Simulation method for strengthening and compounding mechanical properties of gear surface

Abstract

The invention discloses a gear surface mechanical property strengthening compounding simulation method, and particularly relates to the technical field of gear tooth surface fatigue resistance, and the method comprises the following steps: theoretical derivation is carried out to calculate a tooth surface residual stress distribution relation after laser shock-shot peening strengthening; establishing an initial three-dimensional model of the target body; measuring the diameter of the crater; calculating the number of shots required to reach a set value by combining a shot blasting coverage rate formula; establishing a target body laser shock peening three-dimensional finite element analysis and calculation model by combining a laser shock pressure calculation method; analyzing the laser shock peening process of the target body by using a display dynamics solver; a laser shock peening analogue simulation result is extracted and serves as shot peening strengthening stress field input, and a shot peening strengthening three-dimensional model with multiple shots distributed randomly is established; and the display dynamics solver is used again to analyze the process that the projectile flow impacts the target body, and a continuous process induced surface strengthening forming sequence coupling simulation result is obtained.

Description

Technical Field

[0001] The invention relates to the technical field of gear tooth surface fatigue resistance, and in particular to a simulation method for strengthening and compounding mechanical properties of a gear surface. Background Art

[0002] High-performance gears, which are important components in aircraft engines, often work in high-power, low-density working environments, which places stringent requirements on gear transmission performance, service status and fatigue life. Common failure forms of gears include root bending fatigue, tooth surface contact fatigue and tooth surface wear, all of which are related to the fatigue performance of gears. Gear fatigue performance restricts breakthroughs in transmission system performance. By conducting research on gear load-bearing performance, it is helpful to experimentally obtain gear fatigue-related data. Conducting gear surface enhancement performance analysis helps to theoretically derive methods suitable for improving part fatigue performance. Therefore, it is very important to conduct surface enhancement theoretical analysis on gears after processing and manufacturing, explore technologies to improve the corresponding surface integrity, and establish a connection between surface integrity parameters and gear load-bearing performance fatigue data.

[0003] Common gear surface strengthening methods include laser strengthening, shot peening, rolling strengthening, etc. Laser strengthening adjusts the laser incident angle to impact the tooth surface, so that the tooth surface obtains a large residual compressive stress and a deep residual compressive stress layer. Shot peening uses compressed air to drive the pellets to impact the tooth surface, so that the tooth surface obtains a large residual compressive stress.

[0004] However, for high-performance gears in service in aviation, a single strengthening process cannot meet the gear strengthening requirements, and most composite strengthening processes have only been tested. Therefore, there is an urgent need to explore characterization methods for gear composite strengthening processes. Summary of the invention

[0005] In order to solve the problems of poor effect in the existing single surface strengthening technology and heavy reliance on experience in the composite strengthening process, the present invention provides a gear laser shock-shot peening composite process surface mechanical properties simulation strengthening method. It combines the two analysis methods of laser strengthening and shot peening. First, the problem of residual stress change under the composite process is theoretically analyzed. Secondly, a simulation analysis model is established to display the simulation analysis process of the single process and the composite process, which is helpful to compare the strengthening effect of the single process and the composite process, and further obtain the prediction result that the composite process strengthening is better than the single process strengthening. These prediction results have a guiding role in the gear surface strengthening, improve the effect of the gear strengthening treatment, and solve the problems raised in the background technology.

[0006] The technical solution provided is as follows: A simulation method for strengthening the composite mechanical properties of a gear surface, comprising the following steps: Step 1, simplify the three-dimensional model of a single gear tooth whose surface is strengthened by laser impact and projectile impact, import the three-dimensional model into the finite element simulation calculation platform, and establish a three-dimensional model of the initial state of the gear tooth surface and tooth root; Step 2, establish a single projectile three-dimensional finite element simulation analysis model, use the target body initial state three-dimensional model established in step 1, that is, the gear tooth surface tooth root initial state three-dimensional model, create a display dynamic analysis step and contact relationship, simulate the process of a single projectile impacting the tooth surface, obtain the crater left after the single projectile impacts the tooth surface, measure the crater radius, and compare it with the theoretical calculation crater radius result; Step 3: According to the measured crater radius and the Avrami formula of shot peening coverage, the required number of shots per unit area coverage is calculated, and a finite element simulation analysis model for target shot peening is established. The process of random shots impacting the target is analyzed using a display dynamics analysis solver, and the residual compressive stress at the tooth root of the gear tooth surface after shot peening is obtained, which is compared with the theoretical calculation results. Step 4: Re-establish a new finite element simulation calculation platform, use the three-dimensional model of the initial state of the gear tooth surface and tooth root established in step 1, combine the laser shock pressure theoretical equation with the actual laser performance parameters, calculate the shock pressure required for laser strengthening, and compare it with the theoretical calculation results, use the Fortran programming language to write the actual laser shock strengthening pressure equation, embed the Johnson-Cook constitutive equation into the laser strengthening three-dimensional model calculation, create a multi-step display dynamic analysis step, refine the mesh at the tooth root and tooth surface laser impact, and establish a target laser strengthening finite element simulation analysis model; Step 5, using the target laser strengthening finite element simulation analysis model established in step 4, simulate and calculate the laser pressure impact process on the gear, obtain the residual compressive stress at the tooth root of the gear tooth surface after laser impact, and compare it with the theoretical calculation result; Step 6, re-import the last analysis step and the last frame result of the simulation analysis in step 5 into the simulation platform in the odb file format, use the Python programming language to generate random positions of the projectile assembly, generate random projectiles in the shot peening area in the three-dimensional space above the tooth surface, and the number of shot peening is taken from the calculation result of step 3, and establish a three-dimensional model of composite strengthening of laser shock-projectile impact target body; Step 7: Use the explicit dynamics analysis solver to analyze the composite strengthening process, simulate and calculate the residual compressive stress on the target surface after the composite process, and compare it with the theoretical calculation results. The simulation results are extracted using Python language.

[0007] Preferably, in step 3, the theoretical calculation result is based on the contact mechanics theory combined with the spherical cavity expansion model to calculate the plane stress field after the projectile hits the target.

[0008] Preferably, in step 5, the theoretical calculation result is a calculation of the residual stress field on the target surface under laser strengthening based on the laser pressure shock principle.

[0009] Preferably, in step 7, the theoretical calculation result is to use the residual stress of the target body after laser shock strengthening as the initial stress state of the target body surface before shot peening, and calculate the residual stress state of the target body surface after composite process strengthening.

[0010] The present invention has the following advantages: The present invention uses laser shock-shot peening composite process simulation analysis to obtain the sequential coupling simulation results of continuous process-induced surface strengthening. The analysis steps of the simulation method match the actual test steps, the simulation results are similar to the actual test results, and the method is short in time, which can provide a reference for specific test development, and is conducive to the further development of laser shock-shot peening simulation process. Compared with the prior art, the present invention has the characteristics of high accuracy and high efficiency. Compared with the single process, the advantage of the composite process is that it improves the surface strengthening effect of laser strengthening and shot peening, improves the surface integrity parameter results, obtains the process parameter data of laser strengthening and shot peening strengthening on the gear tooth root and tooth surface, deepens the understanding of the composite process method, and meets the requirements of the surface integrity of the gear tooth surface and tooth root in actual production. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 Flowchart provided for this embodiment; Figure 2 This is a simulation analysis flow chart provided for this embodiment. DETAILED DESCRIPTION

[0012] The following is a description of the implementation of the present invention by specific embodiments. People familiar with the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0013] The theoretical calculation method includes the following steps: Step 1: Calculate the residual stress field on the target surface under laser strengthening based on the principle of laser pressure shock.

[0014] Step 2: Based on the contact mechanics theory and the spherical cavity expansion model, calculate the plane stress field after the projectile hits the target.

[0015] Step 3: The residual stress of the target body after laser shock strengthening is used as the initial stress state of the target body surface before shot peening, and the residual stress state of the target body surface after composite process strengthening is calculated based on steps 1 and 2.

[0016] To further verify the accuracy of the theoretical calculation method in steps 1 to 3, Figure 1 As shown, the present invention uses the finite element method to carry out simulation verification. The specific simulation method is shown in steps a to g.

[0017] Step a, simplifying the three-dimensional model of a single gear tooth whose surface is strengthened by laser impact and projectile impact, importing the three-dimensional model into a finite element simulation calculation platform, and establishing a three-dimensional model of the initial state of the gear tooth surface and tooth root; Step b, establishing a single projectile three-dimensional finite element simulation analysis model, using the target body initial state three-dimensional model established in step a, creating a display dynamic analysis step and contact relationship, simulating the process of a single projectile impacting the tooth surface, obtaining the crater left after the single projectile impacts the tooth surface, measuring the crater radius, and comparing it with the theoretical calculation crater radius result; Step c, according to the crater radius, combined with the Avrami formula of shot peening coverage, the required number of shots per unit area coverage is calculated, a finite element simulation analysis model of target shot peening is established, and the process of random shot impacting the target is analyzed using a display dynamics analysis solver to obtain the residual compressive stress at the tooth root of the gear tooth surface after shot peening, and compared with the theoretical calculation results; Step d, re-establishing a new finite element simulation calculation platform, using the three-dimensional model of the initial state of the gear tooth surface and tooth root established in step a, combining the laser shock pressure theoretical equation with the actual laser performance parameters, calculating the shock pressure required for laser strengthening, using the Fortran programming language to write the actual laser shock strengthening pressure equation, embedding the Johnson-Cook constitutive equation into the laser strengthening three-dimensional model calculation, creating a multi-step display dynamic analysis step, refining the mesh at the tooth root and tooth surface laser impact, and establishing a target laser strengthening finite element simulation analysis model; Step e, using the target laser strengthening finite element simulation analysis model established in step d, simulate and calculate the laser pressure impact process on the gear, obtain the residual compressive stress at the tooth root of the gear tooth surface after laser impact, and compare it with the theoretical calculation result; Step f, re-import the last analysis step and the last frame result of the simulation analysis in step e into the simulation platform in the odb file format, use the Python programming language to generate random positions of the projectile assembly, generate random projectiles in the shot peening area in the three-dimensional space above the tooth surface, and establish a composite strengthening three-dimensional model of laser shock-projectile impact target body; Step g: Use the display dynamics analysis solver to analyze the composite process strengthening process, and simulate and calculate the residual compressive stress on the target surface after the composite process. The simulation results are extracted using Python language.

[0018] The effect of the present invention is further described below in conjunction with the accompanying drawings and embodiments: like Figure 2 As shown, this embodiment includes the following steps: Step 1: Calculate the residual stress field on the target surface during laser strengthening. The peak pressure of the shock wave during laser shock is expressed as (1) in, is the plasma internal energy increase coefficient, A is a constant, Z is the shock wave impedance of the material and the confinement layer, is the laser power density.

[0019] (2) in, : laser shock pressure; λ, ν are Lame coefficients, σ y , σ0 are the bending strength of the material and the initial surface stress, C el , C pl are the propagation speeds of plastic waves and elastic waves in the material, respectively. The depth of the plastic influence layer can be expressed as: (3) (4) in, : Material density of the target.

[0020] Therefore, the residual compressive stress generated in the elastic-plastic semi-infinite body obtained by laser shock hardening is: (5) in, : Plastic strain of material; : Raman coefficient; Step 2: Based on the contact mechanics theory and the spherical cavity expansion model, calculate the plane stress field after the projectile hits the target. First calculate the stress change in the elastic zone when the projectile hits: (6) (7) (8) Among them, σ y is the yield strength of the material, r c is the yield surface radius, r0 is the outer surface radius of the material, : radius of the spherical cavity; is the radial stress; , is the circumferential stress; : Yield limit.

[0021] Then, combined with the Johnson-Cook constitutive model, the change of the stress field of the spherical cavity loading is derived and calculated: (9) (10) (11) Among them, a is the radius of the crater, θ is the polar angle corresponding to r, and r a is the crater boundary, (m means mth power) is the temperature parameter, is the elastic modulus, is the strain hardening coefficient, is the equivalent plastic strain (n also means nth power), is the strain rate sensitivity coefficient, is the normalized equivalent plastic strain rate, , It is the stress field component of the spherical cavity loading during the projectile loading process.

[0022] When the projectile is unloaded, the internal pressure p i All of them are removed, and the spherical shell is subjected to an internal pressure of p i When , the spherical shell is subjected to elastic stress, and the loading components are: (12) (13) in, , , The stress field component of the spherical cavity loading during the projectile unloading process; Step 3: Take the residual stress of the target after laser strengthening as the initial stress state of the target surface before shot peening, and calculate the residual stress of the target surface after composite process strengthening based on steps 1 and 2: (14) (15) In the formula, , , is the residual stress distribution component of the target after impact, : The residual compressive stress component generated by laser impact on the target; k1 and k2 are the stress calculation correction coefficients.

[0023] Step 4: To further verify the accuracy of the theoretical calculation method in step 3, the finite element method is used to carry out verification simulation. The simulation steps are shown in steps 4 to 10. First, simplify the three-dimensional model of a single gear tooth whose surface is strengthened by laser impact and projectile impact, import the three-dimensional model into the finite element simulation calculation platform, and establish a three-dimensional model of the initial state of the gear tooth surface and tooth root; Step 5. On the Abauqs finite element simulation platform, a target of 5mm×5mm×7mm is established. The target material is 45# steel, and the material mechanical properties of the target are: σ0=1080Mpa, E=210GPa, υ=0.3. Assign the target material properties, establish a single projectile three-dimensional model, select the commonly used ASH230 as the projectile material, determine the diameter of the projectile to be 0.6mm, and the basic mechanical properties of the projectile material are: σ0=1500Mpa, E=210GPa, υ=0.3. The initial velocity of the projectile is set to 40m / s, 60m / s, 70m / s, 80m / s, 90m / s, and 100m / s. Assign the projectile material, and use the ideal elastic-plastic constitutive model for projectile calculation. At the same time, the projectile is meshed, and the mesh form uses the C3D8R three-dimensional eight-node reduced integration unit.

[0024] Step 6. Use the three-dimensional model of the target created in step 5 to mesh it. There are three areas for meshing: impact area, transition area, and edge area. The impact area and transition area meshes are all C3D8R three-dimensional eight-node reduced integration elements, and the edge area meshes are CIN3D8 infinite elements to reduce the impact of stress waves on the calculation results. The impact area mesh is encrypted, and the mesh size is 0.3mm×0.3mm×0.3mm. The transition area mesh size gradually increases.

[0025] Assemble the created single projectile model and the target model, create a display dynamics analysis step, and set the contact form between the projectile and the target surface to face-to-face contact.

[0026] The established finite element model of projectile impacting the target is used to simulate the impact of a single projectile on the target, and the crater left by the single projectile impacting the target surface is obtained, and the radius of the crater is measured.

[0027] Step 7: The number of shots is related to the shot peening coverage. The number of shots at a specific coverage is: (18) (19) In the formula, Cr is the shot peening coverage, Ar is the intermediate variable, N is the number of shots, and d iis the diameter of the projectile crater, and D is the radius of the statistical calculation area of ​​the plastic deformation zone. In the shot peening test, when the coverage rate reaches 98%, it is equivalent to a coverage rate of 100%. Take the intermediate variable Ar=4, and the coverage rate reaches 100% after calculation. Therefore, the number of projectiles required under different process parameters can be calculated. Use the random function in the Python programming language to generate random numbers, write the relationship between the random numbers and the center coordinates of the projectile assembly position, generate randomly distributed projectiles above the target body, and then establish a finite element simulation analysis model for target shot peening. Use the Abaqus / Explicit Daynamic display dynamics module analysis solver to analyze the process of random projectiles impacting the target body. The analysis time step is 0.0005s. Use the python program to write the extraction code, set the extraction path, and then extract the stress S33 corresponding to the impact area according to the node, and calculate the average value to obtain the residual stress result after shot peening.

[0028] Step 8: Re-establish a new finite element simulation calculation platform and import the target model established in step 4. When laser strengthening the actual gear, high power density (GW / cm 2 ), short pulse width (5-30ns) laser beam. The beam acts on the absorption layer on the surface of the gear tooth to form plasma, which is then transformed into shock waves. The surface of the shock wave material undergoes plastic deformation, generating residual compressive stress.

[0029] In this embodiment, the laser parameters are: Nd:YAG laser system with a wavelength of 1064nm, a pulse duration of 18ns, and a frequency of 2Hz. The laser model is YD60-M165. When the laser strikes, the laser spot is 1 / e 2 (e is the base of natural logarithm) The radius R is 1.10 nm, and the energy of a single laser pulse is 5 J. The energy is Gaussian distributed in space.

[0030] According to the laser shock pressure calculation model, the calculation equation of laser shock pressure in the continuous stage of laser shock is derived.

[0031] During the laser shock continuation stage, the laser power density The relationship between the impact pressure P(t) is: (20) Where A is the laser energy absorption rate; is the ratio of laser-induced plasma thermal energy to internal energy; du and dt are time differentials; Z is the combined impact impedance of the target plate and the confinement layer. Assuming that the laser power density is constant, dP / dt = 0, and equation (6) is the commonly used impact pressure calculation formula, where I0 is a constant laser power density.

[0032] Since the pressure is not constant during laser impact, the calculated pressure data is combined with the Fortan programming language to write the pressure mathematical relationship. During simulation calculation, the VUMAT subroutine of pressure is called in the "load" module.

[0033] Create multiple analysis steps with different analysis times, establish a finite element simulation model for laser strengthening of gear tooth surface and tooth root, and carry out finite element simulation analysis of laser strengthening. Use Python program to write extraction code, set the extraction path, and then extract the stress S33 corresponding to the impact area according to the node, and calculate the average value to obtain the residual stress result after laser shock.

[0034] Step 9. Re-establish the finite element simulation platform, and extract the results of the last analysis step and the last frame of the simulation calculation in step 8 as an odb file. Use the random function in the Python programming language to generate random numbers, write the relationship between the random numbers and the coordinates of the center of the projectile assembly position, generate randomly distributed projectiles above the target, and use the "Predefined field" function in the software to add initial residual stress to the projectile concentration area. Use the Abaqus / ExplicitDaynamic explicit dynamics module analysis solver to analyze this process, with an analysis time step of 0.0003s, and then establish a composite strengthening simulation model of laser shock-projectile impact target.

[0035] Step 10: Use the display dynamics solver to analyze the random projectile strengthening finite element simulation established in step 9, and obtain the residual compressive stress, surface roughness and other results of the target surface through simulation calculation. Use the python program to write the extraction code, set the extraction path, and then extract the stress S33 corresponding to the impact area according to the node, and calculate the average value to obtain the residual stress result after the composite strengthening process.

[0036] Finally, the theoretical calculation results of step 3 are compared with the simulation calculation results of step 10.

[0037] The present invention analyzes the theoretical calculation method of residual stress under the laser shock and shot peening composite process, establishes the initial three-dimensional model of the gear tooth surface and tooth root, carries out surface laser shock strengthening simulation, extracts the results, and carries out shot peening simulation again on the target surface strengthened by laser shock, and obtains the prediction result of residual stress induced by the laser shock-shot peening continuous process. The present invention has guiding significance for understanding the theoretical analysis and simulation process of composite process surface strengthening.

[0038] Although the present invention has been described in detail above by general description and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements can be made to the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all belong to the scope of protection claimed by the present invention.

Claims

1. A simulation method for strengthening and compounding the mechanical properties of a gear surface, characterized in that: The following steps are involved: Step 1, simplify the three-dimensional model of a single gear tooth whose surface is strengthened by laser impact and projectile impact, import the three-dimensional model into the finite element simulation calculation platform, and establish a three-dimensional model of the initial state of the gear tooth surface and tooth root; Step 2, establish a single projectile three-dimensional finite element simulation analysis model, use the target body initial state three-dimensional model established in step 1, that is, the gear tooth surface tooth root initial state three-dimensional model, create a display dynamic analysis step and contact relationship, simulate the process of a single projectile impacting the tooth surface, obtain the crater left after the single projectile impacts the tooth surface, measure the crater radius, and compare it with the crater radius calculated by shot peening theory; Step 3: According to the measured crater radius and the Avrami formula of shot peening coverage, the required number of shots per unit area coverage is calculated, and a finite element simulation analysis model for target shot peening is established. The process of random shots impacting the target is analyzed using a display dynamics analysis solver, and the residual compressive stress at the tooth root of the gear tooth surface after shot peening is obtained, which is compared with the theoretical calculation results. Step 4: Re-establish a new finite element simulation calculation platform, use the initial state three-dimensional model of the gear tooth surface and tooth root established in step 1, combine the laser shock pressure theoretical equation with the actual laser performance parameters, calculate the shock pressure required for laser strengthening, use the Fortran programming language to write the actual laser shock strengthening pressure equation, embed the Johnson-Cook constitutive equation into the laser strengthening three-dimensional model calculation, create a multi-step display dynamic analysis step, refine the mesh at the tooth root and tooth surface laser impact, and establish a target laser strengthening finite element simulation analysis model; Step 5, using the target laser strengthening finite element simulation analysis model established in step 4, simulate and calculate the laser pressure impact process on the gear, obtain the residual compressive stress at the tooth root of the gear tooth surface after laser impact, and compare it with the theoretical calculation result; Step 6, re-import the last analysis step and the last frame result of the simulation analysis in step 5 into the simulation platform in the odb file format, use the Python programming language to generate random positions of the projectile assembly, generate random projectiles in the shot peening area in the three-dimensional space above the tooth surface, and the number of shot peening is taken from the calculation result of step 3, and establish a three-dimensional model of composite strengthening of laser shock-projectile impact target body; Step 7: Use the explicit dynamics analysis solver to analyze the composite strengthening process, obtain the residual compressive stress on the target surface after composite process strengthening through simulation calculation, and compare it with the theoretical calculation results. The simulation results are extracted using Python language.

2. The simulation method for strengthening and compounding the mechanical properties of a gear surface according to claim 1, characterized in that: In step 3, the theoretical calculation result is based on the contact mechanics theory combined with the spherical cavity expansion model to calculate the plane stress field after the projectile hits the target.

3. The simulation method for strengthening and compounding the mechanical properties of a gear surface according to claim 1 is characterized in that: In step 5, the theoretical calculation result is to calculate the residual stress field on the target surface under laser strengthening according to the principle of laser pressure shock.

4. The simulation method for strengthening and compounding the mechanical properties of a gear surface according to claim 1 is characterized in that: In step 7, the theoretical calculation result is to use the residual stress of the target body after laser shock strengthening as the initial stress state of the target body surface before shot peening, and calculate the residual stress state of the target body surface after composite process strengthening.

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