years, some research institutions have proposed a hybrid structure scheme of metal lining + composite material outer layer. This design attempts to combine the advantages of the two materials, but there are still the following technical difficulties:

[0005] 1. Imperfect stress analysis method: Existing research mostly uses classical laminate theory or simplified two-dimensional models for stress analysis. Such methods cannot accurately describe the complex stress state of the drill pipe under the combined action of internal pressure, axial load, and torque, especially it is difficult to reflect the distribution law of interlayer stress. In addition, there is a lack of in-depth research on the stress concentration effect at the interface between the metal layer and the composite material layer.

[0006] 2. Insufficient optimization of structural parameters: In the selection of the thickness of the metal layer and the ply angle of the composite material, it mainly relies on experience or the optimization results under a single working condition. There is a lack of a systematic optimization method considering various load combinations. At the same time, the research on the coupling effect between different parameters is insufficient, making it difficult to achieve the optimization of the overall performance.

[0007] 3. Imperfect failure prediction mechanism: Currently, a single strength criterion is generally used to evaluate the structural reliability, such as the von Mises criterion for the metal layer and the Tsai-Wu criterion for the composite material layer, etc. This method fails to fully consider the failure evolution process of the material and also ignores the mutual influence between different failure modes.

[0008] 4. Limited design verification means: Due to the lack of systematic theoretical guidance, the design of existing hybrid drill pipes mainly relies on experimental verification. This method not only has high costs and a long cycle but also makes it difficult to quickly optimize and adjust design parameters.

[0009] For example, in the invention patent with the application number 202010835679.1, a method for determining the structural parameters of a composite material, the established stress model is mainly based on the helical winding orthogonal layer structure of the composite material, and there are deficiencies in describing the stress state under complex loads. The Tsai-Wu failure criterion is used to evaluate the strength of the composite material structure, without fully considering various failure modes of the composite material and the mutual influence between different failure modes. Summary of the Invention

[0010] Aiming at the technical problems of imperfect stress analysis methods, insufficient optimization of structural parameters, imperfect failure prediction mechanisms, and limited design verification means in the existing methods, the present invention proposes an optimized design method for a metal-composite hybrid drill pipe, establishing a design method that can accurately predict the stress distribution under complex loads, reliably evaluate the failure modes, realize the systematic optimization of structural parameters, and is convenient for engineering applications, achieving the precise and efficient optimization of the metal-composite hybrid drill pipe.

[0011] To achieve the above object, the technical solution of the present invention is realized as follows:

[0012] An optimized design method for a metal-composite hybrid drill pipe, comprising the steps:

[0013] S1: Establish a three-dimensional elastic mechanics model of the metal-composite hybrid drill pipe;

[0014] S2: Set the initial structural parameters of the metal-composite hybrid drill pipe and set the reference load parameters;

[0015] S3: Based on the three-dimensional elastic mechanics model of the metal-composite hybrid drill pipe and the multi-mode failure analysis method, the maximum load is predicted through an incremental control strategy considering multiple loads, and the critical load ratio coefficient is determined.

[0016] S4: Construct a load capacity map according to the critical load ratio coefficient and structural parameters, and determine the optimal structural parameters according to the load capacity map.

[0017] Furthermore, the method for establishing the three-dimensional elastic mechanics model is as follows:

[0018] Under the cylindrical coordinate system (r, θ, z), based on the axisymmetric load condition, the displacement fields of the metal layer and the composite material layer are defined.

[0019] According to the displacement fields of the metal layer and the composite material layer, the displacement-strain relationships of the metal layer and the composite material layer are established.

[0020] According to the displacement-strain geometric relationships of the metal layer and the composite material layer, the constitutive equations of each layer are established respectively: for the composite material layer, the generalized Hooke's law is adopted to establish the constitutive equation of the composite material layer, and for the metal layer, the constitutive equation of the metal layer is established based on isotropy.

[0021] The boundary conditions, interlayer continuity conditions, and axial compression force and torque balance equations for the metal layer and the composite material layer are established.

[0022] Furthermore, the method of step S3 is as follows: a multi-scale grid strategy is adopted to determine the initial calculation points.

[0023] Calculate the stress components in the cylindrical coordinate system according to the three-dimensional elastic mechanics model of the metal-composite hybrid drill pipe.

[0024] Convert the stress components in the cylindrical coordinate system into the stress components in the material principal axis coordinate system, determine the dominant stress state according to the stress components in the material principal axis coordinate system, and perform multi-mode failure analysis and adaptive node encryption based on the stress components in the material principal axis coordinate system to determine the key failure index.

[0025] Based on the key failure index, the maximum load is predicted through an incremental control strategy considering multiple loads, and the critical load ratio coefficient is obtained.

[0026] Furthermore, the method for performing multi-mode failure analysis based on the stress components in the material principal axis coordinate system to determine the key failure index is as follows:

[0027] According to the stress components in the material principal axis coordinate system, the failure index of each calculation point of the composite material layer is calculated based on the Hashin failure criterion, and the failure index of each calculation point of the metal layer is calculated based on the improved von Mises criterion.

[0028] Weight the failure index of each calculation point of the composite material layer and the failure index of each calculation point of the metal layer, and calculate the critical failure index of each calculation point;

[0029] Obtain the failure index distribution curve FC critical (r k ), and take the position where the critical failure index FC critical (r k ) is the maximum value among the calculation points as the critical failure position;

[0030] For the area where the critical failure position is located, adopt adaptive node encryption to determine the final critical failure index.

[0031] Furthermore, the method for predicting the maximum load based on the critical failure index through an incremental control strategy considering multiple loads is as follows:

[0032] Based on the dominant stress state, adopt the method of a single-parameter loading path to implement the load increment control strategy to simulate the failure process, and determine the critical load ratio coefficient when failure occurs under the current structural parameters;

[0033] Based on the critical load ratio coefficient, conduct a parameter sensitivity analysis to determine the optimization order of the structural parameters, reconstruct the stiffness matrices of the constitutive equations of the material layer and the metal layer, and iterate and calculate the critical load ratio coefficients under multiple groups of structural parameter combinations according to the optimization order of the structural parameters and record them.

[0034] Furthermore, the calculation method of the critical failure index is as follows:

[0035] FC critical = max{w ft FC ft , w fc FC fc , w mt FC mt , w mc FC mc , w vm FC vm};

[0036] Among them, FC critical is the critical failure index. When FC critical > 1, the structure fails. FC ft , FC fc , FC mt and FC mc are the fiber tensile failure index, fiber compressive failure index, matrix tensile failure index, and matrix compressive failure index of the composite material layer respectively. FC vm is the von Mises failure index of the metal layer. w ft , wfc , w mt and w mc are the weight factors of the composite layer failure index, and w vm is the weight factor of the metal layer failure index.

[0037] Furthermore, the method for reconstructing the stiffness matrices of the constitutive equations of the material layer and the metal layer is as follows: Update the material elastic modulus according to the material elastic modulus degradation formula, and reconstruct the stiffness matrix in the constitutive equation of the material layer through the updated material elastic modulus and the ply angle in the current structural parameters;

[0038] The material elastic modulus degradation formula is:

[0039] Fiber tensile failure: E1′ = (1 - d ft )E1, where d ft is the damage variable, E1 is the longitudinal elastic modulus before damage in the case of fiber tensile failure, and E1′ is the effective longitudinal elastic modulus after damage;

[0040] Fiber compressive failure: where d fc is the damage variable, is the longitudinal elastic modulus before damage in the case of fiber compressive failure, is the effective longitudinal elastic modulus after damage;

[0041] Matrix tensile failure: E2′ = (1 - d mt )E2, G 12 ′ = (1 - d mt )G 12 , where d mt is the damage variable, E2 is the transverse elastic modulus before damage in the case of matrix tensile failure, E2′ is the effective transverse elastic modulus after damage; G 12 is the shear modulus before damage in the case of matrix tensile failure, and G 12 ′ is the effective shear modulus after damage;

[0042] Matrix compressive failure: where d mc is the damage variable; is the transverse elastic modulus before damage in the case of matrix compressive failure, is the effective transverse elastic modulus after damage; is the shear modulus before damage in the case of matrix compressive failure, is the effective shear modulus after damage;

[0043] Metal yield failure: where D is the damage variable, where E is the initial stiffness of the metal layer, is the effective stiffness of the metal layer after damage.

[0044] Furthermore, the method of using the multi-scale grid strategy to determine the initial calculation points is as follows:

[0045]

[0046] where r k is the k-th calculation point along the wall thickness direction, and r in is the inner radius, represents the initial grid spacing;

[0047] The method of adaptive node encryption is to divide the area where the critical failure position is located by using the encrypted grid spacing to obtain the calculation points after encrypted division, and repeat the calculation of the critical failure position for the calculation points after encrypted division and perform adaptive node encryption until the adaptive node encryption stop condition is met to obtain the final critical failure index;

[0048] The encrypted grid spacing is:

[0049]

[0050] where Δr coarse is the grid spacing before encryption, Δr refined is the grid spacing after encryption, and k refine is the node encryption coefficient;

[0051] The adaptive node encryption stop condition is:

[0052] |FC critical (r p ) - FC critical (r q )| ≤ ε;

[0053] where r p , r q represent any two calculation points within the area of the critical failure position after adaptive node encryption, and ε is the precision threshold.

[0054] Furthermore, the method of determining the dominant stress state according to the stress components in the material principal axis coordinate system is as follows:

[0055] Calculate the stress triaxiality parameter η for each calculation point:

[0056]

[0057] where σ m is the average value of the principal stresses in the material principal axis coordinate system, and σ eq is the equivalent stress;

[0058] Calculate the Lode angle parameter θ for each calculation point L :

[0059]

[0060] where J2 is the second invariant of the stress deviator and J3 is the third invariant of the stress deviator;

[0061] Determine the dominant stress state of each calculation point according to the stress triaxiality parameter η and the Lode angle parameter θ L :

[0062] Tension-dominated: η > 0.33 and |θ L | < 0.17π;

[0063] Compression-dominated: η < -0.33 and |θ L -π| < 0.17π;

[0064] Shear-dominated: |η| < 0.33 and |θ L -0.5π| < 0.17π;

[0065] The method for implementing the load increment control strategy by using the single-parameter loading path is as follows: Determine the current dominant working condition according to the dominant stress state: When the dominant stress state is tension-dominated, it is determined as the internal pressure dominant working condition; when the dominant stress state is compression-dominated, it is determined as the compression dominant working condition; when the dominant stress state is shear-dominated, it is determined as the torsion dominant working condition;

[0066] For the internal pressure dominant working condition: λ F = λ M = 1, λ P = 1 is incremented until FC critical = 1; Obtain the critical internal pressure coefficient λ P，critical ;

[0067] For the compression dominant working condition: λ M = λ P = 1, λ F = 1 is incremented until FC critical = 1; Obtain the critical compression coefficient λ F,critical ;

[0068] For the torsion dominant working condition: λ F = λ P = 1, λ M = 1 is incremented until FC critical = 1, obtain the critical torsion coefficient λ M,critical .

[0069] Furthermore, the method for performing parameter sensitivity analysis is to calculate the sensitivity coefficient and determine the optimization order of key structural parameters based on the sensitivity coefficient; the calculation method of the sensitivity coefficient is as follows:

[0070]

[0071] where x i is the structural parameter, and λ max is the maximum critical load ratio coefficient; S i is the sensitivity coefficient, Δλ max is the increment of the maximum critical load ratio coefficient between the current iteration and the previous iteration, and Δx i is the structural parameter increment.

[0072] The beneficial effects of the present invention are as follows:

[0073] Establish an accurate stress analysis model: The present invention realizes the accurate prediction of the stress state of the hybrid drill pipe under the action of combined loads by constructing a multi-layer cylinder structure analysis method based on three-dimensional elasticity mechanics. This model breaks through the limitations of the traditional laminate theory and can accurately describe the distribution laws of radial stress and interlaminar stress, providing a reliable theoretical basis for structural design.

[0074] Develop a reasonable failure assessment system. The present invention establishes an assessment system based on multiple failure modes and selects appropriate criteria for the failure characteristics of the metal layer and the composite material layer respectively. The von Mises criterion considering pressure correlation is adopted for the metal layer, and the Hashin criterion capable of distinguishing fiber and matrix failure modes is adopted for the composite material layer. Through this method combining multiple criteria, the overall reliability of the hybrid drill pipe is comprehensively evaluated.

[0075] Propose a scientific optimization design method. The present invention develops a parameter optimization method based on maximum load prediction. By systematically analyzing the influence laws of key parameters such as the thickness of the metal layer and the ply angle of the composite material on the performance of the drill pipe, a quantitative relationship between the structural parameters and the bearing capacity is established. This method not only considers the influence of single parameters, but more importantly reveals the coupling effect between multiple parameters, providing a scientific basis for realizing the optimization of overall performance.

[0076] Determine reasonable design criteria. The present invention summarizes a set of engineering criteria applicable to the design of hybrid drill pipes through a large number of theoretical analyses and numerical simulations. These criteria cover key indicators such as the minimum thickness requirement of the metal layer, the optimal ply angle range of the composite material, and the interface stress control standard, and can directly guide engineering practice. Description of the Drawings

[0077] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0078] Figure 1 It is a schematic flow diagram of the present invention.

[0079] Figure 2 It is a schematic structural diagram of the metal-composite drill pipe of the present invention.

[0080] Figure 3 It is a schematic diagram of the force load of the metal-composite material of the present invention.

[0081] Figure 4 It is the verification result of the analytical solution [AM] and the finite element solution [FEM] of the stress distribution of the present invention.

[0082] Figure 5 It is a two-dimensional load contour map under the internal pressure-dominated working condition of the present invention.

[0083] Figure 6 It is a two-dimensional load contour map under the torsion-dominated working condition of the present invention.

[0084] Figure 7 It is a two-dimensional load contour map under the compression-dominated working condition of the present invention. Specific embodiments

[0085] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0086] An optimization design method for a metal-composite hybrid drill pipe, as Figure 1 shown, includes the steps of:

[0087] S1: Establish a three-dimensional elastic mechanics model of the metal-composite hybrid drill pipe.

[0088] The establishment method is:

[0089] First, in the cylindrical coordinate system (r, θ, z), based on the axisymmetric load condition, define the displacement fields of each layer:

[0090]

[0091]

[0092]

[0093] Among them, j represents the layer number of different material layers of the hybrid drill pipe, and are the radial displacement, circumferential displacement, and axial displacement of the j-th layer, respectively.

[0094] Furthermore, based on the displacement fields of each layer, establish the displacement-strain relationships of each layer:

[0095]

[0096]

[0097]

[0098]

[0099]

[0100] Among them, represents the radial strain, which is determined by the radial displacement gradient; represents the circumferential strain, which is proportional to the radial displacement; represents the axial strain. Assuming uniform deformation along the axial direction, the axial strain is a constant ε0; is the axial-radial shear strain, is the circumferential-radial shear strain; is the axial-circumferential shear strain, and γ0 is the shear strain constant.

[0101] Furthermore, based on the displacement-strain geometric relationships of each layer, establish the constitutive equations of each layer respectively.

[0102] For the composite material layer, adopt the generalized Hooke's law to establish the constitutive equation of the composite material layer:

[0103]

[0104]

[0105] For the metal layer, based on isotropy, adopt the elastic-plastic model to establish the constitutive equation of the metal layer:

[0106]

[0107]

[0108] Among them, is the stiffness matrix of the j-th layer of the composite material layer, which is determined by the material elastic constants and the ply angles, represents the stiffness matrix of the jth metal layer, where j represents the position of the layer, is the axial stress of the jth layer, is the circumferential stress of the jth layer, is the radial stress of the jth layer, is the axial - circumferential shear stress; are the circumferential - radial shear stress and axial - radial shear stress respectively, both are 0.

[0109] Furthermore, establish the boundary conditions, interlayer continuity conditions, and axial compression force and torque balance equations:

[0110] Apply the boundary conditions on the inner and outer surfaces:

[0111]

[0112]

[0113] where N represents the outermost layer, r in represents the inner radius, r out represents the outer radius, P i represents the internal pressure.

[0114] The interlayer continuity conditions are:

[0115]

[0116]

[0117] where r j represents the radius of the jth material layer. The interlayer continuity conditions are used to ensure the continuity of displacement and stress transfer between layers.

[0118] Axial compression force and torque balance equations:

[0119]

[0120] where F c is the axial compression force, M t is the torque.

[0121] S2: Set the initial structural parameters of the metal - composite hybrid drill pipe and set the reference load parameters.

[0122] The described structural parameters include the inner radius r in 、outer radius r out 、total wall thickness t total 、metal layer thickness t m 、total thickness of the composite material layer t c , where the parameters of the composite material layer include the ply angle φ and the number of layers N.

[0123] The described load parameters include torque M t , axial compressive force F c and internal pressure P i . In this embodiment, the reference load parameters are torque M t0 , axial compressive force F c0 and internal pressure P i0 .

[0124] S3: Based on the three-dimensional elastic mechanics model of the metal-composite hybrid drill pipe and the multi-mode failure analysis method, the maximum load is predicted through an incremental control strategy considering multiple loads, and the critical load ratio coefficient is determined.

[0125] The specific method of step S3 is as follows:

[0126] First, a multi-scale grid strategy is adopted to determine the initial calculation points: Set n calculation points in the wall thickness direction (usually n≥3 to ensure sufficient calculation accuracy):

[0127]

[0128] where r k is the k-th calculation point, r in is the inner radius, represents the initial grid spacing, and subsequently, the stress components need to be solved at each calculation point, and each failure index is calculated.

[0129] Second, further, calculate the stress components in the cylindrical coordinate system according to the three-dimensional elastic mechanics model of the metal-composite hybrid drill pipe;

[0130] Under axisymmetric conditions, the stress equilibrium equation is:

[0131]

[0132]

[0133]

[0134] 1. Establishment of control equations: Substitute the constitutive equation and the displacement-strain relationship into the equilibrium equation to obtain the control equation for the radial displacement:

[0135]

[0136] 2. Obtaining the general solution:

[0137] For the composite material layer, the general solution of the radial displacement is:

[0138]

[0139] where:

[0140] is a coefficient, α (j) and β (j) are undetermined coefficients.

[0141] For the metal layer, due to its isotropic property, the general solution is simplified to:

[0142]

[0143] Among them,

[0144] 3. Calculation of strain components:

[0145] Substitute the general solution of displacement into the strain-displacement relationship to obtain:

[0146] Composite material layer:

[0147]

[0148] Metal layer:

[0149]

[0150] 4. Solution of stress components:

[0151] Substitute the strain expression into the constitutive equation to obtain the stress components: For the composite material layer:

[0152]

[0153] For the metal layer:

[0154]

[0155] 5. Expansion of boundary equations:

[0156] For the inner metal layer (j = 1):

[0157]

[0158] For the outer composite material layer (j = N):

[0159]

[0160] 6. Construction of coefficient matrix:

[0161] Combine all boundary conditions and continuity conditions to obtain a system of linear equations:

[0162] [A]{x} = {b}

[0163] Among them:

[0164] {x} = {α(1) , β (1) ,..., α (N) , β (N) , ε0, γ0} T

[0165] is the coefficient vector to be solved.

[0166] [A] is the coefficient matrix, and its elements are composed of material parameters and geometric dimensions;

[0167] {b} is the load vector, including the internal pressure P i , the axial force F c and the torque M t .

[0168] 7. Solution process:

[0169] (1) Construct the characteristic equation:

[0170] det([A]) ≠ 0

[0171] Ensure that the system of equations has a unique solution.

[0172] (2) Use the Gaussian elimination method to solve the system of linear equations:

[0173] {x} = [A] -1 {b}

[0174] (3) Substitute the obtained coefficients into the stress expression to obtain the complete stress distribution:

[0175]

[0176] III. Further, convert the stress components in the cylindrical coordinate system to the stress components in the material principal axis coordinate system, determine the dominant stress state based on the stress components in the material principal axis coordinate system, and perform multi-mode failure analysis and adaptive node encryption based on the stress components in the material principal axis coordinate system to determine the critical failure index.

[0177] 1. Specifically, the method for converting the stress components in the cylindrical coordinate system to the stress components in the material principal axis coordinate system is:

[0178] {σ1, σ2, σ3, τ 23 , τ 13 , τ 12} T = [TF]{σ z , σ θ , σ r , τ θr , τ zr , τ zθ} T

[0179] Among them, σ1, σ2, and σ2 are the first principal stress, the second principal stress, and the third principal stress along the 1-axis direction in the material principal axis coordinate system, respectively, and τ 23 , τ 13 , and τ 12 are the first shear stress, the second shear stress, and the third shear stress, respectively. Here, the and in the stress distribution are respectively represented as σ r , σ θ , σ z , and τ zθ .

[0180] The transformation matrix [TF] is:

[0181]

[0182] Among them, m = cos(φ); n = sin(φ), and φ is the ply angle.

[0183] 2. Specifically, the method for determining the dominant stress state according to the stress components in the material principal axis coordinate system is as follows:

[0184] (1). Calculate the stress triaxiality parameter of each calculation point:

[0185]

[0186] Among them, is the mean stress; σ eq is the equivalent stress

[0187] (2). Calculate the Lode angle parameter of each calculation point:

[0188]

[0189] Among them, is the second invariant of the stress deviator; is the third invariant of the stress deviator.

[0190] (3). Determine the dominant stress state of each calculation point according to the stress triaxiality parameter η and the Lode angle parameter θ L :

[0191] Type I (tensile-dominated): η > 0.33 and |θ L | < 0.17π;

[0192] Type II (compression-dominated): η < -0.33 and |θ L - π| < 0.17π;

[0193] Type III (dominated by shear): |η| < 0.33 and |θ L - 0.5π| < 0.17π.

[0194] 3. Specifically, the method for multi - mode failure analysis and adaptive node encryption to determine the critical failure index based on the stress components in the material principal axis coordinate system is as follows:

[0195] (1). Based on the stress components in the material principal axis coordinate system, calculate the failure index of each calculation point of the composite layer based on the Hashin failure criterion, and calculate the failure index of each calculation point of the metal layer based on the improved von Mises criterion.

[0196] For the composite layer, adopt the Hashin failure criterion and consider four failure modes:

[0197] Fiber tensile failure (σ1 > 0):

[0198]

[0199] where FC ft is the fiber tensile failure index, X T represents the strength in the fiber tensile direction, and S3 represents the shear strength.

[0200] Fiber compressive failure (σ1 < 0):

[0201]

[0202] where FC fc is the fiber compressive failure index, X C represents the strength in the fiber compressive direction.

[0203] Matrix tensile failure (σ2 + σ3 > 0):

[0204]

[0205] where FC mt is the matrix tensile failure index, Y T represents the strength in the matrix transverse tensile direction, and S 23 and S 12 are both shear strengths.

[0206] Matrix compressive failure (σ2 + σ3 < 0):

[0207]

[0208] where FC mc is the matrix compressive failure index, Y C represents the strength in the matrix transverse compressive direction.

[0209] For the metal layer, an improved von Mises failure criterion is adopted:

[0210]

[0211] where FC vm represents the von Mises failure index, and σ yield represents the yield strength of the metal material.

[0212] (2) Weight the failure indices of the composite material layer and the metal layer and calculate the critical failure index at each calculation point.

[0213] The calculation method for weighting and calculating the critical failure index at each calculation point is as follows:

[0214] FC critical = max{w ft FC ft , w fc FC fc , w mt FC mt , w mc FC mc , w vm FC vm}

[0215] where w ft = 1.0, w fc = 0.9, w mt = 0.7, w mc = 0.6, w vm = 0.8; all are weighting factors.

[0216] (3) Obtain the failure index distribution curve FC critical (r k ), and take the position where the critical failure index FC critical (r k ) is the maximum value among the calculation points as the critical failure position.

[0217] The critical failure position is:

[0218]

[0219] where FC critical (r k ) represents the critical failure index at the calculation point r k .

[0220] (4) For the region where the critical failure position r critical indicated by the calculation results is located, i.e., [r critical-1 , r critical+1, further adopt adaptive node encryption to improve the calculation accuracy.

[0221] According to experimental measurements, the critical failure positions are: the interface between the metal layer and the composite material layer, the outer surface of the composite material layer, the inner surface under internal pressure, or the outer surface under torsional load.

[0222] The method of adaptive node encryption is: divide the area where the critical failure position is located by using the encrypted grid spacing to obtain the calculation points after encrypted division, repeat the calculation of the critical failure position for the calculation points after encrypted division and perform adaptive node encryption until the adaptive node encryption stop condition is met, and obtain the final critical failure index.

[0223] The encrypted grid spacing is:

[0224]

[0225] where k refine is the node encryption coefficient, Δr refined is the encrypted grid spacing, and Δr coarse is the grid spacing before encryption.

[0226] Until the critical failure indices of each calculation point in the area where the critical failure position is located are not much different, that is, the adaptive node encryption stop condition is met:

[0227] |FC critical (r p ) - FC critical (r q )| ≤ ε

[0228] where r p , r q represent any two calculation points in the area where the critical failure position r critical is located after adaptive node encryption, and ε is the precision threshold. Here, ε is a very small positive number, and in this embodiment, it is taken as 0.001.

[0229] IV. Further, based on the critical failure index, perform maximum load prediction through an incremental control strategy considering multiple loads. The method is:

[0230] 1. Based on the dominant stress state (Type I, Type II, or Type III), adopt the method of a single-parameter loading path to implement the load increment control strategy and determine the critical load ratio coefficient under the current structural parameters.

[0231] Define the load ratio coefficient: λ = {λ F , λ M , λ P}, where λ F represents the axial compression force coefficient, λM Denote the torque coefficient as λ P Denote the internal pressure coefficient. The actual load expression is P = {λ F ·F c0 , λ M ·M t0 , M t ·P i0};

[0232] Define the key structural parameters: where Denote the current ply angle as t m is the current metal layer thickness;

[0233] Define the failure condition: FC critical (χ, λ) = 1, indicating that the structure fails when the key failure index under the current key structural parameters and load ratio coefficient is equal to 1.

[0234] Determine the current dominant working condition according to the described dominant stress state: When the dominant stress state is mainly tensile, it is determined as the internal pressure dominant working condition; when the dominant stress state is mainly compressive, it is determined as the compression dominant working condition; when the dominant stress state is mainly shear, it is determined as the torsion dominant working condition.

[0235] The described load increment control strategy is as follows:

[0236] Internal pressure dominant: λ F = λ M = 1, λ P = 1 is incremented until FC critical (χ, λ) = 1; Obtain the critical internal pressure coefficient λ P，critical ;

[0237] Compression dominant: λ M = λ P = 1, λ F = 1 is incremented until FC critical (χ, λ) = 1; Obtain the critical compression coefficient λ F，critical ;

[0238] Torsion dominant: λ F = λ P = 1, λ M = 1 is incremented until FC critical (χ, λ) = 1, obtain the critical torsion coefficient λ M，critical .

[0239] Initial increment: Δλ = 0.1;

[0240] FC critical (χ, λ) < 0.5: Δλ’ = 2Δλ;

[0241] 0.5 ≤ FC critical (χ, λ) l <0.8: Δλ’ = Δλ;

[0242] 0.8 ≤ FC critical (χ, λ) < 0.95: Δλ’ = 0.5Δλ;

[0243] 0.95 ≤ FC critical (χ, λ) < 0.99: Δλ’ = 0.1Δλ;

[0244] 0.99 ≤ FC critical (χ, λ) < 1.0: Δλ’ = 0.01Δλ;

[0245] Wherein, Δλ represents the initial increment of the single parameter λ P , λ F or λ M under three principal stress states, and Δλ’ represents the subsequent increment.

[0246] This method can evaluate the bearing capacity of the structure under different load-dominant working conditions respectively. To improve the calculation accuracy, an adaptive load increment control strategy is adopted when approaching the failure point.

[0247] 2. Determine the optimization order of structural parameters by performing parameter sensitivity analysis based on the critical load ratio coefficient under the current structural parameters, reconstruct the stiffness matrices of the constitutive equations of the material layer and the metal layer, and record the critical load ratio coefficients under multiple combinations of structural parameters by iterative calculation according to the optimization order of structural parameters.

[0248] The method for performing parameter sensitivity analysis is as follows:

[0249] Calculate the sensitivity coefficient and determine the optimization order of key structural parameters based on the sensitivity coefficient.

[0250] The calculation formula for the sensitivity coefficient is:

[0251]

[0252] Wherein, x i is a structural parameter, i.e., the metal layer thickness or the ply angle, λ max is the maximum critical load ratio coefficient, i.e., the maximum value among the critical internal pressure coefficient λ P，critical , the critical compression coefficient λ F，critical or the critical torsion coefficient λ M,critical ; S i is the sensitivity coefficient, Δλ max is the increment of the maximum critical load ratio coefficient between the current iteration and the previous iteration, and Δx i is the increment of the structural parameter.

[0253] Based on |S i Determine the parameter optimization order according to the magnitude of |S, and optimize the structural parameters with larger values first.

[0254] 3. Reconstruct the stiffness matrices of the constitutive equations of the material layer and the metal layer, and iteratively calculate the critical load ratio coefficients under multiple sets of structural parameter combinations according to the structural parameter optimization order.

[0255] In this embodiment, after obtaining the ultimate load coefficient in each iteration, that is, when FC critical > 1 and the structure fails, the stiffness matrix is first reconstructed. The method is as follows: Update the material elastic modulus according to the material elastic modulus degradation formula, and reconstruct the stiffness matrix in the constitutive equation of the material layer through the updated material elastic modulus and the ply angle in the current structural parameters.

[0256] The material elastic modulus degradation formula is:

[0257] Fiber tensile failure: E1′ = (1 - d ft )E1, where d ft is the damage variable, E1 is the longitudinal elastic modulus before damage in the case of fiber tensile failure, and E1′ is the effective longitudinal elastic modulus after damage;

[0258] Fiber compressive failure: where d fc is the damage variable, is the longitudinal elastic modulus before damage in the case of fiber compressive failure, is the effective longitudinal elastic modulus after damage;

[0259] Matrix tensile failure: E2′ = (1 - d mt )E2, G 12 ′ = (1 - d mt )G 12 , where d mt is the damage variable, E2 is the transverse elastic modulus before damage in the case of matrix tensile failure, E2′ is the effective transverse elastic modulus after damage; G 12 is the shear modulus before damage in the case of matrix tensile failure, G 12 ′ is the effective shear modulus after damage;

[0260] Matrix compressive failure: where d mc is the damage variable; is the transverse elastic modulus before damage in the case of matrix compressive failure, is the effective transverse elastic modulus after damage; is the shear modulus before damage in the case of matrix compressive failure, is the effective shear modulus after damage;

[0261] Metal damage failure: Based on the Kachanov-Rabotnov theory, a damage variable D (0 ≤ D ≤ 1) is introduced to characterize material degradation: D = 0 represents the undamaged state, and D = 1 represents the completely damaged state;

[0262] Effective stiffness prediction: D is the damage variable, which takes a value of 0.8 in this embodiment; where E is the initial stiffness, is the effective stiffness after damage.

[0263] Then, the increments of the ply angle and the metal layer thickness in the structural parameters are set:

[0264] Preset winding angle:

[0265] [φ1 = 0°, φ2 = 0°]

[0266] Increment setting:

[0267] φ1 ∈ [0°, 90°], Δφ1 = 1°

[0268] φ2 ∈ [0°, 90°], Δφ2 = 1°

[0269] Metal thickness increment: t m = from 0 to the preset total wall thickness, increasing by 0.1 mm each time.

[0270] In this embodiment, the composite material layer has 4 layers. The ply angles of the first two layers are φ1, and the ply angles of the last two layers are φ2. The total wall thickness is 10 mm. The initial ply angles are [φ1 = 0, φ2 = 0]. The ply angles increase to [φ1 = 0, φ2 = 1] in the second iteration and to [φ1 = 0, φ2 = 2] in the third iteration, until the ply angles reach [φ1 = 90, φ2 = 90] and the iteration stops.

[0271] In the sensitivity analysis, it is found that for this embodiment, the influence of the ply angle of the composite material layer on the bearing capacity is significantly greater than that of the layer thickness change. Especially, the ply angle φ1 of the first layer (close to the metal layer) plays a decisive role. Therefore, in this embodiment, the ply angle is optimized first, and then the thickness distribution is considered.

[0272] S4: Construct a load capacity map based on the critical load ratio coefficient and the structural parameters, and determine the optimal structural parameters according to the load capacity map.

[0273] 1. The method for constructing a load capacity map based on the critical load ratio coefficient and the structural parameters is as follows:

[0274] (1) The multiple sets of ultimate load factors obtained according to step S3 include the critical internal pressure factor λ, the critical compression factor λ, and the critical torsion factor λ under three principal stress states, which are three groups of original data. P，critical and the critical compression factor λ F，critical and the critical torsion factor λ M，critical for three groups of original data;

[0275] Perform parameter space partitioning:

[0276] φ1 ∈ [0°, 90°], Δφ1 = 1°;

[0277] φ2 ∈ [0°, 90°], Δφ2 = 1°.

[0278] (2) Perform spline interpolation on the three groups of original data respectively to generate three continuous ultimate load surfaces:

[0279] λ P，critical = f(φ1, φ2, t m );

[0280] λ F，critical = f(φ1, φ2, t m );

[0281] λ M，critical = f(φ1, φ2, t m ).

[0282] (3) Define the safety domain according to the ultimate load surface:

[0283] Definition of the basic safety domain:

[0284] Ω safe,i = (φ1, φ2, t m ) | FC critical (φ1, φ2, t m , λ F , λ M , λ P ) < 1

[0285] Extended safety domain considering the safety factor:

[0286] Ω safe，i = (φ1, φ2, t m ) | FC critical (φ1, φ2, t m , S F λ F , S M λ M , S P λ P ) < 1

[0287] where S F , S M and SP They are the safety factors for axial load, torque, and internal pressure, respectively, with values ranging from 1.2 to 1.5.

[0288] Multi - condition combined safety domain:

[0289]

[0290] Based on multiple safety criteria, the present invention defines the concept of a complete safety domain, providing a reliable theoretical basis for engineering design. In the initial stage of design, through the basic safety domain, obviously unsafe designs are preliminarily excluded. After determining a preliminary feasible scheme, the uncertainties in actual engineering (such as load fluctuations and material property deviations) need to be considered, and a safety margin needs to be reserved. At the same time, the combined safety domain where the structure needs to bear multiple load conditions simultaneously or alternately is considered.

[0291] The method for obtaining the optimal structural parameters is as follows:

[0292] In this embodiment, with the goal of obtaining the maximum load - bearing capacity, geometric constraints and mechanical constraints are established, and the optimal parameters are solved in the safety domain through the gradient - descent algorithm:

[0293] The objective function is: f(x) = min{-λ critical}, x = {t m , φ1, φ2};

[0294] Among them, λ critical is the critical internal - pressure coefficient λ P,critical , the critical compression coefficient λ F，critical or the critical torsion coefficient λ M，critical .

[0295] The constraint conditions are:

[0296] Geometric constraints: t min ≤t m ≤t max ; 0° ≤ φ i ≤90°;

[0297] Mechanical constraints: σ vm ≤[σ]; τ 12 ≤[τ];

[0298] Among them, σ vm represents the yield strength of the metal layer, [σ] is the allowable stress; [τ] is the allowable shear stress.

[0299] In this embodiment, the main symbols involved are explained as follows. The main geometric parameters of the drill pipe include the inner radius r in , the outer radius r out , the total wall thickness t total , the metal - layer thickness t m and the total thickness t of the composite - material layerc 。The design parameters of the composite layer include the ply angle φ and the number of layers N. These parameters together determine the overall structural characteristics of the hybrid drill pipe. For the detailed structure, please refer to Figure 2 。

[0300] The material system selected in this embodiment consists of two parts. The metal layer uses X95 high-strength steel, and its basic mechanical property parameters are: elastic modulus 208 GPa, Poisson's ratio 0.28, shear modulus 81.25 GPa, yield strength 655 MPa. These parameters reflect the good strength and stiffness characteristics of the metal layer. The composite layer selects the AS4 / APC-2 carbon fiber / PEEK system, and this material has significant anisotropic characteristics. Its detailed mechanical property parameters include: longitudinal elastic modulus 141.72 GPa, transverse elastic modulus 9.57 GPa, in-plane shear modulus 5.97 GPa, out-of-plane shear modulus 3.60 GPa. The strength parameters of the material include: longitudinal tensile strength 2068 MPa, longitudinal compressive strength 1196 MPa, transverse tensile strength 79 MPa, transverse compressive strength 177 MPa, in-plane shear strength 185 MPa, out-of-plane shear strength 91 MPa. In addition, the principal Poisson's ratio of this material is 0.37, and the secondary Poisson's ratio is 0.33.

[0301] As a specific implementation, the present invention first designs and analyzes a 5-inch 6.1-meter hybrid drill pipe. The basic dimension parameters of this drill pipe are: inner radius 53.5 mm, outer radius 63.5 mm, total wall thickness 10 mm. Among them, in this embodiment, the thickness of the metal layer is taken as 8 mm, and the composite layer is 2 mm. The composite layer adopts a symmetric ply design, with a total of 4 layers, each layer having a thickness of 0.5 mm, and the ply scheme is [X95 / +φ1 / -φ1 / +φ2 / -φ2]. This ply scheme comprehensively considers the bearing capacity and the feasibility of the manufacturing process.

[0302] According to the requirements of the actual working conditions, the design reference load parameters are as follows: internal pressure 51.7 MPa, axial compressive force 133.5 kN, torque 40.7 kNm. These load data are from the statistics of actual drilling working conditions and engineering experience, representing the typical load combinations that the drill pipe may encounter during service. The force conditions are as Figure 3 shown.

[0303] After verification by comparison with the finite element results, as Figure 4As shown, by comparing with the finite element analysis results, the stress distribution error predicted by this method is controlled within 5%, especially in the prediction of interlaminar stress. This high-precision stress analysis lays a solid theoretical foundation for subsequent structural optimization. The present invention adopts an analytical solution method, and the calculation efficiency is improved by two orders of magnitude compared with the traditional numerical simulation method. Taking a standard 5-inch 6.1-meter drill pipe as an example, it only takes 1 second to complete a full-condition stress analysis, while the equivalent finite element analysis takes about 6 hours. This efficient calculation method makes large-scale parameter optimization possible.

[0304] To illustrate the optimal solutions of the maximum load and winding angle of the metal-composite drill pipe, in this embodiment, the contour lines are extracted to generate a two-dimensional load contour map, as Figure 5 , 6 , and Figure 7 show: It can be seen from Figure 5 that under the condition dominated by internal pressure, the optimal ply angle of the outer layer is 60° - 80°; it can be seen from Figure 6 that under the condition dominated by torsion, the optimal angle of the outer layer is about 45°, which is consistent with the maximum shear stress theory; it can be seen from Figure 7 that under the condition dominated by compression, the optimal angle of the outer layer should adopt a combination of low angles (0° - 15°) and high angles (70° - 90°). The optimized hybrid drill pipe exhibits excellent performance under various load conditions. Compared with the metal composite drill pipe, the specific strength of the metal-composite structure is increased by 10%. Through systematic optimization analysis, the optimal range of the metal layer thickness is 40% - 60% of the total wall thickness. On the premise of meeting the same strength requirements, the weight of the optimized hybrid drill pipe is reduced by 33% compared with the traditional metal drill pipe. Taking a 5-inch drill pipe with a standard root length of 6.1 meters as an example, the weight of a single root is reduced from 174.88 kg to 145.18 kg, and this weight reduction effect is of great significance for deep well operations.

[0305] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An optimization design method for a metal-composite hybrid drill pipe, characterized in that, Including the steps: S1: Establish a three-dimensional elastic mechanics model of the metal-composite hybrid drill pipe; S2: Set the initial structural parameters of the metal-composite hybrid drill pipe and set the reference load parameters; S3: Based on the three-dimensional elastic mechanics model of the metal-composite hybrid drill pipe and the multi-mode failure analysis method, predict the maximum load through an incremental control strategy considering multiple loads, and determine the critical load ratio coefficient; S4: Construct a load capacity map according to the critical load ratio coefficient and structural parameters, and determine the optimal structural parameters according to the load capacity map.

2. The optimized design method of the metal-composite material hybrid drill pipe according to claim 1, wherein The method for establishing the three-dimensional elastic mechanics model is as follows: Under the cylindrical coordinate system (r, θ, z), based on the axisymmetric load condition, define the displacement fields of the metal layer and the composite material layer; According to the displacement fields of the metal layer and the composite material layer, establish the displacement-strain relationship of the metal layer and the composite material layer; According to the displacement-strain geometric relationship of the metal layer and the composite material layer, establish the constitutive equations of each layer respectively: For the composite material layer, use the generalized Hooke's law to establish the constitutive equation of the composite material layer, and for the metal layer, establish the constitutive equation of the metal layer based on isotropy; Establish the boundary conditions, interlayer continuity conditions, and axial compression force and torque balance equations for the metal layer and the composite material layer.

3. The optimized design method of the metal-composite material hybrid drill pipe according to claim 1, characterized in that, The method of step S3 is: Use a multi-scale grid strategy to determine the initial calculation points; Calculate the stress components in the cylindrical coordinate system according to the three-dimensional elastic mechanics model of the metal-composite hybrid drill pipe; Convert the stress components in the cylindrical coordinate system into the stress components in the material principal axis coordinate system, determine the dominant stress state according to the stress components in the material principal axis coordinate system, and perform multi-mode failure analysis and adaptive node encryption based on the stress components in the material principal axis coordinate system to determine the key failure index; Based on the key failure index, predict the maximum load through an incremental control strategy considering multiple loads, and obtain the critical load ratio coefficient.

4. The optimized design method of the metal-composite material hybrid drill pipe according to claim 3, wherein The method for performing multi-mode failure analysis based on the stress components in the material principal axis coordinate system to determine the key failure index is as follows: According to the stress components in the material principal axis coordinate system, calculate the failure index of each calculation point of the composite material layer based on the Hashin failure criterion, and calculate the failure index of each calculation point of the metal layer based on the improved von Mises criterion; Weight the failure index of each calculation point of the composite material layer and the failure index of each calculation point of the metal layer and calculate the key failure index of each calculation point; Obtain the failure index distribution curve FC critical (r k ), take the position where the key failure index FC critical (r k ) is the maximum value as the key failure position; For the area where the key failure position is located, use adaptive node encryption to determine the final key failure index.

5. The optimized design method of the metal-composite material hybrid drill pipe according to claim 3, characterized in that The method for predicting the maximum load through an incremental control strategy considering multiple loads based on the key failure index is as follows: Based on the dominant stress state described above, use the method of a single-parameter loading path to implement the load incremental control strategy to simulate the failure process, and determine the critical load ratio coefficient when failure occurs under the current structural parameters; Based on the critical load ratio coefficient, perform parameter sensitivity analysis to determine the optimization order of the structural parameters, reconstruct the stiffness matrices of the constitutive equations of the material layer and the metal layer, and iteratively calculate the critical load ratio coefficients under multiple sets of structural parameter combinations according to the optimization order of the structural parameters and record them.

6. The optimized design method of the metal-composite material hybrid drill pipe according to any one of claims 3 to 5, characterized in that, The calculation method of the key failure index is as follows: FC critical = max{w ft FC ft , w fc FC fc , w mt FC mt , w mc FC mc , w vm FC vm}; Among them, FC critical is the critical failure index. When FC critical > 1, the structure fails. FC ft , FC fc , FC mt and FC mc are the fiber tensile failure index, fiber compressive failure index, matrix tensile failure index, and matrix compressive failure index of the composite layer, respectively. FC vm is the von Mises failure index of the metal layer, w ft 、w fc 、w mt and w mc are the weight factors of the failure index of the composite layer, and w vm is the weight factor of the failure index of the metal layer.

7. The optimized design method of the metal-composite material hybrid drill pipe according to claim 5, characterized in that, The method for reconstructing the stiffness matrices of the constitutive equations of the material layer and the metal layer is as follows: Update the material elastic modulus according to the material elastic modulus degradation formula, and reconstruct the stiffness matrix in the constitutive equation of the material layer through the updated material elastic modulus and the ply angle in the current structural parameters; The material elastic modulus degradation formula is: Fiber tensile failure: E1′ = (1 - d ft )E1, where d ft is the damage variable, E1 is the longitudinal elastic modulus before damage in the case of fiber tensile failure, and E1′ is the effective longitudinal elastic modulus after damage; Fiber compression failure: where d fc is the damage variable, is the longitudinal elastic modulus before damage in the case of fiber compression failure, is the effective longitudinal elastic modulus after damage; Matrix tensile failure: E2′ = (1 - d mt )E2, G 12 ′ = (1 - d mt )G 12 , where d mt is the damage variable, E2 is the transverse elastic modulus before damage under matrix tensile failure, E2′ is the effective transverse elastic modulus after damage; G 12 is the shear modulus before damage under matrix tensile failure, G 12 ′ is the effective shear modulus after damage; Matrix compression failure: where d mc is the damage variable; is the transverse elastic modulus before damage under matrix compression failure, is the effective transverse elastic modulus after damage; is the shear modulus before damage under matrix compression failure, is the effective shear modulus after damage; Metal yield failure: where D is the damage variable, and E is the initial stiffness of the metal layer, which is the effective stiffness of the metal layer after damage.

8. The optimized design method of the metal-composite material hybrid drill pipe according to claim 3 or 5, characterized in that, The method for determining the initial calculation points using the multi-scale grid strategy is as follows: where r k is the k-th calculation point along the wall thickness direction, r in is the inner radius, represents the initial mesh spacing; The method of adaptive node encryption is to divide the area where the key failure position is located using the encrypted grid spacing to obtain the calculation points after encrypted division, repeat the calculation of the key failure position for the calculation points after encrypted division and perform adaptive node encryption until the adaptive node encryption stop condition is met to obtain the final key failure index; The encrypted grid spacing is: where, Δr coarse is the grid spacing before encryption, and Δr refined is the grid spacing after encryption, and k refine is the node encryption coefficient; The adaptive node encryption stop condition is: |FC critical (r p )-FC critical (r q )|≤ε; where r p and r q represent any two calculation points within the region where the key failure position is located after adaptive node encryption, and ε is the precision threshold.

9. The optimized design method of the metal-composite material hybrid drill pipe according to claim 5, characterized in that The method for determining the dominant stress state based on the stress components in the material principal axis coordinate system is as follows: Calculate the stress triaxiality parameter η for each calculation point: Among them, σ m is the average value of the principal stresses in the principal coordinate system of the material, and σ eq is the equivalent stress; Calculate the Lode angle parameter θ at each calculation point L : where J2 is the second invariant of the stress deviator and J3 is the third invariant of the stress deviator; According to the stress triaxiality parameter η and the Lode angle parameter θ L Determine the dominant stress state of each calculation point: Predominantly tensile: η > 0.33 and |θ L | < 0.17π; Compression - dominated: η < - 0.33 and |θ L - π| < 0.17π; Predominantly shear: |η| < 0.33 and |θ L - 0.5π| < 0.17π; The method for implementing the load increment control strategy using the single-parameter loading path method is as follows: Determine the current dominant working condition according to the dominant stress state: When the dominant stress state is mainly tensile, it is determined as the internal pressure dominant working condition; when the dominant stress state is mainly compressive, it is determined as the compression dominant working condition; when the dominant stress state is mainly shear, it is determined as the torsion dominant working condition; For the internal pressure-dominated condition: λ F = λ M = 1, λ P = 1 increases until FC critical = 1; obtain the critical internal pressure coefficient λ P， cr i ti ca l; For the compression-dominated condition: λ M = λ P = 1, λ F = 1 increases until FC critical = 1; obtaining the critical compression coefficient λ F， cr i ti ca l; For the torsion-dominated condition: λ F = λ P = 1, λ M = 1 is incremented until FC critical = 1, to obtain the critical torsion coefficient λ M， critical.

10. The optimized design method of the metal-composite material hybrid drill pipe according to claim 5 or 7, characterized in that The method for performing parameter sensitivity analysis is to calculate the sensitivity coefficient and determine the optimization order of the key structural parameters based on the sensitivity coefficient; The calculation method of the sensitivity coefficient is: where x i is a structural parameter, λ max is the maximum critical load ratio coefficient; S i is the sensitivity coefficient, Δλ max is the increment of the maximum critical load ratio coefficient in the current iteration and the previous iteration, and Δx i is the increment of the structural parameter.

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