Metal fatigue life prediction method under laser shock peening

Abstract

The application discloses a kind of metal fatigue life prediction methods under laser shock peening, it is related to metal material fatigue life prediction technical field.A kind of metal fatigue life prediction method under laser shock peening, comprising the following steps: roughness model construction, roughness evolution simulation, roughness value calculation, material attribute gives and fatigue life prediction.The application accurately predicts the roughness evolution of metal surface after laser shock peening by laser shock peening on real surface, then uses the method of combining Basquin-Manson-Coffin formula with continuous damage mechanics to predict fatigue life, fully considers the local complex stress-strain state under the roughness surface microstructure evolution after laser shock peening, truly simulates the fatigue progressive damage process of sample after considering laser shock peening, which can effectively improve the fatigue life prediction precision of metal after laser shock peening.

Description

Technical Field

[0001] The present invention relates to the technical field of metal material fatigue life prediction, and in particular to a metal fatigue life prediction method under laser shock strengthening. Background Art

[0002] The roughness of the metal surface is related to the forming method used. For example, the metal specimen obtained by additive manufacturing has a higher surface roughness than the metal specimen obtained by forging, but this will introduce many sharp micro-notches on the material surface and significantly reduce the fatigue strength of the metal specimen. At the same time, laser shock peening (LSP), as a material surface treatment technology, can improve the fatigue strength of metal specimens and extend their fatigue life. However, when using high-energy laser pulses to irradiate the material surface, it will induce severe plastic deformation on the metal surface, causing the roughness of the material surface to change, causing an extremely complex fatigue failure mechanism, and affecting the fatigue life prediction accuracy of the metal after laser shock peening. Therefore, when predicting the fatigue life of metal after laser shock peening (LSP), accurately simulating the evolution of the metal surface roughness after laser shock peening and incorporating its microscopic characteristics into the numerical prediction model is the key to improving the fatigue life prediction accuracy.

[0003] Based on the above situation, the present invention proposes a metal fatigue life prediction method under laser shock strengthening with high prediction accuracy. Summary of the Invention

[0004] In order to overcome the disadvantage that in the existing numerical simulation of laser shock peening, the surface of the sample is usually set to an ideal smooth surface without considering the initial roughness of the sample, and the differences in the uneven shock wave acting on the peaks and valleys of the micro-asperities and the roots of the micro-asperities in laser shock peening are ignored, resulting in a large error between the presented surface and the actual material surface after impact, which in turn leads to the low prediction accuracy of the model for metal fatigue life. The present invention proposes a metal fatigue life prediction method under laser shock peening with high prediction accuracy.

[0005] A method for predicting metal fatigue life under laser shock peening, comprising the following steps:

[0006] Roughness model construction: Based on the actual surface roughness, a two-dimensional round rod model with initial surface roughness is established. The two ends of the two-dimensional round rod model are completely fixed, and a simplified Johnson-Cook model suitable for high strain rate conditions is used to describe the stress-strain response behavior of the metal specimen.

[0007] Roughness evolution simulation: numerical simulation of laser shock peening of the rough surface of a two-dimensional round rod model. The uneven impact pressure causes plastic deformation between the peaks and valleys of the rough surface and reshapes the surface roughness. Then, displacement data of the sampling nodes on the surface of the two-dimensional round rod model is obtained. The displacement data is added to the initial coordinates of the corresponding nodes to obtain new profile data that can directly reflect the change in surface roughness of the sample after laser shock peening.

[0008] Roughness value calculation: Based on the surface roughness profile data of the sample after laser shock, the position of the center line of the sample surface profile is determined by the least squares method, and the surface roughness value of the sample after laser shock is calculated according to the position of the center line;

[0009] Material property assignment: A two-dimensional tensile fatigue specimen model is constructed based on the surface roughness profile data of the specimen after laser shock peening. The stress-strain response data of the specimen is obtained through tensile testing and used as the material property assignment for the two-dimensional tensile fatigue specimen model;

[0010] Fatigue life prediction and simulation combines continuous damage mechanics and fatigue life prediction formulas, and writes the USDFLD subroutine to simulate the fatigue progressive damage process of the sample after laser shock strengthening, realizing fatigue crack initiation life prediction and fatigue crack propagation simulation.

[0011] As a preferred aspect of the invention, the specific steps of establishing a two-dimensional round rod model with an initial surface roughness based on the actual surface roughness are:

[0012] Determine the true surface roughness parameter values, including the arithmetic mean deviation of the profile , maximum profile valley depth and maximum profile height ;

[0013] In Matlab software, the coordinate data of the roughness outer contour is randomly generated based on the parameter values ​​of the actual surface roughness through the Monte Carlo method, and the coordinate data is exported and saved as a TXT file;

[0014] The outer contour coordinate data was extracted from the TXT file using a Python script, and the coordinate data was imported into ABAQUS software to establish a two-dimensional circular rod model with initial roughness.

[0015] As a preferred aspect of the invention, the simplified Johnson-Cook model is expressed as follows:

[0016]

[0017] in represents the magnitude of stress, represents the equivalent plastic strain, represents the equivalent plastic strain rate, represents the reference strain rate, and 、 、 and is a material constant.

[0018] As a preferred aspect of the invention, the specific steps of numerically simulating the laser shock peening of the rough surface of the two-dimensional round rod model and obtaining the displacement data of the sampling nodes on the surface of the two-dimensional round rod model are as follows:

[0019] The VDLOAD subroutine is used to implement the application of laser shock wave on the rough surface. According to the formula, the peak pressure of the applied laser shock wave load is Calculation is performed, where the calculation formula is:

[0020]

[0021]

[0022] in The coefficient of internal energy conversion into thermal energy is in the range of , represents the laser energy density, Represents the reduced impact impedance between the target and the limiting medium, and are the acoustic resistance factors related to the material and the constraint layer, respectively;

[0023] In the one-dimensional expansion model, the laser spot pressure that obeys the Gaussian distribution in two-dimensional space is simplified into a one-dimensional function expression through the formula, where the specific formula is:

[0024]

[0025] in represents the radius of the laser spot, is the radial distance from the center of the laser spot, represents the distribution of shock pressure wave in two-dimensional space, The functional relationship between the shock pressure wave and time;

[0026] The Python script is used to batch extract the surface sampling nodes of the two-dimensional circular rod model in the numerical simulation results to obtain the displacement data of the surface sampling nodes of the two-dimensional circular rod model.

[0027] As a preferred aspect of the invention, based on the surface roughness profile data and using the least squares method to determine the position of the center line of the surface morphology profile of the sample after laser shock, the specific steps of calculating the surface roughness value of the sample after laser shock according to the position of the center line are as follows:

[0028] Project the measurement points in the surface roughness profile data onto a two-dimensional plane and establish a coordinate system, where the horizontal axis represents the horizontal position of the measurement point along the surface and the vertical axis represents the height value of the measurement point;

[0029] Use the least squares method to fit a straight line so that the sum of the squares of the vertical distances between the straight line and all measurement points is minimized. The equation of the fitted straight line can be expressed as: ,in Indicates the height of the center line. Indicates the horizontal position of the measuring point, and are the fitted straight line parameters, and represent the slope and intercept of the straight line respectively;

[0030] According to the principle of least squares method, the slope of the straight line and intercept Calculate and convert the slope and intercept Substitute the value of into the linear equation to obtain the position of the center line of the surface morphology profile of the sample after laser shock;

[0031] Calculate the arithmetic mean deviation of the profile of the sample after laser shock according to the position of the center line , maximum profile valley depth and maximum profile height .

[0032] As a preferred aspect of the invention, a two-dimensional tensile fatigue specimen model is constructed based on the surface roughness profile data of the sample after laser shock peening, and the stress-strain response data of the sample is obtained through a tensile test and the material properties of the two-dimensional tensile fatigue specimen model are assigned in the following specific steps:

[0033] A two-dimensional axisymmetric model was constructed. Based on the surface roughness profile data after laser shock peening, the surface morphology of the sample after shock was remodeled to obtain a two-dimensional tensile fatigue sample model.

[0034] According to the ASTM E8 / E8M-13a metal material tensile test method, a tensile test of the specimen was carried out to obtain the stress-strain response data of the specimen. The stress-strain curve of the specimen was fitted using the Ramberg-Osgood equation. The material properties of the two-dimensional tensile fatigue specimen model were assigned using the fitted stress-strain curve of the specimen. The Ramberg-Osgood equation is specifically as follows:

[0035]

[0036] in represents the cyclic enhancement coefficient, represents the cyclic strain hardening index, represents the cyclic elastic modulus.

[0037] As a preferred aspect of the invention, the specific steps of coupling the continuous damage mechanics and fatigue life prediction formulas and writing the USDFLD subroutine to predict the fatigue crack initiation life and simulate the fatigue crack growth are as follows:

[0038] Obtain the gradient-changing material parameters of the sample under laser shock;

[0039] The maximum strain of each element is extracted from the material parameters to calculate the strain amplitude, and the strain amplitude is used as the input value of the Basquin-Manson-Coffin formula to predict fatigue life. The general form of the Basquin-Manson-Coffin formula is:

[0040]

[0041] in represents the strain amplitude, represents fatigue life, represents the fatigue strength coefficient, represents the fatigue ductility coefficient, represents the fatigue strength index, represents the fatigue ductility index;

[0042] Using continuum damage mechanics and fatigue life The damage increment and total damage of the two-dimensional tensile fatigue specimen model under cyclic loading are calculated after each cycle. When the total damage reaches the damage threshold, the material is judged to have failed and the failed mesh elements are deleted. The specific calculation formulas for the damage increment and total damage are:

[0043]

[0044]

[0045] in Represents the damage variable of the material, and its value range is , represents the damage increment of the material after each cycle, Represents the total damage amount, and its value range is , It is a material parameter that indicates the material's ability to resist damage accumulation.

[0046] The present invention has the following advantages:

[0047] 1. The present invention adopts a model with initial roughness when performing numerical simulation of laser shock peening, which not only can truly reflect the initial surface state of the material, but also more accurately simulate the evolution process of surface roughness after laser shock peening and its influence on fatigue performance, so as to improve the credibility and reliability of the simulation results, but also helps researchers to conduct in-depth research on the interaction between initial roughness and laser shock parameters, and facilitates the subsequent optimization of the parameters of the laser shock peening process to achieve precise control of the surface roughness of the material and enhance the fatigue performance of the material.

[0048] 2. The present invention calculates the strain amplitude by extracting the maximum strain of each unit from the material parameters, and uses the strain amplitude as the input value of the Basquin-Manson-Coffin formula to predict the fatigue life. It fully considers the influence of roughness on the local stress-strain state. Based on the surface roughness evolution results after laser shock peening, the Basquin-Manson-Coffin formula is combined with continuous damage mechanics to predict the fatigue life. This method can not only fully consider the nonlinear characteristics of the material such as cyclic hardening and softening with the help of the Basquin-Manson-Coffin formula, but also use the maximum strain of each unit to reflect the local complex stress-strain state of the sample under the consideration of the evolution of the roughness surface microstructure, and truly simulate the fatigue progressive damage process of the sample after comprehensive consideration of laser shock peening, which can effectively improve the fatigue life prediction accuracy of the metal after laser shock peening.

[0049] 3. The present invention adopts continuous damage mechanics and utilizes fatigue life By calculating the damage increment and total damage of the two-dimensional tensile fatigue specimen model under cyclic load after each cycle, the damage can be nonlinearly accumulated, thereby describing in more detail the cumulative damage process of the material from no damage to failure and more accurately predicting the fatigue life of the material. This not only improves the accuracy of fatigue life prediction, but also provides more reliable data support for the life assessment of metals under complex loading conditions, thereby improving the prediction accuracy of metal fatigue life prediction methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 The figure is a simplified flow chart of a method for predicting metal fatigue life under laser shock strengthening adopted in an embodiment of the present invention.

[0051] Figure 2 A simplified flow chart of the life prediction and simulation steps used in an embodiment of the present invention.

[0052] Figure 3This is a schematic diagram of the model structure of a two-dimensional round rod model with initial roughness used in an embodiment of the present invention.

[0053] Figure 4 This is a comparison chart of the roughness results of the laser shock peening test and numerical simulation used in the embodiment of the present invention. DETAILED DESCRIPTION

[0054] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0055] Example 1, a method for predicting metal fatigue life under laser shock strengthening, the simplified process is as follows Figure 1 As shown, the following steps are included:

[0056] Roughness model construction: A two-dimensional round rod model with an initial surface roughness is established based on the real surface roughness parameters. The two ends of the two-dimensional round rod model are completely fixed, and a simplified Johnson-Cook model suitable for high strain rate conditions is used to describe the stress-strain response behavior of the specimen.

[0057] Roughness evolution simulation: numerical simulation of laser shock peening of the rough surface of a two-dimensional round rod model. The uneven impact pressure causes plastic deformation between the peaks and valleys of the rough surface and reshapes the surface roughness. Then, displacement data of the sampling nodes on the surface of the two-dimensional round rod model is obtained. The displacement data is added to the initial coordinates of the corresponding nodes to obtain new profile data that can directly reflect the change in surface roughness of the sample after laser shock peening.

[0058] Roughness value calculation: Based on the surface roughness profile data of the sample after laser shock, the position of the center line of the sample surface profile is determined by the least squares method, and the surface roughness value of the sample after laser shock is calculated according to the position of the center line;

[0059] Material property assignment: A two-dimensional tensile fatigue specimen model is constructed based on the surface roughness profile data of the specimen after laser shock peening. The stress-strain response data of the specimen is obtained through tensile testing and used as the material property assignment for the two-dimensional tensile fatigue specimen model;

[0060] Life prediction and simulation, combining continuous damage mechanics and fatigue life prediction formulas, and writing USDFLD subroutine to simulate the fatigue progressive damage process of the sample after laser shock strengthening, to achieve fatigue crack initiation life prediction and fatigue crack growth simulation. The simplified process of this step is as follows Figure 2 shown.

[0061] The specific steps for establishing a two-dimensional round rod model with initial surface roughness based on the real surface roughness parameters are as follows:

[0062] Determine the true surface roughness parameter values, including the arithmetic mean deviation of the profile , maximum profile valley depth and maximum profile height ;

[0063] In Matlab software, the coordinate data of the roughness outer contour is randomly generated based on the parameter value of the target roughness through the Monte Carlo method, and the coordinate data is exported and saved as a TXT file;

[0064] The outer contour coordinate data was extracted from the TXT file using a Python script, and the coordinate data was imported into ABAQUS software to establish a two-dimensional circular rod model with initial roughness.

[0065] The simplified Johnson-Cook model is expressed as follows:

[0066]

[0067] in represents the magnitude of stress, represents the equivalent plastic strain, represents the equivalent plastic strain rate, represents the reference strain rate, and 、 、 and is a material constant.

[0068] It should be noted that the complete Johnson-Cook model is expressed as:

[0069]

[0070] However, since a sacrificial ablation layer is used in laser shock peening, the temperature effect in the second half of the formula can be ignored.

[0071] The specific steps for numerically simulating the laser shock peening of the rough surface of a two-dimensional round rod model and obtaining the displacement data of the sampling nodes on the surface of the two-dimensional round rod model are as follows:

[0072] Use the VDLOAD subroutine to implement the application of laser shock waves on rough surfaces, such as Figure 3 As shown, according to the formula, the peak pressure of the applied laser shock wave load Calculation is performed, where the calculation formula is:

[0073]

[0074]

[0075] in The coefficient of internal energy conversion into thermal energy is in the range of , represents the laser energy density, Represents the reduced impact impedance between the target and the limiting medium, and are the acoustic resistance factors related to the material and the constraint layer, respectively;

[0076] In the one-dimensional expansion model, the laser spot pressure that obeys the Gaussian distribution in two-dimensional space is simplified into a one-dimensional function expression through the formula, where the specific formula is:

[0077]

[0078] in represents the radius of the laser spot, is the radial distance from the center of the laser spot, represents the distribution of shock pressure wave in two-dimensional space, The functional relationship between the shock pressure wave and time;

[0079] The Python script is used to batch extract the surface sampling nodes of the two-dimensional circular rod model in the numerical simulation results to obtain the displacement data of the surface sampling nodes of the two-dimensional circular rod model.

[0080] The above steps, by using a model with initial roughness when conducting numerical simulations of laser shock peening, can not only truly reflect the initial surface state of the material, thereby more accurately simulating the evolution of surface roughness after laser shock peening and its impact on fatigue performance, thereby improving the credibility and reliability of the simulation results, but also help researchers to conduct in-depth research on the interaction between initial roughness and laser shock parameters, facilitate subsequent optimization of laser shock peening process parameters, so as to achieve precise control of material surface roughness, enhance the material's fatigue performance and stress corrosion resistance, and improve the prediction accuracy of metal fatigue life prediction methods.

[0081] Based on the surface roughness profile data, the position of the center line of the surface morphology profile of the sample after laser shock is determined by the least squares method. The specific steps for calculating the surface roughness value of the sample after laser shock according to the position of the center line are as follows:

[0082] Project the measurement points in the surface roughness profile data onto a two-dimensional plane and establish a coordinate system, where the horizontal axis represents the horizontal position of the measurement point along the surface and the vertical axis represents the height value of the measurement point;

[0083] Use the least squares method to fit a straight line so that the sum of the squares of the vertical distances between the straight line and all measurement points is minimized. The equation of the fitted straight line can be expressed as: ,in Indicates the height of the center line. Indicates the horizontal position of the measuring point, and are the fitted straight line parameters, and represent the slope and intercept of the straight line respectively;

[0084] According to the principle of least squares method, the slope of the straight line and intercept Calculate and convert the slope and intercept Substitute the value of into the linear equation to obtain the position of the center line of the surface morphology profile of the sample after laser shock;

[0085] Calculate the arithmetic mean deviation of the profile of the sample after laser shock according to the position of the center line , maximum profile valley depth and maximum profile height .

[0086] It should be noted that in order to verify the accuracy of the roughness evolution numerical model, the same LSP process parameters as those in the literature [Dyer, K., Ghadar, S., Zulić, S., Rostohar, D., Asadi, E., & Molaei, R. (2024). Effect of laser shock peening on surface roughness and fatigue behavior of additively manufactured Ti-6Al-4V alloy. Coatings, 14(1), 110.] were used to perform LSP numerical simulation on the sample, that is, the overlap rate was 50%, the laser energy density was 4.15 , the spot size is 0.0841 , and compared with the LSP roughness test results in the literature, considering the credibility of the results, the maximum profile valley depth of the roughness model established and the roughness model of the test specimen To keep consistent, the roughness results of LSP test and numerical simulation are compared. Figure 4 As shown, the g1, g2 and g4 comparison groups have good consistency, with relative error values ​​of 1.6%, 2.6% and 0.14%, respectively, while the relative error value of the g3 comparison group is slightly larger, at 16.5%.

[0087] The specific steps for constructing a two-dimensional tensile fatigue specimen model based on the surface roughness profile data of the sample after laser shock peening, obtaining the stress-strain response data of the sample through a tensile test, and assigning material properties to the two-dimensional tensile fatigue specimen model are as follows:

[0088] A two-dimensional axisymmetric model was constructed. Based on the surface roughness profile data after laser shock peening, the surface morphology of the sample after shock was remodeled to obtain a two-dimensional tensile fatigue sample model.

[0089] According to the ASTM E8 / E8M-13a metal material tensile test method, a tensile test of the specimen was carried out to obtain the stress-strain response data of the specimen. The stress-strain curve of the specimen was fitted using the Ramberg-Osgood equation. The material properties of the two-dimensional tensile fatigue specimen model were assigned using the fitted stress-strain curve of the specimen. The Ramberg-Osgood equation is specifically as follows:

[0090]

[0091] in represents the cyclic enhancement coefficient, represents the cyclic strain hardening index, represents the cyclic elastic modulus.

[0092] The specific steps for coupling the continuum damage mechanics and fatigue life prediction formulas and writing the USDFLD subroutine to predict fatigue crack initiation life and simulate fatigue crack growth are as follows:

[0093] Obtain the gradient-changing material parameters of the sample under laser shock;

[0094] The maximum strain of each element is extracted from the material parameters to calculate the strain amplitude, and the strain amplitude is used as the input value of the Basquin-Manson-Coffin formula to predict fatigue life. The general form of the Basquin-Manson-Coffin formula is:

[0095]

[0096] in represents the strain amplitude, represents fatigue life, represents the fatigue strength coefficient, represents the fatigue ductility coefficient, represents the fatigue strength index, represents the fatigue ductility index;

[0097] Using continuum damage mechanics and fatigue life The damage increment and total damage of the two-dimensional tensile fatigue specimen model under cyclic loading are calculated after each cycle. When the total damage reaches the damage threshold (the damage threshold is 0.999 in this embodiment), the material is judged to have failed and the failed mesh elements are deleted. The specific calculation formulas for the damage increment and total damage are:

[0098]

[0099]

[0100] in Represents the damage variable of the material, and its value range is , represents the damage increment of the material after each cycle, Represents the total damage amount, and its value range is , It is a material parameter that indicates the material's ability to resist damage accumulation.

[0101] The above steps predict fatigue life based on the surface roughness evolution results after laser shock peening by combining the Basquin-Manson-Coffin formula with continuum damage mechanics. This not only fully considers the nonlinear characteristics of the material such as cyclic hardening and softening with the help of the Basquin-Manson-Coffin formula, but also uses the maximum strain of each unit to reflect the local complex stress-strain state of the sample under the consideration of the microstructural evolution of the roughness surface. It truly simulates the progressive fatigue damage process of the sample after comprehensive consideration of laser shock peening, which can effectively improve the fatigue life prediction accuracy of the metal after laser shock peening.

[0102] The above steps are achieved by using continuum damage mechanics and combining fatigue life By calculating the damage increment and total damage of the two-dimensional tensile fatigue specimen model under cyclic load after each cycle, the nonlinear accumulation of damage can be achieved, thereby describing in more detail the cumulative damage accumulation process of the material from no damage to failure and more accurately predicting the fatigue life of the material. This not only improves the accuracy of fatigue life prediction, but also provides more reliable data support for the life assessment of metals under complex loading conditions, thereby improving the prediction accuracy of metal fatigue life prediction methods.

[0103] It should be understood that those skilled in the art may make improvements or modifications based on the above description, and all such improvements and modifications shall fall within the scope of protection of the appended claims. Any portion of this specification not described in detail is prior art known to those skilled in the art.

Claims

1. A method for predicting metal fatigue life under laser shock peening, characterized in that: The following steps are involved: Roughness model construction: Based on the actual surface roughness, a two-dimensional round rod model with initial surface roughness is established. The two ends of the two-dimensional round rod model are completely fixed, and a simplified Johnson-Cook model suitable for high strain rate conditions is used to describe the stress-strain response behavior of the metal specimen. Roughness evolution simulation: numerical simulation of laser shock peening of the rough surface of a two-dimensional round rod model is performed. The uneven impact pressure causes plastic deformation between the peaks and valleys of the rough surface and reshapes the surface roughness. Then, the displacement data of the sampling nodes on the surface of the two-dimensional round rod model is obtained. The displacement data is added to the initial coordinates of the corresponding nodes to obtain new profile data that can directly reflect the change in surface roughness of the sample after laser shock peening. The specific steps are as follows: The VDLOAD subroutine is used to implement the application of laser shock wave on the rough surface. According to the formula, the peak pressure of the applied laser shock wave load is Calculation is performed, where the calculation formula is: in The coefficient of internal energy conversion into thermal energy is in the range of , represents the laser energy density, Represents the reduced impact impedance between the target and the limiting medium, and are the acoustic resistance factors related to the material and the constraint layer, respectively; In the one-dimensional expansion model, the laser spot pressure that obeys the Gaussian distribution in two-dimensional space is simplified into a one-dimensional function expression through the formula, where the specific formula is: in represents the radius of the laser spot, is the radial distance from the center of the laser spot, represents the distribution of shock pressure wave in two-dimensional space, The functional relationship between the shock pressure wave and time; Use Python script to batch extract the surface sampling nodes of the two-dimensional circular rod model in the numerical simulation results to obtain the displacement data of the surface sampling nodes of the two-dimensional circular rod model; Roughness value calculation: Based on the surface roughness profile data of the sample after laser shock, the position of the center line of the surface morphology profile of the sample after laser shock is determined by the least squares method, and the surface roughness value of the sample after laser shock is calculated according to the position of the center line; Material property assignment: A two-dimensional tensile fatigue specimen model is constructed based on the surface roughness profile data of the specimen after laser shock peening. The stress-strain response data of the specimen is obtained through tensile testing and used as the material property assignment for the two-dimensional tensile fatigue specimen model; Fatigue life prediction and simulation combines continuous damage mechanics and fatigue life prediction formulas, and writes the USDFLD subroutine to simulate the fatigue progressive damage process of the sample after laser shock strengthening, realizing fatigue crack initiation life prediction and fatigue crack propagation simulation.

2. The metal fatigue life prediction method under laser shock peening according to claim 1, characterized in that: The specific steps for establishing a two-dimensional round rod model with initial surface roughness based on the actual surface roughness are as follows: Determine the true surface roughness parameter values, including the arithmetic mean deviation of the profile , maximum profile valley depth and maximum profile height ; In Matlab software, the coordinate data of the roughness outer contour is randomly generated based on the parameter values ​​of the actual surface roughness through the Monte Carlo method, and the coordinate data is exported and saved as a TXT file; The outer contour coordinate data was extracted from the TXT file using a Python script, and the coordinate data was imported into ABAQUS software to establish a two-dimensional circular rod model with initial roughness.

3. The metal fatigue life prediction method under laser shock peening according to claim 2, characterized in that: The simplified Johnson-Cook model is expressed as follows: in represents the magnitude of stress, represents the equivalent plastic strain, represents the equivalent plastic strain rate, represents the reference strain rate, and 、 、 and is a material constant.

4. The metal fatigue life prediction method under laser shock strengthening according to claim 3, characterized in that: Based on the surface roughness profile data, the position of the center line of the surface morphology profile of the sample after laser shock is determined by the least squares method. The specific steps for calculating the surface roughness value of the sample after laser shock according to the position of the center line are as follows: Project the measurement points in the surface roughness profile data onto a two-dimensional plane and establish a coordinate system, where the horizontal axis represents the horizontal position of the measurement point along the surface and the vertical axis represents the height value of the measurement point; Use the least squares method to fit a straight line so that the sum of the squares of the vertical distances between the straight line and all measurement points is minimized. The equation of the fitted straight line can be expressed as: ,in Indicates the height of the center line. Indicates the horizontal position of the measuring point, and are the fitted straight line parameters, and represent the slope and intercept of the straight line respectively; According to the principle of least squares method, the slope of the straight line and intercept Calculate and convert the slope and intercept Substitute the value of into the linear equation to obtain the position of the center line of the surface morphology profile of the sample after laser shock; Calculate the arithmetic mean deviation of the profile of the sample after laser shock according to the position of the center line , maximum profile valley depth and maximum profile height .

5. The metal fatigue life prediction method under laser shock strengthening according to claim 4, characterized in that: The specific steps for constructing a two-dimensional tensile fatigue specimen model based on the surface roughness profile data of the sample after laser shock peening and obtaining the stress-strain response data of the sample through tensile testing and assigning it as the material properties of the two-dimensional tensile fatigue specimen model are as follows: A two-dimensional axisymmetric model was constructed. Based on the surface roughness profile data after laser shock peening, the surface morphology of the sample after shock was remodeled and embedded into the two-dimensional axisymmetric model to obtain a two-dimensional tensile fatigue sample model. According to the ASTM E8 / E8M-13a metal material tensile test method, a tensile test of the metal specimen was carried out to obtain the stress-strain response data of the metal specimen. The stress-strain curve of the metal specimen was fitted using the Ramberg-Osgood equation. The material properties of the two-dimensional tensile fatigue specimen model were assigned using the fitted stress-strain curve of the metal specimen. The Ramberg-Osgood equation is specifically as follows: in represents the cyclic enhancement coefficient, represents the cyclic strain hardening index, represents the cyclic elastic modulus.

6. The metal fatigue life prediction method under laser shock peening according to claim 5, characterized in that: Combining the continuous damage mechanics and fatigue life prediction formulas, and writing the USDFLD subroutine to simulate the fatigue progressive damage process of the sample after laser shock strengthening, the specific steps to achieve fatigue crack initiation life prediction and fatigue crack growth simulation are as follows: Obtain the gradient-changing material parameters of the sample under laser shock; The maximum strain of each element is extracted from the material parameters to calculate the strain amplitude, and the strain amplitude is used as the input value of the Basquin-Manson-Coffin formula to predict fatigue life. The general form of the Basquin-Manson-Coffin formula is: in represents the strain amplitude, represents fatigue life, represents the fatigue strength coefficient, represents the fatigue ductility coefficient, represents the fatigue strength index, represents the fatigue ductility index; Using continuum damage mechanics and fatigue life The damage increment and total damage of the two-dimensional tensile fatigue specimen model under cyclic loading are calculated after each cycle. When the total damage reaches the damage threshold, the material is judged to have failed and the failed mesh elements are deleted. The specific calculation formulas for the damage increment and total damage are: in Represents the damage variable of the material, and its value range is , represents the damage increment of the material after each cycle, Represents the total damage amount, and its value range is , It is a material parameter that indicates the material's ability to resist damage accumulation.

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