A method for determining composite surface strengthening process based on stress wave pattern

Abstract

The present invention relates to a method for determining a composite surface strengthening process based on stress wave patterns. The method first qualitatively determines the stress wave patterns of the surface strengthening process through numerical simulation and other methods, then determines the order in which different surface strengthening processes are combined. Subsequently, actual experiments are used to quantitatively determine the composite surface strengthening process parameters, ultimately achieving the determination of composite surface strengthening process conditions for achieving high residual compressive stress field strength. The present invention provides a basis for pre-setting the process, which helps technicians determine in advance whether an existing single-treatment process can achieve the maximum residual compressive stress field strength through compounding, and how to adjust the existing single-treatment process to achieve the maximum residual compressive stress field strength.

Description

Technical Field

[0001] The invention relates to a method for determining a composite surface strengthening process based on stress wave type, and belongs to the field of surface treatment of structural materials. Background Art

[0002] Surface strengthening processes such as shot peening, rolling, and impacting introduce residual compressive stresses inside the material, which causes the surface integrity parameters of the material to evolve positively, thereby achieving the goal of improving service performance such as fatigue life extension of the material or component. However, as the requirements for the introduction of high residual compressive stress fields in industrial scenarios continue to increase, the effect of a single surface strengthening process on high-strength strengthening requirements has revealed limitations. The use of different processes with different technical advantages for composite treatment has become an important and effective way to strengthen high strength. In the implementation of the composite surface strengthening process, the order and parameters of different strengthening processes selected according to the high-strength strengthening requirements directly determine the actual role and specific value of the composite surface strengthening process. Furthermore, how to predetermine the composite order and the specific parameters of different processes has become a problem that technical personnel need to solve.

[0003] In conventional composite surface strengthening processes, the composite strengthening effect of two or more strengthening methods needs to be analyzed based on a large number of combined tests, and then the composite method of different surface strengthening methods with the optimal strengthening effect can be expected. At present, some researchers use numerical simulation and other methods to carry out research on more economical and efficient composite strengthening processes. However, the actual effect of composite strengthening is directly related to the depth of the residual stress layer introduced into the surface layer of the material by the surface strengthening method and the intensity of the surface residual stress. However, numerical simulation cannot truly achieve quantitative consistency with the distribution state of the residual stress field on the material surface. Summary of the Invention

[0004] In response to the shortcomings of the existing technology, the present invention provides a method for determining a composite surface strengthening process based on stress wave patterns. The present invention first qualitatively determines the stress wave pattern of the surface strengthening method through numerical simulation and other means, then determines the composite order of different surface strengthening methods, and then uses actual experiments to quantitatively determine the composite surface strengthening process parameters, and finally realizes the determination of the composite surface strengthening process conditions with high residual compressive stress field intensity.

[0005] The technical solution of the present invention is:

[0006] A method for determining a composite surface strengthening process based on stress wave patterns, comprising:

[0007] (1) Determine the type of surface strengthening process to be used in the composite surface strengthening process, and preliminarily formulate the surface strengthening process conditions in the composite surface strengthening process; based on actual processing requirements and equipment conditions, preliminarily formulate the specific process parameters of different or the same type of surface strengthening processes used in the composite process.

[0008] (2) Characterize and analyze the residual stress field in the direct strengthening area of the material to determine the stress wave pattern generated by different surface strengthening process conditions;

[0009] (3) According to the differences in stress wave patterns generated by different surface strengthening process conditions, the adjustment principles of surface strengthening process conditions in the composite surface strengthening process are determined:

[0010] If different surface strengthening process conditions produce different stress wave patterns, then proceed to step (4);

[0011] If different surface strengthening process conditions produce the same stress wave pattern, but the wave pattern is not completely consistent, then go to step (5);

[0012] (4) According to the composite strengthening sequence of generating plane waves first and then spherical waves, the process parameters of the surface strengthening process are adjusted to determine the composite surface strengthening process; plane waves have a higher tendency to induce large residual compressive stress into the deeper the depth is, while spherical waves have a higher tendency to induce higher surface residual compressive stress. The processing mode of "increasing the depth first and then increasing the strength" is more conducive to forming a larger residual compressive stress field intensity, so the composite sequence of "plane wave → spherical wave" is selected.

[0013] (5) Determine the operating sequence of different surface strengthening processes during the composite treatment process based on the residual stress field distribution characteristics;

[0014] (6) Determine the composite surface strengthening process based on the determined operating sequence of different surface strengthening processes and the corresponding specific process parameter combination of the surface strengthening process.

[0015] Preferably, according to the present invention, in step (1), the surface strengthening process is a surface processing process that can realize strong plastic deformation into a physical form and can realize single-point (i.e., fixed area) treatment, and the surface strengthening process includes mechanical shot peening, ultrasonic shot peening, laser shock, milligram energy shock, etc.; the specific process parameters of different surface strengthening processes are as follows: the parameters of mechanical shot peening include shot peening air pressure, shot flow, material, hardness, size and other shot specifications; the parameters of ultrasonic shot peening include ultrasonic indicators such as power and amplitude, and shot material specifications such as type and size; the parameters of laser shock include the material and specifications of the absorption layer and the constraint layer, and laser parameters such as energy, wavelength, and pulse width; the parameters of milligram energy shock include shock indicators such as amplitude and speed, and shock needle specifications such as diameter.

[0016] Single-point treatment refers to a process whereby technicians select only a fixed area of the surface to be treated for surface strengthening. This process involves a single treatment medium, such as a single shot, a single spot, or a single impact needle, for a fixed area. For example, mechanical and ultrasonic shot peening involve surface treatment using a single shot; laser peening involves surface treatment using a single spot formed by a laser beam; and milligram energy impaction involves surface treatment using a single impact needle.

[0017] The composite surface strengthening is performed by using the same surface strengthening process or different surface strengthening processes, and when the composite surface strengthening is performed by using the same type of surface strengthening process, the specific process conditions used by the surface strengthening process are different.

[0018] Preferably, according to the present invention, in step (2), the direct strengthening area is the area on the material surface that directly bears the external load during the surface treatment process, and the direct strengthening area is the area extending from the material surface to the interior of the material to a depth of 1 mm.

[0019] For various surface strengthening techniques currently used in industry, such as shot peening, ultrasonic treatment, and impact treatment, the maximum depth of residual stress induced within the material is on the order of millimeters. The region from a depth of 1 mm to the material surface most directly represents the stress wave pattern caused by surface strengthening. To facilitate the identification of stress wave patterns, the direct strengthening region described in this invention is within a depth of 1 mm within the material.

[0020] Preferably, according to the present invention, in step (2), the stress distribution cloud map of the directly strengthened area is obtained by finite element numerical simulation to qualitatively judge the stress wave type; when the finite element numerical simulation method is used for qualitative judgment, the cost is lower and the efficiency is higher; or an actual test method is used to quantitatively judge the stress wave type with the help of the residual stress field distribution data of the directly strengthened area.

[0021] Further preferably, an actual test method is adopted to quantitatively judge the stress wave type with the help of the residual stress field distribution data of the directly strengthened area. The specific process is: in a fixed surface area treated at a single point, the residual stress is measured from the surface at different positions to the inside, and the residual stress variation curve along the depth at different positions is obtained, that is, the residual stress field variation curve at different positions is obtained. At the same time, the distribution depth of residual stress with different values at different positions is obtained, and these depth positions are connected to form equal residual stress lines with different values of residual stress; there is no limitation on the testing instrument, and the traditional lossy drilling method, the non-destructive X-ray diffraction method, and the more advanced neutron diffraction method can be used to determine the residual stress field distribution in the directly strengthened area.

[0022] According to the present invention, preferably, in step (2), when the equal residual stress line of the directly strengthened area tends to be parallel to the material surface, it is determined that the material surface stress wave type caused by the surface strengthening process conditions is a plane wave type;

[0023] When the equal residual stress lines in the directly strengthened area of the material surface are arc-shaped and the maximum residual stress value is in the middle of the directly strengthened area, it is determined that the stress wave type on the material surface caused by the process conditions of the surface strengthening method is a spherical wave type.

[0024] The stress wave pattern induced by the surface strengthening method corresponds to the surface strengthening process conditions. However, in conventional knowledge, technicians may identify the stress wave pattern induced by laser shock surface treatment as a plane wave, while the stress wave pattern induced by mechanical shot peening surface treatment as a spherical wave. If based on this conventional knowledge, the same type of surface strengthening process cannot be used to determine the composite order of variable parameter multiple treatment processes. In the present invention, it is believed that different process conditions under different parameter combinations corresponding to the laser shock surface treatment method may lead to different stress wave patterns on the surface of the material. This design treats different processes determined by different parameters differently, and can more accurately distinguish the stress wave patterns of different process conditions, which helps to achieve the composite order determination of variable parameter multiple treatment processes for the same type of surface strengthening process.

[0025] Further preferably, when determining the plane wave stress distribution, if the depth difference between the middle and edge positions of the equal residual stress lines at a depth of 300 μm to 400 μm from the material surface in the direct strengthening area does not exceed 25% of the average depth value of the equal residual stress lines, it is determined to be a plane wave type; otherwise, the measured stress wave type is determined to be a spherical wave type.

[0026] For most currently used surface strengthening technologies that involve strong plastic deformation, this depth is a moderate surface strengthening depth that most technologies can achieve. If the residual stress influence depth of the surface strengthening process used by technicians is too small or too large, the aforementioned depth of 300μm to 400μm can be adjusted lower or higher. It should be noted that based on the influence depth of most surface strengthening processes, the present invention uses the equal residual stress line at 300μm to 400μm as the basic basis for determining stress wave characteristics.

[0027] It should be noted that the stress wave type described in the present invention is determined solely based on the depth difference between the center and edge of the directly strengthened region. If the depth difference between the center and edge does not meet the soccer ball surface wave requirement, but the maximum depth difference at other locations reaches 25% of the average depth of the designated isostress line, the stress wave type is still considered a plane wave.

[0028] Preferably, according to the present invention, in step (4), when adjusting the process parameters of the surface strengthening process, a quantitative analysis of the residual stress field is performed on the different surface strengthening processes used in the composite strengthening treatment proposed in step (2), that is, the maximum residual compressive stress of the outer surface layer induced by the surface strengthening process is obtained; and according to the quantitative analysis results of the residual stress field distribution characteristics, the parameters of the pre- and post-surface strengthening processes are adjusted so that the maximum residual compressive stress intensity generated on the material surface by the pre-surface strengthening process is less than the maximum residual compressive stress intensity generated by the post-surface strengthening process.

[0029] The specific parameters adjusted for different surface enhancement processes vary and are not specifically defined here. For example, for mechanical shot peening, the shot velocity can be varied by adjusting the shot pressure; for laser peening, the laser energy can be adjusted; and for ultrasonic peening or Hawkes energy peening, the impact amplitude can be adjusted.

[0030] This step requires that the residual stress wave types induced by the different surface strengthening processes are different, and a composite surface strengthening processing method with plane wave in front and spherical wave in the back is determined. According to the order set in the composite processing, the first surface treatment is called the front surface strengthening process, and the subsequent surface treatment is called the back surface strengthening process.

[0031] According to the preferred embodiment of the present invention, in step (5), the operation sequence of different surface strengthening processes in the composite treatment process is determined based on the residual stress field distribution characteristics, and the specific process is as follows:

[0032] A comparative analysis of the residual compressive stress field strengths generated by different surface strengthening processes was conducted. The surface strengthening process that produced relatively low residual compressive stress field strengths was designated as the pre-surface strengthening process, while the surface strengthening process that produced relatively high residual compressive stress field strengths was designated as the post-surface strengthening process. On the residual stress distribution curve along the material depth, the area enclosed by the residual compressive stress curve and the horizontal and vertical coordinates is the residual compressive stress field strength, where the horizontal coordinate represents the depth from the material surface to the interior, and the vertical coordinate represents the residual stress value.

[0033] It should be pointed out that the above method for determining the order of surface strengthening processes is applicable to all cases where the residual stress wave types induced by the different surface strengthening processes are all plane waves, as well as some cases where the residual stress wave types induced by the different surface strengthening processes are all spherical waves.

[0034] The residual compressive stress field intensity is the area enclosed by the residual stress curve and the horizontal and vertical coordinates on the residual stress distribution curve along the depth direction of the material, where the horizontal coordinate is the depth extending from the surface of the material to the inside, and the vertical coordinate is the residual stress value.

[0035] Further preferably, when the stress waves induced by different surface strengthening processes are all spherical wave types, if the difference in the residual compressive stress field intensities induced by the different surface strengthening processes is less than 10% of the average value of the residual compressive stress field intensities induced by the different surface strengthening processes, it is necessary to determine the order of the different surface strengthening processes by comparing the obviousness of the stress wave types. The specific determination method is: comparing the depth difference between the middle and edge positions in the stress wave type, and determining the surface strengthening process corresponding to the relatively large depth difference as the post-surface strengthening process, and determining the surface strengthening process corresponding to the relatively small depth difference as the pre-surface strengthening process.

[0036] Since the degree of difference in stress wave patterns has a stronger impact on variable parameter multiple composite treatments, the effect is more obvious when the order of the different surface strengthening processes is determined by the degree of significance of the corresponding stress wave patterns, compared with comparing the difference in residual compressive stress field intensities induced by the different surface strengthening processes.

[0037] The beneficial effects of the present invention are:

[0038] 1. The present invention first qualitatively determines the stress wave type of the surface strengthening method through numerical simulation and other means, and determines the composite order of different surface strengthening methods. Then, it uses actual experiments to quantitatively determine the composite surface strengthening process parameters, and finally determines the composite surface strengthening process conditions with high residual compressive stress field intensity.

[0039] In the process of determining the order, numerical simulation and other methods are used to determine which wave type the stress waves of different surface strengthening methods tend to approach. According to the change of wave type, the strengthening order is determined according to the basic principle of plane wave first and spherical wave last.

[0040] In the process of determining the process conditions, the process parameters of the surface strengthening method that approaches the plane wave stress wave are first determined, and the depth of influence of the surface strengthening effect of the material under the pre-process conditions is tested and characterized. Then, under the requirement that the depth of influence of the composite strengthening effect is not lower than the depth of the strengthening layer induced by the pre-strengthening process, the specific process parameters of the strengthening method that approaches the spherical wave stress wave are determined by parameter adjustment.

[0041] 2. In the present invention, different surface strengthening technologies are not simply and invariably corresponded to fixed induced stress wave patterns; rather, the stress wave patterns induced by the surface strengthening treatment are corresponded to the specific processes of a certain technology with specific parameters. For example, in conventional cognition, technicians may identify the stress wave patterns induced by laser shock surface treatment as plane waves, and the stress wave patterns induced by mechanical shot peening surface treatment as spherical waves; in the present invention, it is believed that different processes under different parameter combinations corresponding to laser shock (or mechanical shot peening) surface treatment may lead to different stress wave patterns on the surface of the material. Differentiating different processes determined by different parameters can more accurately distinguish stress wave patterns under different process conditions, which is helpful to determine the composite sequence of variable parameter multiple treatment processes of the same type of surface strengthening process.

[0042] 3. The method provided by the present invention can achieve the introduction of higher residual compressive stress field intensity inside the material, and has important application value for high-strength surface strengthening of high-strength materials or components; the method provided by the present invention can avoid technicians from conducting complicated comparative tests on the specific processes of variable parameter multiple surface strengthening through trial and error. Through a small amount of preliminary stress wave characterization work, the composite process setting of variable parameter multiple surface strengthening can be realized, showing outstanding economic value. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a schematic diagram of the wave state of the plane stress wave caused by the surface strengthening described in the present invention.

[0044] Figure 2 This is a schematic diagram of the wave state of the spherical stress wave caused by the surface strengthening described in the present invention.

[0045] Figure 3 This is a schematic diagram of the direct strengthening area directly affected by the external load of the surface strengthening treatment described in the invention. DETAILED DESCRIPTION

[0046] The present invention will be further described below with reference to the embodiments and the accompanying drawings, but is not limited thereto.

[0047] A method for determining a composite surface strengthening process based on stress wave patterns, comprising:

[0048] (1) Determine the type of surface strengthening process to be used in the composite surface strengthening process, and preliminarily formulate the surface strengthening process conditions in the composite surface strengthening process; based on actual processing requirements and equipment conditions, preliminarily formulate the specific process parameters of different or the same type of surface strengthening processes used in the composite process.

[0049] The surface strengthening process is a surface processing process that can realize strong plastic deformation in physical form and can realize single-point (i.e., fixed area) treatment. The surface strengthening process includes mechanical shot peening, ultrasonic shot peening, laser shock, milligram energy shock, etc.; the specific process parameters of different surface strengthening processes are as follows: the parameters of mechanical shot peening include shot peening air pressure, shot flow, material, hardness, size and other shot specifications; the parameters of ultrasonic shot peening include ultrasonic indicators such as power and amplitude, and shot material specifications such as type and size; the parameters of laser shock include the material and specifications of the absorption layer and the constraint layer, and laser parameters such as energy, wavelength, and pulse width; the parameters of milligram energy shock include impact indicators such as amplitude and speed, and impact needle specifications such as diameter.

[0050] Single-point treatment refers to a process whereby technicians select only a fixed area of the surface to be treated for surface strengthening. This process involves a single treatment medium, such as a single shot, a single spot, or a single impact needle, for a fixed area. For example, mechanical and ultrasonic shot peening involve surface treatment using a single shot; laser peening involves surface treatment using a single spot formed by a laser beam; and milligram energy impaction involves surface treatment using a single impact needle.

[0051] The composite surface strengthening is performed by using the same surface strengthening process or different surface strengthening processes, and when the composite surface strengthening is performed by using the same type of surface strengthening process, the specific process conditions used by the surface strengthening process are different.

[0052] (2) Characterize and analyze the residual stress field in the direct strengthening area of the material to determine the stress wave pattern generated by different surface strengthening process conditions;

[0053] In step (2), if Figure 3 As shown in FIG, the direct strengthening area is the area on the material surface that directly bears the external load during the surface treatment process, and the direct strengthening area is the area extending from the material surface to the inside of the material to a depth of 1 mm.

[0054] For various surface strengthening techniques currently used in industry, such as shot peening, ultrasonic treatment, and impact treatment, the maximum depth of residual stress induced within the material is on the order of millimeters. The region from a depth of 1 mm to the material surface most directly represents the stress wave pattern caused by surface strengthening. To facilitate the identification of stress wave patterns, the direct strengthening region described in this invention is within a depth of 1 mm within the material.

[0055] The stress distribution cloud map of the directly strengthened area is obtained by finite element numerical simulation to qualitatively judge the stress wave type. When the finite element numerical simulation method is used for qualitative judgment, its cost is lower and the efficiency is higher. Alternatively, the actual test method can be used to quantitatively judge the stress wave type with the help of the residual stress field distribution data of the directly strengthened area.

[0056] The actual test method is adopted to quantitatively judge the stress wave type with the help of the residual stress field distribution data of the direct strengthening area. The specific process is: in the fixed surface area of single-point treatment, the residual stress is measured from the surface of different positions to the inside, and the residual stress variation curve along the depth of different positions is obtained, that is, the residual stress field variation curve of different positions is obtained. At the same time, the distribution depth of different numerical residual stresses at different positions is obtained, and these depth positions are connected to form the equal residual stress lines of different numerical residual stresses; there is no limitation on the test instrument, and the traditional lossy drilling method, the non-destructive X-ray diffraction method, and the more advanced neutron diffraction method can be used to determine the residual stress field distribution of the direct strengthening area.

[0057] like Figure 1 As shown in Figure 2, when the equal residual stress line in the directly strengthened area tends to be parallel to the material surface, it is determined that the surface stress wave type of the material caused by the surface strengthening process conditions is a plane wave type;

[0058] like Figure 2 As shown in the figure, when the equal residual stress lines in the direct strengthening area of the material surface are arc-shaped and the maximum residual stress value is in the middle of the direct strengthening area, it is determined that the stress wave type on the material surface caused by the process conditions of the surface strengthening method is a spherical wave type.

[0059] The stress wave pattern induced by the surface strengthening method corresponds to the surface strengthening process conditions. However, in conventional knowledge, technicians may identify the stress wave pattern induced by laser shock surface treatment as a plane wave, while the stress wave pattern induced by mechanical shot peening surface treatment as a spherical wave. If based on this conventional knowledge, the same type of surface strengthening process cannot be used to determine the composite order of variable parameter multiple treatment processes. In the present invention, it is believed that different process conditions under different parameter combinations corresponding to the laser shock surface treatment method may lead to different stress wave patterns on the surface of the material. This design treats different processes determined by different parameters differently, and can more accurately distinguish the stress wave patterns of different process conditions, which helps to achieve the composite order determination of variable parameter multiple treatment processes for the same type of surface strengthening process.

[0060] Further preferably, when determining the plane wave stress distribution, if the depth difference between the middle and edge positions of the equal residual stress lines at a depth of 300 μm to 400 μm from the material surface in the direct strengthening area does not exceed 25% of the average depth value of the equal residual stress lines, it is determined to be a plane wave type; otherwise, the measured stress wave type is determined to be a spherical wave type.

[0061] For most currently used surface strengthening technologies that involve strong plastic deformation, this depth is a moderate surface strengthening depth that most technologies can achieve. If the residual stress influence depth of the surface strengthening process used by technicians is too small or too large, the aforementioned depth of 300μm to 400μm can be adjusted lower or higher. It should be noted that based on the influence depth of most surface strengthening processes, the present invention uses the equal residual stress line at 300μm to 400μm as the basic basis for determining stress wave characteristics.

[0062] It should be noted that the stress wave type described in the present invention is determined solely based on the depth difference between the center and edge of the directly strengthened region. If the depth difference between the center and edge does not meet the soccer ball surface wave requirement, but the maximum depth difference at other locations reaches 25% of the average depth of the designated isostress line, the stress wave type is still considered a plane wave.

[0063] (3) According to the differences in stress wave patterns generated by different surface strengthening process conditions, the adjustment principles of surface strengthening process conditions in the composite surface strengthening process are determined:

[0064] If different surface strengthening process conditions produce different stress wave patterns, then proceed to step (4);

[0065] If different surface strengthening process conditions produce the same stress wave pattern, but the wave pattern is not completely consistent, then go to step (5);

[0066] (4) According to the composite strengthening sequence of first generating a plane wave and then generating a spherical wave, the process parameters of the surface strengthening process are adjusted to determine the composite surface strengthening process;

[0067] In step (4), when adjusting the process parameters of the surface strengthening process, a quantitative analysis of the residual stress field is performed on the different surface strengthening processes used in the composite strengthening treatment proposed in step (2), that is, the maximum residual compressive stress of the outer surface layer induced by the surface strengthening process is obtained; and according to the quantitative analysis results of the residual stress field distribution characteristics, the parameters of the pre- and post-surface strengthening processes are adjusted so that the maximum residual compressive stress intensity generated on the material surface by the pre-surface strengthening process is less than the maximum residual compressive stress intensity generated by the post-surface strengthening process.

[0068] The specific parameters adjusted for different surface enhancement processes vary and are not specifically defined here. For example, for mechanical shot peening, the shot velocity can be varied by adjusting the shot pressure; for laser peening, the laser energy can be adjusted; and for ultrasonic peening or Hawkes energy peening, the impact amplitude can be adjusted.

[0069] This step requires that the residual stress wave types induced by the different surface strengthening processes are different, and a composite surface strengthening processing method with plane wave in front and spherical wave in the back is determined. According to the order set in the composite processing, the first surface treatment is called the front surface strengthening process, and the subsequent surface treatment is called the back surface strengthening process.

[0070] (5) Determine the operating sequence of different surface strengthening processes during the composite treatment process based on the residual stress field distribution characteristics;

[0071] In step (5), based on the residual stress field distribution characteristics, the operation sequence of different surface strengthening processes in the composite treatment process is determined. The specific process is as follows:

[0072] A comparative analysis of the residual compressive stress field strengths generated by different surface strengthening processes was conducted. The surface strengthening process that produced relatively low residual compressive stress field strengths was designated as the pre-surface strengthening process, while the surface strengthening process that produced relatively high residual compressive stress field strengths was designated as the post-surface strengthening process. On the residual stress distribution curve along the material depth, the area enclosed by the residual compressive stress curve and the horizontal and vertical coordinates is the residual compressive stress field strength, where the horizontal coordinate represents the depth from the material surface to the interior, and the vertical coordinate represents the residual stress value.

[0073] It should be pointed out that the above method for determining the order of surface strengthening processes is applicable to all cases where the residual stress wave types induced by the different surface strengthening processes are all plane waves, as well as some cases where the residual stress wave types induced by the different surface strengthening processes are all spherical waves.

[0074] The residual compressive stress field intensity is the area enclosed by the residual stress curve and the horizontal and vertical coordinates on the residual stress distribution curve along the depth direction of the material, where the horizontal coordinate is the depth extending from the surface of the material to the inside, and the vertical coordinate is the residual stress value.

[0075] Further preferably, when the stress waves induced by different surface strengthening processes are all spherical wave types, if the difference in the residual compressive stress field intensities induced by the different surface strengthening processes is less than 10% of the average value of the residual compressive stress field intensities induced by the different surface strengthening processes, it is necessary to determine the order of the different surface strengthening processes by comparing the obviousness of the stress wave types. The specific determination method is: comparing the depth difference between the middle and edge positions in the stress wave type, and determining the surface strengthening process corresponding to the relatively large depth difference as the post-surface strengthening process, and determining the surface strengthening process corresponding to the relatively small depth difference as the pre-surface strengthening process.

[0076] Since the degree of difference in stress wave patterns has a stronger impact on variable parameter multiple composite treatments, the effect is more obvious when the order of the different surface strengthening processes is determined by the degree of significance of the corresponding stress wave patterns, compared with comparing the difference in residual compressive stress field intensities induced by the different surface strengthening processes.

[0077] (6) Determine the composite surface strengthening process based on the determined operating sequence of different surface strengthening processes and the corresponding specific process parameter combination of the surface strengthening process.

[0078] Example 2

[0079] A method for determining a composite surface strengthening process based on stress wave patterns, comprising:

[0080] This embodiment takes the surface strengthening treatment of a blade part in the field of aviation manufacturing as an example. (1) The technicians determined to use a composite treatment of two surface strengthening processes, laser shock and mechanical shot peening, as its surface treatment method. The preliminary proposed laser shock process conditions are: Nd-YAG laser wavelength 1064nm, pulse width 18ns, laser energy 2J, circular beam with a diameter of 2.5mm, beam energy distribution characteristic of flat top distribution, absorption layer of 1mm deionized water curtain, absorption layer of black 3M tape; mechanical shot peening process conditions are: pneumatic shot peening machine shot peening pressure 3MPa, shot peening flow rate 8kg·min -1 , S230 steel shot with a diameter of 0.6mm, shot peening time 16s.

[0081] (2) The residual stress field changes induced by the single-point impact of mechanical shot peening are obtained through the finite element model of the corresponding process. Finite element simulations are performed on the surface strengthening processes under the above two specific process conditions. Analysis of the numerical simulation results shows that the residual stress wave type induced by laser shock is a plane wave, while the residual stress wave type induced by mechanical shot peening is a spherical wave.

[0082] (3) Determine the composite treatment sequence of laser shock first and mechanical shot peening later. In addition, it can be obtained from the numerical simulation results that the residual compressive stress on the material surface induced by laser shock is greater than that induced by mechanical shot peening, so the specific processes of the two different technologies need to be adjusted. The shot peening pressure used in mechanical shot peening is increased to 5 MPa. At this time, the residual compressive stress on the material surface induced by mechanical shot peening with the corresponding change in the projectile incident speed exceeds that induced by laser shock. Finally, the composite strengthening treatment process of the blade part is determined as follows: first, the laser shock treatment of the above process (process parameters are not adjusted) is used for pre-surface strengthening, and then the mechanical shot peening of the above adjustment process (shot peening pressure is increased from 3 MPa to 5 MPa) is used for post-surface strengthening.

[0083] The key value of the determination provided by this invention lies in its pre-emptive (i.e., composite) determination (i.e., determining whether composite processing is feasible and, if composite processing does not achieve the maximum residual compressive stress field intensity, determining how to adjust the existing single-processing process). Compared to conventional trial-and-error methods for obtaining the optimal composite process, the method described in this invention is more economical. This significant improvement can be directly reflected in the magnitude of the residual compressive stress field intensity.

[0084] The composite strengthening treatment process determined in this embodiment is referred to as process 1; process 1: laser shock process as the pre-strengthening process; mechanical shot peening process as the post-strengthening process, and the shot peening gas pressure is set to 5 MPa.

[0085] Process 2, process 3 and process 4 are used for comparison. Specifically,

[0086] Process 2: Laser shock process is used as the pre-strengthening process, and the process conditions are the same as those in process 1; mechanical shot peening process is used as the post-strengthening process, and the shot peening gas pressure is set to 3 MPa.

[0087] Process 3: Mechanical shot peening is used as the pre-strengthening process, and the shot peening pressure is 3 MPa; laser shock process is used as the post-strengthening process, and the process conditions are the same as those of the laser shock process in process 1.

[0088] Process 4: Mechanical shot peening is used as the pre-strengthening process, and the shot peening pressure is 5 MPa; laser shock process is used as the post-strengthening process, and the process conditions are the same as those of the laser shock process in process 1.

[0089] The X-ray diffraction method was used to obtain the residual compressive stress field intensity of the materials induced by processes 1-4. The results showed that the residual compressive stress field intensity induced by process 1 was approximately 5%, 10%, and 15% higher than that of processes 2, 3, and 4, respectively.

[0090] Example 3

[0091] A method for determining a composite surface strengthening process based on stress wave patterns, comprising:

[0092] Taking the surface strengthening treatment of a blade part in the aviation manufacturing field as an example, the technicians decided to use a composite treatment of different process conditions of a surface strengthening technology such as laser shock as its surface treatment method. They preliminarily proposed one laser shock process condition: Nd-YAG laser wavelength 1064nm, pulse width 18ns, laser energy 2J, circular beam with a diameter of 2.5mm, beam energy distribution characteristic of flat-top distribution, absorption layer of 1mm deionized water curtain, absorption layer of black 3M tape; another laser shock process condition: Nd-YAG laser wavelength 1064nm, pulse width 18ns, laser energy 2J, circular beam with a diameter of 2.5mm, beam energy distribution characteristic of Gaussian distribution, absorption layer of 1mm deionized water curtain, absorption layer of black 3M tape.

[0093] The surface strengthening technologies under the above two specific process conditions were used to conduct actual experimental treatment on blade materials. The residual stress field distribution data at different positions on the surface of the material at a certain depth were measured using a stress analyzer. Through analysis, it can be seen that the residual stress wave types induced by the two laser shock treatment processes are both plane wave types.

[0094] Furthermore, after comparing the residual compressive stress field intensity at the center of the direct strengthening area, the results showed that the laser shock process with a flat-top energy distribution characteristic induced the material to obtain a relatively larger residual compressive stress field intensity. Therefore, the flat-top energy distribution laser shock process was used as a post-surface strengthening process, while the Gaussian energy distribution laser shock process was used as a pre-surface strengthening process.

[0095] Without adjusting the parameters, the composite strengthening treatment process of the blade part was finally determined as follows: first, the laser shock process with the above-mentioned Gaussian beam energy distribution form was used for pre-strengthening, and then the laser shock process with the above-mentioned flat-top beam energy distribution form was used for post-strengthening.

[0096] The composite strengthening treatment process determined in this embodiment is referred to as process 1, that is, process 1: the laser shock process with Gaussian beam energy distribution is determined as the pre-strengthening process, and the laser shock process with flat-top beam energy distribution is determined as the post-strengthening process.

[0097] The laser shock process with flat-top beam energy distribution was determined as the pre-strengthening process, the laser shock process with Gaussian beam energy distribution was determined as the post-strengthening process, and the composite strengthening treatment of the above processes was determined as process 2 for comparison.

[0098] The X-ray diffraction method was used to test and compare the residual compressive stress field intensity of the materials induced by processes 1 and 2. The results showed that the residual compressive stress field intensity induced by process 1 was about 10% higher than that of process 2.

[0099] Example 4

[0100] A method for determining a composite surface strengthening process based on stress wave patterns, comprising:

[0101] Taking the surface strengthening treatment of a blade part in the aviation manufacturing field as an example, the technicians decided to use a composite treatment of different process conditions of mechanical shot peening as its surface treatment method. The preliminary process conditions for the first mechanical shot peening were: pneumatic shot peening machine with a shot pressure of 3 MPa and a shot flow rate of 8 kg min -1 , 0.6mm diameter steel shot, shot peening time 16s; the second mechanical shot peening process conditions are: pneumatic shot peening machine shot peening pressure 4MPa, shot peening flow rate 8kg·min -1 , 1mm diameter steel shot, shot peening time 16s.

[0102] The surface strengthening technologies under the above two specific process conditions were used to conduct actual experimental treatment on blade materials. The residual stress field distribution data at different positions on the surface of the material at a certain depth were measured using a stress analyzer. Through analysis, it can be seen that the residual stress wave types induced by the two mechanical shot peening processes are both spherical wave types.

[0103] Furthermore, a comparison of the residual compressive stress field intensity at the center of the directly strengthened area showed that the residual compressive stress field intensity induced by the two mechanical shot peening processes was essentially equal. By comparing and analyzing the morphological characteristics of the stress wave patterns induced by the two processes, it was found that the depth difference between the center and edge of the stress wave pattern induced by the first process condition was greater, thus determining that the second process condition was a pre-surface strengthening process, while the first process condition was a post-surface strengthening process.

[0104] Without adjusting the parameters, the final composite strengthening process for this blade component was determined as follows: first using the second mechanical shot peening process for pre-strengthening, and then using the first mechanical shot peening process for post-strengthening. The two surface strengthening processes determined were referred to as process 1.

[0105] The first mechanical shot peening process was determined as the pre-strengthening process, the second mechanical shot peening process was determined as the post-strengthening process, and the composite strengthening treatment of the above processes was designated as process 2 for comparison.

[0106] The neutron diffraction method was used to test and compare the residual compressive stress field intensity of the materials induced by processes 1 and 2. The results showed that the residual compressive stress field intensity induced by process 1 was about 15% higher than that of process 2.

[0107] In pursuit of higher residual compressive stress field strength, the present invention provides a simple method for determining a variable parameter multiple surface strengthening composite process. According to the current technical requirements for surface strengthening treatment, if the material or component to be treated is subjected to variable parameter multiple treatments, it is necessary to determine the composite treatment process based on comparative analysis of different surface strengthening effects by setting comparative tests of different composite sequences or setting comparative tests of multiple groups of different single process composites. The present invention provides a basis for pre-process setting, which helps technicians to pre-judge whether the existing single treatment process can obtain the maximum residual compressive stress field strength through composite, and how to adjust the existing single treatment process if the maximum residual compressive stress field strength is to be obtained.

Claims

1. A method for determining a composite surface strengthening process based on stress wave patterns, characterized in that: include: (1) Determine the type of surface strengthening process to be used in the composite surface strengthening process and preliminarily formulate the surface strengthening process conditions in the composite surface strengthening process; (2) Characterize and analyze the residual stress field in the direct strengthening area of the material to determine the stress wave pattern generated by different surface strengthening process conditions; (3) According to the differences in stress wave patterns generated by different surface strengthening process conditions, the adjustment principles of surface strengthening process conditions in the composite surface strengthening process are determined: If different surface strengthening process conditions produce different stress wave patterns, then proceed to step (4); If different surface strengthening process conditions produce the same stress wave pattern, but the wave pattern is not completely consistent, then go to step (5); (4) According to the composite strengthening sequence of first generating a plane wave and then generating a spherical wave, the process parameters of the surface strengthening process are adjusted to determine the composite surface strengthening process; (5) Determine the operating sequence of different surface strengthening processes during the composite treatment process based on the residual stress field distribution characteristics; (6) Determine the composite surface strengthening process based on the determined operating sequence of different surface strengthening processes and the corresponding specific process parameter combination of the surface strengthening process.

2. The method for determining a composite surface strengthening process based on stress wave patterns according to claim 1, characterized in that: In step (1), the surface strengthening process is a surface processing process that can achieve plastic deformation and single-point treatment; The composite surface strengthening is performed by using the same surface strengthening process or different surface strengthening processes, and when the composite surface strengthening is performed by using the same type of surface strengthening process, the specific process conditions used by the surface strengthening process are different.

3. The method for determining a composite surface strengthening process based on stress wave patterns according to claim 1, characterized in that: In step (2), the direct strengthening area is the area on the material surface that directly bears the external load during the surface treatment process, and the direct strengthening area is the area extending from the material surface to the inside of the material to a depth of 1 mm.

4. The method for determining a composite surface strengthening process based on stress wave patterns according to claim 1, wherein: In step (2), the stress distribution cloud map of the directly strengthened area is obtained by finite element numerical simulation to qualitatively determine the stress wave type; or the stress wave type is quantitatively determined by actual test method with the help of residual stress field distribution data of the directly strengthened area.

5. The method for determining a composite surface strengthening process based on stress wave patterns according to claim 4, characterized in that: The actual test method is used to quantitatively determine the stress wave type with the help of the residual stress field distribution data of the directly strengthened area. The specific process is as follows: in a fixed surface area treated at a single point, the residual stress is measured from the surface to the inside at different positions, and the residual stress variation curve along the depth at different positions is obtained, that is, the residual stress field variation curve at different positions is obtained. At the same time, the distribution depth of different residual stress values at different positions is obtained. These depth positions are connected to form the equal residual stress lines of different residual stress values. The residual stress field distribution in the direct strengthening area is measured by drilling method, X-ray diffraction method or neutron diffraction method.

6. The method for determining a composite surface strengthening process based on stress wave patterns according to claim 1, characterized in that: In step (2), when the equal residual stress line of the directly strengthened area tends to be parallel to the material surface, it is determined that the material surface stress wave type caused by the surface strengthening process conditions is a plane wave type; When the equal residual stress lines in the directly strengthened area of the material surface are arc-shaped and the maximum residual stress value is in the middle of the directly strengthened area, it is determined that the stress wave type on the material surface caused by the process conditions of the surface strengthening method is a spherical wave type.

7. The method for determining a composite surface strengthening process based on stress wave patterns according to claim 6, characterized in that: When determining the plane wave stress distribution, if the depth difference between the middle and edge positions of the equal residual stress lines at a depth of 300μm to 400μm from the material surface in the direct strengthening area does not exceed 25% of the average depth value of the equal residual stress lines, it is determined to be a plane wave type; otherwise, the measured stress wave type is determined to be a spherical wave type.

8. The method for determining a composite surface strengthening process based on stress wave patterns according to claim 1, characterized in that: In step (4), when adjusting the process parameters of the surface strengthening process, a quantitative analysis of the residual stress field is performed on the different surface strengthening processes used in the composite strengthening treatment proposed in step (2), that is, the maximum residual compressive stress of the outer surface layer induced by the surface strengthening process is obtained; According to the quantitative analysis results of the residual stress field distribution characteristics, the parameters of the pre- and post-surface strengthening processes are adjusted so that the maximum residual compressive stress intensity generated on the material surface by the pre-surface strengthening process is smaller than the maximum residual compressive stress intensity generated by the post-surface strengthening process.

9. The method for determining a composite surface strengthening process based on stress wave patterns according to claim 1, characterized in that: In step (5), based on the residual stress field distribution characteristics, the operation sequence of different surface strengthening processes in the composite treatment process is determined. The specific process is as follows: According to the comparative analysis of the residual compressive stress field strength generated by different surface strengthening processes, the surface strengthening process that obtains a relatively small residual compressive stress field strength is set as the pre-surface strengthening process, while the surface strengthening process that obtains a relatively large residual compressive stress field strength is set as the post-surface strengthening process.

10. The method for determining a composite surface strengthening process based on stress wave patterns according to claim 9, characterized in that: When the stress waves induced by different surface strengthening processes are all spherical wave types, if the difference in the residual compressive stress field intensities induced by the different surface strengthening processes is less than 10% of the average value of the residual compressive stress field intensities induced by the different surface strengthening processes, it is necessary to determine the order of the different surface strengthening processes by comparing the degree of prominence of the stress wave types. The specific determination method is: comparing the depth difference between the middle and edge positions in the stress wave type, determining the surface strengthening process corresponding to the relatively large depth difference as the post-surface strengthening process, and determining the surface strengthening process corresponding to the relatively small depth difference as the pre-surface strengthening process.

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