Method for evaluating corrosion fatigue life of metal-composite material bonding structure

Abstract

The invention relates to the technical field of composite material fatigue life evaluation, in particular to a metal-composite material bonding structure corrosion fatigue life evaluation method which comprises the following steps: establishing a pre-corroded metal-composite material bonding structure finite element model; establishing a progressive fatigue damage theoretical model of the metal plate, the composite material plate and the adhesive layer; and constructing the fatigue life evaluation method of the pre-corroded metal-composite material cementing structure. According to the method, the influence of the corrosion environment on the metal plate, the composite material plate and the adhesive layer is considered, and the progressive fatigue damage theoretical model of the metal plate, the composite material plate and the adhesive layer is combined with a finite element analysis technology, so that the corrosion fatigue life and the progressive damage expansion process of the metal-composite material bonding structure can be effectively evaluated; therefore, the purpose of considering the influence of the corrosion environment and the fatigue load on the composite material plate and the adhesive layer is achieved.

Description

Technical Field

[0001] The invention relates to the technical field of composite material fatigue life assessment, in particular to a method for assessing the corrosion fatigue life of a metal-composite material adhesively bonded structure. Background Art

[0002] As the demand for lightweight, high-strength and long-life structures in advanced aircraft is increasing, lightweight alloy materials (such as aluminum alloys and titanium alloys) and composite materials have become important aviation structural materials. In structural assembly, it is inevitable to connect metal structures and composite structures. The adhesive connection method uses adhesives to bond the two materials into a whole, which will not damage the internal fibers of the composite material and can overcome the stress concentration problem in mechanical connections. It is widely used in metal-composite connection structures. In the service process, metal-composite adhesive structures not only need to withstand long-term fatigue loads, but also need to withstand harsh external environmental tests such as temperature, humidity, and corrosion. Metal materials are prone to electrochemical corrosion in humid environments and produce a large number of corrosion products under the action of corrosive media. Although composite materials and adhesive layers have good corrosion resistance, they are prone to hygroscopic aging in humid environments. Due to the large difference in the wet expansion coefficients of fibers and resins, non-negligible wet stress will be generated inside the structure. These will affect the fatigue performance and damage mechanism of metal-composite adhesive structures, seriously threatening the safety and reliability of aircraft. Therefore, it is very necessary to pay attention to the corrosion fatigue behavior of metal-composite adhesive structures.

[0003] However, when the existing technology is actually used, the research on the corrosion fatigue performance and life assessment methods of the connection structure is mostly concentrated on metal-metal connection structures, and there are few related studies on metal-composite connection structures. The few existing corrosion fatigue life assessment methods for connection structures are difficult to consider the impact of the corrosion environment and fatigue load on the composite material plates and adhesive layers. Summary of the invention

[0004] The purpose of the present invention is to provide a corrosion fatigue life assessment method for a metal-composite adhesively bonded structure to solve the problem that it is difficult to consider the effects of the corrosion environment and fatigue load on the composite material plate and the adhesive layer.

[0005] To achieve the above object, the present invention provides the following technical solution: A method for evaluating the corrosion fatigue life of a metal-composite adhesively bonded structure, comprising the following steps:

[0006] S1. Establish a finite element model of the metal-composite bonding structure after pre-corrosion, specifically:

[0007] S11. Based on the scanning measurement and statistical analysis results of the corrosion depth of the metal plate surface, the corrosion damage is explicitly modeled and a finite element model of the metal plate with a random corrosion depth surface is established;

[0008] S12. Based on the geometric dimensions and moisture absorption measurement results of the composite material plate, an implicit modeling of moisture absorption aging damage is performed to establish a finite element model of the composite material plate with reduced material strength performance;

[0009] S13. The adhesive layer is simulated by inserting zero-thickness cohesive units at the joints of the metal plate and the composite plate assembly. The performance of the adhesive layer is reduced according to the corrosion environment conditions and the length of time, and the moisture absorption and aging damage of the adhesive layer are implicitly modeled.

[0010] S2. Establish a theoretical model of progressive fatigue damage of metal plates, composite materials and adhesive layers, specifically:

[0011] S21. For the metal plate part, the progressive fatigue cumulative damage theoretical model of the material is calculated according to the Miner linear cumulative damage model. It is assumed that the stiffness and strength properties of the material do not change during fatigue loading, and the cumulative damage coefficient reaching 1 is taken as the fatigue failure criterion;

[0012] S22. For the composite material plate, the material progressive fatigue cumulative damage theoretical model is calculated according to the residual strength model, and the residual strength of the material is gradually degraded during the fatigue loading process. The strength value in the Tsai–Wu failure criterion is replaced by the fatigue residual strength value. When the criterion judgment coefficient reaches 1, fatigue failure is considered to have occurred, that is, the criterion judgment coefficient is used as the fatigue failure criterion of the composite material plate;

[0013] S23. For the adhesive layer, a two-parameter fatigue cumulative damage model is introduced into the bilinear cohesive constitutive relation to establish a cohesive fatigue damage model. Based on this, a theoretical model of progressive fatigue cumulative damage of the material is calculated, and the residual stiffness of the material is gradually degraded during fatigue loading. The cumulative damage coefficient reaching 1 is taken as the fatigue failure criterion.

[0014] S3. Construct a fatigue life assessment method for metal-composite bonded structures after pre-corrosion, specifically:

[0015] The established theoretical model of progressive fatigue damage of metal plates, composite plates and adhesive layers is combined with finite element analysis technology. Fatigue load is applied to the established finite element model of metal-composite adhesively bonded structure. The fatigue life and progressive damage expansion process of the adhesively bonded structure are evaluated through iterative calculation of stress / strain analysis of each unit, fatigue damage accumulation and failure judgment.

[0016] Preferably, the scanning measurement of the metal plate surface corrosion depth in step S11 adopts non-contact three-dimensional topography scanning technology to obtain high-precision corrosion surface topography data, and the statistical analysis in step S11 adopts Weibull distribution for fitting.

[0017] Preferably, the fatigue load in step S3 is applied in a constant amplitude loading manner, and the number of loading cycles is recorded until the adhesive structure is completely destroyed.

[0018] Preferably, in step S3, finite element analysis software is used to perform iterative calculations to simulate the progressive damage expansion process of the metal-composite adhesive structure under the action of a corrosive environment and fatigue load, and output fatigue life assessment results.

[0019] Preferably, during the iterative calculation process of step S3, the units that meet the fatigue failure criterion are deleted from the finite element model, and the iterative calculation is continued for the remaining units until the entire structure is destroyed.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1. The present invention combines the theoretical model of progressive fatigue damage of metal plates, composite materials and adhesive layers with finite element analysis technology by considering the influence of the corrosive environment on the metal plates, composite materials and adhesive layers, and can realize the effective evaluation of the corrosion fatigue life and progressive damage expansion process of metal-composite adhesive structures. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 The present invention is a system block diagram of a corrosion fatigue life assessment method for a metal-composite material bonded structure. DETAILED DESCRIPTION

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] See also Figure 1 The present invention provides a technical solution: a method for evaluating the corrosion fatigue life of a metal-composite material bonded structure, comprising the following steps:

[0025] S1. Establish the finite element model of the metal-composite bonding structure after pre-corrosion:

[0026] S11. For the metal plate part, according to the scanning results of the metal plate surface morphology after the pre-corrosion test, it can be generally considered that the corrosion depth on the rough surface after corrosion obeys the Weibull distribution. The probability distribution parameters of the corrosion depth are calculated by mathematical statistics method. Then, according to the geometric dimensions of the metal plate and the statistical analysis results of the corrosion depth, the corrosion damage is explicitly modeled, and a finite element model of the metal plate with a random corrosion depth surface is established.

[0027] S12. For the composite material plate, due to the excellent corrosion resistance of the composite material, it is believed that it will not produce damage such as corrosion pits in a corrosive environment. Therefore, a finite element model of the composite material plate is established according to the geometric dimensions of the composite material plate. However, since the composite material is sensitive to a humid environment and is prone to a decrease in bearing capacity after absorbing moisture, the material strength performance is reduced according to the measurement results of the moisture absorption of the composite material plate after the pre-corrosion test, and the moisture absorption aging damage of the composite material plate is implicitly modeled.

[0028] S13. The finite element models of the metal plate and the composite plate are assembled, and the adhesive layer is simulated by inserting zero-thickness cohesive units at the joints. Similarly, since adhesives are prone to moisture absorption and aging damage in corrosive and humid environments, the material properties of the adhesive layer are reduced according to the environmental conditions and time length of the pre-corrosion test, and the moisture absorption and aging damage of the adhesive layer is implicitly modeled.

[0029] S2. Establish theoretical models of progressive fatigue damage of metal plates, composite materials and adhesive layers:

[0030] S21. For the metal plate part, the Miner linear cumulative damage model is used to calculate the material's progressive fatigue cumulative damage theoretical model. The formula is:

[0031]

[0032] Where D m is the fatigue cumulative damage coefficient of the metal plate;

[0033] Since the damage propagation of the connection structure during the fatigue process will lead to stress / strain redistribution, the fatigue stress level of the element will change even under constant amplitude fatigue external load, n i and N i are the number of loading cycles and fatigue life at the i-th stress level, respectively, where the fatigue life N i It can be determined by the fatigue stress-life (SN) curve model, and the model expression can be written as:

[0034] (S-S0) m N=C (2)

[0035] Where S is fatigue stress, N is fatigue life, S0 is fitting fatigue limit, and m and C are model parameters.

[0036] It is generally believed that the stiffness and strength properties of metal materials do not change during fatigue cyclic loading. According to the linear cumulative damage theory, when the cumulative damage coefficient D m When it reaches 1, fatigue failure is considered to have occurred, that is, D m =1 is used as the fatigue failure criterion for metal plates.

[0037] S22. For composite material plates, the residual strength model is used to calculate the material's progressive fatigue cumulative damage theoretical model. The fatigue cumulative damage coefficient based on residual strength can be defined as

[0038]

[0039] Where D c is the fatigue cumulative damage coefficient of the composite plate, R(n) is the residual strength of the material, and R0 is the initial strength of the material.

[0040] The strength properties of composite materials will gradually degrade under fatigue cyclic loading. The residual strength R(n) after degradation can be determined by the fatigue residual strength model. The model expression can be written as

[0041] n=A(SK) p [R0-R(n)] q (4)

[0042] Where n is the number of loading cycles, and A, K, p and q are model parameters.

[0043] Similarly, since the fatigue stress level of the unit will change, by transforming equation (4), the relationship between the residual strength before and after a loading cycle at any stress level can be obtained, that is,

[0044]

[0045] The residual strength of the composite material is gradually degraded according to formula (5).

[0046] Since composite materials are anisotropic materials, their strength properties in various directions (including longitudinal, transverse and shear directions) are different. Therefore, it is necessary to degrade the residual strength values ​​in various directions under fatigue loading according to formula (5), and then calculate the fatigue cumulative damage coefficient in various directions according to formula (3).

[0047] In addition, based on the Tsai–Wu failure criterion to judge fatigue failure, the expression can be written as

[0048]

[0049] In the formula,

[0050]

[0051] is the Tsai–Wu criterion judgment coefficient, σ 11 , σ 22 and σ 33 is the normal stress, σ 12 , σ 13 and σ 23is shear stress, X T and X C are longitudinal tensile strength and compressive strength, Y T and Y C are the transverse tensile strength and compressive strength, S 12 , S 13 and S 23 It is worth noting that these strength values ​​will gradually degrade with the increase of the number of loading cycles. Therefore, the strength values ​​in the Tsai–Wu criterion are replaced by fatigue residual strength values.

[0052] When the criterion judgment coefficient When it reaches 1, fatigue failure is considered to have occurred, that is, the criterion judgment coefficient is used. as a fatigue failure criterion for composite plates.

[0053] S23. For the adhesive layer, a bilinear model is used to characterize the continuous damage constitutive relation of the cohesive unit under quasi-static loading, in which the damage initiation criterion adopts the quadratic stress criterion and the damage evolution law adopts a linear model.

[0054] On this basis, the two-parameter progressive fatigue cumulative damage theoretical model is introduced into the bilinear cohesive force constitutive relation, and the cohesive force progressive fatigue cumulative damage theoretical model is established to calculate the fatigue damage of the adhesive layer material, namely:

[0055]

[0056] Where D a is the fatigue cumulative damage coefficient of the adhesive layer, σ e and σ ec is the equivalent stress and its critical value, γ and α are model parameters.

[0057] Similarly, since the fatigue stress level of the unit will change, by transforming equation (8), we can obtain the relationship between the cumulative damage coefficient before and after a loading cycle at any stress level, that is,

[0058]

[0059] The fatigue damage of the adhesive layer material is gradually accumulated according to formula (9).

[0060] During the fatigue damage accumulation process, the residual stiffness performance of the material will gradually degrade, and the stiffness degradation model can be written as

[0061]

[0062] In the formula, K is the residual stiffness of the material, K0 is the initial stiffness of the material, δ0 and δ f are the damage initiation displacement and failure displacement, respectively.

[0063] In addition, when the cumulative damage factor D a When it reaches 1, fatigue failure is considered to have occurred, that is, D a =1 is used as the fatigue failure criterion for the adhesive layer.

[0064] S3. Construct fatigue life assessment method for metal-composite bonded structures after pre-corrosion:

[0065] S31. Combine the theoretical model of progressive fatigue damage with finite element analysis technology, apply fatigue load to the established finite element model of metal-composite bonded structure, simplify one load cycle in the actual loading process to apply the maximum load, calculate the stress / strain distribution results, accumulate the fatigue damage of each unit, and judge whether the unit fails according to the fatigue failure criterion. If a failed unit appears, it will be killed. Repeat the calculation and record the number of loading cycles until the overall destruction of the bonded structure occurs.

[0066] S32. The number of loading cycles recorded when the overall failure of the bonded structure occurs is the fatigue life estimation result. This method can also obtain the progressive expansion process of fatigue damage of the metal-composite bonded structure after pre-corrosion.

[0067] The present invention includes three core steps: first, a finite element model of a pre-corroded metal-composite adhesively bonded structure is established, and the model takes into account the random corrosion depth of the metal plate surface, the moisture absorption and aging damage of the composite material plate, and the performance reduction of the adhesive layer; second, a theoretical model of progressive fatigue damage of the metal plate, the composite material plate, and the adhesive layer is established, and the Miner linear cumulative damage model, the residual strength model, and the two-parameter fatigue cumulative damage model are used to calculate the fatigue cumulative damage of each part, and the corresponding fatigue failure criterion is defined; finally, a fatigue life assessment method for a pre-corroded metal-composite adhesively bonded structure is constructed, and the theoretical model is combined with the finite element analysis technology. Through the iterative calculation of each unit stress / strain analysis, fatigue damage accumulation, and failure judgment, an effective assessment of the fatigue life and progressive damage expansion process of the adhesive structure is achieved.

[0068] Specifically, the present invention takes into account the influence of the corrosive environment on metal plates, composite plates and adhesive layers, and incorporates corrosion damage and moisture absorption aging damage into the finite element model through explicit modeling and implicit modeling. At the same time, different fatigue damage calculation models and failure criteria are used for metal plates, composite plates and adhesive layers to more accurately reflect their fatigue behavior in the actual working environment. By combining finite element analysis and fatigue damage accumulation calculation, an accurate assessment of the corrosion fatigue life of metal-composite adhesive structures is achieved, thereby achieving the purpose of considering the influence of corrosive environment and fatigue load on composite plates and adhesive layers, and providing important technical support for related engineering applications.

[0069] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0070] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the invention, and the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for evaluating the corrosion fatigue life of a metal-composite bonded structure, characterized by: The following steps are involved: S1. Establish a finite element model of the metal-composite bonding structure after pre-corrosion, specifically: S11. Based on the scanning measurement and statistical analysis results of the corrosion depth of the metal plate surface, the corrosion damage is explicitly modeled and a finite element model of the metal plate with a random corrosion depth surface is established; S12. Based on the geometric dimensions and moisture absorption measurement results of the composite material plate, an implicit modeling of moisture absorption aging damage is performed to establish a finite element model of the composite material plate with reduced material strength performance; S13. The adhesive layer is simulated by inserting zero-thickness cohesive units at the joints of the metal plate and the composite plate assembly. The performance of the adhesive layer is reduced according to the corrosion environment conditions and the length of time, and the moisture absorption and aging damage of the adhesive layer are implicitly modeled. S2. Establish a theoretical model of progressive fatigue damage of metal plates, composite materials and adhesive layers, specifically: S21. For the metal plate part, the progressive fatigue cumulative damage theoretical model of the material is calculated according to the Miner linear cumulative damage model. It is assumed that the stiffness and strength properties of the material do not change during fatigue loading, and the cumulative damage coefficient reaching 1 is taken as the fatigue failure criterion; S22. For the composite material plate, the material progressive fatigue cumulative damage theoretical model is calculated according to the residual strength model, and the residual strength of the material is gradually degraded during the fatigue loading process. The strength value in the Tsai–Wu failure criterion is replaced by the fatigue residual strength value. When the criterion judgment coefficient reaches 1, fatigue failure is considered to have occurred, that is, the criterion judgment coefficient is used as the fatigue failure criterion of the composite material plate; S23. For the adhesive layer, a two-parameter fatigue cumulative damage model is introduced into the bilinear cohesive constitutive relation to establish a cohesive fatigue damage model. Based on this, a theoretical model of progressive fatigue cumulative damage of the material is calculated, and the residual stiffness of the material is gradually degraded during fatigue loading. The cumulative damage coefficient reaching 1 is taken as the fatigue failure criterion. S3. Construct a fatigue life assessment method for metal-composite bonded structures after pre-corrosion, specifically: The established theoretical model of progressive fatigue damage of metal plates, composite plates and adhesive layers is combined with finite element analysis technology. Fatigue load is applied to the established finite element model of metal-composite adhesively bonded structure. The fatigue life and progressive damage expansion process of the adhesively bonded structure are evaluated through iterative calculation of stress / strain analysis of each unit, fatigue damage accumulation and failure judgment.

2. The corrosion fatigue life assessment method of a metal-composite material bonded structure according to claim 1, characterized in that: The scanning measurement of the corrosion depth on the metal plate surface in step S11 adopts non-contact three-dimensional topography scanning technology to obtain high-precision corrosion surface topography data, and the statistical analysis in step S11 adopts Weibull distribution for fitting.

3. The corrosion fatigue life assessment method of a metal-composite material bonded structure according to claim 1, characterized in that: The fatigue load in step S3 is applied in a constant amplitude loading manner, and the number of loading cycles is recorded until the adhesive structure is completely destroyed.

4. The corrosion fatigue life assessment method of a metal-composite adhesively bonded structure according to claim 1, characterized in that: In step S3, finite element analysis software is used to perform iterative calculations to simulate the progressive damage expansion process of the metal-composite adhesive structure under the action of a corrosive environment and fatigue load, and output fatigue life assessment results.

5. The corrosion fatigue life assessment method of a metal-composite adhesively bonded structure according to claim 1, characterized in that: During the iterative calculation process of step S3, the units that meet the fatigue failure criterion are deleted from the finite element model, and the iterative calculation is continued for the remaining units until the entire structure is destroyed.

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