Method for evaluating interface bonding performance of carbon fiber composite material reinforced steel structure

Abstract

The application provides a method for evaluating the bonding performance of a carbon fiber composite material reinforced steel structure interface, comprising: calculating the steel bonding interface shear stress tau and the steel matrix slip s; calculating the maximum shear stress tau of the bonding interface max ; calculating the interface fracture energy G f ; calculating the initial slip s1; calculating the maximum slip s f ; and drawing a CFRP-steel interface bonding performance evaluation model prediction curve. The application provides a method for evaluating the bonding performance of a carbon fiber composite material reinforced steel structure interface, comprehensively considers different surface treatment forms that may be involved in actual engineering, has a wider application range than a traditional single surface treatment method, obtains a shear stress-slip hyperbolic curve under different surface treatment conditions based on parameter fitting and a simplification method, is more accurate and reliable than a traditional method, and does not need a high-performance computer, is convenient and simple to calculate, is fast, and has low cost.

Description

Technical Field

[0001] The present invention relates to the field of marine platform steel structure reinforcement, and in particular to a method for evaluating the interface bonding performance of a carbon fiber composite material reinforced steel structure. Background Art

[0002] Offshore platforms are primarily steel structures used for offshore oil and gas development. Given the harsh marine environment and their service life, some offshore platforms urgently require reinforcement to meet continued operational requirements. Long-term exposure to harsh marine environments, such as salt spray, moisture, and seawater, can deteriorate the mechanical properties of steel structures, reducing their reliability and severely impacting their service life and safety. Steel structures are susceptible to corrosion and fatigue cracking in marine environments. It is imperative to implement effective measures to improve the performance of steel structures and extend their service life. In recent years, the use of carbon fiber reinforced polymer (CFRP) to reinforce steel structures has gradually gained application. CFRP is bonded to steel components through adhesives to form new composite components, enhancing the overall mechanical properties of the steel structure. The interfacial bonding performance of CFRP-reinforced steel structures plays a decisive role in the mechanical properties of the composite components. Inadequate bonding can lead to premature debonding of the CFRP, resulting in reinforcement failure. CFRP-steel interfacial bonding performance assessment methods are typically used to reflect the constitutive relationship of the CFRP-steel interface and are a key component in the numerical analysis of the mechanical properties of CFRP-reinforced steel structures. This method can be achieved by CFRP-steel double lap shear joints (such as Figure 1 Typical CFRP-steel interface bonding performance evaluation model, such as Figure 2 shown.

[0003] The surface treatment of steel plays a decisive role in the bonding performance, and there is a certain gap in the bonding performance obtained by different surface treatments. At present, in the research on the bonding of CFRP and steel, sandblasting is mostly used for the steel surface. However, in the actual reinforcement of offshore platforms, some areas with restricted working space (for example, high-altitude areas) cannot be sandblasted. On this basis, mechanical grinding has become another irreplaceable surface treatment method. The existing interface performance evaluation method does not consider the influence of different steel surface treatment methods, which leads to huge limitations of the method and is not suitable for actual engineering. In addition, since different surface treatment methods are not taken into account, the above method will lead to an overestimation of the mechanical properties of some bonding interfaces. Summary of the Invention

[0004] The present invention provides a method for evaluating the interfacial bonding performance of a steel structure reinforced with carbon fiber composite materials. To provide a basic understanding of some aspects of the disclosed embodiments, a brief summary is provided below. This summary is not intended to be a comprehensive review, identify key or important elements, or delineate the scope of these embodiments. Its sole purpose is to present some concepts in a simplified form, serving as a prelude to the detailed description that follows.

[0005] This invention provides a method for evaluating the interface properties of carbon fiber composite reinforced steel structures. This method takes into account various common surface treatment methods and directly calculates CFRP-steel interface performance evaluation curves for different surface treatments. Compared to traditional CFRP-steel interface performance evaluation methods, the proposed method is more universal and safer.

[0006] The embodiment of the present invention provides a method for evaluating the interfacial bonding performance of a carbon fiber composite material reinforced steel structure, the improvement of which is that it includes:

[0007] (1) Calculate the shear stress τ at the steel bonding interface and the slip s of the steel matrix;

[0008] (2) Calculation of the maximum shear stress τ at the bonding interface max ;

[0009] (3) Calculation of interface fracture energy G f ;

[0010] (4) Calculate the initial slip s1;

[0011] (5) Calculate the maximum slip s f ;

[0012] (6) Draw the prediction curve of the CFRP-steel interface bonding performance evaluation model;

[0013] Preferably, the step (1) includes using the strain difference method to calculate the measured data of the shear stress τ of the CFRP-steel bonding interface and the slip amount s of the CFRP relative to the steel matrix.

[0014] Further,

[0015] The calculation expression of the slip amount s is as follows:

[0016]

[0017] Where, is the relative slip between the i-th strain gauge and the i+1-th strain gauge; ε i With ε i+1 are the measured values ​​of the i-th strain gauge and the i+1-th strain gauge respectively; Δl iis the distance between the i-th strain gauge and the i+1-th strain gauge;

[0018] The bonding interface shear stress τ can be calculated by the following formula:

[0019]

[0020] Where, is the shear stress between the i-th strain gauge and the i+1-th strain gauge; E c , t c are the elastic modulus and thickness of CFRP, respectively.

[0021] Preferably, step (2) includes calculating the maximum shear stress τ by formula (5) max :

[0022] τ max =34.17-3.37E a ×10 -3 (5)

[0023] Where, E a is the elastic modulus of the binder.

[0024] Preferably, the step (3) includes calculating the interface fracture energy G by formula (7): f :

[0025] G f =40.5t a 0.196 w 1.22 (1-0.53e -(Z / 115) ) (7)

[0026] Where, t a is the thickness of the adhesive; Z is the mechanical grinding or sandblasting particle size; w is the shear dissipation energy between CFRP layers, which can be calculated by the following formula:

[0027]

[0028] Where σ a is the tensile strength of the adhesive, E a is the elastic modulus of the adhesive.

[0029] Furthermore, in order to fit the measured bond interface fracture energy Gf, the mechanical polishing mesh size P is converted into the particle size Z. The relationship between the two can be expressed as:

[0030]

[0031] Preferably, step (4) includes calculating the initial slip amount s1 using formula (9):

[0032]

[0033] Where, t a is the thickness of the adhesive; G a is the shear modulus of the adhesive, which can be calculated by the following formula:

[0034]

[0035] Where, E a is the elastic modulus of the binder; μ a is the Poisson's ratio of the binder.

[0036] Preferably, step (5) includes calculating the maximum slip sf using formula (11):

[0037]

[0038] τ max =34.17-3.37E a ×10 -3 (5)

[0039] G f =40.5t a 0.196 w 1.22 (1-0.53e -(Z / 115) ) (7)

[0040]

[0041] Combining formula (4), formula (5) and formula (7), the expression (11) of the maximum slip sf can be obtained;

[0042] Where, E a is the elastic modulus of the binder, t a is the thickness of the adhesive; Z is the mechanical grinding or sandblasting particle size; w is the shear dissipation energy between CFRP layers, σ a is the tensile strength of the adhesive.

[0043] Preferably, step (6) includes drawing a prediction curve of the CFRP-steel interface bonding performance evaluation model according to formula (3):

[0044]

[0045] Furthermore, the interface bonding performance evaluation method of carbon fiber composite reinforced steel structure, i.e., the CFRP-steel interface bonding performance evaluation model, is obtained by formula (5), formula (7), formula (9), and formula (11);

[0046] τ max =34.17-3.37Ea ×10 -3 (5)

[0047] G f =40.5t a 0.196 w 1.22 (1-0.53e -(Z / 115) ) (7)

[0048]

[0049]

[0050] Where, E a is the elastic modulus of the binder, t a is the thickness of the adhesive; Z is the mechanical grinding or sandblasting particle size; w is the shear dissipation energy between CFRP layers, σ a is the tensile strength of the adhesive, G a is the shear modulus of the adhesive.

[0051] The technical solution provided by the embodiment of the present invention may have the following beneficial effects:

[0052] Based on experimental test data, the present invention proposes a method for evaluating the interfacial bonding performance of carbon fiber composite reinforced steel structures, which can be used to characterize the constitutive relationship of the CFRP-steel interface; the experimental data are fitted with a high-order curve and simplified using a bilinear method, and this simplified method can be directly applied to actual engineering; using particle size as a unified variable, a method for evaluating the interfacial bonding performance of CFRP-steel suitable for sandblasting and mechanical polishing is proposed, and the present invention can be widely used in the prediction of interfacial bonding performance of various steel structure surface treatments (various surface treatment methods that can be characterized by particle size).

[0053] Based on experimental measured data, the present invention proposes a method for evaluating the interfacial bonding performance of carbon fiber composite material reinforced steel structures. The present invention comprehensively considers the different surface treatment forms that may be involved in actual engineering. Compared with the traditional single surface treatment method, the present invention has a wider scope of application. Based on parameter fitting and simplification methods, a shear stress-slip hyperbola that is convenient for actual engineering application under different surface treatment conditions is obtained. Compared with traditional methods, the present invention is more accurate and more reliable. The present invention does not require the use of high-performance computers, and the calculation is convenient and concise, fast, and low-cost.

[0054] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention and, together with the description, serve to explain the principles of the invention.

[0056] Figure 1 is a schematic diagram of a CFRP-steel double lap shear joint according to an exemplary embodiment;

[0057] In the figure, 1-adhesive, 2-carbon fiber cloth, 3-steel plate, 4-gap, 5-adhesive thickness control pad, 6-strain gauge

[0058] Figure 2 is a schematic diagram of a method for evaluating CFRP-steel interface bonding performance according to an exemplary embodiment;

[0059] Figure 3 Schematic diagrams of CFRP-steel interface bonding and slipping methods under different surface treatment conditions according to an exemplary embodiment, wherein (a) a schematic diagram of mechanical polishing with 40-grit sandpaper, (b) a schematic diagram of mechanical polishing with 80-grit sandpaper, (c) a schematic diagram of mechanical polishing with 120-grit sandpaper, (d) a schematic diagram of mechanical polishing with 240-grit sandpaper, and (e) a schematic diagram of sandblasting;

[0060] Figure 4 is a schematic diagram of parameter fitting of interface fracture energy Gf according to an exemplary embodiment;

[0061] Figure 5 1 is a schematic diagram showing parameter fitting of the initial slip amount s1 of the TT node according to an exemplary embodiment;

[0062] Figure 6 is a schematic diagram of a double lap shear joint specimen mechanically polished with 120-grit sandpaper according to an exemplary embodiment;

[0063] Figure 7 is a schematic diagram of a prediction curve of the present invention according to an exemplary embodiment;

[0064] Figure 8 The present invention is a flow chart of a method for evaluating the interfacial bonding performance of a carbon fiber composite material reinforced steel structure according to an exemplary embodiment. DETAILED DESCRIPTION

[0065] The following description and accompanying drawings sufficiently illustrate specific embodiments of the present invention to enable those skilled in the art to practice them. The examples represent only possible variations. Unless expressly required, individual components and functions are optional, and the order of operations may vary. Portions and features of some embodiments may be included in or substituted for portions and features of other embodiments. The scope of the embodiments of the present invention includes the entire scope of the claims, as well as all available equivalents of the claims. Herein, various embodiments may be referred to individually or collectively by the term "invention," which is merely for convenience and is not intended to automatically limit the scope of application to any single invention or inventive concept if more than one invention is disclosed. Herein, relational terms such as first and second, etc., are used solely to distinguish one entity or operation from another, and do not require or imply any actual relationship or order between these entities or operations. Furthermore, the terms "comprise," "comprising," or any other variations thereof are intended to encompass non-exclusive inclusion, such that a process, method, or apparatus comprising a set of elements includes not only those elements, but also other elements not explicitly listed. The various embodiments herein are described in a progressive manner, with each embodiment focusing on the differences from the other embodiments. Reference can be made to the common and similar parts between the various embodiments. For structures, products, etc. disclosed in the embodiments, the description is relatively simple because they correspond to the parts disclosed in the embodiments. For relevant parts, refer to the method description.

[0066] Based on tensile tests on CFRP-steel double lap shear joints, this study examined the effects of various surface treatments, including mechanical grinding and sandblasting with varying particle sizes (particle size), on the CFRP-steel interface properties. Five surface preparation methods were employed. Classes 1-4 involved mechanical grinding, using four commonly used sandpapers with different mesh sizes: 40, 80, 120, and 240. Class 5 involved sandblasting, using aluminum oxide abrasive particles with an average particle size of 180 μm.

[0067] Based on the experimental method, the measured data of shear stress and slip were obtained. The measured data were fitted with a high-order curve and simplified using a bilinear method to determine the maximum shear stress τ of the CFRP-steel double lap shear joint under different surface treatment conditions. f , initial slip s1, maximum slip s f and interfacial fracture energy G f By analyzing the influence of different surface treatment methods on the above parameters, a CFRP-steel interface bonding performance evaluation model considering different surface treatment conditions was established.

[0068] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0069] The present invention adopts the strain difference method to obtain the measured data of the shear stress (τ) of the CFRP-steel bonding interface and the slip amount (s) of the CFRP relative to the steel matrix.

[0070] Due to the axial stiffness of the steel matrix (E s A s ) is much higher than the axial stiffness of CFRP (E c A c ), ignoring the shear deformation of the steel matrix, the calculation expression of the relative slip is as follows:

[0071]

[0072] Where, is the relative slip between the i-th strain gauge and the i+1-th strain gauge; ε i With ε i+1 are the measured values ​​of the i-th strain gauge and the i+1-th strain gauge respectively; Δl i is the distance between the i-th strain gauge and the i+1-th strain gauge.

[0073] The shear stress at the bonding interface can be calculated using the following formula:

[0074]

[0075] Where, is the shear stress between the i-th strain gauge and the i+1-th strain gauge; E c , t c are the elastic modulus and thickness of CFRP, respectively.

[0076] The strain data obtained from the test are processed using formulas (1) and (2), and we can obtain Figure 3 The experimental data points in .

[0077] CFRP-steel interface bonding performance evaluation method, such as Figure 3 As shown, its mathematical expression is as follows:

[0078]

[0079] Depend on Figure 2 As shown in the figure, to establish an evaluation method for the interface bonding performance of carbon fiber composite reinforced steel structures, three parameters need to be determined, namely, the maximum shear stress τ max , initial slip s1 and maximum slip s f . Figure 2 The area enclosed by the middle curve is represented by the interface fracture energy G f , is an important indicator for evaluating the mechanical properties of the bonding interface.f The larger the value, the less likely the CFRP-steel bonding interface is to debond. f The calibration parameter τ of the present invention max and s f The relationship between them is as follows:

[0080]

[0081] For the joints bonded to carbon fiber cloth and steel, the main failure mode is CFRP delamination failure, which leads to the maximum shear stress τ max Only with the elastic modulus of the binder (E a ) is directly related to τ max It can be expressed as:

[0082] τ max =34.17-3.37E a ×10 -3 (5)

[0083] To obtain the initial slip s1 and interface fracture energy G f , it is necessary to fit the measured shear stress-slip data points. Use the 6th order curve to fit the test data points, such as Figure 3 The dotted line shows the maximum shear stress τ corresponding to different surface treatment conditions. f , initial slip s1, maximum slip s f and interfacial fracture energy G f The measured data are also shown in Figure 3 middle.

[0084] To fit the measured bonding interface fracture energy G f , the mechanical grinding mesh number P is converted into the particle size Z, and the relationship between the two can be expressed as:

[0085]

[0086] Interface fracture energy G f The test results were fitted with data, such as Figure 4 As shown, we get G f The expression is as follows:

[0087] G f =40.5t a 0.196 w 1.22 (1-0.53e -(Z / 115) ) (7)

[0088] Where, t ais the thickness of the adhesive; Z is the mechanical grinding or sandblasting particle size; w is the shear dissipation energy between CFRP layers, which can be calculated by the following formula:

[0089]

[0090] Where σ a is the tensile strength of the adhesive, E a is the elastic modulus of the adhesive.

[0091] The data fitting of the initial slip s1 test results is performed, as shown in the following example: Figure 5 As shown, the expression of s1 is as follows:

[0092]

[0093] Where, t a is the thickness of the adhesive; G a is the shear modulus of the adhesive, which can be calculated by the following formula:

[0094]

[0095] Where, E a is the elastic modulus of the binder; μ a is the Poisson's ratio of the binder.

[0096] Combining formula (4), formula (5) and formula (7), the maximum slip s can be obtained f The expression is as follows:

[0097]

[0098] Through formula (5), formula (7), formula (9) and formula (11), a complete method for evaluating the interface bonding performance of carbon fiber composite reinforced steel structures, namely the CFRP-steel interface bonding performance evaluation model, can be obtained.

[0099] Example 1

[0100] Double lap shear joint specimens mechanically polished with 120 grit sandpaper are shown in Figure 2. Figure 6 As shown, the basic parameters of the specimen are: adhesive tensile strength σ a =33.4MPa, elastic modulus E a =4740MPa, Poisson's ratio μ a =0.34 and thickness t a =0.4mm.

[0101] The calculation steps are as follows:

[0102] (a) Calculate the maximum shear stress τ at the bonding interface according to formula (5) max

[0103] τ max =34.17-3.37E a ×10 -3 , where E a =4740MPa, we get τ max =18.2MPa.

[0104] (b) Calculate the interface fracture energy G according to formula (7) f ;

[0105] G f =40.5t a 0.196 w 1.22 (1-0.53e -(Z / 115) ), where t a =0.4mm, w=0.1177 can be calculated by formula (8), Z=128.3 can be calculated by formula (6), and G f =2.06mj / mm 2 .

[0106] (c) Calculate the initial slip s1 according to formula (9);

[0107] Among them G a =1786MPa can be calculated by formula (10), and s1 = 0.076mm is obtained.

[0108] (d) Calculate the maximum slip s according to formula (11) f ;

[0109] Get s f =0.226mm.

[0110] (e) According to formula (3), the prediction curve of the CFRP-steel interface bonding performance evaluation model is drawn, as shown in Figure 7 shown.

[0111] (d) verification and conclusion;

[0112] The prediction results of the present invention are compared with the experimental results, as shown in Table 1:

[0113] Table 1 Comparison of the test results of mechanical polishing with 120-grit sandpaper and the predicted results of the method:

[0114]

[0115]

[0116] It should be understood that the present invention is not limited to the processes and structures described above and shown in the drawings, and various modifications and changes can be made without departing from the scope thereof. The scope of the present invention is limited only by the appended claims.

Claims

1. A method for evaluating the interfacial bonding performance of carbon fiber composite reinforced steel structures, characterized in that: include: (1) Calculate the shear stress τ at the CFRP-steel bond interface and the steel matrix slip s; (2) Calculation of the maximum shear stress τ at the CFRP-steel bonding interface max ; (3) Calculation of interface fracture energy G f ; (4) Calculate the initial slip s1; (5) Calculate the maximum slip s f ; (6) Draw the prediction curve of the CFRP-steel interface bonding performance evaluation model; The step (2) includes calculating the maximum shear stress τ of the CFRP-steel interface by formula (5) max : t max =34.17-3.37E a ×10 -3 (5) Where, E a is the elastic modulus of the binder; The step (3) includes calculating the interface fracture energy G by formula (7): f : G f =40.5t a 0.196 w 1.22 (1-0.53e -(Z / 115) ) (7) Where, t a is the thickness of the adhesive; Z is the mechanical grinding or sandblasting particle size; w is the shear dissipation energy between CFRP layers, which can be calculated by the following formula: Where σ a is the tensile strength of the adhesive, E a is the elastic modulus of the binder; To fit the measured bonding interface fracture energy G f , the mechanical grinding mesh number P is converted into the particle size Z, and the relationship between the two can be expressed as: The step (4) includes calculating the initial slip amount s1 by formula (9): Where, t a is the thickness of the adhesive; G a is the shear modulus of the adhesive, which can be calculated by the following formula: Where, E a is the elastic modulus of the binder; μ a is the Poisson's ratio of the binder.

2. The method for evaluating the interfacial bonding performance of a carbon fiber composite material reinforced steel structure according to claim 1, characterized in that: The step (1) includes using the strain difference method to calculate the measured data of the shear stress τ of the CFRP-steel bonding interface and the slip amount s of the CFRP relative to the steel matrix.

3. The method for evaluating the interfacial bonding performance of a carbon fiber composite material reinforced steel structure according to claim 2, characterized in that: The slip amount s is calculated using the following formula: Where, is the relative slip between the i-th strain gauge and the i+1-th strain gauge; ε i With ε i+1 are the measurement values ​​of the i-th strain gauge and the i+1-th strain gauge respectively; Δl i is the distance between the i-th strain gauge and the i+1-th strain gauge; The CFRP-steel bond interface shear stress τ can be calculated by the following formula: Where, is the shear stress at the CFRP-steel bonding interface between the i-th strain gauge and the i+1-th strain gauge; E c , t c are the elastic modulus and thickness of CFRP, respectively.

4. The method for evaluating the interfacial bonding performance of a carbon fiber composite material reinforced steel structure according to claim 1, characterized in that: The step (5) includes calculating the maximum slip s by formula (11): f : t max =34.17-3.37E a ×10 -3 (5) G f =40.5t a 0.196 w 1.22 (1-0.53e -(Z / 115) ) (7) Combining formula (4), formula (5) and formula (7), the maximum slip s can be obtained f Expression (11); Where, E a is the elastic modulus of the binder, t a is the thickness of the adhesive; Z is the mechanical grinding or sandblasting particle size; w is the shear dissipation energy between CFRP layers, σ a is the tensile strength of the adhesive.

5. The method for evaluating the interfacial bonding performance of a carbon fiber composite material reinforced steel structure according to claim 1, characterized in that: The step (6) includes drawing a prediction curve of the CFRP-steel interface bonding performance evaluation model according to formula (3):

6. The method for evaluating the interfacial bonding performance of a carbon fiber composite material reinforced steel structure according to claim 5, characterized in that: Through formula (5), formula (7), formula (9) and formula (11), the interface bonding performance evaluation method of carbon fiber composite material reinforced steel structure, namely the CFRP-steel interface bonding performance evaluation method, is obtained; t max =34.17-3.37E a ×10 -3 (5) G f =40.5t a 0.196 w 1.22 (1-0.53e -(Z / 115) ) (7) Where, E a is the elastic modulus of the binder, t a is the thickness of the adhesive; Z is the mechanical grinding or sandblasting particle size; w is the shear dissipation energy between CFRP layers, σ a is the tensile strength of the adhesive, G a is the shear modulus of the adhesive.

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