A material selection method for a metal bonded structure with a low interface stress anti-fatigue design

Abstract

An embodiment of the present invention discloses a material selection method for a metal bonding structure with a low interface stress anti-fatigue design, including: determining the influencing factors for fatigue debonding of the metal bonding structure and the basic material selection principles for the anti-fatigue design of the metal bonding structure according to the failure mode of the metal bonding structure; taking the metal bonding interface of the metal bonding structure as the object to obtain the interface stress coefficient and the material selection criteria for the low interface stress design of the metal bonding structure; applying the interface stress coefficient f to the material selection process of the metal bonding structure to establish a material selection strategy for a metal bonding structure with a low interface stress anti-fatigue design. The technical solution provided by the embodiment of the present invention solves the existing solutions for the interface debonding problem of the metal bonding structure. Since other key influencing factors for interface fatigue debonding of the metal bonding structure are not comprehensively considered, the existing technical solutions cannot fundamentally improve the problem of fatigue debonding of the metal bonding structure.

Description

Technical Field

[0001] The present application relates to, but is not limited to, the field of nuclear accident simulation technology, and particularly refers to a material selection method for a metal bonded structure with a low interface stress anti-fatigue design. Background Art

[0002] Metal bonded structures are widely used in the main load-bearing and secondary load-bearing structures of helicopters. As Figure 1 shown, it is a schematic diagram of an actual application structure of an existing metal bonded structure. Figure 1 The aluminum alloy panel-honeycomb core (aluminum core or paper core) bonded assembly structure shown in it is the main component structure of the helicopter equipment cabin floor, the fuselage passenger cabin floor, the special equipment cabin equipment installation plate, etc. It has the advantages of light weight, high specific strength, sound insulation, heat insulation, moisture resistance, and good sealing performance; as Figure 2 shown, it is a schematic diagram of another actual application structure of an existing metal bonded structure. Figure 2 It specifically shows the bonded structure of the blade leading edge iron wrap in it, and its function is to protect the leading edge of the composite blade from abrasion and damage by sand and gravel; in addition, the application of the metal bonded structure also includes the bonded structure of the metal at the root of the thrust blade and the beam belt.

[0003] The characteristic of the metal bonded structure is a three-material sandwich structure composed of metal, adhesive, and composite materials, and usually contains two interfaces, namely the metal-adhesive interface and the adhesive-composite interface; due to the difference in the elastic constants of the materials on both sides of the interface, under the action of an external load, under the restraint of the same deformation, additional interface stresses will inevitably be generated near the interface, directly affecting the static and fatigue strengths of the overall structure.

[0004] The most common failure form of the metal bonded structure is interface debonding. For the interface debonding problem of the metal bonded structure, the existing solution idea is to select an adhesive or the adherend material with the highest possible bonding strength during the structural design material selection process. The main solution measures are to compare the test results of the bonding shear strength of the bonded structures composed of different adhesive materials through a trial-and-error method according to the structural service environment, screen out the material combination with the highest strength, and then reduce the defects such as voids, inclusions, and surface scratches in the adhesive layer from the perspective of optimizing the bonding process.

[0005] The above existing solution idea for the interface debonding problem of the metal bonded structure is simple and direct, but it does not comprehensively consider other key influencing factors for the interface fatigue debonding of the metal bonded structure. Therefore, the existing technical solutions cannot fundamentally improve the problem of fatigue debonding of the metal bonded structure. Summary of the Invention

[0006] Objective of the present invention: To solve the above technical problems, embodiments of the present invention provide a material selection method for a metal bonding structure with a low interface stress anti-fatigue design, so as to solve the existing solutions for the interface debonding problem of the metal bonding structure. Since other key influencing factors causing interface fatigue debonding of the metal bonding structure are not comprehensively considered, the existing technical solutions cannot fundamentally improve the problem of fatigue debonding of the metal bonding structure.

[0007] Technical solution of the present invention: Embodiments of the present invention provide a material selection method for a metal bonding structure with a low interface stress anti-fatigue design, including:

[0008] Step 1, according to the failure form of the metal bonding structure, determine the influencing factors causing fatigue debonding of the metal bonding structure and the basic material selection principles for the anti-fatigue design of the metal bonding structure. The influencing factors include the bonding shear strength and the interface stress of the material combination. The basic material selection principle is to select a material combination with low interface stress on the premise of improving the interface bonding shear strength;

[0009] Step 2, taking the metal bonding interface of the metal bonding structure as the object, conduct interface stress analysis based on the three-dimensional elasticity theory to obtain the interface stress coefficient f. Among them, in the process of analyzing and obtaining the interface stress coefficient f, the material selection criteria for the low interface stress design of the metal bonding structure are obtained;

[0010] Step 3, according to the basic material selection principles for the anti-fatigue design of the metal bonding structure and the material selection criteria for the low interface stress design of the metal bonding structure, apply the interface stress coefficient f to the material selection process of the metal bonding structure, and establish a material selection strategy for the metal bonding structure with a low interface stress anti-fatigue design.

[0011] Optionally, in the above-mentioned material selection method for a metal bonding structure with a low interface stress anti-fatigue design, the Step 2 includes:

[0012] Step 21, specifically abstract the metal-adhesive structure in the metal bonding structure into a dissimilar material joint model;

[0013] Step 22, conduct interface stress analysis on the dissimilar material joint model by using the three-dimensional elasticity theory to obtain a tool for evaluating the interface stress magnitude of the dissimilar material joint, that is, the interface stress coefficient f.

[0014] Optionally, in the above-mentioned material selection method for a metal bonding structure with a low interface stress anti-fatigue design, the interface stress coefficient f is:

[0015]

[0016] Wherein, v 1 、v 2are the Poisson's ratios of the materials on both sides of the interface, respectively, E 1 , E 2 are the Young's moduli of the materials on both sides of the interface, respectively. The Poisson's ratio and the Young's modulus are both elastic constants of the materials. The interface stress coefficient f is used to qualitatively and quantitatively reflect the magnitude of the interface stress of the dissimilar material joint interface and the law of the change rate of the interface stress changing with the external load.

[0017] Optionally, in the material selection method of the metal bonding structure with low interface stress anti-fatigue design as described above, the acquisition method of the interface stress coefficient f is as follows:

[0018] Step a, according to the different influences of each elastic constant of the material on the interface stress of the dissimilar material joint, and the influence law of one elastic constant of the material on the interface stress changes with the change of another elastic constant, determine the relationship between the interface stress of the dissimilar material joint model and the material elastic constant as:

[0019] σ int = f(E 1 , E 2 , v 1 , v 2 )·σ;

[0020] Among them, σ int is the interface stress of the joint, σ is the external load, and f(E 1 , E 2 , v 1 , v 2 ) is the interface stress coefficient;

[0021] Step b, use the three-dimensional elastic theory to solve the interface stress of the dissimilar material joint. During the solution process, establish a Cartesian coordinate system according to the dissimilar material joint model, select the center of the dissimilar material joint interface as the coordinate origin, analyze the mechanical elements on the free edge near the dissimilar material joint interface, and solve the stress components near the interface when the dissimilar material joint bears the load to obtain the analytical solution of the interface stress of the dissimilar material joint under uniaxial load;

[0022] Step c, according to the relationship between the interface stress of the dissimilar material joint model and the material elastic constant, and the analytical solution of the interface stress of the dissimilar material joint under uniaxial load, obtain the interface stress coefficient f.

[0023] Optionally, in the material selection method of the metal bonding structure with low interface stress anti-fatigue design as described above, the solution method in step b is as follows:

[0024] Step b1, assume that during the loading process of the dissimilar material joint, the interface always remains flat, that is, the first stress boundary condition to be satisfied is:

[0025]

[0026] Among them, and are the shear stress components of the mechanical unit near the interface of Material 1 in the dissimilar material joint, and are the shear stress components of the mechanical unit near the interface of Material 2 in the dissimilar material joint;

[0027] When the first stress boundary condition is satisfied, the displacement components of the mechanical unit near the interface are expressed as:

[0028] {u(x), v(y), w(z)};

[0029] Among them, u(x) is the displacement component of the mechanical unit near the interface along the x-axis, v(y) is the displacement component of the mechanical unit near the interface along the y-axis, and w(z) is the displacement component of the mechanical unit near the interface along the z-axis;

[0030] Step b2, assume that the interface of the dissimilar material joint is well-bonded and has no initial cracks or crack-like defects. Therefore, the deformations of the materials on both sides of the interface are consistent at the interface, that is, the satisfied displacement boundary condition is:

[0031] {u 1 (z = 0) = u 2 (z = 0), v 1 (z = 0) = v 2 (z = 0)};

[0032] Among them, u 1 (z = 0) is the displacement component of the mechanical unit near the interface of Material 1 along the x-axis at z = 0, u 2 (z = 0) is the displacement component of the mechanical unit near the interface of Material 2 along the x-axis at z = 0, v 1 (z = 0) is the displacement component of the mechanical unit near the interface of Material 1 along the y-axis at z = 0, v 2 (z = 0) is the displacement component of the mechanical unit near the interface of Material 2 along the y-axis at z = 0;

[0033] Step b3, according to Newton's third law and the small deformation assumption of elasticity, the second stress boundary condition is obtained as:

[0034]

[0035] Among them, is the stress component of the mechanical unit near the interface of Material 1 along the x-axis at z = 0, is the stress component of the mechanical unit near the interface of Material 2 along the x-axis at z = 0, is the stress component of the mechanical unit near the interface of Material 1 along the y-axis at z = 0, The stress component along the y-axis of the mechanical unit near the interface of Material 2 when z = 0 The stress component along the z-axis of the mechanical unit near the interface of Material 1 The stress component along the z-axis of the mechanical unit near the interface of Material 2, and σ is the external load;

[0036] Step b4, according to the first stress boundary condition, the second stress boundary condition and the displacement boundary condition, the analytical solution of the interface stress of the dissimilar material joint under uniaxial load is obtained as follows:

[0037]

[0038] Optionally, in the material selection method of the metal bonding structure with low interface stress anti-fatigue design as described above, Step 2 further includes:

[0039] According to the analysis of the analytical solution of the interface stress of the dissimilar material joint under uniaxial load, the material selection criterion for the low interface stress design of the metal bonding structure is obtained; the material selection criterion is: the ratio of the Poisson's ratio to the Young's modulus of the materials on both sides of the interface should approach 1 infinitely.

[0040] Optionally, in the material selection method of the metal bonding structure with low interface stress anti-fatigue design as described above,

[0041] The material selection strategy of the metal bonding structure with low interface stress anti-fatigue design formed in Step 3 includes: passive material selection strategy and positive material selection strategy.

[0042] Optionally, in the material selection method of the metal bonding structure with low interface stress anti-fatigue design as described above, the passive material selection strategy means that the material selection range of the metal bonding structure is limited to the materials that have been identified or the mature materials that have been applied in models;

[0043] In the material selection process of the passive material selection strategy, when the structure form and one or two materials in the structure are determined, the elastic constants of the determined materials and all other component materials that meet the requirements of adhesive static strength are substituted into the interface stress coefficient for calculation. According to the calculation results of the interface stress coefficient, the material selection combination of the metal bonding structure with the minimum interface stress is selected for the next strength calculation.

[0044] Optionally, in the material selection method of the metal bonding structure with low interface stress anti-fatigue design as described above, the positive material selection strategy means that the material selection range of the metal bonding structure is not limited to the materials that have been applied in models or the mature materials that have been identified, but also includes the new materials developed directionally according to the needs of structure design;

[0045] In the material selection process of the forward material selection strategy, after the structural form and one or two materials in the structure are determined, substitute the elastic constants of the determined materials and all other component materials that meet the requirements of the adhesive static strength into the interface stress coefficient for calculation. Make a judgment based on the calculation result of the interface stress coefficient. If a material combination that meets the requirements of the low interface stress design of the structure can be screened out, proceed to the next strength calculation; if none of the existing material combinations can meet the requirements of the low interface stress design of the structure, conduct research and development of new materials according to the requirements of the low interface stress design of the structure, and optimize the structural design according to the new material research and development structure.

[0046] Advantages of the present invention: The material selection method for a metal adhesive structure with a low interface stress anti-fatigue design provided by the embodiments of the present invention is aimed at the metal adhesive structure widely used in the main load-bearing and secondary load-bearing structures of helicopters. First, it is analyzed that the most common failure form is interface fatigue debonding. Since the interface stress is the key factor causing interface fatigue debonding, for the problem of interface fatigue debonding of metal adhesive structures, the traditional solution idea is to improve the adhesive shear strength of the adhesive interface. This solution idea ignores the influence of the interface stress, and there are few domestic and international adhesive structure design material selection methods that consider the interface stress at present. The main difficulty lies in the efficient and accurate analysis and evaluation of the interface stress of the adhesive structure. The embodiments of the present invention take the metal-adhesive interface as the research object, obtain a tool for interface stress analysis based on the three-dimensional elasticity theory, that is, the interface stress coefficient, and further establish a material selection method for the low interface stress anti-fatigue design of metal adhesive structures based on the interface stress coefficient, providing theoretical guidance for improving the fatigue debonding problem of metal adhesive structures, enhancing the fatigue bearing capacity and service life of the adhesive structure. The material selection method proposed by the embodiments of the present invention has the following beneficial effects:

[0047] (1) Aiming at the defects of the traditional solution idea for the debonding problem of metal adhesive structures, it is proposed that the basic rule for the anti-fatigue design material selection of metal adhesive structures is to select a material combination with low interface stress as much as possible while improving the adhesive shear strength of the interface;

[0048] (2) Taking the metal-adhesive interface of the metal adhesive structure as the research object, conducting interface stress analysis based on the three-dimensional elasticity theory, and obtaining the interface stress coefficient f(E 1 ,E 2 ,v 1 ,v 2 ), which can more accurately and efficiently evaluate the magnitude of the interface stress of dissimilar material joints compared with the traditional method;

[0049] (3) According to the basic principle of the anti-fatigue design material selection of the metal adhesive structure and the analysis result of the interface stress coefficient, it is proposed that the material selection criterion for the low interface stress design of the metal adhesive structure is that the ratio of the Poisson's ratio to the Young's modulus of the materials on both sides of the interface should approach 1 infinitely, and this criterion can be used to directly guide engineering design;

[0050] (4) According to the basic principles of material selection for anti-fatigue design of metal bonded structures and the criteria for material selection for low interface stress design of metal bonded structures, the interface stress coefficient is used in the material selection for the design of helicopter metal bonded structures, and a material selection strategy for metal bonded structures with low interface stress anti-fatigue design is specifically proposed; compared with the traditional material selection method for structural design, the calculation and determination steps of the interface stress coefficient are added, so as to achieve the low interface stress design of metal bonded structures, and new materials can be developed directionally according to the requirements of the low interface stress design of the structure. Description of the Drawings

[0051] The drawings are used to provide a further understanding of the technical solutions of the present invention, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solutions of the present invention, and do not constitute a limitation to the technical solutions of the present invention.

[0052] Figure 1 It is a schematic diagram of an actual application structure of an existing metal bonded structure;

[0053] Figure 2 It is a schematic diagram of another actual application structure of an existing metal bonded structure;

[0054] Figure 3 It is a flowchart of a material selection method for a metal bonded structure with low interface stress anti-fatigue design provided by an embodiment of the present invention;

[0055] Figure 4 a is a schematic diagram of the physical model of the dissimilar material joint in the embodiment of the present invention;

[0056] Figure 4 b is Figure 4 a three-dimensional finite element model schematic diagram of the physical model of the dissimilar material joint shown in a;

[0057] Figure 5 It is a schematic diagram of the finite element calculation result of the influence law of the material elastic constant difference on the interface stress of the dissimilar material joint obtained by analysis in the embodiment of the present invention;

[0058] Figure 6 It is a schematic diagram of the comparison between the numerical analysis result and the analytical analysis result of the influence law of the material elastic constant difference on the interface stress coefficient of the dissimilar material joint obtained by analysis of the present invention;

[0059] Figure 7 It is a flowchart of the passive material selection strategy for the low interface stress anti-fatigue design of the metal bonded structure proposed by the embodiment of the present invention;

[0060] Figure 8 It is a flowchart of the positive material selection strategy for the low interface stress anti-fatigue design of the metal bonded structure proposed by the embodiment of the present invention. Detailed implementation manners

[0061] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined arbitrarily with each other.

[0062] As described in the above background art, for the problem of interfacial debonding of metal bonding structures, the main idea of the existing solutions is to select adhesives or adherends with as high bonding strength as possible during the structural design and material selection process, and screen out the material combinations with the highest strength. However, the existing solutions for the problem of interfacial debonding of metal bonding structures do not comprehensively consider the key influencing factors of interfacial fatigue debonding of metal bonding structures, that is, the influence of interfacial stress on interfacial fatigue debonding is ignored.

[0063] When the bonding strengths of two material combinations are equivalent, under the same load-bearing conditions, it must be the material combination with larger additional interfacial stress that undergoes fatigue debonding first. Therefore, the existing solutions for the problem of interfacial debonding of metal bonding structures cannot fundamentally improve the problem of fatigue debonding of metal bonding structures.

[0064] The embodiments of the present invention propose a technical solution for solving the problem of interfacial fatigue debonding of metal bonding structures. The idea is: while improving the interfacial bonding shear strength, select material combinations with as low interfacial stress as possible. However, currently, there are few domestic and international material selection methods for bonding structure design that consider interfacial stress. Therefore, the embodiments of the present invention specifically provide a material selection method for metal bonding structures with low interfacial stress anti-fatigue design, providing engineering guidance for improving the fatigue load-bearing capacity and service life of metal bonding structures.

[0065] The present invention provides the following specific embodiments that can be combined with each other. For the same or similar concepts or processes, they may not be repeated in some embodiments.

[0066] Figure 3 It is a flowchart of a material selection method for a metal bonding structure with low interfacial stress anti-fatigue design provided by the embodiments of the present invention. The material selection method for a metal bonding structure with low interfacial stress anti-fatigue design provided by the embodiments of the present invention may include the following steps:

[0067] Step 1, according to the failure mode of the metal bonding structure, determine the influencing factors of fatigue debonding of the metal bonding structure and the basic principles of material selection for anti-fatigue design of the metal bonding structure.

[0068] The material selection method provided by the embodiments of the present invention first analyzes the influencing factors of the failure modes of metal bonding structures. The most common failure mode of metal bonding structures is interfacial fatigue debonding. Two important factors affecting interfacial fatigue debonding are the adhesive shear strength and the interfacial stress of the material combination.

[0069] It should be noted that interfacial debonding usually does not occur under static loads, but gradually appears during long-term service, that is, debonding under fatigue loads. In the embodiments of the present invention, the interfacial debonding phenomenon of metal bonding structures is very similar to the delamination failure phenomenon of laminated structures. Some studies have shown that progressive delamination is the main form of fatigue failure of laminated structures, and the interlaminar interfacial stress is the main reason for fatigue delamination of laminated structures. According to the above analysis, for the existing solutions to the interfacial debonding problem of metal bonding structures, since they ignore the key influencing factors causing interfacial fatigue debonding of metal bonding structures, that is, they ignore the influence of interfacial stress on interfacial fatigue debonding, the existing solutions cannot fundamentally improve the problem of fatigue debonding of metal bonding structures.

[0070] Aiming at the problems existing in the existing solutions, the material selection method provided by the embodiments of the present invention first proposes a basic material selection principle that comprehensively considers two influencing factors, namely, the adhesive shear strength and the interfacial stress of the material combination. Specifically: on the premise of improving the interfacial adhesive shear strength, materials with low interfacial stress are preferably selected.

[0071] Step 2: Taking the metal bonding interface of the metal bonding structure as the object, perform interfacial stress analysis based on the three-dimensional elasticity theory to obtain the interfacial stress coefficient f. Among them, in the process of analyzing and obtaining the interfacial stress coefficient f, the material selection criterion for low interfacial stress design of the metal bonding structure is obtained.

[0072] Step 3: According to the basic material selection principle for anti-fatigue design of the metal bonding structure and the material selection criterion for low interfacial stress design of the metal bonding structure, apply the interfacial stress coefficient f to the material selection process of the metal bonding structure to form a material selection strategy for low interfacial stress design of the metal bonding structure.

[0073] The material selection method provided by the embodiments of the present invention takes the metal bonding structure as the research object. The specific implementation of Step 2 may include: First, abstract the metal-adhesive structure in the metal bonding structure into a dissimilar material joint model, and perform interfacial stress analysis on the dissimilar material joint model using the three-dimensional elasticity theory to obtain a tool for evaluating the interfacial stress magnitude of the dissimilar material joint, that is, the interfacial stress coefficient f. In the process of analyzing and deriving the interfacial stress coefficient f, the material selection criterion for low interfacial stress design of the metal bonding structure is obtained. Subsequently, the interfacial stress coefficient is applied to the material selection process of the metal bonding structure design, and a material selection strategy for a metal bonding structure with low interfacial stress anti-fatigue design is established.

[0074] It should be noted that in the embodiments of the present invention, considering the influence of interface stress on the metal bonding structure, on the one hand, based on the two influencing factors that cause fatigue debonding (mainly including the bonding shear strength and the interface stress of the material combination), the basic material selection principle for the anti-fatigue design of the metal bonding structure is proposed for the first time, that is, on the premise of improving the interface bonding shear strength, materials with low interface stress are selected as much as possible; on the other hand, according to the interface stress coefficient f, the material selection criterion for the low interface stress design of the metal bonding structure is proposed for the first time; furthermore, the above basic material selection principle and material selection criterion are applied to the material selection process of the metal bonding structure design, forming a new material selection method for the metal bonding structure with low interface stress anti-fatigue design, providing theoretical support and engineering guidance for the material selection work in the anti-fatigue design process of the metal bonding structure and the formulation of the technical requirements for the new developed materials to be used in the future metal bonding structure.

[0075] In the embodiments of the present invention, the symbol of the interface stress coefficient f is expressed as f(E 1 ,E 2 ,v 1 ,v 2 ), and its physical meaning is that it can qualitatively and quantitatively reflect the law that the interface stress magnitude and the interface stress change rate of the dissimilar material joint change with the change of the external load. Its specific expression is:

[0076]

[0077] Among them, v 1 and v 2 are the Poisson's ratios of the materials on both sides of the interface respectively, and E 1 and E 2 are the Young's moduli of the materials on both sides of the interface respectively. The Poisson's ratio and the Young's modulus are both material elastic constants.

[0078] Figure 4 Figure a is a schematic diagram of the physical model of the dissimilar material joint in the embodiments of the present invention, Figure 4 Figure b is Figure 4 a schematic diagram of the three-dimensional finite element model of the physical model of the dissimilar material joint shown in a. The following specifically describes the acquisition method of the interface stress coefficient f in the embodiments of the present invention, which may include the following steps:

[0079] Step a, according to Figure 4 the physical model shown in a and Figure 4 the three-dimensional finite element analysis result shown in b, it can be found that the influence of each elastic constant of the material on the interface stress of the dissimilar material joint is different. In addition, the influence law of one elastic constant on the interface stress will change with the change of another elastic constant. Therefore, it can be inferred that there is the following functional relationship between the joint interface stress σ int and the material elastic constants:

[0080] σ int = f(E 1 , E 2 , v 1 , v 2 )·σ; (2)

[0081] where σ int is the joint interface stress, σ is the external load, and f(E 1 , E 2 , v 1 , v 2 ) is the interface stress coefficient;

[0082] Step b: Solve the interface stress of the dissimilar material joint using the three-dimensional elastic theory. The solution of the interface stress of the dissimilar material joint belongs to a boundary value problem in the three-dimensional elastic theory.

[0083] For the above formula (2), since it is difficult to obtain the coefficient f(E 1 , E 2 , v 1 , v 2 ) through the method of mathematical regression of numerical results, the analytical method can solve this problem.

[0084] The solution of the interface stress of the dissimilar material joint belongs to a boundary value problem in the three-dimensional elastic theory. Therefore, in the solution process, a series of basic equations in the three-dimensional elastic theory must be satisfied and solved. This series of basic equations includes:

[0085] (a) Cauchy strain-displacement equation:

[0086]

[0087] In formula (3), ε ij are the components in the 3×3 matrix of the strain tensor ε in a certain coordinate system;

[0088] u i are the components of the displacement vector u in the corresponding coordinate system, and there is

[0089] (b) Saint-Venant compatibility equation:

[0090] ε ij + ε kl,ij - ε jl,ik - ε ik,jl = 0; (4)

[0091] In formula (4), the subscript after the comma of the strain tensor is: the second-order derivative of each strain component with respect to the coordinate system component, that is

[0092] (c) Lamé constitutive equation:

[0093]

[0094] In formula (5), δ ij is the Kronecker operator, and δ ij = 1 when i = j, and δ ij = 0 when i ≠ j;

[0095] ε kk is expressed as ε kk = ε 11 + ε 22 + ε 33 .

[0096] (d) Navier's second law of motion:

[0097] σ ij，j = 0; (6)

[0098] The prerequisite for formula (6) is that the body force of the analysis object can be ignored. Finally, the relationship, that is, the Lamé-Navier equation, namely the L-N equation, is obtained:

[0099]

[0100] As Figure 4 a and Figure 4 b show, in the solution process of step b, a Cartesian coordinate system is established according to the dissimilar material joint model, the center of the dissimilar material joint interface is selected as the coordinate origin, and the mechanical elements on the free edge near the dissimilar material joint interface are analyzed to solve the stress components near the interface when the dissimilar material joint bears load.

[0101] The specific solution method for the stress components near the interface when the dissimilar material joint bears load in the above step b is as follows:

[0102] Step b1, assume that during the loading process of the dissimilar material joint, the interface always remains planar, that is, the first stress boundary condition to be satisfied is:

[0103]

[0104] In the above formula (8), and are the shear stress components of the mechanical elements near the interface of material 1 in the dissimilar material joint, and are the shear stress components of the mechanical elements near the interface of material 2 in the dissimilar material joint.

[0105] At the same time, the displacement components of the mechanical elements near the interface are expressed as:

[0106] {u(x), v(y), w(z)}; (9)

[0107] In the above formula (9), u(x) is the displacement component of the mechanical unit near the interface along the x-axis, v(y) is the displacement component of the mechanical unit near the interface along the y-axis, and w(z) is the displacement component of the mechanical unit near the interface along the z-axis.

[0108] Step b2, assume that the interface of the dissimilar material joint is well-bonded without initial cracks or crack-like defects. Therefore, the deformations of the materials on both sides of the interface at the interface are consistent, that is, the displacement boundary conditions to be satisfied are:

[0109] {u 1 (z = 0) = u 2 (z = 0), v 1 (z = 0) = v 2 (z = 0)}; (10)

[0110] In the above formula (10), u 1 (z = 0) is the displacement component of the mechanical unit near the interface of Material 1 along the x-axis when z = 0, u 2 (z = 0) is the displacement component of the mechanical unit near the interface of Material 2 along the x-axis when z = 0, v 1 (z = 0) is the displacement component of the mechanical unit near the interface of Material 1 along the y-axis when z = 0, v 2 (z = 0) is the displacement component of the mechanical unit near the interface of Material 2 along the y-axis when z = 0.

[0111] Step b3, according to Newton's third law and the small deformation assumption of elasticity, the second stress boundary condition is obtained as:

[0112]

[0113] In the above formula (11), is the stress component of the mechanical unit near the interface of Material 1 along the x-axis when z = 0, is the stress component of the mechanical unit near the interface of Material 2 along the x-axis when z = 0, is the stress component of the mechanical unit near the interface of Material 1 along the y-axis when z = 0, is the stress component of the mechanical unit near the interface of Material 2 along the y-axis when z = 0, is the stress component of the mechanical unit near the interface of Material 1 along the z-axis, is the stress component of the mechanical unit near the interface of Material 2 along the z-axis, and σ is the external load;

[0114] Step b4, by substituting the first stress boundary condition, the second stress boundary condition, and the displacement boundary condition into the basic equations of elasticity, the analytical solution of the interfacial stress of the dissimilar material joint under uniaxial load can be obtained as follows:

[0115]

[0116] As can be seen from the above formula (12), when or , the interfacial stress is zero, that is, σ int = 0. This indicates that when the ratio of the Poisson's ratio to the Young's modulus of the materials on both sides of the interface is equal, the interfacial stress of the dissimilar material joint will be reduced to 0.

[0117] Step c, according to the relationship between the interfacial stress of the dissimilar material joint model and the material elastic constants, and the analytical solution of the interfacial stress of the dissimilar material joint under uniaxial load, the interfacial stress coefficient f is obtained.

[0118] Specifically, according to the above formula (2) and formula (12), the above formula (1) can be obtained, that is,

[0119]

[0120] As can be seen from formula (2) and formula (12), the larger f(E 1 , E 2 , v 1 , v 2 ), the faster the interfacial stress of the dissimilar material joint increases with the increase of the external load. And when the external load is constant, the larger f(E 1 , E 2 , v 1 , v 2 ), the greater the interfacial stress of the dissimilar material joint. That is to say, f(E 1 , E 2 , v 1 , v 2 ) can qualitatively and quantitatively reflect the law of the interfacial stress magnitude and the change rate of the interfacial stress changing with the external load. Therefore, f(E 1 , E 2 , v 1 , v 2 ) is defined as the interfacial stress coefficient.

[0121] The material selection method provided by the embodiments of the present invention, based on the basic principles of material selection for anti-fatigue design of the above metal bonding structure and the material selection criteria for low interface stress design of the metal bonding structure, uses the interface stress coefficient for the design and material selection of the helicopter metal bonding structure, and proposes a material selection strategy for the metal bonding structure with low interface stress anti-fatigue design. Since this material selection strategy not only considers the influence of the bonding shear strength on fatigue debonding, but also considers the influence of the interface stress of the material combination on fatigue debonding, therefore, adopting this material selection strategy can effectively improve the interface debonding problem of the metal bonding structure and achieve the goal of improving the fatigue bearing capacity and service life of the metal bonding structure.

[0122] The material selection method for the metal bonding structure with low interface stress anti-fatigue design provided by the embodiments of the present invention is aimed at the metal bonding structure widely used in the main load-bearing and secondary load-bearing structures of helicopters. First, it is analyzed that the most common failure form is interface fatigue debonding. Since interface stress is the key factor causing interface fatigue debonding, for the interface fatigue debonding problem of the metal bonding structure, the traditional solution idea is to improve the bonding shear strength of the bonding interface. This solution idea ignores the influence of interface stress, and there are few domestic and international material selection methods for bonding structure design that consider interface stress at present. The main difficulty lies in the efficient and accurate analysis and evaluation of the interface stress of the bonding structure. The embodiments of the present invention take the metal-adhesive interface as the research object, obtain a tool for interface stress analysis based on the three-dimensional elastic theory, that is, the interface stress coefficient, and further establish a material selection method for low interface stress anti-fatigue design of the metal bonding structure based on the interface stress coefficient, providing theoretical guidance for improving the fatigue debonding problem of the metal bonding structure and enhancing the fatigue bearing capacity and service life of the bonding structure. The material selection method proposed by the embodiments of the present invention has the following beneficial effects:

[0123] (1) Aiming at the defects of the traditional solution idea for the debonding problem of the metal bonding structure, it is proposed that the basic rule for material selection in the anti-fatigue design of the metal bonding structure is to select a material combination with low interface stress as much as possible while improving the bonding shear strength of the interface;

[0124] (2) Taking the metal-adhesive interface of the metal bonding structure as the research object, interface stress analysis is carried out based on the three-dimensional elastic theory, and the interface stress coefficient f(E 1 , E 2 , v 1 , v 2 ) is obtained, which can more accurately and efficiently evaluate the magnitude of the interface stress of dissimilar material joints compared with the traditional method;

[0125] (3) According to the basic principles of material selection for anti-fatigue design of the metal bonding structure and the analysis results of the interface stress coefficient, it is proposed that the material selection criterion for low interface stress design of the metal bonding structure is that the ratio of the Poisson's ratio to the Young's modulus of the materials on both sides of the interface should approach 1 infinitely, and this criterion can be used to directly guide engineering design;

[0126] (4) According to the basic principles of material selection for the anti-fatigue design of metal bonded structures and the material selection criteria for the low interface stress design of metal bonded structures, the interface stress coefficient is used in the material selection for the design of helicopter metal bonded structures, and a material selection strategy for metal bonded structures with low interface stress anti-fatigue design is specifically proposed; compared with the traditional structural design material selection method, the calculation and determination steps of the interface stress coefficient are added, so as to realize the low interface stress design of metal bonded structures, and new materials can be developed directionally according to the requirements of the low interface stress design of the structure.

[0127] It should be noted that in the embodiment of the present invention, in order to verify the accuracy of the interface stress coefficient, that is, formula (1), the numerical solution of the interface stress obtained by the three-dimensional finite element method is substituted into formula (2) to obtain the numerical solution of the interface stress coefficient; the material property parameters used for finite element calculation are substituted into formula (1) to obtain the analytical solution of the interface stress coefficient, and the comparison results of the numerical solution and the analytical solution of the influence law of material property differences on the interface stress coefficient are obtained as Figure 6 shown. Specifically, Figure 5 is a schematic diagram of the finite element calculation results of the influence law of the difference in material elastic constants on the interface stress of dissimilar material joints obtained by analysis in the embodiment of the present invention, Figure 6 is a schematic diagram of the comparison of the numerical analysis results and the analytical analysis results of the influence law of the difference in material elastic constants on the interface stress coefficient of dissimilar material joints obtained by analysis in the present invention. Among them, Figure 5 and Figure 6 in the a diagrams are all the results of fixing v 1 / v 2 and varying E 1 / E 2 , and the b diagrams are all the results of fixing E 1 / E 2 and varying v 1 / v 2 .

[0128] According to Figure 6 the comparison results shown, the numerical and analytical results of the influence law of material property differences on the interface stress coefficient f(E 1 , E 2 , v 1 , v 2 ) follow the same trend. In addition, it should also be noted that, whether it is the numerical result or the analytical result, when , all the curves will intersect with the interface stress coefficient being zero, that is, f(E 1 , E 2 , v 1 , v 2) = 0 curve has intersections, which once again verifies that the criterion for the interfacial stress to be 0 when a dissimilar material joint bears load is that the ratio of the Poisson's ratio to the Young's modulus of the materials on both sides of the interface is equal. Moreover, the application of the interfacial stress coefficient can replace the numerical method to more efficiently and accurately evaluate the influence of material property differences on the interfacial stress.

[0129] To better illustrate the accuracy and efficiency of using the interfacial stress coefficient to evaluate the interfacial stress, the embodiment of the present invention also uses an analysis example in the literature for comparative analysis. Wu analyzed the interfacial stress of Al-PMMA and Al-PC butt joints using the three-dimensional finite element method. The results show that whether at the corner or the edge of the joint, the interfacial stress of Al-PC is greater than that of Al-PMMA. That is to say, under the condition that the geometric factors remain unchanged, the interfacial stress of the Al-PC joint caused by material inhomogeneity is always greater than that of the Al-PMMA joint. Substitute the material elastic constants used by Wu into the expression of the interfacial stress coefficient f(E 1 ,E 2 ,v 1 ,v 2 ). The results show that the value of the interfacial stress coefficient of the Al-PC joint is 0.684, which is higher than the value of 0.481 of the interfacial stress coefficient of the Al-PMMA joint. Therefore, when using the interfacial stress coefficient f(E 1 ,E 2 ,v 1 ,v 2 ) to evaluate the interfacial stress of dissimilar material joints, the same conclusion as the three-dimensional finite element analysis results can be obtained. However, using the interfacial stress coefficient is obviously more efficient and convenient. Because only the elastic constants of the material need to be substituted into the expression of the interfacial stress coefficient, without worrying about the mesh quality and quantity of the finite element model or solving complex mathematical and physical equations.

[0130] Through the analysis of the key factors affecting the failure forms of metal bonding structures and the analysis of the interfacial stress of metal bonding interfaces in the embodiments of the present invention, the following two material selection rules applied to metal bonding structures are specifically obtained:

[0131] Material selection rule one, the basic principle of material selection for anti-fatigue design of metal bonding structures:

[0132] According to the main failure form of metal bonding structures is fatigue debonding caused by interfacial stress, aiming at the defect of the solution idea for the debonding problem of traditional metal bonding structures, that is, simply pursuing high adhesive shear strength while ignoring the influence of interfacial stress in the process of structural design and material selection, it is proposed that the basic principle of material selection for anti-fatigue design of metal bonding structures is to select material combinations with low interfacial stress as much as possible while improving the interfacial adhesive shear strength.

[0133] Material selection rule two, the material selection criterion for low interfacial stress design of metal bonding structures:

[0134] According to the analysis results of the interface stress of dissimilar material joints based on the application interface stress coefficient, under the action of uniaxial load, when the ratio of the Poisson's ratio to the Young's modulus of the materials on both sides of the interface is equal, the interface stress of the dissimilar material joint is zero. The low interface stress design material selection criterion for metal bonding structures is proposed that the ratio of the Poisson's ratio to the Young's modulus of the materials on both sides of the interface should approach 1 infinitely, that is:

[0135]

[0136] In the above formula (13), μ 1 is the ratio of the Poisson's ratio to the Young's modulus of material 1 on one side of the interface;

[0137] μ 2 is the ratio of the Poisson's ratio to the Young's modulus of material 2 on the other side of the interface.

[0138] According to the above material selection rule 1 and material selection rule 2, applying the interface stress coefficient to the material selection of helicopter metal bonding structures, a material selection strategy for metal bonding structures with low interface stress and anti-fatigue design is proposed. Since this material selection strategy not only considers the influence of the bonding shear strength on fatigue debonding, but also considers the influence of the interface stress of the material combination on fatigue debonding, therefore, adopting this material selection strategy can effectively improve the interface debonding problem of metal bonding structures and achieve the goal of improving the fatigue bearing capacity and service life of metal bonding structures. Specifically, according to the cycle and funding requirements of the model development project, a passive material selection strategy and a positive material selection strategy for structural design are given, so that designers can select one of them for material selection work according to the specific situation of the model project.

[0139] As Figure 7 shown, it is the flowchart of the passive material selection strategy for the low interface stress and anti-fatigue design of the metal bonding structure proposed in the embodiment of the present invention.

[0140] The above passive material selection strategy means that the material selection range of the metal bonding structure is limited to the materials that have been identified or the mature materials that have been applied in the model. The low interface stress and anti-fatigue design process of the metal bonding structure at this time is as Figure 7 shown, that is, when the structure form and one or two materials (which can be metals, adhesives) in the structure are basically determined, the elastic constants of the determined materials and all other component materials that meet the requirements of the bonding static strength can be substituted into the interface stress coefficient for calculation. According to the calculation results of the interface stress coefficient, the material selection combination of the metal bonding structure with the minimum interface stress is screened out for the next strength calculation. Compared with the traditional structural material selection method, the passive material selection method adds the interface stress coefficient calculation and determination steps, that is Figure 7 the part within the dotted line frame in, so as to achieve the low interface stress design of the metal bonding structure.

[0141] As Figure 8 shown, it is a flowchart of the forward material selection strategy for the low interface stress anti-fatigue design of the metal bonding structure proposed in the embodiment of the present invention.

[0142] The above forward material selection strategy means that the material selection range of the metal bonding structure is not limited to the mature materials that have been applied in the model or have been identified, but also includes new materials that can be developed directionally according to the structural design requirements.

[0143] At this time, the low interface stress anti-fatigue design process of the metal bonding structure is as Figure 8 shown. When the structural form and one or two materials (which can be metals, adhesives) in the structure are basically determined, the elastic constants of the determined materials and all other component materials that meet the adhesive static strength requirements can be substituted into the interface stress coefficient for calculation. According to the calculation results of the interface stress coefficient, a judgment is made. If a material combination that meets the requirements of the low interface stress design of the structure can be selected, the next strength calculation can be carried out; if none of the existing material combinations can meet the requirements of the low interface stress design of the structure, new materials need to be developed according to the requirements of the low interface stress of the structure, and the structural design can be further optimized according to the development of the new materials.

[0144] Although the disclosed embodiments of the present invention are as above, the content is only an embodiment adopted for the convenience of understanding the present invention and is not used to limit the present invention. Any person skilled in the art within the scope of the present invention can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed by the present invention. However, the scope of patent protection of the present invention shall still be subject to the scope defined by the appended claims.

Claims

1. A material selection method for a metal bonded structure with a low interface stress anti-fatigue design, characterized in that, it includes: Step 1, according to the failure mode of the metal bonded structure, determine the influencing factors for fatigue debonding of the metal bonded structure and the basic material selection principles for the anti-fatigue design of the metal bonded structure. The influencing factors include the adhesive shear strength and the interface stress of the material combination. The basic material selection principle is to select a material combination with low interface stress on the premise of improving the interface adhesive shear strength; Step 2, taking the metal adhesive interface of the metal bonded structure as the object, conduct interface stress analysis based on the three-dimensional elasticity theory to obtain the interface stress coefficient f. Among them, in the process of analyzing and obtaining the interface stress coefficient f, the material selection criterion for the low interface stress design of the metal bonded structure is obtained; Step 3, according to the basic material selection principles for the anti-fatigue design of the metal bonded structure and the material selection criterion for the low interface stress design of the metal bonded structure, apply the interface stress coefficient f to the material selection process of the metal bonded structure to establish a material selection strategy for a metal bonded structure with a low interface stress anti-fatigue design.

2. The material selection method for a metal bonded structure with a low interface stress anti-fatigue design according to claim 1, characterized in that, the said Step 2 includes: Step 21, specifically abstract the metal - adhesive structure in the metal bonded structure into a dissimilar material joint model; Step 22, conduct interface stress analysis on the dissimilar material joint model using the three-dimensional elasticity theory to obtain a tool for evaluating the interface stress magnitude of the dissimilar material joint, that is, the interface stress coefficient f.

3. The material selection method for a metal bonded structure with a low interface stress anti-fatigue design according to claim 2, characterized in that, the said interface stress coefficient f is: where v 1 and v 2 are the Poisson's ratios of the materials on both sides of the interface, E 1 and E 2 are the Young's moduli of the materials on both sides of the interface. The Poisson's ratio and the Young's modulus are both material elastic constants. The interface stress coefficient f is used to qualitatively and quantitatively reflect the law of the interface stress magnitude and the change rate of the interface stress of the dissimilar material joint varying with the external load.

4. The material selection method for a metal bonded structure with a low interface stress anti-fatigue design according to claim 3, characterized in that, the obtaining method of the said interface stress coefficient f is: Step a, according to the different influences of each elastic constant of the material on the interface stress of the dissimilar material joint, and the influence law of one elastic constant of the material on the interface stress will change with the change of another elastic constant, determine the relationship between the interface stress of the dissimilar material joint model and the material elastic constant as: σ int = f(E 1 , E 2 , v 1 , v 2 ) · σ; Among them, σ int is the joint interface stress, σ is the external load, f(E 1 , E 2 , v 1 , v 2 ) is the interface stress coefficient; Step b, use the three-dimensional elasticity theory to solve the interface stress of the dissimilar material joint. During the solving process, establish a Cartesian coordinate system according to the dissimilar material joint model, select the center of the dissimilar material joint interface as the coordinate origin, analyze the mechanical elements on the free edge near the dissimilar material joint interface, solve the stress components near the interface when the dissimilar material joint bears load, and obtain the analytical solution of the interface stress of the dissimilar material joint under uniaxial load; Step c, according to the relationship between the interface stress of the dissimilar material joint model and the material elastic constant, and the analytical solution of the interface stress of the dissimilar material joint under uniaxial load, obtain the interface stress coefficient f.

5. The material selection method for a metal bonded structure with a low interface stress anti-fatigue design according to claim 4, characterized in that, the solving method in the said Step b is: Step b1, set that during the loading process of the dissimilar material joint, the interface always remains planar, that is, the first stress boundary condition to be satisfied is: Among them, and are the shear stress components of the mechanical unit near the interface of Material 1 in the dissimilar material joint, and are the shear stress components of the mechanical unit near the interface of Material 2 in the dissimilar material joint; When the first stress boundary condition is satisfied, the displacement components of the mechanical elements near the interface are expressed as: {u(x), v(y), w(z)}; where u(x) is the displacement component of the mechanical element near the interface along the x-axis, v(y) is the displacement component of the mechanical element near the interface along the y-axis, and w(z) is the displacement component of the mechanical element near the interface along the z-axis; Step b2, set that the interface of the dissimilar material joint is well-bonded without initial cracks or crack-like defects. Therefore, the deformations of the materials on both sides of the interface are consistent at the interface, that is, the displacement boundary condition to be satisfied is: {u 1 (z = 0) = u 2 (z = 0), v 1 (z = 0) = v 2 (z = 0)}; where, u 1 (z = 0) is the displacement component along the x-axis of the mechanical element near the interface of Material 1 when z = 0, u 2 (z = 0) is the displacement component along the x-axis of the mechanical element near the interface of Material 2 when z = 0, v 1 (z = 0) is the displacement component along the y-axis of the mechanical element near the interface of Material 1 when z = 0, v 2 (z = 0) is the displacement component along the y-axis of the mechanical element near the interface of Material 2 when z = 0; Step b3, according to Newton's third law and the small deformation assumption of elasticity, the second stress boundary condition is obtained as: Among them, is the stress component along the x-axis of the mechanical element near the interface of Material 1 when z = 0, is the stress component along the x-axis of the mechanical element near the interface of Material 2 when z = 0, is the stress component along the y-axis of the mechanical element near the interface of Material 1 when z = 0, is the stress component along the y-axis of the mechanical element near the interface of Material 2 when z = 0, is the stress component along the z-axis of the mechanical element near the interface of Material 1, is the stress component along the z-axis of the mechanical element near the interface of Material 2, and σ is the external load; Step b4, according to the first stress boundary condition, the second stress boundary condition, and the displacement boundary condition, the analytical solution of the interface stress of the dissimilar material joint under uniaxial load is obtained as:

6. The material selection method for a metal bonded structure with a low interface stress anti-fatigue design according to claim 5, characterized in that the said step 2 further includes: According to the analysis of the analytical solution of the interface stress of the dissimilar material joint under uniaxial load, the material selection criterion for the low interface stress design of the metal bonded structure is obtained; the material selection criterion is: the ratio of the Poisson's ratio to the Young's modulus of the materials on both sides of the interface should approach 1 infinitely.

7. The material selection method for a metal bonded structure with a low interface stress anti-fatigue design according to claim 6, characterized in that the material selection strategy for the metal bonded structure with a low interface stress anti-fatigue design formed in the said step 3 includes: a passive material selection strategy and a positive material selection strategy.

8. The material selection method for a metal bonded structure with a low interface stress anti-fatigue design according to claim 7, characterized in that the said passive material selection strategy means that the material selection range of the metal bonded structure is limited to the materials that have been identified or the mature materials that have been applied in models; In the material selection process of the passive material selection strategy, when the structure form and one or two materials in the structure are determined, substitute the elastic constants of the determined materials and all other component materials that meet the adhesive static strength requirements into the interface stress coefficient for calculation. According to the calculation results of the interface stress coefficient, screen out the material selection combination of the metal bonded structure with the minimum interface stress, and perform the next strength calculation.

9. The material selection method for a metal bonded structure with a low interface stress anti-fatigue design according to claim 7, characterized in that the said positive material selection strategy means that the material selection range of the metal bonded structure is not limited to the mature materials that have been applied in models or have been identified, but also includes new materials developed directionally according to the structural design requirements; In the material selection process of the positive material selection strategy, when the structure form and one or two materials in the structure are determined, substitute the elastic constants of the determined materials and all other component materials that meet the adhesive static strength requirements into the interface stress coefficient for calculation. According to the calculation results of the interface stress coefficient, make a judgment. If a material combination that meets the requirements of the low interface stress design of the structure can be screened out, then perform the next strength calculation; If none of the existing material combinations can meet the requirements of the low interface stress design of the structure, new materials shall be developed according to the needs of the low interface stress design of the structure, and the structure design shall be optimized based on the new materials developed.

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