A gear fatigue life prediction method based on laser shock peening composite reinforcement

Abstract

The present application relates to the technical field of fatigue life prediction, and discloses a gear fatigue life prediction method based on laser shock peening composite strengthening, wherein the first residual stress field of the gear strengthening area after laser shock peening is determined according to laser shock process parameters and gear material parameters, the second residual stress field after peening strengthening is determined based on the ball cavity expansion model and the contact mechanics theory, combined with the peening process parameters and the material parameters, the first residual stress field is coupled with the second residual stress field as the initial stress state before peening strengthening, the equivalent residual stress field after laser peening composite strengthening is obtained, and finally the fatigue cycle number of the gear is calculated through the fatigue life conversion model. The method can reflect the stress coupling effect in the laser shock and peening composite strengthening process, and can realize the prediction of the gear fatigue life after laser shock peening composite strengthening for high-performance service gears in the aviation field.

Description

Technical Field

[0001] This invention relates to the field of fatigue life prediction technology, and discloses a method for predicting the fatigue life of gears based on laser shock peening composite reinforcement. Background Technology

[0002] The transmission system is a core functional component of high-end equipment such as aero-engines and helicopter main gearboxes. Gear components, in particular, endure high-speed alternating loads, strong contact stresses, and complex service conditions over extended periods. Bending fatigue and contact fatigue are their main failure modes, directly determining the operational reliability and service life of the equipment. To improve the fatigue resistance and service life of high-performance gears in the aerospace field, surface strengthening technology has become a core process in high-performance gear manufacturing. Laser shock peening and shot peening are currently the two most widely used surface strengthening technologies in industry. However, current methods for predicting the service life of strengthened gears are mostly based on single laser shock peening or single shot peening scenarios, lacking methods for predicting the fatigue life of gears after combined laser shock peening and shot peening strengthening. Summary of the Invention

[0003] The purpose of this invention is to provide a method for predicting the fatigue life of gears based on laser shock peening composite strengthening, which can predict the fatigue life of high-performance service gears in the aerospace field after laser shock peening composite strengthening.

[0004] To achieve the above-mentioned technical effects, the technical solution adopted by the present invention is as follows: A method for predicting the fatigue life of gears based on laser shock peening composite strengthening includes the following steps: Based on the laser shock process parameters and the gear material parameters, the first residual stress field on the surface of the gear strengthening area after laser shock strengthening was analyzed and determined. Based on the shot peening process parameters and the material parameters, the second residual stress field on the surface of the gear reinforcement region after shot peening is determined using the spherical cavity expansion model and the Johnson-Cook constitutive model of the gear. The first residual stress field is used as the initial stress state of the gear strengthening area surface before shot peening, and coupled with the second residual stress field to obtain the equivalent residual stress field of the gear strengthening area surface after laser shot peening composite strengthening. Based on the equivalent residual stress field, the number of cycles of the gear under the design conditions is calculated using a fatigue life conversion model, which serves as the predicted fatigue life value of the gear.

[0005] Furthermore, based on the laser shock process parameters and the gear material parameters, the steps for analyzing and determining the first residual stress field on the surface of the laser-strengthened gear region include: The peak pressure of the shock wave generated when the laser impacts the surface of the gear reinforcement area is determined based on the laser absorption intensity. The dynamic yield strength of the gear is determined based on the first Lamé coefficient, the second Lamé coefficient, the yield strength, and the initial residual stress. Based on Gaussian distribution theory, the depth of the plastic influence layer generated by a single laser shock on the target point is determined by analyzing the distance between the laser spot center and the target point in the gear reinforcement area, the laser pulse duration, the shock wave peak pressure, the standard deviation of the plastic influence radius, as well as the dynamic yield strength, first Lamé coefficient, second Lamé coefficient, and density of the gear. The cumulative plastic influence layer depth of the target point is obtained by summing the plastic influence layer depths generated by all laser shocks. Then, the area of ​​the reinforced area on the gear surface is integrated to obtain the plastic influence volume of the gear reinforced area. The first residual stress field is determined based on the plastic influence volume.

[0006] Furthermore, the expression for the depth of the plastic influence layer generated by the single-pass laser shock on the target point is: ; ; ; in: For the first Depth of the plastic effect layer produced by each laser shock on the target point; The duration of the laser pulse; The standard deviation of the radius of influence of plasticity; This is the distance between the center of the laser spot and the target point in the gear-enhanced region; For the peak pressure of the shock wave; Dynamic yield strength; The first Lamé coefficient of the gear; This is the second Lamé coefficient of the gear; The density of the gear.

[0007] Furthermore, the expression for the first residual stress field is: ; in: The first residual stress field on the surface of the gear reinforcement area after laser shock strengthening; This represents the initial residual stress of the gear; This refers to the total number of laser impacts. The yield strength of the gear; This is the gear reinforcement area; Gear reinforcement area Surface area; Let be the Poisson's ratio of the gear.

[0008] Further, the step of determining the second residual stress field on the surface of the gear strengthened region after shot peening, based on the shot peening process parameters and the material parameters, using the spherical cavity expansion model and the Johnson-Cook constitutive model of the gear, includes: Based on contact mechanics theory and spherical cavity expansion model, the impact force generated by the projectile impacting the surface of the gear reinforcement area is equivalent to the internal pressure acting on the inner wall of the crater. Then, the internal pressure is determined based on the impact velocity of the projectile and the density, elastic modulus, and Poisson's ratio of the gear. Based on the impact velocity of the projectile, the radius of the projectile, the density of the gear, and the internal pressure, the depth of the crater, the radius of the crater, and the boundary of the crater are analyzed and determined. Based on the gear's yield strength, yield surface radius, outer surface radius, and the distance from the target point on the surface of the gear's reinforced region to the center of the crater, the stress field on the surface of the gear's reinforced region during the projectile impact loading stage is obtained by combining the elastic solution of the spherical cavity expansion model and the Johnson-Cook constitutive model of the gear. Based on the internal pressure, the outer surface radius of the gear, and the distance from the target point on the surface of the gear reinforcement region to the center of the crater, the stress field on the surface of the gear reinforcement region during the projectile impact unloading stage is analyzed and determined. The second residual stress field of the gear-reinforced region surface after shot peening is obtained by subtracting the stress field of the gear-reinforced region surface during the shot impact loading stage from the stress field of the gear-reinforced region surface during the unloading stage.

[0009] Furthermore, the stress field expression for the surface of the gear-reinforced region during the projectile impact loading stage is as follows: ; ; ; in: During the projectile impact loading stage, after correction using the stress transformation function, the distance from the surface of the gear-reinforced region to the center of the crater is... Radial normal stress at the target point; During the projectile impact loading stage, after correction using the stress transformation function, the distance from the surface of the gear-reinforced region to the center of the crater is... Tangential shear stress at the target point; Within the gear's elastic zone, the distance from the surface of the gear's reinforced area to the center of the crater is... Radial normal stress at the target point; Within the gear's elastic zone, the distance from the surface of the gear's reinforced area to the center of the crater is... Tangential shear stress at the target point; The radial normal stress at the target point on the inner wall of the crater within the elastic zone of the gear; The tangential shear stress at the target point on the inner wall of the crater within the elastic zone of the gear; The radius of the crater; The distance from the target point on the surface of the gear-reinforced area to the center of the crater; The boundary of the crater; This is the stress transformation function constructed based on the Johnson-Cook constitutive model; This serves as the input to the stress transformation function; The elastic modulus of the gear; The dimensionless equivalent plastic strain rate of the gear; The yield strength of the gear; The hardening modulus of the gear; The hardening index; The strain rate sensitivity coefficient; Dimensionless temperature; The thermal softening index of gears.

[0010] Furthermore, the stress field expression for the surface of the gear-reinforced region during the projectile impact unloading stage is as follows: ; ; in: During the unloading phase following projectile impact, the distance from the surface of the gear-reinforced area to the center of the crater is... Radial normal stress at the target point; During the unloading phase following projectile impact, the distance from the surface of the gear-reinforced area to the center of the crater is... Tangential shear stress at the target point; The radial normal stress at the target point on the inner wall of the crater during the unloading phase of the projectile impact; During the unloading phase of projectile impact, the tangential shear stress at the target point on the inner wall of the crater; This refers to the internal pressure acting on the inner wall of the crater. The radius of the yield surface; Let be the radius of the outer surface of the gear.

[0011] Furthermore, the expression for the second residual stress field is: ; ; in: After shot peening, the distance from the center of the crater to the surface of the gear reinforcement area is... Radial normal stress at the target point; After shot peening, the distance from the center of the crater to the surface of the gear reinforcement area is... The tangential shear stress at the target point.

[0012] Furthermore, the equivalent residual stress field expression on the surface of the gear strengthened region after laser shot peening composite strengthening is as follows: ; ; in: The average residual radial normal stress on the surface of the gear reinforcement region after area averaging and coupling reinforcement; The average residual tangential shear stress on the surface of the gear reinforcement region after area averaging and coupling reinforcement; , All are stress calculation correction factors; This is the gear reinforcement area; Gear reinforcement area Surface area.

[0013] Furthermore, the expression for the fatigue life conversion model is as follows: ; in, The number of loops. This is a correction factor.

[0014] Compared with the prior art, the beneficial effects of this invention are: This invention determines the first residual stress field in the strengthened region of the gear after laser shock peening based on laser shock process parameters and gear material parameters. It then determines the second residual stress field after shot peening based on a spherical cavity expansion model and contact mechanics theory, combined with shot peening process parameters and material parameters. The first residual stress field is coupled with the second residual stress field as the initial stress state before shot peening to obtain the equivalent residual stress field after laser-peening composite strengthening. Finally, the fatigue cycle number of the gear is calculated using a fatigue life conversion model. This method can reflect the stress coupling effect during the laser shock and shot peening composite strengthening process. For high-performance service gears in the aerospace field, it can predict the fatigue life of gears after laser shock and shot peening composite strengthening, providing a reliable analytical method for the design optimization and service life assessment of gear composite strengthening processes. Attached Figure Description

[0015] Figure 1 This is a flowchart of the gear fatigue life prediction method based on laser shock peening composite strengthening in the embodiment. Detailed Implementation

[0016] The present invention will now be described in further detail with reference to the embodiments and accompanying drawings. However, this should not be construed as limiting the scope of the above-described subject matter of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0017] See Figure 1 This invention provides a method for predicting the fatigue life of gears based on laser shock peening composite strengthening, comprising the following steps: Based on the laser shock process parameters and the gear material parameters, the first residual stress field on the surface of the gear strengthening area after laser shock strengthening was analyzed and determined. Based on the shot peening process parameters and the material parameters, the second residual stress field on the surface of the gear reinforcement region after shot peening is determined using the spherical cavity expansion model and the Johnson-Cook constitutive model of the gear. The first residual stress field is used as the initial stress state of the gear strengthening area surface before shot peening, and coupled with the second residual stress field to obtain the equivalent residual stress field of the gear strengthening area surface after laser shot peening composite strengthening. Based on the equivalent residual stress field, the number of cycles of the gear under the design conditions is calculated using a fatigue life conversion model, which serves as the predicted fatigue life value of the gear.

[0018] This invention determines the first residual stress field in the strengthened region of the gear after laser shock peening based on laser shock process parameters and gear material parameters. It then determines the second residual stress field after shot peening based on a spherical cavity expansion model and contact mechanics theory, combined with shot peening process parameters and material parameters. The first residual stress field is coupled with the second residual stress field as the initial stress state before shot peening to obtain the equivalent residual stress field after laser-peening composite strengthening. Finally, the fatigue cycle number of the gear is calculated using a fatigue life conversion model. This method can reflect the stress coupling effect during the laser shock and shot peening composite strengthening process. For high-performance service gears in the aerospace field, it can predict the fatigue life of gears after laser shock and shot peening composite strengthening, providing a reliable analytical method for the design optimization and service life assessment of gear composite strengthening processes.

[0019] Example This embodiment further elaborates on the detailed steps of the gear fatigue life prediction method based on laser shock peening composite strengthening, as follows.

[0020] See Figure 1 This embodiment describes a gear fatigue life prediction method based on laser shock peening composite strengthening. The laser shock peening composite strengthening includes laser shock strengthening and shot peening, and the laser shock strengthening is laser shock strengthening with a constrained layer. The gear fatigue life prediction method includes the following steps: Step 1: Based on the laser shock process parameters and the gear material parameters, analyze and determine the first residual stress field on the surface of the gear strengthening area after laser shock strengthening.

[0021] The laser shock process parameters include laser absorption intensity. Laser pulse duration and the total number of laser impacts The material parameters of the gear include the gear's elastic modulus. First Lamé coefficient Second Lamé coefficient Poisson's ratio ,density Yield strength and initial residual stress .

[0022] This step includes the following steps: Step 11: Based on laser absorption intensity The peak pressure of the shock wave generated when laser-shocks the surface of the gear reinforcement region is determined by the following formula: ; in: The peak pressure of the shock wave is expressed in GPa. It is a constant, with a value of 0.1; Laser absorption intensity, in GW / cm² 2 ; The ratio of thermal energy to internal energy in the plasma is taken as 0.1. The laser beam acts on the absorption layer on the surface of the gear to form plasma, which is then transformed into a shock wave. The shock wave causes plastic deformation on the surface of the gear, thereby generating residual compressive stress. It is the reduced impact impedance of the gear and the constraint medium, which is twice the harmonic average of the impedances of the gear and the constraint medium.

[0023] Step 12: Based on the first Lamé coefficient, second Lamé coefficient, yield strength, and initial residual stress of the gear, determine the dynamic yield strength of the gear using the following formula: ; ; ; in: The dynamic yield strength of the gear; The first Lamé coefficient of the gear; This is the second Lamé coefficient of the gear; The yield strength of the gear is obtained from the material parameter table; The initial residual stress of the gear is determined by measurement. The elastic modulus of the gear; Let be the Poisson's ratio of the gear.

[0024] Step 13: Based on Gaussian distribution theory, by analyzing the distance between the laser spot center and the target point in the gear reinforcement region, the laser pulse duration, the shock wave peak pressure, the standard deviation of the plastic influence radius, and the gear's dynamic yield strength, first Lamé coefficient, second Lamé coefficient, and density, the depth of the plastic influence layer generated by a single laser shock on the target point is determined using the following formula: ; ; ; in: For the first Depth of the plastic effect layer produced by each laser shock on the target point ; The duration of the laser pulse; The standard deviation of the radius of plastic influence is taken as 1 / 5 to 1 / 3 of the laser spot diameter. Those skilled in the art can determine or adjust the specific value based on experience. This is the distance between the center of the laser spot and the target point in the gear-enhanced region; For the peak pressure of the shock wave; Dynamic yield strength; This represents the propagation speed of the elastic wave in the gear material. The propagation speed of the plastic wave in the gear material; The first Lamé coefficient of the gear; This is the second Lamé coefficient of the gear; The density of the gear.

[0025] In determining the depth of the plastic influence layer generated by a single laser shock on the target point, this embodiment considers the distance between the laser spot center and the target point in the gear reinforcement region, the standard deviation of the plastic influence radius, and the Gaussian distribution law, reflecting the influence of the non-uniform spatial distribution of laser energy on the surface plastic deformation. It also considers the laser pulse duration and the elastic and plastic wave velocities of the material, reflecting the effect of the elastoplastic wave propagation characteristics on the depth of plastic deformation during shock wave propagation. Furthermore, it considers the difference between the shock wave peak pressure and the dynamic yield strength of the material, reflecting the driving effect on surface plastic deformation after the impact load exceeds the yield threshold. Simultaneously, it incorporates the first Lamé coefficient, the second Lamé coefficient, and density parameters of the gear material to ensure that the calculation results match the intrinsic mechanical properties of the gear material, thus characterizing the depth of the plastic influence layer at the target point under a single laser shock. This provides a reliable calculation basis for subsequent calculations of the cumulative plastic influence volume across multiple passes and accurate solutions for the first residual stress field.

[0026] Step 14: Accumulate the plastic influence layer depths generated by all laser shock passes on the target point to obtain the cumulative plastic influence layer depth of the target point; then perform area integration on the reinforced area of ​​the gear surface to obtain the plastic influence volume of the gear reinforced area, and determine the total number of laser shock passes based on the plastic influence volume. The residual compressive stress in a laser-shock-strengthened elastoplastic semi-infinite body, i.e., the first residual stress field on the surface of the gear-strengthened region after laser-shock strengthening, is expressed as: ; in: The first residual stress field on the surface of the gear reinforcement area after laser shock strengthening is a uniform field independent of position parameters; This represents the initial residual stress of the gear; The yield strength of the gear; For the first Depth of the plastic effect layer produced by each laser shock on the target point; This refers to the total number of laser impacts. This is the gear reinforcement area; Gear reinforcement area Surface area; Let be the Poisson's ratio of the gear.

[0027] In this embodiment, when determining the first residual stress field on the surface of the gear strengthened region after laser shock peening, process parameters such as the shock wave peak pressure corresponding to the laser absorption intensity, the laser pulse duration, and the cumulative effect of the total number of laser shock passes are considered. The dynamic yield strength is determined by combining material parameters such as the gear's yield strength, initial residual stress, first Lamé coefficient, second Lamé coefficient, density, and Poisson's ratio. The spatial distribution characteristics of the laser spot energy are characterized based on Gaussian distribution theory. The depth of the plastic influence layer on the target point is calculated by single-pass laser shock, and the accumulation of all passes is completed. Then, the area integration of the gear strengthened region is performed to obtain the plastic influence volume. Finally, a quantitative correlation between the residual stress field and the plastic influence volume is established to characterize the residual compressive stress distribution law on the surface of the strengthened region under multi-pass laser shock, providing a reliable initial stress field basis for subsequent stress coupling calculations of laser shot peening composite strengthening.

[0028] Step 2: Based on the shot peening process parameters and the material parameters, determine the second residual stress field on the surface of the gear reinforcement region after shot peening, using the spherical cavity expansion model and the Johnson-Cook constitutive model of the gear.

[0029] This step includes the following steps: Step 21: Based on contact mechanics theory and the spherical cavity expansion model, the impact force generated by the projectile striking the surface of the gear reinforcement region is equivalent to the internal pressure acting on the inner wall of the crater. Specifically, when shot peening the surface of the gear reinforcement region, according to contact mechanics theory, the projectile striking the gear can be considered as a sphere striking a semi-infinite body, forming a crater on the gear surface. Then, the spherical cavity expansion model is used to analyze the complex stress field generated inside the gear. In the spherical cavity expansion model, the impact force generated by the projectile striking the surface of the gear reinforcement region is equivalent to the internal pressure acting on the inner wall of the crater. .

[0030] Based on the projectile's impact velocity and the gear's density, elastic modulus, and Poisson's ratio, the internal pressure acting on the crater's inner wall is determined using Hertzian contact theory. The calculation formula is: ; in: This refers to the internal pressure acting on the inner wall of the crater. The density of the gear; The impact velocity of the projectile; The elastic modulus of the gear; Let be the Poisson's ratio of the gear.

[0031] Step 22: Based on the projectile's impact velocity, projectile radius, gear density, and internal pressure, determine the crater depth, crater radius, and crater boundary using the following formulas: ; ; ; in: The depth of the crater refers to the vertical distance from the surface of the gear-reinforced area to the lowest point of the crater. The density of the gear; The impact velocity of the projectile; Where is the radius of the projectile; The radius of the crater refers to the radius of the boundary profile between the crater and the surface of the gear-reinforced area. The crater boundary refers to the radius of the region at the center of the crater where there is no radial normal stress or tangential shear stress.

[0032] After determining the internal pressure acting on the inner wall of the crater crater depth crater radius and the edge of the crater Then, the stress field on the gear surface during the projectile impact can be calculated. The entire impact process can be divided into two stages: loading and unloading.

[0033] Step 23: Based on the yield strength, yield surface radius, outer surface radius of the gear, and the distance from the target point on the surface of the gear reinforcement region to the center of the crater, the stress field on the surface of the gear reinforcement region during the projectile impact loading stage is obtained by combining the elastic solution of the spherical cavity expansion model and the Johnson-Cook constitutive model of the gear.

[0034] Specifically, during the loading phase, the inner wall of the crater is subjected to internal pressure. When the gear material enters the elastic stage, elastic stress is generated inside the gear. At this time, the distance from the center of the crater within the gear's elastic zone is... Radial normal stress at each target point and tangential shear stress The distribution of can be given by the elastic solution of the spherical cavity expansion model, and the expression is: ; ; in: Within the gear's elastic zone, the distance from the surface of the gear's reinforced area to the center of the crater is... Radial normal stress at the target point; Within the gear's elastic zone, the distance from the surface of the gear's reinforced area to the center of the crater is... Tangential shear stress at the target point; The yield strength of the gear; Where is the radius of the yield surface, and is the boundary radius between the elastic and plastic regions, with a value of . ; The outer radius of the gear is... , Let be the Poisson's ratio of the gear; The distance from the target point on the surface of the gear-reinforced area to the center of the crater.

[0035] Then, as the loading stage continues, when the gear material enters the plastic stage, the Johnson-Cook constitutive model needs to be introduced to derive and calculate the change of the stress field under loading in the spherical cavity. This model comprehensively considers strain hardening, strain rate effect and temperature softening effect.

[0036] Therefore, combining the loading and unloading stages, this step utilizes a stress transformation function based on the Johnson-Cook constitutive model to analyze the surface stress of the gear material in the elastoplastic stage. The expression for the stress transformation function based on the Johnson-Cook constitutive model is as follows: ; in: This is the stress transformation function constructed based on the Johnson-Cook constitutive model; This serves as the input to the stress transformation function; The yield strength of the gear; The elastic modulus of the gear; Let be the dimensionless equivalent plastic strain rate of the gear, usually taken as 1s. -1 ; The value represents the yield strength of the gear. In this embodiment, the gear material is 45 steel. The value is 0.3 GPa; The hardening modulus of the gear, in this embodiment The value is 0.292 GPa; The hardening index can be 0.31. The strain rate sensitivity coefficient can be set to 0.025. For dimensionless temperature, it is defined as ,in This represents the current temperature of the gear. This is a reference temperature (usually room temperature, 293.15K). This is the melting temperature of the gear; The thermal softening index of the gear is related to the thermophysical properties and microstructure of the gear material itself. In this embodiment... The value is 1.06.

[0037] Combining the stress transformation function constructed based on the Johnson-Cook constitutive model, the stress field on the surface of the gear reinforcement region during the projectile impact loading stage can be obtained. This stress field includes the radial normal stress field. and tangential shear stress field Their expressions are as follows: ; ; in: During the projectile impact loading stage, after correction using the stress transformation function, the distance from the surface of the gear-reinforced region to the center of the crater is... Radial normal stress at the target point; During the projectile impact loading stage, after correction using the stress transformation function, the distance from the surface of the gear-reinforced region to the center of the crater is... Tangential shear stress at the target point; The radial normal stress at the target point on the inner wall of the crater within the elastic zone of the gear; The tangential shear stress at the target point on the inner wall of the crater within the elastic zone of the gear; This is the stress transformation function constructed based on the Johnson-Cook constitutive model; The radius of the crater; The distance from the target point on the surface of the gear-reinforced area to the center of the crater; This represents the boundary of the crater.

[0038] The analysis process of the surface stress field of the gear reinforcement region during the projectile impact loading stage is as follows: First, based on the elastic solution of the spherical cavity expansion model, the distance from the surface of the gear reinforcement region within the gear elastic zone to the center of the crater is obtained as follows: Radial normal stress at the target point and tangential shear stress ; Then, the radial normal stress and tangential shear stress Each as input Substituting the stress transformation function constructed based on the Johnson-Cook constitutive model Make corrections if Less than the yield strength of the gear Then the radial normal stress is retained. and tangential shear stress The original value, if Greater than the yield strength of the gear Then through the formula right Modify the parameters to obtain the radial normal stress. and tangential shear stress Correction value , ; Finally, values ​​are assigned in segments based on the region where the target point is located: The distance from the target point to the center of the crater At time (outside the crater), the tangential shear stress at the target point is the correction value. The tangential shear stress is a correction value. ; The distance from the target point to the center of the crater satisfy At time (between the crater wall and the crater boundary), the tangential shear stress at the target point is the corrected value at the crater wall. The tangential shear stress is the correction value at the crater wall. ; The distance from the target point to the center of the crater satisfy At time (within the crater boundary), both the tangential shear stress and the tangential shear stress at the target point are zero; Thus, the radial normal stress field on the surface of the gear-reinforced region after correction by the stress transformation function during the projectile impact loading stage is obtained. and tangential shear stress field .

[0039] Step 24: Based on the internal pressure, the outer surface radius of the gear, and the distance between the target point on the surface of the gear reinforcement region and the center of the crater, analyze and determine the stress field on the surface of the gear reinforcement region during the unloading stage of the projectile impact.

[0040] Specifically, when the projectile impact enters the unloading phase, after the projectile leaves the surface of the gear-reinforced area, the internal pressure originally applied to the inner wall of the crater... Complete removal is equivalent to applying an elastic stress field opposite to the loading direction to the inner wall of the ball cavity. The stress field on the surface of the gear-reinforced region during the projectile impact unloading stage includes a radial normal stress field. and tangential shear stress field Their expressions are as follows: ; ; in: During the unloading phase following projectile impact, the distance from the surface of the gear-reinforced area to the center of the crater is... Radial normal stress at the target point; During the unloading phase following projectile impact, the distance from the surface of the gear-reinforced area to the center of the crater is... Tangential shear stress at the target point; The radial normal stress at the target point on the inner wall of the crater during the unloading phase of the projectile impact; During the unloading phase of projectile impact, the tangential shear stress at the target point on the inner wall of the crater; This refers to the internal pressure acting on the inner wall of the crater. The radius of the yield surface; The radius of the outer surface of the gear; The distance from the target point on the surface of the gear-reinforced area to the center of the crater; The radius of the crater; This represents the boundary of the crater.

[0041] Step 25: Subtract the stress field on the surface of the gear reinforcement region during the shot impact loading stage from the stress field on the surface of the gear reinforcement region during the unloading stage to obtain the second residual stress field on the surface of the gear reinforcement region after shot peening.

[0042] Specifically, the second residual stress field on the surface of the gear-reinforced region after shot peening is the difference between the stress field generated during the loading stage and the stress field released during the unloading stage. The second residual stress field on the surface of the gear-reinforced region after shot peening includes the radial normal stress field. and tangential shear stress field Therefore, the second residual stress field is expressed as: ; ; in: After shot peening, the distance from the center of the crater to the surface of the gear reinforcement area is... Radial normal stress at the target point; After shot peening, the distance from the center of the crater to the surface of the gear reinforcement area is... The tangential shear stress at the target point.

[0043] Step 3: Take the first residual stress field as the initial stress state of the gear strengthening area surface before shot peening, and couple it with the second residual stress field to obtain the equivalent residual stress field of the gear strengthening area surface after laser shot peening composite strengthening.

[0044] In implementing this step, the first residual stress field and the second residual stress field are coupled using the following formula to obtain the equivalent residual stress field on the surface of the gear strengthened region after laser shot peening composite strengthening: ; ; in: The average residual radial normal stress on the surface of the gear-strengthened region after area averaging and coupling strengthening is expressed in GPa. The average residual tangential shear stress on the surface of the gear-strengthened region after area averaging and coupling strengthening is expressed in GPa. , All values ​​are stress calculation correction factors, ranging from 0.2 to 0.5. Laser shock peening-shot peening composite strengthening experiments were conducted on gears under different laser shock peening process parameters and shot peening process parameters. Based on the data obtained after the experiments, the values ​​were fitted to determine the correct values. , The specific value to be taken; This is the gear reinforcement area; Gear reinforcement area Surface area; The first residual stress field on the surface of the gear reinforcement area after laser shock strengthening; The yield strength of the gear.

[0045] Step 4: Based on the equivalent residual stress field, calculate the number of cycles of the gear under the design conditions using the fatigue life conversion model, which serves as the predicted fatigue life value of the gear. The expression for the fatigue life conversion model is: ; in: The number of iterations (×10) 6 ); As a correction factor, the surface roughness of the gear reinforcement area in this embodiment is 0.1 to 1 μm. The value range is 0.45 to 0.87, and those skilled in the art can determine or adjust the specific value based on experience. It should be noted that the fatigue life conversion model is obtained by fitting data under design conditions.

[0046] In this embodiment, when calculating the first residual stress field, the shock wave peak pressure is first determined based on the laser absorption intensity, and the dynamic yield strength of the gear is determined by combining material parameters. Then, based on Gaussian distribution theory, the influence of the distance between the laser spot center and the target point in the gear reinforcement region, and the laser pulse duration on the depth of the plastic influence layer of a single laser shock are analyzed. By accumulating the plastic influence layer depth of all passes and completing the area integration of the reinforcement region, the plastic influence volume is obtained, thus yielding the first residual stress field. In this analysis, the cumulative effect of the total number of laser shock passes on the stress field is considered. Simultaneously, based on the spherical cavity expansion model and contact mechanics theory, the... The Johnson-Cook constitutive model is used to solve the stress fields during the loading and unloading stages of the projectile impact separately and then subtract them to obtain a second residual stress field that reflects the stress evolution of shot peening. Subsequently, the first residual stress field is used as the initial stress state before shot peening for coupled calculation, and a stress calculation correction coefficient is introduced to improve the calculation accuracy of the equivalent residual stress field. Finally, the fatigue cycle number prediction value of the gear is output through the fatigue life conversion model. This method can predict the fatigue life of high-performance service gears after laser shock peening composite strengthening in the aerospace field, providing reliable calculation support for gear composite strengthening process design and service life assessment.

[0047] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for predicting the fatigue life of gears based on laser shock peening composite strengthening, characterized in that, Includes the following steps: Based on the laser shock process parameters and the gear material parameters, the first residual stress field on the surface of the gear strengthening area after laser shock strengthening was analyzed and determined. Based on the shot peening process parameters and the material parameters, the second residual stress field on the surface of the gear reinforcement region after shot peening is determined using the spherical cavity expansion model and the Johnson-Cook constitutive model of the gear. The first residual stress field is used as the initial stress state of the gear strengthening area surface before shot peening, and coupled with the second residual stress field to obtain the equivalent residual stress field of the gear strengthening area surface after laser shot peening composite strengthening. Based on the equivalent residual stress field, the number of cycles of the gear under the design conditions is calculated using a fatigue life conversion model, which serves as the predicted fatigue life value of the gear.

2. The gear fatigue life prediction method according to claim 1, characterized in that, The steps for analyzing and determining the first residual stress field on the surface of the gear's strengthened region after laser shock stabilization, based on the laser shock stabilization process parameters and the gear's material parameters, include: The peak pressure of the shock wave generated when the laser impacts the surface of the gear reinforcement area is determined based on the laser absorption intensity. The dynamic yield strength of the gear is determined based on the first Lamé coefficient, the second Lamé coefficient, the yield strength, and the initial residual stress. Based on Gaussian distribution theory, the depth of the plastic influence layer generated by a single laser shock on the target point is determined by analyzing the distance between the laser spot center and the target point in the gear reinforcement area, the laser pulse duration, the shock wave peak pressure, the standard deviation of the plastic influence radius, as well as the dynamic yield strength, first Lamé coefficient, second Lamé coefficient, and density of the gear. The cumulative plastic influence layer depth of the target point is obtained by summing the plastic influence layer depths generated by all laser shocks. Then, the area of ​​the reinforced area on the gear surface is integrated to obtain the plastic influence volume of the gear reinforced area. The first residual stress field is determined based on the plastic influence volume.

3. The gear fatigue life prediction method according to claim 2, characterized in that, The expression for the depth of the plastic influence layer generated by the single-pass laser shock on the target point is: ； ； ； in: For the first Depth of the plastic effect layer produced by each laser shock on the target point; The duration of the laser pulse; The standard deviation of the radius of influence of plasticity; This is the distance between the center of the laser spot and the target point in the gear-enhanced region; For the peak pressure of the shock wave; Dynamic yield strength; The first Lamé coefficient of the gear; This is the second Lamé coefficient of the gear; The density of the gear.

4. The gear fatigue life prediction method according to claim 3, characterized in that, The expression for the first residual stress field is: ； in: The first residual stress field on the surface of the gear reinforcement area after laser shock strengthening; This represents the initial residual stress of the gear; This refers to the total number of laser impacts. The yield strength of the gear; This is the gear reinforcement area; Gear reinforcement area Surface area; Let be the Poisson's ratio of the gear.

5. The gear fatigue life prediction method according to claim 4, characterized in that, The steps for determining the second residual stress field on the surface of the gear reinforced region after shot peening, based on the shot peening process parameters and the material parameters, and using the Johnson-Cook constitutive model of the gear, include: Based on contact mechanics theory and spherical cavity expansion model, the impact force generated by the projectile impacting the surface of the gear reinforcement area is equivalent to the internal pressure acting on the inner wall of the crater. Then, the internal pressure is determined based on the impact velocity of the projectile and the density, elastic modulus, and Poisson's ratio of the gear. Based on the impact velocity of the projectile, the radius of the projectile, the density of the gear, and the internal pressure, the depth of the crater, the radius of the crater, and the boundary of the crater are analyzed and determined. Based on the gear's yield strength, yield surface radius, outer surface radius, and the distance from the target point on the surface of the gear's reinforced region to the center of the crater, the stress field on the surface of the gear's reinforced region during the projectile impact loading stage is obtained by combining the elastic solution of the spherical cavity expansion model and the Johnson-Cook constitutive model of the gear. Based on the internal pressure, the outer surface radius of the gear, and the distance from the target point on the surface of the gear reinforcement region to the center of the crater, the stress field on the surface of the gear reinforcement region during the projectile impact unloading stage is analyzed and determined. The second residual stress field of the gear-reinforced region surface after shot peening is obtained by subtracting the stress field of the gear-reinforced region surface during the shot impact loading stage from the stress field of the gear-reinforced region surface during the unloading stage.

6. The gear fatigue life prediction method according to claim 5, characterized in that, The stress field expression for the surface of the gear-reinforced region during the projectile impact loading stage is as follows: ； ； ； in: During the projectile impact loading stage, after correction using the stress transformation function, the distance from the surface of the gear-reinforced region to the center of the crater is... Radial normal stress at the target point; During the projectile impact loading stage, after correction using the stress transformation function, the distance from the surface of the gear-reinforced region to the center of the crater is... Tangential shear stress at the target point; Within the gear's elastic zone, the distance from the surface of the gear's reinforced area to the center of the crater is... Radial normal stress at the target point; Within the gear's elastic zone, the distance from the surface of the gear's reinforced area to the center of the crater is... Tangential shear stress at the target point; The radial normal stress at the target point on the inner wall of the crater within the elastic zone of the gear; The tangential shear stress at the target point on the inner wall of the crater within the elastic zone of the gear; The radius of the crater; The distance from the target point on the surface of the gear-reinforced area to the center of the crater; The boundary of the crater; This is the stress transformation function constructed based on the Johnson-Cook constitutive model; This serves as the input to the stress transformation function; The elastic modulus of the gear; The dimensionless equivalent plastic strain rate of the gear; The yield strength of the gear; The hardening modulus of the gear; The hardening index; The strain rate sensitivity coefficient; Dimensionless temperature; The thermal softening index of gears.

7. The gear fatigue life prediction method according to claim 6, characterized in that, The stress field expression for the surface of the gear-reinforced region during the projectile impact unloading stage is as follows: ； ； in: During the unloading phase following projectile impact, the distance from the surface of the gear-reinforced area to the center of the crater is... Radial normal stress at the target point; During the unloading phase following projectile impact, the distance from the surface of the gear-reinforced area to the center of the crater is... Tangential shear stress at the target point; The radial normal stress at the target point on the inner wall of the crater during the unloading phase of the projectile impact; During the unloading phase of projectile impact, the tangential shear stress at the target point on the inner wall of the crater; This refers to the internal pressure acting on the inner wall of the crater. The radius of the yield surface; Let be the radius of the outer surface of the gear.

8. The gear fatigue life prediction method according to claim 7, characterized in that, The expression for the second residual stress field is: ； ； in: After shot peening, the distance from the center of the crater to the surface of the gear reinforcement area is... Radial normal stress at the target point; After shot peening, the distance from the center of the crater to the surface of the gear reinforcement area is... The tangential shear stress at the target point.

9. The gear fatigue life prediction method according to claim 8, characterized in that, The equivalent residual stress field expression on the surface of the gear strengthened region after laser shot peening composite strengthening is as follows: ； ； in: The average residual radial normal stress on the surface of the gear reinforcement region after area averaging and coupling reinforcement; The average residual tangential shear stress on the surface of the gear reinforcement region after area averaging and coupling reinforcement; , All are stress calculation correction factors; This is the gear reinforcement area; Gear reinforcement area Surface area.

10. The gear fatigue life prediction method according to claim 9, characterized in that, The expression for the fatigue life conversion model is as follows: ； in, The number of loops. This is a correction factor.

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