Fatigue crack growth rate prediction method for dissimilar titanium alloy diffusion bonded laminate structures

Abstract

The present application relates to a method for predicting fatigue crack propagation rate of a diffusion bonded dissimilar titanium alloy laminate structure, which is based on the mechanical properties of the constituent materials of the dissimilar titanium alloy laminate structure, i.e., the quasi-static tensile properties of the two titanium alloy plies. The method for predicting fatigue crack propagation rate of the diffusion bonded dissimilar titanium alloy laminate structure first establishes the relationship between the fatigue crack propagation rate of the laminate structure and the mechanical properties of the laminate structure, and then establishes the relationship between the mechanical properties of the laminate structure and the mechanical properties of the dissimilar titanium alloy single ply, thereby describing the relationship of the fatigue crack propagation rate of the laminate structure. Compared with the prior art, the method of the present application has the advantages of simple and convenient test, engineering precision, rapid and practical, etc., and effectively reduces the test cost and test time required for crack propagation test of the dissimilar titanium alloy laminate structure processed from different parameters.

Description

Technical Field

[0001] This invention relates to the field of machining and materials joining engineering, and in particular to a method for predicting the fatigue crack propagation rate of diffusion-bonded laminated structures of dissimilar titanium alloys. Background Technology

[0002] In recent years, metals have received widespread attention and development due to their unique performance advantages, material savings, diverse shapes, and ease of industrial manufacturing. For dissimilar titanium alloy laminates, the differences in interlayer materials and the connection between dissimilar materials form a bonding layer of a certain width, which is non-uniform in its microstructure along the thickness direction. This non-uniformity causes uneven micro-stress and strain within the bulk material structure. Damage typically occurs at the locations of maximum stress, minimum strength, or structural weakness, leading to defects such as matrix cracking and interface delamination, resulting in discontinuities in localized material stress, displacement, and strain.

[0003] By using diffusion bonding technology to process multilayer titanium alloy plates of different types into laminated structures, the presence of heterogeneous interfaces and the performance differences between the interlayer materials significantly inhibit fatigue crack propagation, thereby greatly improving the fatigue damage tolerance of the laminated structure. In fatigue crack propagation, the passivation of the crack tip at the heterogeneous interface is the main mechanism for inhibiting crack propagation. Simultaneously, cracks may preferentially initiate and propagate across the ductile layer in the brittle layer, accompanied by numerous secondary cracks, thus improving the distribution of the stress field and plastic deformation field at the crack tip.

[0004] Compared to tensile, shear, impact, and compression tests, fatigue crack propagation testing is characterized by high material consumption and complex processing in specimen preparation, long experimental cycles, and high costs. Fatigue crack propagation rate can be used to estimate the remaining life of a part, while performance parameters from tests such as tensile testing do not directly reflect the remaining life of the part. Therefore, based on the mechanical properties of dissimilar titanium alloy diffusion-bonded laminates and previous research, this paper derives a predictive model suitable for the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminates, reducing experimental workload, improving economic efficiency, and achieving energy conservation and emission reduction.

[0005] Currently, many researchers incorporate experimental results and mechanical models into extended finite element method (EFM) simulations to predict fatigue crack propagation behavior, rate, and life. Xie Peiyu et al., based on Findley's improved critical surface method, established a fatigue life prediction model for the diffusion-bonded interface of TC4 titanium alloy under loads in different directions. Their life prediction results are generally within the three-fold error band, meeting engineering application requirements (Study on Fatigue Performance of TC4 Diffusion-Bonded Joints. Master's Thesis, Nanjing University of Aeronautics and Astronautics, 2016). Liu et al. established a failure process analysis model for titanium alloy laminates containing unbonded areas based on the extended finite element method, and conducted simulation analysis on the titanium alloy laminate structure based on this model. The simulation results are in good agreement with experimental results (Effect of unbonded areas around hole on the fatigue crack growth life of diffusion-bonded titanium alloy laminates. Engineering Fracture Mechanics, 2016, 163: 176-188). Currently, no fatigue crack propagation life prediction model for diffusion-bonded laminates of dissimilar materials has been reported. Shi et al. established a generalized Paris model based on mechanical properties for homogeneous Ti-55511 titanium alloy with basket-weave microstructure. This model can describe the fatigue crack growth rate of Ti-55511 titanium alloy well (Study on the fatiguecrack growth rates of Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy with basket-weave microstructure, Materials Science & Engineering A 2015, 621:143-148). Currently, no fatigue crack growth prediction model for dissimilar material diffusion-bonded laminates based on room temperature quasi-static tensile properties has been reported. Therefore, a method for predicting the fatigue crack growth rate of dissimilar titanium alloy diffusion-bonded laminates is urgently needed. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology by providing a method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminated structures. Based on the mechanical properties of the constituent materials of the dissimilar titanium alloy laminated structure, the method first establishes the relationship between the fatigue crack propagation rate of the laminated structure and its mechanical properties, and then establishes the relationship between the mechanical properties of the laminated structure and the mechanical properties of a single layer of dissimilar titanium alloy. The method requires fewer parameters for prediction, which can improve the efficiency of engineering applications and reduce engineering costs.

[0007] This invention can be achieved through the following technical solutions:

[0008] The purpose of this invention is to provide a method for predicting the fatigue crack propagation rate of a diffusion-bonded laminate structure of dissimilar titanium alloys, the method comprising the following steps:

[0009] Preparation of diffusion-bonded laminated structures of dissimilar titanium alloys with different precipitate phase characteristics;

[0010] Fatigue crack propagation experiments were conducted on dissimilar titanium alloy laminates obtained by different diffusion bonding and heat treatment processes.

[0011] The key parameters describing the fatigue crack propagation rate of laminated structures are analyzed, and the relationships between these parameters are established to reduce parameter variables.

[0012] Quasi-static uniaxial tensile tests were conducted on the laminated structure to obtain its mechanical properties;

[0013] Quasi-static uniaxial tensile tests were conducted on dissimilar titanium alloy layers to obtain their mechanical properties, and the mechanical properties of the dissimilar titanium alloy laminate structure were predicted based on the mixing criterion.

[0014] A quantitative model of fracture toughness for laminated structures is established, considering key parameters that describe the fatigue crack propagation rate of laminated structures, and mechanical properties are determined to describe the fatigue crack propagation rate.

[0015] Based on the mechanical properties of dissimilar titanium alloy laminates and a quantitative model of fracture toughness of laminates, the mechanical properties of dissimilar titanium alloy layers are determined, and the relationship of fatigue crack propagation rate of laminates is described.

[0016] Furthermore, in the preparation of dissimilar titanium alloy diffusion-bonded laminates with different microstructures, the dissimilar titanium alloy laminates are prepared using a diffusion bonding process, and the heat treatment process after diffusion bonding is changed. The heat treatment process includes solution treatment and isothermal aging treatment to obtain dissimilar titanium alloy diffusion-bonded laminates with different microstructures.

[0017] Furthermore, in the fatigue crack propagation experiment of dissimilar titanium alloy laminates obtained by different diffusion bonding and heat treatment processes, fatigue crack propagation experiments of dissimilar titanium alloy laminates are carried out. Based on the preparation of specimens obtained by diffusion bonding of dissimilar titanium alloy laminates with different microstructures, fatigue crack propagation specimens are first designed, including the specimen size and the defect characteristics and locations that cause initial fatigue damage; then fatigue crack propagation experiments are carried out, including the initial crack pre-forming process and the subsequent crack propagation test process. It is necessary to design cyclic external loading modes and fatigue crack propagation length observation standards.

[0018] Furthermore, in the process of analyzing the key parameters describing the fatigue crack propagation rate of laminated structures and establishing relationships between parameters to reduce parameter variables, fatigue crack propagation rate data of dissimilar titanium alloy laminated structures were obtained based on fatigue crack propagation experiments on dissimilar titanium alloy laminated structures obtained by different diffusion bonding and heat treatment processes. The key parameters of the Paris model for the fatigue crack propagation rate of four laminated structures, the exponent m and the coefficient C, were analyzed, and relationships between parameters were established to reduce parameters.

[0019] Furthermore, in the process of conducting quasi-static uniaxial tensile tests on the laminated structure to obtain mechanical properties, the design and tensile testing method of the tensile specimen of the dissimilar titanium alloy laminated structure is as follows: the width of the tensile specimen of the dissimilar titanium alloy laminated structure is in the direction of the dissimilar titanium alloy stack, and the quasi-static uniaxial tensile direction is perpendicular to the direction of the dissimilar titanium alloy stack.

[0020] Furthermore, quasi-static uniaxial tensile tests were conducted on the dissimilar titanium alloy layers to obtain mechanical properties. Based on the mixing criterion, the mechanical properties of the dissimilar titanium alloy laminate were predicted, specifically the determination of the quasi-static uniaxial tensile mechanical properties of the dissimilar titanium alloy layers. Referring to the heat treatment process for dissimilar titanium alloy laminates, single-layer titanium alloy plates underwent thermal cycling similar to diffusion bonding followed by solution and aging treatments. The dimensions of the single-layer titanium alloy plate tensile specimens were consistent with those of the laminate specimens used in the quasi-static uniaxial tensile tests, and parameters such as tensile strain rate and extensometer specifications were kept consistent. Based on the mixing criterion for the mechanical properties of metal composite materials, the mechanical properties of the dissimilar titanium alloy laminate were predicted.

[0021] Furthermore, in establishing a quantitative model of fracture toughness for laminated structures, considering key parameters describing the fatigue crack propagation rate of laminated structures, and determining mechanical properties to describe the fatigue crack propagation rate, a generalized model of fracture toughness for dissimilar titanium alloy laminated structures is established based on obtaining mechanical properties through quasi-static uniaxial tensile tests on the laminated structures. This model considers key parameters describing the fatigue crack propagation rate of laminated structures and determines mechanical properties of dissimilar titanium alloy laminated structures to describe the fatigue crack propagation rate of dissimilar titanium alloy laminated structures.

[0022] Furthermore, in the process of determining the mechanical properties of the dissimilar titanium alloy layer based on the mechanical properties of the dissimilar titanium alloy laminate and the quantitative model of the fracture toughness of the laminate, and describing the fatigue crack propagation rate relationship of the laminate, the mechanical properties of the dissimilar titanium alloy layer are used to describe the fatigue crack propagation rate relationship of the laminate. The relationship between the mechanical properties of the dissimilar titanium alloy laminate and the mechanical properties of a single-layer titanium alloy is introduced into the generalized model of the fatigue crack propagation rate of the dissimilar titanium alloy laminate.

[0023] Furthermore, in the process of conducting quasi-static uniaxial tensile tests on the dissimilar titanium alloy layers to obtain mechanical properties, and predicting the mechanical properties of the dissimilar titanium alloy laminate structure according to the mixing criterion, it is determined whether the percentage error between the mechanical properties predicted by the mixing criterion, including strength and elongation, and the experimental mechanical property values ​​is within the allowable range for engineering applications. The error value should generally be within 10%, that is, the percentage error between the mechanical properties predicted by the mixing criterion and the experimental mechanical property values ​​should be controlled within 10%.

[0024] Furthermore, the key parameters describing the fatigue crack propagation rate of the laminated structure include the Paris parameter C and the value of m, where m and logC are directly related and depend on material properties.

[0025] Furthermore, the method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminates, namely, the method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminates based on the quasi-static tensile properties of two titanium alloy plates, includes the following steps:

[0026] Step 1: Referring to the heat treatment process for diffusion-bonded laminated structures of dissimilar titanium alloys, two single-layer titanium alloy plates underwent thermal cycling similar to that of diffusion bonding, followed by solution treatment and aging. Room temperature quasi-static tensile tests were conducted on the single-layer plates to obtain the engineering stress-strain curves for both types of single-layer titanium alloy plates.

[0027] Step 2: Based on the mixing criterion relationship between the strength of the bimetallic composite material and the strength and fraction of each component, predict the mechanical properties of the dissimilar titanium alloy diffusion bonding laminate structure.

[0028] Step 3: Determine whether the percentage error between the mechanical properties predicted by the hybrid criteria, including strength and elongation, and the experimental mechanical property values ​​is within the allowable range for engineering applications. The error value should generally be within 10%.

[0029] Step 4: In predicting fatigue crack propagation rates, the key is to accurately describe the macroscopic crack propagation law. When the radius of the plastic zone at the crack tip is much smaller than the crack length, the plastic zone can be ignored, and fracture mechanics analysis can be performed based on the assumption of linear elasticity.

[0030] Step 5: Paris et al. proposed the concept of stress intensity factor amplitude (ΔK), and the main parameter characterizing the crack propagation rate da / dN should also be ΔK, and proposed:

[0031] da / dN=C(ΔK) m (1)

[0032] In the formula, a is the fatigue crack length, N is the number of external load cycles, and C and m are material-related constants, which are related to material properties, test stress ratio, and stress state.

[0033] Step 6: Summarize the research results and data on fatigue crack propagation rate of some metallic materials, and conclude that m and logC are directly related and depend on material properties. Furthermore, the prediction of fatigue crack propagation behavior can be reduced from two variables to one variable, thus simplifying the model variable parameters.

[0034] Step 7: Explore the relationship between the exponent m and the material's mechanical properties. When the fatigue crack propagation rate is at 10... -6 ~10 - 2 At mm / cycle, the exponent m is related to the stress intensity factor threshold value and fracture toughness for fatigue crack propagation.

[0035] Step 8: Determine the mechanical property parameters. Yield strength and true strain at fracture are important parameters closely related to the Paris exponent m.

[0036] Step 9: Based on the mechanical property parameters of the diffusion-bonded laminated structure of dissimilar titanium alloys, the fatigue crack propagation rate Paris parameters C and m are predicted by yield strength and true strain at fracture.

[0037] Step 10: Based on the room temperature quasi-static tensile properties of a single-layer plate, predict the mechanical properties of the dissimilar titanium alloy diffusion-bonded laminate structure, and then predict the fatigue crack propagation rate Paris parameters C and m values ​​of the dissimilar titanium alloy diffusion-bonded laminate structure.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1) The fatigue crack propagation rate prediction method for dissimilar titanium alloy diffusion-bonded laminate structure provided in this technical solution is based on the mechanical properties of the constituent materials of the dissimilar titanium alloy laminate structure, namely the quasi-static tensile properties of the two titanium alloy laminates. The fatigue crack propagation rate prediction method for dissimilar titanium alloy diffusion-bonded laminate structure first establishes the relationship between the fatigue crack propagation rate of the laminate structure and the mechanical properties of the laminate structure, and then establishes the relationship between the mechanical properties of the laminate structure and the mechanical properties of the dissimilar titanium alloy single-layer plate.

[0040] 2) The fatigue crack propagation rate prediction method for dissimilar titanium alloy diffusion bonded laminate structure provided in this technical solution is a simple generalized fatigue crack propagation rate prediction relationship. The prediction requires few parameters, only the tensile test results of the constituent titanium alloy plates and the volume ratio of the constituent plates.

[0041] 3) The fatigue crack propagation rate prediction method for dissimilar titanium alloy diffusion bonded laminate structures provided in this technical solution can reduce the number of fatigue crack propagation experiments for dissimilar titanium alloy diffusion bonded laminate structures. Under the premise of ensuring prediction accuracy, it can improve engineering application efficiency and reduce engineering costs based on simple tensile tests.

[0042] 4) The fatigue crack propagation rate prediction method for dissimilar titanium alloy diffusion bonded laminate structures provided by this technical solution has the advantages of simple and convenient testing, meeting engineering accuracy, and being fast and practical. It effectively reduces the test cost and time required for crack propagation testing of dissimilar titanium alloy laminate structures processed with different parameters. Attached Figure Description

[0043] Figure 1 Fabrication of center crack tensile (CCT) specimens and quasi-static tensile specimens for the FCG (fatigue crack propagation) test of this invention: (a,c) orientation of the specimen in the laminated structure, (b,d) geometry of the specimen, (a,b) center crack tensile (CCT) specimen, (c,d) quasi-static tensile specimen (unit: mm).

[0044] Figure 2 The fatigue crack propagation curve da / dN-ΔK of the TC4 / TB8 titanium alloy laminate structure of this invention is shown.

[0045] Figure 3 This represents the linear relationship between the parameter log Cm in the Paris expression for fatigue crack propagation rate in this invention.

[0046] Figure 4 For the present invention log(σ) y / ε f The linear relationship between ) and 1 / m. Detailed Implementation

[0047] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0048] In this invention, any component models, material names, connection structures, control methods, etc., not explicitly stated are considered common technical features disclosed in the prior art.

[0049] Example 1

[0050] This embodiment takes TC4 and TB8 titanium alloys as examples and proposes a method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminate structures, including the following steps:

[0051] Step 1: Roughly grind and finely grind the surfaces of the initial 2mm thick TC4 alloy plate and 1.5mm thick TB8 titanium alloy plate to be welded. Fine grinding is done with 1500# sandpaper to ensure that the roughness Ra value does not exceed 1.0μm. Then, the plates are placed in anhydrous ethanol for ultrasonic cleaning for 10 minutes and blown dry to obtain clean and bright plates.

[0052] Step 2: A total of 34 layers of two types of titanium alloy plates were alternately stacked. The diffusion bonding experiment of the multilayer TC4 / TB8 titanium alloy plates was still conducted by heating to 870℃ at a rate of 10℃ / min, pressurizing to 10MPa, holding at that temperature and pressure for 2 hours, and stabilizing the vacuum level inside the furnace at 10 MPa. -3 Pa level, furnace cooled to near room temperature.

[0053] Step 3: The multilayer TC4 / TB8 titanium alloy sheet after diffusion bonding is sliced ​​by wire cutting. The cutting surface is parallel to the plane formed by the rolling direction and normal direction of the titanium alloy sheet, and the thickness of each slice is 3mm. The sliced ​​TC4 / TB8 titanium alloy laminate structure is then selectively subjected to solution treatment and aging treatment, and the alloy sheet is rapidly heated (the furnace temperature is raised to the set temperature, and then the sample to be heat treated is placed in). The subsequent heat treatments were as follows: (I) No heat treatment was performed on the heterogeneous laminated structure (sample abbreviated as DB); (II) Rapid heating to 520℃ and holding for 2 hours for aging treatment (sample abbreviated as DB-520); (III) Rapid heating to 830℃ and holding for 0.25 hours for solution treatment, followed by water cooling to room temperature, then rapid heating to 520℃ again and holding for 2 hours for aging treatment, followed by water cooling to room temperature (sample abbreviated as DBS-520); (IV) Solution treatment at 830℃ for 0.25 hours, followed by aging treatment at 580℃ for 2 hours (sample abbreviated as DBS-580).

[0054] Step 4: Perform heat treatment experiments on single-layer TC4 and TB8 titanium alloy plates using the same thermal cycling process as in Step 3 to obtain single-layer titanium alloy plates. The TC4 and TB8 materials in this plate are the same as those in the interlayer of the dissimilar titanium alloy diffusion bonded laminate structure.

[0055] Step 5: A tensile specimen with a central crack is wire-cut in a dissimilar TC4 / TB8 titanium alloy laminate structure. The fatigue crack propagation direction is perpendicular to the alloy layer. Specific dimensions are as follows: Figure 1 a and b. Fatigue crack propagation experiments under constant amplitude loading were conducted at room temperature using a servo-hydraulic testing machine. Fatigue crack propagation tests and data acquisition were performed, and the maximum stress (σ) was recorded. max With a stress of 280 MPa, a stress ratio (R) of 0.1, and a frequency (f) of 8 Hz, the crack length *a* was measured every 1000 cycles. The stress intensity factor amplitude ΔK of the centrally cracked tensile specimen in practical engineering applications is calculated using the following formula:

[0056]

[0057]

[0058] In equation (2): σ maxLet A be the maximum applied stress (MPa), and let A be the projected area of ​​the fatigue crack in a plane perpendicular to the loading axis. To simplify the calculation of A, it is assumed that the crack is 1 / 4 circular before penetrating the specimen thickness and rectangular after penetration. Let a be the crack length (mm) in the specimen width direction. C and m are material-related constants.

[0059] Step 6: The single-layer TC4 and TB8 titanium alloy plates underwent thermal cycling similar to diffusion bonding, followed by solution treatment and aging. Mechanical properties, including yield strength, tensile strength, and total elongation, are summarized in Table 1.

[0060] Table 1 Mechanical properties of single-layer TC4 and TB8 titanium alloy plates under heat treatment with similar laminated structures.

[0061]

[0062]

[0063] Step 7: Determine the room temperature quasi-static uniaxial tensile stress and strain curves of the TC4 / TB8 titanium alloy laminate. Table 2 summarizes the mechanical properties, including yield strength, tensile strength and total elongation.

[0064] Table 2 Mechanical properties of TC4 / TB8 alloy laminate structure.

[0065]

[0066] Step 8: Conduct fatigue crack propagation experiments on four TC4 / TB8 titanium alloy laminate structures to observe the macroscopic characteristics of fatigue crack propagation behavior, including the propagation path of fatigue cracks within dissimilar titanium alloy layers and at the interface.

[0067] Step 9: Figure 2 The da / dN-ΔK data for four TC4 / TB8 titanium alloy laminates are described. It can be found that the fatigue crack propagation rates of the four specimens are basically similar with the increase of ΔK. The Paris coefficient C and exponent m are calculated according to the Paris model (1) and are listed in Table 3.

[0068] Table 3. Paris model parameters for four TC4 / TB8 titanium alloy laminate structures.

[0069]

[0070] Step 10: The relationship between the strength of the bimetallic composite material and the strength and fraction of each component can be described by the mixing criterion (4), and the relationship between the strain of the composite material and the strain and fraction of each component can be described by the mixing criterion (5).

[0071] σ c=σ1×V1+σ2×V2 (4)

[0072] ε f =(Vσ) 1,UE1 ε 1,UE +Vσ 2,UE2 ε 2,UE ) / (Vσ 1,UE1 +Vσ 2,UE2 (5)

[0073] In the formula, σ c and ε f V represents the strength and true strain of a composite material. i σ represents the volume fraction of component i. i σ represents the intensity of component i. i,UE and ε i,UE The true strength and true strain of composite material i are represented. The predicted strength and percentage error are listed in Table 4. The percentage error between the strength predicted by the mixing criterion and the experimental strength is controlled between 1.6% and 9.3%.

[0074] Table 4 shows the predicted strength of the TC4 / TB8 alloy laminate structure based on the mixing criteria.

[0075]

[0076] Step 11: The relationship between the exponent m and log C in the Paris equation for the fatigue crack propagation curve of TC4 / TB8 titanium alloy is as follows: Figure 3 As shown. Fitting the data revealed a strong linear relationship, expressed as follows:

[0077] logC = -3.79 - 1.15m (6)

[0078] Step 12: Based on the direct correlation between m and logC, by combining Paris equations (1) and (6), the generalized Paris equation for the TC4 / TB8 alloy laminate structure can be expressed as equation (7).

[0079] da / dN = 10 -3.79-1.15m (ΔK) m (7)

[0080] Step 13: The exponent m and the stress intensity factor amplitude threshold value (ΔK) for fatigue crack propagation th ) and fracture toughness (K IC (This relates to) Establishing a quantitative model for the fracture toughness of materials. Regarding the stress intensity factor amplitude threshold prediction model, when the strain hardening exponent of the material is 1 and the fatigue test cyclic loading stress ratio is 0, the following simple analytical relationship exists:

[0081] log(K IC / ΔKth )∝1 / m (8)

[0082]

[0083]

[0084] Where, ρ min Let be the minimum radius of the crack tip during fatigue crack propagation, which can be considered a constant. Combining equations (8), (9), and (10), we can obtain...

[0085]

[0086] For the same titanium alloy, its elastic modulus E and ρ min The differences are relatively small, and equation (11) can be further simplified to

[0087] log(σ y / ε f )∝1 / m (12)

[0088] Mechanical property parameter: yield strength σ f and fracture true strain ε f It is an important parameter closely related to the Paris exponent m. Figure 4 Show Paris model 1 / m and log(σ) f / ε f The positive linear relationship between ) is expressed as follows:

[0089] log(σ y / ε f = -0.95 + 11.96 / m (13)

[0090] By combining formulas (12) and (13), the final Paris prediction model (14) for the fatigue crack propagation rate of the TC4 / TB8 alloy laminate structure can be obtained.

[0091]

[0092] The mechanical properties of the TC4 / TB8 titanium alloy laminate structure include yield strength σ. f and fracture true strain ε f The calculated fatigue crack propagation rate Paris parameters are summarized in Table 5.

[0093] Table 5 shows the predicted C and m values ​​for the mechanical properties of laminated titanium alloys.

[0094]

[0095] Combining formulas (4), (5), and (14), the da / dN-ΔK model (15) of the TC4 / TB8 laminate structure based on the mechanical properties of a single-layer plate can be obtained. The predicted C and m values ​​based on the mechanical properties of single-layer TC4 and TB8 alloy plates are shown in Table 6. The model predicts C and m values ​​with small errors.

[0096]

[0097] Example 2

[0098] This embodiment provides a method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminates, comprising the following steps: preparing dissimilar titanium alloy diffusion-bonded laminates with different precipitate characteristics; conducting fatigue crack propagation experiments on dissimilar titanium alloy laminates obtained by different diffusion bonding and heat treatment processes; analyzing key parameters describing the fatigue crack propagation rate of the laminates and establishing relationships between these parameters to reduce parameter variables; conducting quasi-static uniaxial tensile tests on the laminates to obtain mechanical properties; conducting quasi-static uniaxial tensile tests on the dissimilar titanium alloy layers to obtain mechanical properties, and predicting the mechanical properties of the dissimilar titanium alloy laminates based on a mixing criterion; establishing a quantitative model of the fracture toughness of the laminates, considering key parameters describing the fatigue crack propagation rate of the laminates, and determining mechanical properties to describe the fatigue crack propagation rate; and determining the mechanical properties of the dissimilar titanium alloy layers based on the mechanical properties of the dissimilar titanium alloy laminates and the quantitative model of the fracture toughness of the laminates, thereby describing the relationship between the fatigue crack propagation rate of the laminates. This invention has the advantages of simple and convenient testing, meeting engineering accuracy, and being fast and practical, effectively reducing the testing cost and time required for crack propagation testing of dissimilar titanium alloy laminated structures processed with different parameters.

[0099] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for predicting the fatigue crack propagation rate of a diffusion-bonded laminate structure of dissimilar titanium alloys, characterized in that, The method includes the following steps: Preparation of diffusion-bonded laminated structures of dissimilar titanium alloys with different precipitate phase characteristics; Fatigue crack propagation experiments were conducted on dissimilar titanium alloy laminates obtained by different diffusion bonding and heat treatment processes. The key parameters describing the fatigue crack propagation rate of laminated structures are analyzed, and the relationships between these parameters are established to reduce parameter variables. Quasi-static uniaxial tensile tests were conducted on the laminated structure to obtain its mechanical properties; Quasi-static uniaxial tensile tests were conducted on dissimilar titanium alloy layers to obtain their mechanical properties, and the mechanical properties of the dissimilar titanium alloy laminate structure were predicted based on the mixing criterion. A quantitative model of fracture toughness for laminated structures is established, considering key parameters that describe the fatigue crack propagation rate of laminated structures, and mechanical properties are determined to describe the fatigue crack propagation rate. Based on the mechanical properties of dissimilar titanium alloy laminates and a quantitative model of fracture toughness of laminates, the mechanical properties of dissimilar titanium alloy layers are determined, and the relationship of fatigue crack propagation rate of laminates is described.

2. The method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminated structures according to claim 1, characterized in that, In the preparation of dissimilar titanium alloy diffusion-bonded laminates with different precipitate characteristics, the dissimilar titanium alloy laminates are prepared by diffusion bonding process, and the heat treatment process after diffusion bonding is changed. The heat treatment process includes solution treatment and isothermal aging treatment to obtain dissimilar titanium alloy diffusion-bonded laminates with different precipitate characteristics.

3. The method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminated structures according to claim 1, characterized in that, In the fatigue crack propagation experiment of dissimilar titanium alloy laminates obtained by different diffusion bonding and heat treatment processes, fatigue crack propagation experiments of dissimilar titanium alloy laminates are carried out. Based on the preparation of specimens obtained by diffusion bonding laminates of dissimilar titanium alloys with different precipitate phase characteristics, fatigue crack propagation specimens are first designed, including the specimen size and the defect characteristics and location that cause initial fatigue damage; then fatigue crack propagation experiments are carried out, including the initial crack pre-fabrication process and the subsequent crack propagation test process, and the cyclic external loading mode and fatigue crack propagation length observation criteria are designed.

4. The method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminated structures according to claim 1, characterized in that, The analysis describes the key parameters of the fatigue crack propagation rate of laminated structures and establishes the relationships between these parameters to reduce parameter variables. Based on fatigue crack propagation experiments on dissimilar titanium alloy laminated structures obtained through different diffusion bonding and heat treatment processes, fatigue crack propagation rate data for dissimilar titanium alloy laminated structures were obtained. The key parameter exponent of the Paris model for the fatigue crack propagation rate of laminated structures was analyzed. m Sum of coefficients C And establish relationships between parameters to reduce parameters.

5. The method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminated structures according to claim 1, characterized in that, In the process of conducting quasi-static uniaxial tensile tests on the laminated structure to obtain mechanical properties, the width of the tensile specimen of the dissimilar titanium alloy laminated structure is in the direction of the dissimilar titanium alloy stack, and the quasi-static uniaxial tensile direction is perpendicular to the direction of the dissimilar titanium alloy stack.

6. The method for predicting the fatigue crack propagation rate of a dissimilar titanium alloy diffusion-bonded laminate structure according to claim 1, characterized in that, Quasi-static uniaxial tensile tests were conducted on the dissimilar titanium alloy layers to obtain mechanical properties. Based on the mixing criterion, the mechanical properties of the dissimilar titanium alloy laminate structure were predicted. Referring to the heat treatment process of the dissimilar titanium alloy laminate structure, the single-layer titanium alloy plates underwent diffusion bonding thermal cycling and subsequent solution and aging treatments. The dimensions of the single-layer titanium alloy plate tensile specimens were consistent with those of the laminate structure specimens in the quasi-static uniaxial tensile tests. The tensile strain rate and extensometer specifications were consistent. Based on the mixing criterion of the mechanical properties of metal composite materials, the mechanical properties of the dissimilar titanium alloy laminate structure were predicted.

7. The method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminated structures according to claim 1, characterized in that, The proposed quantitative model for fracture toughness of laminated structures considers key parameters describing the fatigue crack propagation rate of laminated structures, determines mechanical properties to describe the fatigue crack propagation rate, and establishes a generalized model for the fracture toughness of dissimilar titanium alloy laminated structures based on the mechanical properties obtained from quasi-static uniaxial tensile tests on the laminated structures.

8. The method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminated structures according to claim 1, characterized in that, The mechanical properties of dissimilar titanium alloy laminates are determined based on the mechanical properties and fracture toughness quantitative model of the laminate structure. The relationship between the mechanical properties of the dissimilar titanium alloy layers and the fatigue crack propagation rate of the laminate structure is described by determining the mechanical properties of the dissimilar titanium alloy layers. The relationship between the mechanical properties of the dissimilar titanium alloy laminate structure and the mechanical properties of a single-layer titanium alloy is introduced into the generalized model of the fatigue crack propagation rate of the dissimilar titanium alloy laminate structure.

9. The method for predicting the fatigue crack propagation rate of dissimilar titanium alloy diffusion-bonded laminated structures according to claim 1, characterized in that, The dissimilar titanium alloy layers were subjected to quasi-static uniaxial tensile tests to obtain mechanical properties. Based on the mixing criterion, the mechanical properties of the dissimilar titanium alloy laminate structure were predicted, and the percentage error between the mechanical properties predicted by the mixing criterion and the experimental mechanical properties was controlled to be within 10%.

10. The method for predicting the fatigue crack propagation rate of a dissimilar titanium alloy diffusion-bonded laminate structure according to claim 1, characterized in that, The key parameters describing the fatigue crack propagation rate of laminated structures include the Paris parameter. C and m value, m and log C Directly related to and dependent on material properties.

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