An analysis method for mechanical behavior of composite interface bonding

Abstract

The present application relates to the field of building materials and structural engineering, and particularly relates to a method for analyzing the mechanical behavior of composite interface bonding. The method for analyzing the mechanical behavior of composite interface bonding comprises forming a composite interface; applying tensile load and alternating electric field in the axial and transverse directions of the modified carbon fiber respectively; establishing a three-linear bonding-slip constitutive model; measuring the phase angle of interface impedance in real time and calculating the interface damage index; correcting the three-linear bonding-slip constitutive model by using the damage index and analyzing the mechanical behavior of the composite interface bonding. The present application successfully deposits nano-SiO2 on the surface of carbon fiber, and also realizes the synchronous collection of interface slip, strain and impedance spectrum under multi-coupling stress, which facilitates the revelation of the synergistic mechanism of multi-field on interface damage.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of building materials and structural engineering, and particularly relates to an analysis method of mechanical behavior of composite interface bonding. BACKGROUND

[0002] Carbon fiber reinforced cement-based composites (CFRC) are widely used in the fields of intelligent structure monitoring and self-repairing materials due to their excellent mechanical properties and electrical conductivity. The interface bonding performance is a key factor determining the overall performance of CFRC, and the damage mechanism under the coupling effect of force, electricity and chemical multi-physical fields is not fully clear.

[0003] The prior art has the following disadvantages: (1) the traditional interface test method (such as the single filament pull-out method) can only obtain mechanical parameters, and cannot simultaneously monitor the interface damage process under the coupling effect of electric and chemical fields; (2) the interface performance quantification relies on a single mechanical index, and lacks a multi-dimensional (mechanical, electrochemical, etc.) collaborative analysis means; (3) the interface constitutive model parameters are obtained by relying on empirical formulas, which deviates from the actual coupling stress state.

[0004] Therefore, the prior art still needs to be improved and developed. SUMMARY

[0005] In view of the deficiencies of the prior art, the purpose of the present application is to provide an analysis method of mechanical behavior of composite interface bonding, aiming to realize the synchronous collection of interface slip, strain and impedance spectrum under multi-coupling stress, and facilitate the revelation of the synergistic mechanism of multi-physical fields on interface damage.

[0006] The present application is realized by the following technical solutions:

[0007] The present application provides an analysis method of mechanical behavior of composite interface bonding, comprising the following steps:

[0008] Part of the modified carbon fiber is vertically embedded in the cement-based material to form a composite interface composed of modified carbon fiber and cement-based material;

[0009] A tensile load is applied in the axial direction of the modified carbon fiber, and a alternating electric field is simultaneously applied in the transverse direction of the modified carbon fiber;

[0010] A data set in the tensile process is obtained, the data set in the tensile process includes tensile load, interface slip amount and interface shear strain, the data set in the tensile process is input into a trilinear bond-slip constitutive model for training, and a trained trilinear bond-slip constitutive model is obtained;

[0011] The impedance phase angle in the stretching process is obtained, the interface damage index is calculated by using the impedance phase angle, the trained tri-linear bond-slip constitutive model is corrected by using the interface damage index, a corrected tri-linear bond-slip constitutive model is obtained, and the composite interface bond mechanical behavior is analyzed by using the corrected tri-linear bond-slip constitutive model.

[0012] Optionally, when the tensile load is applied, a constant displacement is maintained for 5-10 minutes after the tensile load reaches the peak load; and the frequency scanning range for obtaining the impedance is 0.1-100 kHz.

[0013] Optionally, the length of the part of the modified carbon fiber embedded in the cement-based material is 10-20 mm.

[0014] Optionally, the loading rate of the tensile load is 0.1-2 mm / min.

[0015] Optionally, the field strength of the applied alternating electric field is 1-10 V / cm, and the frequency is 0.1-100 Hz.

[0016] Optionally, when the interface slip is obtained, the sampling frequency is ≥100 Hz; and the digital image correlation method is used to calculate the interface shear strain distribution, and the strain resolution is ≤0.01%.

[0017] Optionally, the modified carbon fiber is prepared by the following method:

[0018] The carbon fiber is placed in a cathode electrolyte for electrophoretic deposition, the deposition voltage is 1-5 V, and the deposition time is 10-60 minutes.

[0019] The cathode electrolyte mainly contains an active SiO2 aqueous solution and a soluble calcium salt.

[0020] The mass fraction of the active SiO2 in the cathode electrolyte is 2.5-10 w.t.%, and the soluble calcium salt is CaCl2 or Ca(NO3)2 with a concentration of 1-3 mol / L.

[0021] Optionally, the mass fraction of the active SiO2 in the cathode electrolyte is 5.7-7.7 w.t.%, the deposition voltage is 2.6-3.6 V, and the deposition time is 35-44 minutes.

[0022] The active SiO2 is in an amorphous state and has the following key parameters: the pH value is between 9.0 and 10.5, the density at 20°C is 1.28-1.30 g / cm 3 , the particle size is 8-15 nm, and the viscosity is ≤30 mPa·s.

[0023] Optionally, the elastic modulus of the carbon fiber is 150-250 GPa, and the density is 1.6-1.9 g / cm 3The diameter of the carbon fiber monofilament is 5-9 μm.

[0024] Compared with the prior art, the present application has the following beneficial effects:

[0025] The present application can realize the synchronous collection of interface slip, strain and impedance spectrum under multiple coupling stresses (including force, electricity and chemical), and facilitate the revelation of the synergistic mechanism of multiple physical fields on interface damage. First, based on the real-time monitoring of the interface slip amount, the interface shear strain distribution is obtained in combination with the tensile load, and a trained tri-linear bond-slip constitutive model of the modified carbon fiber-cement-based interface is obtained; then, the interface damage index is calculated by using the impedance phase angle; the obtained tri-linear bond-slip constitutive model of the modified carbon fiber-cement-based interface is corrected by using the damage index, the bond mechanical behavior of the composite interface is analyzed, and the accuracy of the interface stress distribution analysis and the applicability of the constitutive model are ensured. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a flowchart of the analysis method of the bond mechanical behavior of the composite interface.

[0027] Figure 2 It is a surface micro-morphology diagram of unmodified fiber (Raw CF).

[0028] Figure 3 It is a surface micro-morphology diagram of modified carbon fiber (MCF).

[0029] Figure 4 It is an AFM diagram of the modified carbon fiber surface.

[0030] Figure 5 It is an XPS full spectrum diagram. DETAILED DESCRIPTION

[0031] The present application provides an analysis method of the bond mechanical behavior of the composite interface, in order to make the purpose, technical scheme and effects of the present application more clear and explicit, the present application is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0032] The present embodiment provides an analysis method of the bond mechanical behavior of the composite interface, as shown in Figure 1 The method comprises the following steps:

[0033] S1, vertically embedding part of the modified carbon fiber into the cement base to form a composite interface composed of the modified carbon fiber and the cement base;

[0034] S2, applying a tensile load in the axial direction of the modified carbon fiber, and synchronously applying an alternating electric field in the transverse direction of the modified carbon fiber;

[0035] S3, acquire the data set in the stretching process, the data set in the stretching process including the stretching load, the interface slip amount, the interface shear strain, input the data set in the stretching process into the trilinear bond-slip constitutive model for training, obtain the trained trilinear bond-slip constitutive model;

[0036] S4, acquire the impedance phase angle in the stretching process, calculate the interface damage index by using the impedance phase angle, correct the trained trilinear bond-slip constitutive model by using the interface damage index, obtain the corrected trilinear bond-slip constitutive model, and analyze the composite interface bonding mechanical behavior by using the corrected trilinear bond-slip constitutive model.

[0037] In the embodiment, the modified carbon fibers are partially embedded in the cement-based material vertically to prepare a modified carbon fiber-cement-based interface, a tensile load and an alternating electric field are applied to the modified carbon fibers (specifically, a tensile load is applied to the carbon fibers in the axial direction, and an alternating electric field is applied to the carbon fibers in the transverse direction), then the interface slip amount is monitored in real time, and the interface shear strain distribution is calculated, a trilinear bond-slip constitutive model of the modified carbon fiber-cement-based interface is established according to the obtained data, the interface impedance is measured in real time to obtain the impedance phase angle, and finally the interface damage index is calculated by using the impedance phase angle; the trilinear bond-slip constitutive model of the modified carbon fiber-cement-based interface is corrected by using the damage index, and the composite interface bonding mechanical behavior is analyzed. The interface slip, the strain and the impedance spectrum can be collected synchronously under the action of multiple coupling stresses (including force, electricity and chemical), and the synergistic action mechanism of the multiple physical fields on the interface damage can be revealed.

[0038] Specifically, the interface impedance can be measured by using an electrochemical workstation. Since it takes a certain time to measure the interface impedance, the load needs to be kept for a period of time after reaching the peak load to facilitate the measurement.

[0039] It should be noted that, by synchronously applying the force-electricity-chemical multi-field load to the modified carbon fibers, and combining the obtained interface slip amount, the interface shear strain distribution and the impedance phase angle, the phase angle offset can be fitted to the damage degree (the interface damage degree refers to the deterioration state of the carbon fiber-cement-based interface under the action of the multi-field coupling), the intelligent analysis from the original signal to the damage characteristics is realized, and then the "data-damage" conversion hub in the dynamic monitoring can be used. Abstract interface damage (such as debonding and micro-crack propagation) is converted into a calculable numerical index (damage degree index), the cross-physical field mapping from the electrochemical parameter to the mechanical damage is realized, and the interface impedance measurement has great significance.

[0040] The present application establishes a curve relationship between the damage index (calculated based on DRT) and the key phase angle characteristics through experimental data for damage evaluation. The curve can be described as: damage degree index = 0.35 x (phase angle offset) + 0.12. It should be noted that the model is a linear regression model, which is established based on the linear correlation between the phase angle parameters of electrochemical impedance spectroscopy (EIS) and the interface damage degree, and the fitting accuracy is ensured through statistical method verification.

[0041] In some embodiments, when the tensile load is applied, a constant displacement is maintained for 5-10 min after the detection of the tensile load reaches the peak load; and the frequency scanning range for obtaining the impedance is 0.1-100 kHz.

[0042] In some embodiments, the length of the part of the modified carbon fiber embedded in the cement-based material is 10-20 mm (for example, it can be 10 mm, 12 mm, 14 mm, 16 mm, 18 mm, or 20 mm).

[0043] In some embodiments, the loading rate of the applied tensile load is 0.1-2 mm / min (for example, it can be 0.1 mm / min, 0.5 mm / min, 1 mm / min, 1.5 mm / min, or 2 mm / min). It should be noted that the application of the tensile load is performed on a mechanical testing system (MTS testing machine). A laser displacement sensor is used to monitor the interface slip in real time.

[0044] In some embodiments, the field strength of the applied alternating electric field is 1-10 V / cm (for example, it can be 2 V / cm, 3 V / cm, 4 V / cm, 5 V / cm, 6 V / cm, 7 V / cm, 8 V / cm, 9 V / cm, or 10 V / cm), and the frequency is 0.1-100 Hz (for example, it can be 1 Hz, 2 Hz, 3 Hz, 4 Hz, 5 Hz, 6 Hz, 7 Hz, 8 Hz, 9 Hz, or 10 Hz, etc.).

[0045] In some embodiments, when the interface slip is obtained, the sampling frequency is ≥100 Hz (for example, it can be 100 Hz, 110 Hz, 120 Hz, 130 Hz, 140 Hz, or 150 Hz, etc.); the digital image correlation method is used to calculate the interface shear strain distribution, and the strain resolution is ≤0.01% (for example, it can be 0.001%, 0.003%, 0.005%, 0.007%, 0.009%, or 0.01%, etc.).

[0046] Optionally, the modified carbon fiber is prepared by the following method:

[0047] The carbon fiber is placed in a cathode electrolyte for electrophoretic deposition, the deposition voltage is 1-5 V, and the deposition time is 10-60 min,

[0048] The cathode electrolyte mainly comprises active SiO2 aqueous solution and soluble calcium salt,

[0049] The mass fraction of active SiO2 in the cathode electrolyte is 2.5-10 w.t.%, and the soluble calcium salt is CaCl2 or Ca(NO3)2 with a concentration of 1-3 mol / L.

[0050] Optionally, the mass fraction of active SiO2 in the cathode electrolyte is 5.7-7.7 w.t.%, the deposition voltage is 2.6-3.6 V, and the deposition time is 35-44 min.

[0051] The active SiO2 is in amorphous form, and has the following key parameters: the pH value is between 9.0-10.5, the density at 20℃ is 1.28-1.30 g / cm 3 , the particle size is 8-15 nm, and the viscosity is ≤30 mPa·s.

[0052] Optionally, the elastic modulus of the carbon fiber is 150-250 GPa, the density is 1.6-1.9 g / cm 3 , and the carbon fiber monofilament diameter is 5-9 μm.

[0053] The nanoindentation test is performed on the fiber surface, the indentation spacing is ≤1 μm, and the load range is 0.1-5 mN, so as to obtain the elastic modulus distribution curve of the interface transition zone. The interface transition zone elastic modulus distribution curve shows that the modulus in the 0-5 μm region from the fiber surface is 15-25 GPa, and the modulus in the 5-10 μm region is 10-15 GPa. The interface transition zone morphology is observed by scanning electron microscope (SEM), and the porosity is reduced from 18% of the unmodified to 5-8%. The interface chemical composition is analyzed by X-ray photoelectron spectroscopy (XPS), and the Si-O-C bond content ratio is increased from 3.2% of the unmodified to 8.5-12.7%. The interface C-S-H gel content is detected by Raman spectroscopy, and the characteristic peak intensity ratio (I 1080 / I 1000 ) is increased from 0.7 of the unmodified to 1.2-1.5.

[0054] The above test data is used for fitting of the trilinear bond-slip constitutive model. First, a geometric model containing the details of the interface transition zone is established, the interface region is subjected to grid densification processing, and the material parameters of the fiber, matrix and interface transition zone are input, including but not limited to elastic modulus, strength parameters, etc. The force-electricity coupling load consistent with the actual test conditions is applied, the stress field distribution of the interface region is solved through multi-physical field coupling calculation, the shear stress peak value and its distribution characteristics are extracted, and the trilinear bond-slip constitutive relationship model is fitted based on the obtained results.

[0055] The trilinear bond-slip constitutive model is:

[0056] Elastic stage: τ = k 1· s ( s ≤ s max =0.05mm);

[0057] Softening stage: τ = τ max - k 2·( s - s max )( s max < s ≤ s 0=0.15mm);

[0058] Friction stage: τ = τ 0( s > s 0)。

[0059] The parameters include: initial cohesive stiffness k 1=120-150MPa / mm, peak cohesive strength τ max =6-8MPa, residual friction strength τ 0=2MPa, k 2=40-60MPa / mm, positively correlated with SiO2 concentration (R 2 =0.92).

[0060] Then the obtained three-linear bond-slip constitutive model is corrected by the obtained interface damage index and other data, if the error of the key indicators exceeds a certain value, the interface parameters or the grid density are adjusted until convergence, and finally the accuracy of the interface stress distribution analysis and the applicability of the constitutive model are ensured.

[0061] In some embodiments, the modified carbon fiber is prepared by the following method:

[0062] The carbon fiber is placed in a cathode electrolyte for electrophoretic deposition, the deposition voltage is 1-5V (such as 1V, 2V, 3V, 4V, 5V, and any voltage within the range), and the deposition time is 10-60min (such as 10min, 20min, 30min, 35min, 40min, 45min, 50min, 60min, and any time within the range),

[0063] The cathode electrolyte mainly contains active SiO2 aqueous solution and soluble calcium salt,

[0064] The mass fraction of active SiO2 in the cathode electrolyte is 2.5 w.t.%-10 w.t.% (for example, 2.5 w.t.%, 3.5 w.t.%, 4.5 w.t.%, 5.5 w.t.%, 6.5 w.t.%, 7.5 w.t.%, 8.5 w.t.%, 9.5 w.t.%, 10 w.t.% and any mass fraction in the range), and the soluble calcium salt is CaCl2 or Ca(NO3)2 with a concentration of 1-3 mol / L (for example, 1 mol / L, 2 mol / L, 3 mol / L and any concentration in the range).

[0065] The present application proposes a modified carbon fiber obtained by electrophoretic deposition using SiO2 and calcium salt combination as electrolyte. The present application successfully deposits nano-SiO2 on the surface of carbon fiber. After modification, the surface of the carbon fiber is wrapped with relatively uniform SiO2 particles, the surface area is increased, and the average roughness is increased. The modification process enhances the surface reactivity of the carbon fiber, reduces the content of defective carbon atoms, and increases the concentration of oxygen-containing functional groups. The tensile properties of the modified fiber are significantly improved, which is because the deposition product helps to improve the structural defects on the surface of the carbon fiber, covers the defects and pores on the surface of the fiber, effectively prevents the stress concentration phenomenon from forming at the defects, prevents the crack from spreading, and consumes part of the load through the shearing action between the carbon fiber, ultimately leading to the increase of the tensile strength of the fiber. Thus, the rule of electrophoretic deposition modification for improving the surface properties of the carbon fiber can be established, and the influence mechanism of electrophoretic deposition modification on the mechanical properties of the carbon fiber is revealed. Therefore, the present application uses the above parameters, which can not only realize the effective modification of the carbon fiber, but also establish the rule of electrophoretic deposition modification for improving the surface properties of the carbon fiber, and reveal the influence mechanism of electrophoretic deposition modification on the mechanical properties of the carbon fiber.

[0066] It should be noted that before electrophoretic deposition, the carbon fiber needs to be cleaned and vacuum dried. The carbon fiber needs to be fixed with a plastic tube to make an electrode for subsequent power operation. The cathode electrolyte is configured as follows: first, add the corresponding proportion of silica aqueous solution into the container, and adjust the pH value to neutral by using HCl or HNO3. Since SiO2 will react with hydroxyl ions (OH - ) under alkaline conditions, forming silicate ions (SiO3 2- ). When calcium salt (such as calcium chloride) is added, calcium ions (Ca 2 + ) will combine with silicate ions to form water-insoluble calcium silicate (CaSiO3) precipitate.

[0067] The reaction equation is: SiO2( aq )+Ca 2+ ( aq )→CaSiO3( s )

[0068] However, under neutral or acidic conditions, the solubility of silica is higher, and the concentration of silicate ions is lower, so the combination of calcium ions and silicate ions is weakened, and thus it is difficult to form precipitates. In addition, hydrogen ions (H + ) in an acidic environment can combine with silicate ions to prevent the formation of precipitates.

[0069] The reaction equation is: SiO2( aq )+2 H+ ( aq )→H2SiO3( aq )

[0070] Therefore, it is necessary to adjust the pH value to neutral using HCl or HNO3. Specifically, if a soluble calcium salt CaCl2 is subsequently added, HCl is used for pH adjustment; and if Ca(NO3)2 is added, HNO3 should be used for adjustment. After adjusting the pH value to neutral, the required soluble calcium salt is gradually added to the electrolyte to ensure its full dissolution and uniformity.

[0071] Electrophoretic deposition process: the cleaned carbon fiber is made into an electrode as a cathode and placed in the cathode electrolyte; at the same time, stainless steel material is selected as an anode and immersed in the anode electrolyte. One end of the anode and one end of the cathode are connected to the power source. The water-absorbing material containing the anode electrolyte is used as a salt bridge to connect the other end of the anode and the other end of the cathode. After power-on, in the cathode electrolyte, water molecules undergo electrolysis under the action of the electric field to obtain hydrogen and hydroxide ions: 2H2O + 2e - → H2 + 2OH - .

[0072] The deposition process occurs on the surface of the carbon fiber, and calcium ions combine with hydroxide ions to form calcium hydroxide:

[0073] 2OH - + Ca 2+ → Ca(OH)2

[0074] The generated calcium hydroxide then reacts with silicon dioxide to generate calcium silicate and water:

[0075] Ca(OH)2 + SiO2 → CaSiO3 + H2O

[0076] Amorphous nanosilica reaction:

[0077] nSiO2 → … -O-Si-O-Si-O-…

[0078] Amorphous nanosilica can further react with calcium ions or calcium hydroxide to form hydrated silicate.

[0079] Hydroxide ions (OH-) will be present in the cathode electrolyte after deposition. - ), silicon dioxide (SiO2), calcium ions (Ca) 2+ ), calcium hydroxide (Ca(OH)2) and calcium carbonate (CaCO3) and other components.

[0080] It should be noted that unmodified fiber is referred to as Raw CF, and modified carbon fiber is abbreviated as MCF. The naming method is as follows: for example, "5-Cl", the first number "5" indicates that its silica mass fraction is 5w.t.%, the second letter "Cl" indicates that the calcium salt type is CaCl2, and if the second letter is "N", it indicates that the calcium salt type is Ca(NO3)2.

[0081] Figure 2 Images show the surface microstructure of unmodified carbon fiber (Raw CF), where (a) is a raw SEM image of Raw CF, and (b) is a SEM image of unmodified Raw CF after immersion in cement pore solution for 7 days. The surface morphology of Raw CF and modified carbon fiber was observed using a scanning electron microscope (SEM) (FEITitan Cubed Themis G2300). Figure 2 The SEM image in (a) shows that Raw CF has a clean, impurity-free surface and distinct, regular groove morphology. This is due to the morphological characteristics formed after carbonization of the polyacrylonitrile-based carbon fiber precursor prepared by wet spinning. After immersing unmodified Raw CF in cement pore solution for 7 days, most of the surface remained smooth and clean, with only extremely fine particles. This is because the hydrophobicity of Raw CF makes it difficult for cement hydration products to grow onto its surface; therefore, only a very small amount of fine mineral structures appear on the Raw CF surface, such as... Figure 2 As shown in (b).

[0082] After electrophoretic deposition modification, a thin, uniform nanofilm can be observed coating the MCF surface, such as... Figure 3(a) is the surface micro-morphology of the modified carbon fiber obtained using a catholyte of 2.5 w.t.% active Si02 and 2 mol / L CaCl2, (b) is the surface micro-morphology of the modified carbon fiber obtained using a catholyte of 5 w.t.% active Si02 and 2 mol / L CaCl2, (c) is the surface micro-morphology of the modified carbon fiber obtained using a catholyte of 10 w.t.% active Si02 and 2 mol / L CaCl2, (d) is the surface micro-morphology of the modified carbon fiber obtained using a catholyte of 2.5 w.t.% active Si02 and 2 mol / L Ca(N03)2, (e) is the surface micro-morphology of the modified carbon fiber obtained using a catholyte of 5 w.t.% active Si02 and 2 mol / L Ca(N03)2, other conditions being the same. They are the nanometer Si02 and hydrated calcium silicate etc. products deposited on the carbon fiber surface during the modification process. With the increase of the Si02 mass fraction in the electrolyte, the amount of the deposition products increases obviously, and the agglomerates become larger. After immersion in the cement pore solution for 7 days, a large amount of cement hydration products with a size of several microns are distributed on the surface of the MCF, which can enhance the surface activity of the fiber and strengthen the subsequent chemical bonding with the cement base. These hydration products are calcite and calcium silicate hydrate (C-S-H), which are firmly combined with the surface and adhere to the CF surface due to the nucleation effect and pozzolanic effect of the deposited nanometer Si02 particles, i.e.:

[0083] Pozzolanic effect: xCa(OH)2+ ySi02+ zH20→ xCaO-ySi02-(x+z)H20

[0084] With the increase of the Si02 mass fraction in the electrolyte, the surface roughness increases obviously, and the diameter of the carbon fiber also increases obviously, which can strengthen the subsequent physical anchoring with the cement base. Therefore, it can be seen that the Si02 concentration in the electrolyte has a significant effect on the deposition morphology of the carbon fiber surface.

[0085] Atomic force microscopy (AFM) (MFP-3D Infinity) was used to characterize the surface morphology and roughness of the carbon fiber before and after electrophoretic deposition, as shown in Figure 4Figure 6 shows the AFM images of the modified carbon fibers, where (a) is the AFM image of the unmodified carbon fiber, (b) is the AFM image of the modified carbon fiber obtained using a catholyte with 2.5 w.t.% of active Si02 and 2 mol / L of CaCl2 as the soluble calcium salt, (c) is the AFM image of the modified carbon fiber obtained using a catholyte with 5 w.t.% of active Si02 and 2 mol / L of CaCl2 as the soluble calcium salt, (d) is the AFM image of the modified carbon fiber obtained using a catholyte with 10 w.t.% of active Si02 and 2 mol / L of CaCl2 as the soluble calcium salt, (e) is the AFM image of the modified carbon fiber obtained using a catholyte with 2.5 w.t.% of active Si02 and 2 mol / L of Ca(N03)2 as the soluble calcium salt, (f) is the AFM image of the modified carbon fiber obtained using a catholyte with 5 w.t.% of active Si02 and 2 mol / L of Ca(N03)2 as the soluble calcium salt, (g) is the AFM image of the modified carbon fiber obtained using a catholyte with 10 w.t.% of active Si02 and 2 mol / L of Ca(N03)2 as the soluble calcium salt, and the other conditions are the same. The results show that the average surface roughness of the MCFs is changed to different degrees compared to the Raw CF. According to the characterization results of the AFM and SEM, it can be observed that the Raw CF has grooves arranged parallel to the length direction, and the groove width is large, with a R a of 148 nm. In the modified fibers with 2.5 w.t.% of Si02, the deposition products on the fiber surface are sparse, and these deposition products cover the small grooves on the fiber surface, so that the surface roughness becomes smaller than that of the raw fiber. With the gradual increase of the Si02 mass fraction in the electrolyte, the deposition products become more and more, and the surface roughness of the MCF gradually increases, with the R a maximum increase of 199 nm, which is increased by 34.5% compared to the Raw CF. The enhanced surface roughness helps to increase the interlocking and friction between the fiber and the cement, thereby improving the mechanical bonding and effectively improving the interface performance of the composite material.

[0086] The Raw CF immersed in the cement pore solution for 7 days was subjected to elemental characterization using the energy dispersive spectrometer (EDS) attached to the SEM instrument, and the results showed that there were almost only C and N elements on the surface of the Raw CF. Only at the small particles on the fiber surface, there were aggregations of O and Ca elements, which were a small amount of calcite (CaC03) after immersion.

[0087] Then the MCF was characterized by EDS element, it can be seen that the main elements of carbon fiber body are C and N, and a large number of Si, O and Ca elements appear on the surface of the fiber. A large number of Si and O indicate that the fiber surface has successfully deposited hydration products, and the increase of Ca element strongly proves the formation of C-S-H gel. With the increase of the mass fraction of SiO2 in the modification conditions, the thickness of nano-SiO2 on the surface of carbon fiber is also increasing, and the agglomeration of C-S-H gel is more obvious. The particle size of these products will directly affect the interface performance of the composite. For the calcium nitrate group, Ca is less, and the possible reason is that Cl ¯ Generally, it shows reduction, and is more conducive to promoting the oxidation reaction in the solution, thus promoting the pozzolanic reaction on the surface of the fiber. NO3 ¯ Generally, it shows oxidation, and the promoting effect is weak.

[0088] The XPS full spectrum analysis was performed on the fiber by using an X-ray photoelectron spectrometer (ESCALAB250Xi) to explore the element proportion on the surface of the fiber after the modification treatment. The XPS full spectrum characterization results are shown in Figure 5 For the Raw CF, two obvious characteristic peaks are shown at 532.5 eV and 284.8 eV, which correspond to the characteristic peaks of O1s and C1s respectively, and there is no Si element and Ca element on the surface. In addition to the characteristic peaks of O1s and C1s, the MCF after the electrophoresis treatment also shows a new characteristic peak at 103.5 eV, which corresponds to the characteristic peak of Si2p, indicating that Si element appears on the carbon fiber.

[0089] In some embodiments, the mass fraction of active SiO2 in the cathode electrolyte is 5.7-7.7 w.t.%, such as 5.7 w.t.%, 6 w.t.%, 6.7 w.t.%, 7.7 w.t.%, and any mass fraction within the range, the deposition voltage is 2.6-3.6 V, such as 2.6 V, 3 V, 3.6 V, and any voltage within the range, and the deposition time is 35-44 min, such as 35 min, 36 min, 37 min, 38 min, 39 min, 40 min, 41 min, 42 min, 43 min, 44 min, and any time within the range. Based on the machine learning method and the meso-mechanical analysis, combined with the prediction model of the interface bonding performance, the optimal modification parameters are obtained as follows: the mass fraction of SiO2 is 5.7-7.7 w.t.%, the deposition voltage is 2.6-3.6 V, and the deposition time is 35-44 min.

[0090] In some embodiments, the active SiO2 is in amorphous state, and has the following key parameters: the pH value is 9.0-10.5, the ingredient content is 40±1%, the density at 20°C is 1.28-1.30 g / cm 3, particle size is 8-15nm, viscosity is less than or equal to 30mPa·s.

[0091] In one embodiment, the anode electrolyte for electrophoretic deposition is saturated Ca(OH)2 solution.

[0092] In one embodiment, the elastic modulus of the carbon fiber is 150-250GPa, and the density is 1.6-1.9g / cm 3 Each bundle of carbon fibers contains 3000 fiber filaments, and each fiber filament has a diameter of 5-9μm.

[0093] It should be noted that the present embodiment proposes a modified carbon fiber for electrophoretic deposition using a combination of SiO2 and calcium salt as electrolyte, and the present application successfully deposits nano-SiO2 on the surface of the carbon fiber. After modification, the surface of the modified carbon fiber is wrapped with relatively uniform SiO2 particles, the surface area is increased, and the average roughness is increased. The modification process enhances the surface reactivity of the carbon fiber, reduces the content of defective carbon atoms, and increases the concentration of oxygen-containing functional groups. The tensile properties of the modified fiber are significantly improved, which is because the deposition product helps to improve the structural defects on the surface of the carbon fiber, covers the defects and pores on the surface of the fiber, effectively prevents the stress concentration phenomenon from forming at the defects, prevents the diffusion of cracks, and consumes a part of the load through the shearing action between the carbon fiber and the fiber, ultimately leading to an increase in the tensile strength of the fiber. Thus, the rule of electrophoretic deposition modification for improving the surface properties of the carbon fiber is established, and the influence mechanism of electrophoretic deposition modification on the mechanical properties of the carbon fiber is revealed.

[0094] The present application can establish an effective interface performance improvement method by electrophoretic deposition modification of carbon fibers to generate high-activity, functional deposition products on the surface of the carbon fibers. This method can regulate the chemical properties and structure of the deposition product at the micro level, and can significantly improve the interfacial bonding strength between the carbon fiber and the cement-based material by using electrophoretic deposition for interface modification between the carbon fiber and the cement-based material. The combination of micro analysis and macro performance can reveal the evolution rule and mechanism of the interface micro properties and mechanical properties of the carbon fiber and the cement-based material.

[0095] In summary, the present application can realize the synchronous acquisition of interface slip, strain and impedance spectrum under multiple coupled stresses (including force, electricity and chemical), and can be used to reveal the synergistic mechanism of multiple physical fields on interface damage.

[0096] The data collected by the present application is applied to the construction and correction of the tri-linear bond-slip constitutive model, ensuring the accuracy of the interface stress distribution analysis and the applicability of the constitutive model.

[0097] It is to be understood that the application is not limited to the examples described above, which can be modified or adapted in several ways by those skilled in the art without departing from the scope of the present application, as defined by the appended claims.

Claims

1. A method of analyzing the mechanical behavior of a composite interfacial bond, characterized in that, The method comprises the following steps: vertically embedding part of the modified carbon fiber into the cement base to form a composite interface composed of the modified carbon fiber and the cement base; applying a tensile load in the axial direction of the modified carbon fiber and synchronously applying an alternating electric field in the transverse direction of the modified carbon fiber; obtaining a set of data in the tensile process, the set of data in the tensile process including the tensile load, the interface slip amount, and the interface shear strain, inputting the set of data in the tensile process into a tri-linear bond-slip constitutive model for training to obtain a trained tri-linear bond-slip constitutive model; obtaining an impedance phase angle in the tensile process, calculating an interface damage index by using the impedance phase angle, correcting the trained tri-linear bond-slip constitutive model by using the interface damage index to obtain a corrected tri-linear bond-slip constitutive model, and analyzing the bond mechanical behavior of the composite interface by using the corrected tri-linear bond-slip constitutive model.

2. The method of analyzing the mechanical behavior of the interfacial adhesion of a composite according to claim 1, characterized in that, When the tensile load is applied, the constant displacement is maintained for 5-10 min after the detected tensile load reaches the peak load; the frequency scanning range for obtaining the impedance is 0.1-100 kHz.

3. The method of analyzing the mechanical behavior of a composite interfacial bond according to claim 2, wherein, The length of the part of the modified carbon fiber embedded in the cement base is 10-20 mm.

4. The method of analyzing the mechanics of interfacial adhesion of a composite according to claim 1, wherein The loading rate of the applied tensile load is 0.1-2 mm / min.

5. The method of analyzing the mechanics of interfacial adhesion of a composite according to claim 1, wherein The field strength of the applied alternating electric field is 1-10 V / cm, and the frequency is 0.1-100 Hz.

6. The method of analyzing the mechanics of interfacial adhesion of a composite according to claim 1, wherein When the interface slip amount is obtained, the sampling frequency is ≥100 Hz; the digital image correlation method is used to calculate the interface shear strain distribution, and the strain resolution is ≤0.01%.

7. The method of analyzing the mechanics of interfacial adhesion of a composite according to claim 1, wherein The modified carbon fiber is prepared by the following method: placing the carbon fiber in a cathode electrolyte for electrophoretic deposition, the deposition voltage being 1-5 V, and the deposition time being 10-60 min, the cathode electrolyte mainly containing active SiO2 aqueous solution and soluble calcium salt, the mass fraction of the active SiO2 in the cathode electrolyte being 2.5-10 w.t.%, and the soluble calcium salt being CaCl2 or Ca(NO3)2 with a concentration of 1-3 mol / L.

8. The method of analyzing the mechanics of interfacial adhesion of a composite according to claim 7, wherein the mass fraction of the active SiO2 in the cathode electrolyte being 5.7-7.7 w.t.%, the deposition voltage being 2.6-3.6 V, and the deposition time being 35-44 min.

9. The method of analyzing the mechanics of interfacial adhesion of a composite according to claim 7, wherein The active SiO2 is in amorphous form, with the following key parameters: pH value between 9.0-10.5, density of 1.28-1.30 g / cm3 at 20°C 3 , particle size of 8-15 nm, viscosity ≤ 30 mPa·s.

10. The method of analyzing the mechanics of interfacial adhesion of a composite of claim 7, wherein, The carbon fiber has an elastic modulus of 150-250 GPa and a density of 1.6-1.9 g / cm 3 , and a carbon fiber monofilament diameter of 5-9 μm.

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