Titanium alloy three-point bending fatigue life prediction method considering tungsten clamping defect

Abstract

According to the titanium alloy three-point bending fatigue life prediction method considering the tungsten clamping defect, tungsten clamping defects of different sizes are introduced into a TC4 titanium alloy welded joint by introducing a defect method, and three-point bending fatigue tests of TC4 titanium alloy welded joint test pieces under different defect sizes are carried out through a fatigue testing machine; obtaining the three-point bending fatigue life of the welding joint test piece under the fatigue loading stress amplitude; the method comprises the following steps: establishing a three-point bending fatigue life prediction model considering a tungsten clamping defect by combining a Basquin theory and a Goodman theory, and calibrating various physical parameters in a formula according to the measured fatigue life of a welding joint test piece under different defect sizes; through the fatigue life prediction model, the fatigue life of the titanium alloy welding joint under different tungsten clamping defect characteristics can be predicted, and the method has important guiding significance on optimization of process parameters and formulation of a maintenance period of the titanium alloy welding joint.

Description

Technical Field

[0001] The present invention belongs to the technical field of fatigue performance evaluation of key mechanical welding components, and particularly relates to a method for predicting the three-point bending fatigue life of titanium alloy considering tungsten inclusion defects. Background Art

[0002] Titanium alloy, as a light alloy, is gradually used in armored vehicles. The vehicle shell plates are subjected to dynamic loads such as bending and torsion during service. However, the influence mechanism of internal tungsten inclusion defects on the bending fatigue performance of titanium alloy welded joints is not yet clear. Therefore, it is of great guiding significance for the optimization of titanium alloy welding process to carry out the fatigue mechanism research on titanium alloy welded joints with tungsten inclusion defects and establish a relationship model between tungsten inclusion defects and fatigue life of titanium alloy welded joints. At present, most studies analyze the fatigue performance of titanium alloy welded joints from the perspectives of microstructure, residual stress, surface defects, process optimization, etc. There are few studies on the fatigue failure mechanism of titanium alloy bending caused by internal tungsten inclusion defects, and the research on the prediction of bending fatigue life of titanium alloy welded joints considering internal tungsten inclusion defects is not perfect. It is necessary to explore the influence law of tungsten inclusion defects on the fatigue life of titanium alloy welded joint specimens, establish a method for predicting the bending fatigue life of titanium alloy welded joints considering the size of tungsten inclusion defects, and provide technical support for the process optimization of anti-fatigue titanium alloy welded joints. Summary of the Invention

[0003] (1) Technical Problems to be Solved

[0004] The present invention proposes a method for predicting the three-point bending fatigue life of titanium alloy considering tungsten inclusion defects to solve the technical problem of how to predict the three-point bending fatigue life of titanium alloy with tungsten inclusion defects.

[0005] (2) Technical Solutions

[0006] To solve the above technical problems, the present invention proposes a method for predicting the three-point bending fatigue life of titanium alloy considering tungsten inclusion defects. The method for predicting the three-point bending fatigue life of titanium alloy includes the following steps:

[0007] S1. Prepare titanium alloy three-point bending welded joint specimens and introduce different tungsten inclusion defect sizes into the specimens;

[0008] S2. Use a CT device to characterize the welding area of the titanium alloy three-point bending welded joint specimens, obtain tungsten inclusion defect photos of the welded joint specimens, and analyze the quantity, size, depth and shape characteristics of the tungsten inclusion defects according to the tungsten inclusion defect photos;

[0009] S3. Based on the actual service conditions of the titanium alloy three-point bending welded joint, static bending mechanical experiments and bending fatigue experiments are carried out on the titanium alloy three-point bending welded joint specimens with different tungsten inclusion defect sizes obtained in step S1, and the static bending curves and bending fatigue lives of the titanium alloy three-point bending welded joint specimens with different tungsten inclusion defect sizes are obtained;

[0010] S4. Combining the Basquin theory and the Goodman theory, a fatigue life prediction formula for titanium alloy welded joints considering tungsten inclusions is established as follows:

[0011]

[0012] where, N f is the fatigue life; σ a is the fatigue stress amplitude; σ uss is the maximum bending stress; σ m is the mean stress; b is the fatigue strength index, is the equivalent defect area of multiple tungsten inclusions, which is calculated according to the following formula:

[0013]

[0014] where, n is the number of defects; area n is the projected area of the nth defect;

[0015] S5. According to the fatigue test conditions and the static bending curve obtained in step S4, the values of σ a , σ uss and σ m are determined, and the relationship between the fatigue life and in formula (1) is fitted to obtain a titanium alloy three-point bending fatigue life prediction model, and the titanium alloy three-point bending fatigue life is predicted based on this model.

[0016] Furthermore, in step S1, titanium alloy three-point bending welded joint specimens are prepared by tungsten inert gas welding. During the preparation process, the tungsten electrode tip is controlled to contact the weld, and the tungsten tip is broken and retained in the molten weld to obtain titanium alloy three-point bending welded joint specimens with different tungsten inclusion defect sizes.

[0017] Furthermore, in step S2, the characterization parameters are: tube voltage 100 kV, tube current 1.5 mA, focal spot size 0.4 mm, and sampling time 45 milliseconds.

[0018] Further, in step S3, a three-point bending fatigue test of a titanium alloy three-point bending welded joint is carried out on a fatigue testing machine, and the fatigue test refers to JB / T7716-95; a three-point static bending test is carried out on a titanium alloy welded joint specimen with tungsten inclusion defects through a fatigue testing machine, and the static bending test refers to the GB / T232-2024 standard to obtain a static bending curve and a bending fracture photo.

[0019] Further, in step S3, the frequency of the three-point bending fatigue test is 10 Hz, the loading waveform is a sine wave, the stress amplitude is 275 MPa, the mean stress is 825 MPa, the stress ratio R is 0.5, and the test temperature is room temperature.

[0020] Further, in step S3, the loading rate of the static bending test is 0.5 mm / min.

[0021] Further, in step S5, σ a takes 275 MPa, σ uss is 1777 MPa, σ m is 825 MPa, and after fitting, a prediction model is obtained as shown in the following formula:

[0022]

[0023] Among them, the determination coefficient of the fitting function is ~98.5%.

[0024] (III) Beneficial Effects

[0025] The present invention proposes a method for predicting the three-point bending fatigue life of a titanium alloy considering tungsten inclusion defects. By introducing tungsten inclusion defects of different sizes into the TC4 titanium alloy welded joint through the defect introduction method, a three-point bending fatigue test of the TC4 titanium alloy welded joint specimen with different defect sizes is carried out through a fatigue testing machine to obtain the three-point bending fatigue life of the welded joint specimen under the fatigue loading stress amplitude; a three-point bending fatigue life prediction model considering tungsten inclusion defects is established by combining the Basquin theory and the Goodman theory, and each physical parameter in the formula is calibrated according to the measured fatigue life of the welded joint specimen with different defect sizes. Through the above fatigue life prediction model, the fatigue life of the titanium alloy welded joint with different tungsten inclusion defect characteristics can be predicted, which has important guiding significance for the process parameter optimization and maintenance period formulation of the titanium alloy welded joint. Description of the Drawings

[0026] Figure 1 is a flow chart of the method for predicting the three-point bending fatigue life of a titanium alloy of the present invention;

[0027] Figure 2 is a schematic structural diagram of a titanium alloy welded joint specimen with tungsten inclusion defects of the present invention;

[0028] Figure 3 The static bending curve of the titanium alloy welded specimen with tungsten inclusion defects of the present invention;

[0029] Figure 4 The relationship diagram between the fatigue life of the titanium alloy welded joint and the equivalent area of tungsten inclusion defects of the present invention. Specific embodiments

[0030] To make the objectives, contents and advantages of the present invention clearer, the following further describes in detail the specific embodiments of the present invention with reference to the drawings and embodiments.

[0031] This embodiment proposes a method for predicting the three-point bending fatigue life of a titanium alloy considering tungsten inclusion defects, and its process is as Figure 1 shown, mainly including the following steps:

[0032] S1. Prepare a three-point bending welded joint specimen of titanium alloy by tungsten inert gas welding. During the preparation process, control the tungsten electrode tip to contact the weld seam, break the tungsten tip and retain it in the molten weld seam to obtain a three-point bending welded joint specimen of titanium alloy with different tungsten inclusion defect sizes.

[0033] S2. Use an industrial CT device (CD-500Bx) to characterize the welding area of the three-point bending welded joint specimen of titanium alloy. The characterization parameters are: tube voltage 100 kV, tube current 1.5 mA, focal spot size 0.4 mm, and sampling time 45 milliseconds. Obtain the tungsten inclusion defect photos of the welded joint specimen through the industrial CT device, and analyze the characteristics such as the number, size, depth and shape of the tungsten inclusion defects based on the tungsten inclusion defect photos.

[0034] S3. Based on the actual service conditions of the three-point bending welded joint of titanium alloy, conduct static bending mechanical experiments and bending fatigue experiments on the three-point bending welded joint specimens of titanium alloy with different tungsten inclusion defect sizes obtained in step S1 to obtain the static bending curves and bending fatigue lives of the three-point bending welded joint specimens of titanium alloy with different tungsten inclusion defect sizes.

[0035] In this embodiment, conduct a three-point bending fatigue experiment on the three-point bending welded joint of titanium alloy on a fatigue testing machine of model HDT-105A. The fatigue experiment refers to JB / T 7716-95. The frequency of the three-point bending fatigue experiment is 10 Hz, the loading waveform is a sine wave, the stress amplitude is 275 MPa, the mean stress is 825 MPa, the stress ratio R is 0.5, the experimental temperature is room temperature, and the structure of the tungsten inclusion defect titanium alloy welded joint specimen is as Figure 2 shown. Conduct a three-point static bending experiment on the tungsten inclusion defect titanium alloy welded joint specimen through the fatigue testing machine. The static bending experiment refers to the GB / T232-2024 standard, and the loading rate is 0.5 mm / min to obtain the static bending curve (as Figure 3as shown) and the bending fracture photos.

[0036] S4. Combine the Basquin theory and the Goodman theory to establish a fatigue life prediction formula for titanium alloy welded joints considering tungsten inclusions defects, as follows:

[0037]

[0038] where, N f is the fatigue life; σ a is the fatigue stress amplitude; σ uss is the maximum bending stress; σ m is the mean stress; b is the fatigue strength index, is the equivalent defect area of multiple tungsten inclusions defects, calculated according to the following formula:

[0039]

[0040] where, n is the number of defects; area n is the projected area of the nth defect;

[0041] S5. According to the static bending curve obtained from the fatigue test conditions and step S4, determine the values of σ a , σ uss and σ m , fit the relationship between the fatigue life and in formula (1) to obtain a three-point bending fatigue life prediction model for titanium alloy, and predict the three-point bending fatigue life of titanium alloy based on this model.

[0042] In this embodiment, σ a is taken as 275 MPa, σ uss is 1777 MPa, σ m is 825 MPa. After fitting, the prediction model is obtained as follows:

[0043]

[0044] where, the determination coefficient of the fitting function is ~98.5%.

[0045] To verify the accuracy of the prediction model, predict the fatigue life of the titanium alloy welded joint specimens. The results are as shown by the triangles in Figure 4 . By comparing the gap between the verification experimental data and the prediction curve, the estimated error of the model is ~6.64%, indicating that the prediction accuracy of the model obtained in the present invention is relatively high.

[0046] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for predicting the fatigue life of titanium alloy three-point bending considering tungsten inclusion defects, characterized in that: The titanium alloy three-point bending fatigue life prediction method comprises the following steps: S1. Prepare titanium alloy three-point bending welded joint specimens and introduce different tungsten inclusion defect sizes into the specimens; S2 used CT equipment to characterize the welding area of ​​the titanium alloy three-point bending welded joint specimen, obtained photos of tungsten inclusion defects in the welded joint specimen, and analyzed the number, size, depth and shape characteristics of the tungsten inclusion defects based on the photos of tungsten inclusion defects; S3. Based on the actual service conditions of the titanium alloy three-point bending welded joint, static bending mechanics tests and bending fatigue tests are performed on the titanium alloy three-point bending welded joint specimens with different tungsten inclusion defect sizes obtained in step S1 to obtain static bending curves and bending fatigue lives of the titanium alloy three-point bending welded joint specimens with different tungsten inclusion defect sizes; S4. Combining Basquin theory and Goodman theory, the fatigue life prediction formula of titanium alloy welded joints considering tungsten inclusion defects is established as follows: Among them, N f is fatigue life; a is the fatigue stress amplitude; σ uss is the maximum bending stress; σ m is the mean stress; b is the fatigue strength index, is the equivalent defect area of ​​multiple tungsten inclusion defects, calculated according to the following formula: Where n is the number of defects; area n is the projection area of ​​the nth defect; S5. Determine σ according to the fatigue test conditions and the static bending curve obtained in step S4. a , σ uss and σ m The value of is, for the fatigue life and The relationship between the three-point bending fatigue life of titanium alloy is fitted to obtain the three-point bending fatigue life prediction model of titanium alloy. The three-point bending fatigue life of titanium alloy is predicted based on the model.

2. The method for predicting the three-point bending fatigue life of titanium alloy considering tungsten inclusion defects as claimed in claim 1, characterized in that: In step S1, a titanium alloy three-point bending weld joint specimen is prepared by tungsten inert gas welding. During the preparation process, the tungsten electrode tip is controlled to contact the weld, and the tungsten tip is broken and retained in the molten weld, thereby obtaining a titanium alloy three-point bending weld joint specimen with different tungsten defect sizes introduced.

3. The method for predicting the three-point bending fatigue life of titanium alloy considering tungsten inclusion defects as claimed in claim 1, characterized in that: In step S2, the characterization parameters are: tube voltage 100 kV, tube current 1.5 Ma, focal spot size 0.4 mm, sampling time 45 milliseconds.

4. The method for predicting the three-point bending fatigue life of titanium alloy considering tungsten inclusion defects as claimed in claim 1, characterized in that: In step S3, a three-point bending fatigue test of the titanium alloy three-point bending welded joint is carried out on a fatigue testing machine, and the fatigue test refers to JB / T 7716-95; a three-point static bending test is carried out on the titanium alloy welded joint specimen with tungsten defects by using a fatigue testing machine, and the static bending test refers to GB / T 232-2024 standard to obtain a static bending curve and a bending fracture photograph.

5. The method for predicting the three-point bending fatigue life of titanium alloy considering tungsten inclusion defects as claimed in claim 4, characterized in that: In step S3, the frequency of the three-point bending fatigue test is 10 Hz, the loading waveform is a sine wave, the stress amplitude is 275 MPa, the average stress is 825 MPa, the stress ratio R is 0.5, and the experimental temperature is room temperature.

6. The method for predicting the three-point bending fatigue life of titanium alloy considering tungsten inclusion defects as claimed in claim 4, characterized in that: In step S3, the loading rate of the static bending test is 0.5 mm / min.

7. The titanium alloy three-point bending fatigue life prediction method considering tungsten inclusion defects as claimed in claim 1, characterized in that: In step S5, σ a Take 275MPa, σ uss is 1777MPa, σ m is 825MPa. After fitting, the prediction model is obtained as shown in the following formula: The coefficient of determination of the fitting function was ∼98.5%.

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