Method for regulating and controlling monotonicity and non-monotonicity distribution trend of residual compressive stress field on surface layer of structural material

Abstract

The invention discloses a method for regulating and controlling the monotonicity and non-monotonicity distribution trend of a residual compressive stress field of a surface layer of a structural material, and belongs to the technical field of plastic deformation surface strengthening of the structural material. The method comprises the following steps: determining a target requirement for introducing a residual compressive stress field distribution trend in surface strengthening, and determining a surface strengthening process technology to be adopted by judging whether a given surface strengthening process technology exists or not and judging whether the surface strengthening process technology is changed or not according to influence factors capable of changing the surface strengthening process technology. And parameter setting is determined based on the process condition of deformation time difference of positions inside and outside the material surface layer impact area, so that the strengthening effect meeting the distribution trend requirement of the target residual compressive stress is obtained. Through the regulation and control method, the residual stress distribution state that monotonicity regulation and control is non-monotonicity, non-monotonicity regulation and control is monotonicity, and monotonicity regulation and control is further close to monotonicity can be realized, or the residual stress distribution state that non-monotonicity regulation and control is further close to non-monotonicity can be realized.

Description

Technical Field

[0001] The invention belongs to the technical field of plastic deformation surface strengthening of structural materials, and specifically relates to a method for regulating the monotonicity and non-monotonicity distribution trend of residual compressive stress field in the surface layer of structural materials. Background Art

[0002] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention, and should not necessarily be regarded as an admission or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art.

[0003] High-end equipment in important industries such as aerospace, transportation, etc. needs to operate stably for a long time under harsh service conditions such as high loads. The long life and high reliability manufacturing of structural materials for high-end equipment have become the basic premise and important guarantee for maintaining the normal operation of equipment. Surface strengthening process technologies such as mechanical shot peening and laser shock induce a certain intensity of residual compressive stress field in the surface layer of structural materials by high-speed impact, which achieves engineering application effects such as fatigue life extension through the offset effect relative to the external load. The maximum residual compressive stress introduced into the surface layer of the material by plastic deformation surface strengthening appears at different locations under different process conditions. When the maximum residual compressive stress appears on the surface or sub-surface, it plays a role in inhibiting the initiation or extension of fatigue cracks at different locations. Based on the above, for the specific location of service failure of structural materials of engineering equipment, changing the location of the maximum residual compressive stress introduced into the surface layer of the material by surface strengthening can achieve the optimal effect in closing failure cracks or delaying their expansion.

[0004] The different locations of the maximum residual compressive stress lead to the monotonic and non-monotonic distribution trends of the residual compressive stress field on the surface of the material. However, technicians are unable to qualitatively or quantitatively adjust or control the distribution trend of the residual compressive stress field from the aspects of the formation principle and its inducing factors. Regulating the location of the maximum residual compressive stress induced by surface strengthening according to the different locations of the fatigue failure cracking of engineering structures has important engineering application value. Therefore, regulating the monotonic and non-monotonic distribution trends of the residual compressive stress field on the surface of structural materials has become a problem that technicians need to solve. Summary of the invention

[0005] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a method for regulating the monotonicity and non-monotonicity distribution trends of the residual compressive stress field in the surface layer of a structural material, which can achieve effective regulation of the monotonicity and non-monotonicity distribution trends of the residual compressive stress field in the surface layer of a structural material, and can achieve monotonicity regulation to non-monotonicity, non-monotonicity regulation to monotonicity, monotonicity regulation to a residual stress distribution state that is further close to monotonicity, or non-monotonicity regulation to a residual stress distribution state that is further close to non-monotonicity.

[0006] In order to achieve the above object, the technical solution of the present invention is:

[0007] In a first aspect, the present invention provides a method for regulating the monotonicity and non-monotonicity distribution trend of the residual compressive stress field in the surface layer of a structural material, comprising the following steps:

[0008] S1: Determine the target requirements for the distribution trend of residual compressive stress field to be introduced by surface strengthening;

[0009] S2: According to the target requirements, select and determine the surface strengthening process technology and its parameters, and the parameter selection is based on the process conditions that cause the difference in deformation time between the inner and outer positions of the material surface impact area;

[0010] When a monotonic residual compressive stress distribution is required, the process parameters are selected so that the deformation time difference between the inner and outer positions of the impact area is small;

[0011] When a non-monotonic residual compressive stress distribution is required, the process parameters that result in a large difference in deformation time between positions inside and outside the impact area are selected;

[0012] S3: The surface strengthening process technology and its parameters are used to perform surface strengthening treatment on the structural material to be strengthened, so as to obtain a strengthening effect that meets the requirements of the residual compressive stress distribution trend.

[0013] In one or more embodiments, in step S1, it is assumed that the strengthening requirements of the structural material to be strengthened have been analyzed, and the target requirements of the residual stress distribution state to be introduced for surface strengthening are clarified. Preferably, if the failure analysis shows that the fatigue cracking of the structural material to be strengthened occurs in the sub-surface of the material, it is necessary to introduce the maximum residual compressive stress at the sub-surface of the structural material to be strengthened; and if the fatigue cracking occurs on the outermost surface of the material, it is necessary to introduce the maximum residual compressive stress at the outermost surface of the material.

[0014] In one or more embodiments, in step S2, the surface strengthening process technology includes a contact surface strengthening process technology and a non-contact surface strengthening process technology. The contact surface strengthening process technology includes but is not limited to mechanical shot peening and ultrasonic shot peening; the non-contact surface strengthening process technology includes laser shock and the like. The contact surface strengthening process technology (such as mechanical shot peening) induces a non-monotonic residual stress distribution trend in the material surface layer, while the non-contact surface strengthening process technology (such as laser shock) induces a monotonic residual stress distribution trend in the material surface layer.

[0015] In one or more embodiments, in step S2, the selection of the surface strengthening process technology is determined based on the influencing factors of the changeable surface strengthening process technology, specifically including:

[0016] a: If there is no established surface strengthening process technology for the structural material to be strengthened, then if the hardware conditions permit, choose the surface strengthening process technology that is most likely to obtain the residual stress distribution trend of the current state;

[0017] b: If there is an established surface strengthening process technology for the structural material to be strengthened, whether to change the surface strengthening process technology shall be determined based on the influencing factors that can change the surface strengthening process technology.

[0018] In one or more embodiments, in step S2, the influencing factors of the changeable surface strengthening process technology include but are not limited to hardware conditions, the regulation range of residual stress distribution trend and the characteristic requirements of the structural material to be strengthened.

[0019] The hardware conditions include whether there are processing equipment and whether the process condition setting range of the existing processing equipment is sufficient; the characteristic requirements of the structural material to be strengthened include the structural characteristics, mechanical properties and surface integrity of the structural material to be strengthened. If any aspect of the characteristic requirements of the structural material to be strengthened is not allowed, it means that the characteristic requirements are not met.

[0020] Preferably, the structural features of the structural material to be strengthened may include the presence of curved surfaces, hidden surfaces, and other conditions that affect the implementation of the process. For example, the presence of shielding structures on gears, tooth surfaces, or tooth bottoms indicates that the structural features are not allowed.

[0021] Preferably, the surface integrity of the structural material to be strengthened includes residual stress, surface roughness, and depth of penetration into the surface layer of the material.

[0022] In one or more embodiments, in step a, when hardware conditions permit, the surface strengthening process technology that is most likely to obtain the residual stress distribution trend of the current state is selected, including: if a monotonic residual compressive stress field is to be introduced, a non-contact surface strengthening process technology is preferred, that is, a short-pulse laser shock surface strengthening technology with a flat-top distribution of laser energy; and if a non-monotonic residual compressive stress field is to be introduced, a contact surface strengthening process technology is preferred, that is, mechanical shot peening or ultrasonic shot peening.

[0023] In one or more embodiments, in step b, under the premise of the existence of an established surface strengthening process technology, based on the influencing factors of the changeable surface strengthening process technology, within the scope permitted by conditions, the surface strengthening process technology is changed to a surface strengthening process technology that can obtain the target stress state; if conditions do not permit, the established surface process technology is maintained, and the trend adjustment of the residual stress distribution state to be introduced is performed within the adjustable range of the process parameters of the established surface strengthening process technology, or the trend adjustment within the adjustable range of the process parameters is not performed.

[0024] In one or more embodiments, in step b, based on the determination of the target requirements for the introduced residual stress distribution state, if the residual stress distribution trend introduced by the currently used surface strengthening process technology does not meet the target requirements, the surface processing technology may be changed if other conditions permit. The other conditions may be that both the hardware conditions and the characteristic requirements of the structural material to be strengthened are permitted, or that the hardware conditions are permitted, but the characteristic requirements of the structural material to be strengthened are not permitted.

[0025] Preferably, for structural materials that are to be treated for life extension using non-contact (laser shock) surface strengthening technology, if a non-monotonic residual stress distribution state is to be obtained, it is possible to consider changing the non-contact (laser shock) surface strengthening technology that is difficult to obtain a non-monotonic residual stress state to a contact surface strengthening technology (mechanical shot peening, etc.).

[0026] In one or more embodiments, in step b, based on the determination of the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the currently used surface strengthening process technology does not meet the target requirements, and the characteristic requirements of the structural characteristics, mechanical properties and surface integrity of the structural material to be strengthened do not allow the surface strengthening process technology to be changed. In this case (hardware conditions do not allow), the trend of the residual stress distribution state to be introduced can only be adjusted within the adjustable range of the process parameters of the established surface strengthening process technology, so that the residual stress distribution state is as close to the required target state as possible.

[0027] In one or more embodiments, in step b, based on determining the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the currently used surface strengthening process technology does not meet the target requirements, the characteristic requirements of the structural characteristics, mechanical properties and surface integrity of the structural material to be strengthened allow changes to the surface strengthening process technology, but the hardware conditions do not allow, then the trend of the residual stress distribution state to be introduced can only be adjusted within the adjustable range of the process parameters of the established surface strengthening process technology, so that the residual stress distribution state is as close to the required target state as possible.

[0028] In one or more embodiments, in step b, based on determining the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the currently used surface strengthening process technology meets the target requirements, and the characteristic requirements of the structural characteristics, mechanical properties and surface integrity of the structural material to be strengthened also allow changes to the surface strengthening process technology, in this case (including hardware conditions permitting and hardware conditions not permitting), the original established surface process and the original process parameters are maintained, that is, the process is not changed, and there is no need to adjust the process parameters of the established surface strengthening process technology.

[0029] In one or more embodiments, in step b, based on determining the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the currently used surface strengthening process technology meets the target requirements, but the hardware conditions do not allow, and the characteristic requirements of the structural characteristics, mechanical properties and surface integrity of the structural material to be strengthened do not allow changes to the surface strengthening process technology, in this case, the trend of the residual stress distribution state to be introduced can only be adjusted within the adjustable range of the process parameters of the established surface strengthening process technology, so that the residual stress distribution state is as close to the required target state as possible.

[0030] In one or more embodiments, in step b, based on determining the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the currently used surface strengthening process technology meets the target requirements and the hardware conditions allow, but the structural characteristics, mechanical properties, surface integrity and other characteristics of the structural material to be strengthened do not allow changes to the surface strengthening process technology, in this case, consider changing the surface strengthening process technology.

[0031] In one or more embodiments, if the surface of the structural material to be strengthened has a quantitative upper limit requirement on the maximum surface roughness, if the non-contact (such as laser shock) surface strengthening process technology that can obtain a smaller surface roughness (Ra2.0μm to Ra6.0μm) is changed to a contact surface strengthening process technology (such as mechanical shot peening) that can obtain a larger surface roughness (Ra6.0μm to Ra12.0μm), it will cause the surface state of the structural material to be strengthened to be unqualified, and at this time, the conditions for changing the surface strengthening process technology are not met.

[0032] In one or more embodiments, if the structural material to be strengthened has a quantitative lower limit requirement on the depth of the surface layer of the material into which the residual stress is to be introduced, if the non-contact (such as laser shock) surface strengthening process technology that can obtain a larger residual compressive stress depth is changed to a contact surface strengthening process technology (such as mechanical shot peening) that can obtain a smaller residual compressive stress depth, it will cause the residual stress introduction depth of the structural material to be strengthened to not meet the standard, and at this time, the conditions for changing the surface strengthening process technology are also not met.

[0033] In one or more embodiments, in step S2, the smaller the time difference for deformation of the inner and outer positions of the impact zone, the smaller the height difference of the impact zone is (the difference is less than 20% of the plane width or diameter of the impact zone); the larger the time difference for deformation of the inner and outer positions of the impact zone, the larger the height difference of the impact zone is (the difference is not less than 20% of the plane width or diameter of the impact zone).

[0034] Furthermore, the different depths of the pressed material surface result in different differences in deformation time at positions inside and outside the impact area, and the corresponding residual stress distribution trends present different states, specifically: when the depth of the pressed material surface is greater, the deformation time of the center of the impact area is longer, the mechanical / laser contact of the projectile / spot and the constraint of the edge of the impact area that has completed elastic recovery both make the elastic deformation release of the sub-surface at the center of the impact area weaker, and the more likely it is to cause a significant non-monotonic stress field distribution in which the maximum residual compressive stress appears in the sub-surface of the material; conversely, when the depth of the pressed material surface is smaller, the difference between the deformation time of the center of the impact area and the deformation time of the edge of the impact area is smaller, the elastic deformation release of the sub-surface at the center of the impact area is stronger, the non-monotonicity of the residual stress distribution is less obvious or the residual stress distribution presents a monotonicity.

[0035] Furthermore, the process conditions that lead to the difference in deformation time between the inner and outer positions of the impact area on the surface of the material also include but are not limited to the following aspects:

[0036] (1) When the surface strengthening process technology to be adopted is changed, the contact deformation is changed to non-contact free deformation, such as mechanical shot peening to laser impact, ultrasonic shot peening to laser impact;

[0037] (2) When the proposed surface strengthening process technology is changed, the process time directly determines the strain rate, such as mechanical shot peening to laser shock, ultrasonic shot peening to laser shock;

[0038] (3) When the proposed surface strengthening process technology does not change, the shot size in the variable contact surface strengthening process (such as mechanical shot peening) causes the curvature diameter of the direct deformation area to change;

[0039] (4) When the proposed surface strengthening process technology remains unchanged, the beam energy distribution in the non-contact surface strengthening (such as laser shock) process is changed, for example, the transition from flat-top distribution to Gaussian distribution.

[0040] It should be pointed out that, regardless of whether the surface strengthening process technology is changed, when the residual stress distribution state proposed by the present invention is changed through regulation, the change of the residual compressive stress field strength and its main influencing indexes should not have a negative effect on the long-life service of the structural material to be strengthened, or the negative effect of the change of the residual compressive stress field strength and its main influencing indexes on the long-life service of the structural material to be strengthened should be lower than the positive effect brought about by the change of the residual stress distribution state. The main influencing indexes of the residual compressive stress field strength include surface residual compressive stress, maximum residual compressive stress, residual compressive stress depth, etc.

[0041] Specifically, when the residual stress distribution state plays a key role in the long service life of structural materials, when the stress distribution state is regulated according to the technical solution proposed in the present invention, the principle to be followed in changing the surface strengthening process technology or the established surface strengthening process parameters is that the residual compressive stress field intensity introduced into the material surface layer and its main influencing indicators do not change significantly, and the basis for judging the significant change is that the service life of the structural material subjected to surface processing by the final surface strengthening process technology must be improved.

[0042] In one or more embodiments, after completing step S3, the structural material to be strengthened obtains the intended residual stress distribution state, or compared with the state without surface processing, the surface residual stress distribution state of the structural material to be strengthened is further close to the intended residual stress distribution state.

[0043] One or some of the above technical solutions have the following advantages or beneficial effects:

[0044] (1) The control method provided by the present invention determines the surface strengthening process technology to be adopted based on the target requirement of the residual compressive stress field distribution trend to be introduced by surface strengthening, determines whether there is an established surface strengthening process technology and determines whether to change the surface strengthening process technology based on the influencing factors of the changeable surface strengthening process technology, and clarifies its parameter settings. The parameter selection is based on the process conditions of the deformation time difference between the inner and outer positions of the impact zone of the material surface. When a monotonic residual compressive stress distribution is required, the process parameters are selected to make the deformation time difference between the inner and outer positions of the impact zone smaller (that is, the height difference of the impact zone is less than 20% of the plane width or diameter of the impact zone); when a non-monotonic residual compressive stress distribution is required, the process parameters are selected to make the deformation time difference between the inner and outer positions of the impact zone larger (that is, the height difference of the impact zone is not less than 20% of the plane width or diameter of the impact zone); finally, the surface strengthening treatment of the structural material to be strengthened is performed according to the determined surface strengthening process technology and its parameter settings to obtain a strengthening effect that meets the target residual compressive stress distribution trend requirements. Through the above control method, it is possible to achieve monotonic control to non-monotonicity, non-monotonic control to monotonicity, monotonic control to a residual stress distribution state that is further approaching monotonicity, or non-monotonic control to a residual stress distribution state that is further approaching non-monotonicity.

[0045] (2) Aiming at the different failure modes of engineering equipment at different crack initiation locations, the corresponding residual stress distribution states that suppress failure are pointed out, and the technical strategies and corresponding measures that can achieve qualitative or quantitative regulation of the residual stress distribution states are implemented, making it possible to actively design and adjust the distribution position of the maximum residual compressive stress.

[0046] (3) The specific measures for regulating the residual stress distribution state are diverse and highly selective. Technicians can freely try and apply them within all process settings that can change the deformation time inside and outside the impact area. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0048] Figure 1 It is a logic flow chart of the method for regulating the monotonicity and non-monotonicity distribution trend of the residual compressive stress field in the surface layer of the structural material in Example 1 of the present invention;

[0049] Figure 2 It is a typical example of the residual stress distribution state of the surface layer of the material induced by the plastic deformation surface strengthening process technology described in the present invention;

[0050] Figure 3 A schematic diagram of the elastic-plastic deformation and its recovery caused by a typical mechanical shot peening process corresponding to a large difference in the deformation time at different positions of a single / time (shot / spot) impact area described in the present invention;

[0051] Figure 4 It is a schematic diagram of the elastic-plastic deformation and its recovery caused by the typical mechanical shot peening process corresponding to the small difference in deformation time at different positions in the single / time (shot / light spot) impact area described in the present invention. DETAILED DESCRIPTION

[0052] In the relevant expressions of the present invention, "surface" refers only to a "face" without the concept of thickness, and "surface layer" refers to a layered material area including the surface and a certain depth from the surface to the inside.

[0053] The matrix premise for the existence of residual stress is the stored elastic deformation that cannot be released inside the material. The position where the residual stress reaches the maximum value is where the elastic deformation storage is the largest. In the current technical results, mechanical shot peening and laser shock generally show two different residual stress distribution trends. Under normal circumstances, the residual stress distribution trend of the surface layer of the material induced by mechanical shot peening is non-monotonic, while the residual stress distribution trend of the surface layer of the material induced by laser shock is monotonic.

[0054] The present invention points out that the change in the residual stress distribution trend induced by different surface strengthening process technologies depends on the difference in deformation time at positions inside and outside the single / time (projectile / light spot) impact area; when the relative difference in deformation time at different positions (the ratio of the difference in deformation time at different positions to the total deformation time of all positions) is large, the degree of plastic deformation of the outermost surface at the inner position of the single / time (projectile / light spot) impact area on the surface of the material is also large, which directly leads to the inability to release the elastic deformation within a certain depth of the surface of the material to a large extent, and ultimately causes the maximum residual compressive stress on the surface of the material to appear in the sub-surface, and the residual compressive stress field distribution state is non-monotonic.

[0055] Figure 2 This is a typical example of the residual stress distribution state of the material surface induced by the plastic deformation surface strengthening process technology. Rx is a monotonic distribution stress field in which the maximum residual compressive stress of the material surface is located in the subsurface, and Ry and Rz are non-monotonic distribution stress fields in which the maximum residual compressive stress of the material surface is located on the outermost surface.

[0056] Figure 3 and Figure 4 The following are schematic diagrams of the elastic-plastic deformation and its recovery caused by the typical mechanical shot peening process when the difference in deformation time at different positions of a single / time (shot / spot) impact area is large and small. The diagram shows that in the process of surface strengthening treatment using mechanical shot peening technology, the inconsistent impact pressure causes the circular shot to press into the material surface at different depths; when the pressing depth is large, the center of the impact area maintains deformation for a long time, and the mechanical contact of the shot and the constraint of the edge of the impact area that has completed elastic recovery both make the elastic deformation release of the sub-surface at the center of the impact area weak, which is easy to cause the significant non-monotonic stress field distribution in the sub-surface of the material with the maximum residual compressive stress; on the contrary, when the circular shot is introduced into a small depth, the difference between the deformation time at the center of the impact area and the deformation time at the edge of the impact area is not obvious, the elastic deformation release of the sub-surface at the center of the impact area is strong, and the non-monotonicity of the residual stress distribution is relatively insignificant or the residual stress distribution is monotonic.

[0057] The above is a situation where the residual stress distribution trend corresponding to the different depths of the circular projectile pressed into the material surface under specific process conditions presents different states. In addition, the process conditions that can lead to the deformation time of the position inside and outside the impact area of ​​the single / time (projectile / spot) impact of the material surface also include but are not limited to: changing the contact deformation to non-contact free deformation, such as changing the mechanical shot peening to laser impact; changing the duration of the process that directly determines the strain rate, such as changing the mechanical shot peening to laser impact; changing the projectile size in the mechanical shot peening process, causing the curvature diameter of the direct deformation area to change; changing the beam energy distribution in the laser impact process, such as the transition from flat-top distribution to Gaussian distribution.

[0058] According to different process facility conditions, the process method of surface strengthening is modified or the relevant parameters of a single strengthening process are adjusted to achieve qualitative or quantitative regulation of the residual compressive stress field distribution trend on the surface of the structural material. The technical means described in the present invention are only applicable to the regulation of the residual stress distribution state when the existing hardware conditions permit, and are not applicable to the regulation of the strengthening effect beyond the existing hardware conditions. The hardware conditions include both whether there are processing equipment and whether the process condition setting range of the existing processing equipment is sufficient. In addition, when the residual stress distribution state changes due to changes in process conditions, the probability of a significant change in the overall residual compressive stress field strength is also relatively large. Therefore, the technical means described in the present invention are only applicable to industrial conditions where the residual stress distribution state plays a key role in the service life of structural materials, and are not applicable to specific scenarios where the overall residual compressive stress field strength determines the service life of structural materials.

[0059] In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below in conjunction with specific embodiments.

[0060] Example 1

[0061] A method for regulating the monotonicity and non-monotonicity distribution trend of residual compressive stress field in a surface layer of a structural material, comprising:

[0062] S1: Clarify the qualitative or quantitative requirements for the distribution trend of the residual compressive stress field to be introduced by surface strengthening.

[0063] This step assumes that the technicians have analyzed the strengthening requirements of the structural material to be strengthened and clarified the specific requirements for the residual stress distribution state to be introduced for surface strengthening. For example, if the failure analysis shows that the fatigue cracking of the structural material to be strengthened is likely to occur in the sub-surface of the material, then it is required that the maximum residual compressive stress to be introduced is located on the sub-surface of the material; and if the fatigue cracking is likely to occur on the outermost surface of the material, then it is required that the maximum residual compressive stress to be introduced is located on the outermost surface of the material.

[0064] S2: According to the target requirements, select and determine the surface strengthening process technology and its parameters, and the parameter selection is based on the process conditions that cause the difference in deformation time between the inner and outer positions of the material surface impact area;

[0065] When a monotonic residual compressive stress distribution is required, the process parameters are selected so that the deformation time difference between the inner and outer positions of the impact area is small;

[0066] When a non-monotonic residual compressive stress distribution is required, process parameters are selected that result in a large deformation time difference between locations inside and outside the impact region.

[0067] This step requires determining the surface strengthening process technology and parameter settings to be adopted.

[0068] The surface strengthening process technology includes contact surface strengthening process technology and non-contact surface strengthening process technology. The contact surface strengthening process technology includes but is not limited to mechanical shot peening and ultrasonic shot peening; the non-contact surface strengthening process technology includes laser shock and the like. The residual stress distribution trend of the surface layer of the material induced by the contact surface strengthening process technology (such as mechanical shot peening) is non-monotonic, while the residual stress distribution trend of the surface layer of the material induced by the non-contact surface strengthening process technology (such as laser shock) is monotonic.

[0069] The selection of surface enhancement technology is based on the factors that can affect the surface enhancement technology, including:

[0070] a: If there is no established surface strengthening process technology for the structural material to be strengthened, then if the hardware conditions permit, choose the surface strengthening process technology that is most likely to obtain the residual stress distribution trend of the current state;

[0071] b: If there is an established surface strengthening process technology for the structural material to be strengthened, whether to change the surface strengthening process technology shall be determined based on the influencing factors that can change the surface strengthening process technology.

[0072] The influencing factors of the changeable surface strengthening process technology include but are not limited to hardware conditions, the regulation range of residual stress distribution trend and the characteristic requirements of the structural materials to be strengthened. Among them, the hardware conditions include whether there are processing equipment, and whether the process condition setting range of the existing processing equipment is sufficient; the characteristic requirements of the structural materials to be strengthened include the structural characteristics, mechanical properties and surface integrity of the structural materials to be strengthened. If one of the characteristic requirements of the structural materials to be strengthened is not allowed, it means that the characteristic requirements are not met. The structural characteristics of the structural materials to be strengthened can be whether there are curved surfaces, hidden surfaces, etc. that affect the implementation of the process. For example, if there is a shielding structure on the gear, tooth surface or tooth bottom, it means that the structural characteristics are not allowed. The surface integrity of the structural materials to be strengthened includes residual stress, surface roughness, and the depth of the surface layer of the pressed material.

[0073] In step a, when hardware conditions permit, the surface strengthening process technology that is most likely to obtain the residual stress distribution trend of the current state is selected, including: if a monotonic residual compressive stress field is to be introduced, a non-contact surface strengthening process technology is preferably used, that is, a short-pulse laser shock surface strengthening technology with flat-top distribution of laser energy; and if a non-monotonic residual compressive stress field is to be introduced, a contact surface strengthening process technology is preferably used, that is, mechanical shot peening or ultrasonic shot peening.

[0074] In step b, under the premise of the existence of a given surface strengthening process technology, according to the influencing factors of the changeable surface strengthening process technology, within the scope permitted by conditions, the surface strengthening process technology is changed to a surface strengthening process technology that can obtain the target stress state; if conditions do not allow, the given surface process technology is maintained, and the trend adjustment of the residual stress distribution state to be introduced is performed within the adjustable range of the process parameters of the given surface strengthening process technology, or the trend adjustment within the adjustable range of the process parameters is not performed. See Table 1 for details.

[0075] Table 1 Analysis of the influence factors of the changeable surface strengthening process technology on whether to change the process under the premise of meeting the target requirements:

[0076]

[0077]

[0078] √ represents: the influencing factor meets the requirements; × represents: the influencing factor does not meet the requirements.

[0079] In step b, on the basis of determining the target requirements for introducing the residual stress distribution state, if the residual stress distribution trend introduced by the currently used surface strengthening process technology does not meet the target requirements, if other conditions permit, the surface processing technology can be changed. Among them, the other conditions allow for both the hardware conditions and the characteristic requirements of the structural material to be strengthened, or the hardware conditions allow, but the characteristic requirements of the structural material to be strengthened do not allow, corresponding to the first and third processes in the table. Specifically: For structural materials that are intended to be treated with non-contact (laser shock) surface strengthening technology for life extension, if a non-monotonic residual stress distribution state is intended to be obtained, it can be considered to change the non-contact (laser shock) surface strengthening process technology that is difficult to obtain a non-monotonic residual stress state to a contact surface strengthening process technology (mechanical shot peening, etc.).

[0080] On the basis of determining the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the currently used surface strengthening process technology does not meet the target requirements, and the characteristic requirements of the structural characteristics, mechanical properties and surface integrity of the structural material to be strengthened do not allow the surface strengthening process technology to be changed. In this case (hardware conditions do not allow, corresponding to the second type in the table), the trend of the residual stress distribution state to be introduced can only be adjusted within the adjustable range of the process parameters of the established surface strengthening process technology, so that the residual stress distribution state is as close to the required target state as possible. For example: If the surface of the structural material to be strengthened has a quantitative upper limit requirement for the maximum surface roughness, if the non-contact (such as laser shock) surface strengthening process technology that can obtain a smaller surface roughness (Ra2.0μm to Ra6.0μm) is changed to a contact surface strengthening process technology (such as mechanical shot peening) that can obtain a larger surface roughness (Ra6.0μm to Ra12.0μm), it will cause the surface state of the structural material to be strengthened to be unqualified, and at this time, the conditions for changing the surface strengthening process technology are not met. If the structural material to be strengthened has a quantitative lower limit requirement on the depth of the surface layer of the material into which the residual stress is to be introduced, if the non-contact (such as laser shock) surface strengthening process technology that can obtain a larger residual compressive stress depth is changed to a contact surface strengthening process technology (such as mechanical shot peening) that can obtain a smaller residual compressive stress depth, it will cause the residual stress introduction depth of the structural material to be strengthened to not meet the standard. At this time, the conditions for changing the surface strengthening process technology are also not met.

[0081] On the basis of determining the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the currently used surface strengthening process technology does not meet the target requirements, and the characteristic requirements of the structural characteristics, mechanical properties and surface integrity of the structural material to be strengthened allow changes to the surface strengthening process technology, but the hardware conditions do not allow, then the trend of the residual stress distribution state to be introduced can only be adjusted within the adjustable range of the process parameters of the established surface strengthening process technology, so that the residual stress distribution state is as close to the required target state as possible (corresponding to the fourth type in the table).

[0082] On the basis of determining the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the currently used surface strengthening process technology meets the target requirements, and the characteristic requirements of the structural characteristics, mechanical properties and surface integrity of the structural material to be strengthened also allow changes to the surface strengthening process technology, in this case (including hardware conditions permitting and hardware conditions not permitting), maintain the original established surface process and the original process parameters, that is, do not change the process, and there is no need to adjust the process parameters of the established surface strengthening process technology (corresponding to types 5 and 7 in the table).

[0083] On the basis of determining the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the currently used surface strengthening process technology meets the target requirements, but the hardware conditions do not allow, and the characteristic requirements of the structural characteristics, mechanical properties and surface integrity of the structural material to be strengthened do not allow changes to the surface strengthening process technology, in this case, the trend of the residual stress distribution state to be introduced can only be adjusted within the adjustable range of the process parameters of the established surface strengthening process technology, so that the residual stress distribution state is as close to the required target state as possible (corresponding to the 6th type in the table).

[0084] On the basis of determining the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the currently used surface strengthening process technology meets the target requirements and the hardware conditions permit, but the structural characteristics, mechanical properties, surface integrity and other characteristic requirements of the structural material to be strengthened do not allow changes to the surface strengthening process technology, in this case, consider changing the surface strengthening process technology (corresponding to the 8th type in the table).

[0085] This step requires technicians to clarify the parameter settings of the surface strengthening process technology based on the target residual stress distribution state to be obtained. The relevant requirements for the parameter settings are based on the process conditions that can cause the deformation time of the position inside and outside the impact area of ​​the material surface by a single / time (projectile / spot).

[0086] The change in the residual stress distribution trend induced by different surface strengthening process technologies depends on the difference in deformation time at locations inside and outside the single / time (projectile / light spot) impact area; when the relative difference in deformation time at different locations (the ratio of the difference in deformation time at different locations to the total deformation time of all locations) is large, the degree of plastic deformation of the outermost surface at the inner position of the single / time (projectile / light spot) impact area on the surface of the material is also large, which directly leads to the inability to release the elastic deformation within a certain depth of the surface of the material to a large extent, and ultimately causes the maximum residual compressive stress on the surface of the material to appear in the sub-surface, and the distribution state of the residual compressive stress field is non-monotonic.

[0087] Making the relative difference in deformation time of inner and outer positions of the impact zone small means that the height difference of the impact zone is less than 20% of the plane width or diameter of the impact zone; making the relative difference in deformation time of inner and outer positions of the impact zone large means that the height difference of the impact zone is not less than 20% of the plane width or diameter of the impact zone.

[0088] Figure 2 This is a typical example of the residual stress distribution state of the material surface induced by the plastic deformation surface strengthening process technology. Rx is a monotonic distribution stress field in which the maximum residual compressive stress of the material surface is located in the subsurface, and Ry and Rz are non-monotonic distribution stress fields in which the maximum residual compressive stress of the material surface is located on the outermost surface.

[0089] Figure 3 and Figure 4 The following are schematic diagrams of the elastic-plastic deformation and its recovery caused by the typical mechanical shot peening process when the difference in deformation time at different positions of a single / time (shot / spot) impact area is large and small. The diagram shows that in the process of surface strengthening treatment using mechanical shot peening technology, the inconsistent impact pressure causes the circular shot to press into the material surface at different depths; when the pressing depth is large, the center of the impact area maintains deformation for a long time, and the mechanical contact of the shot and the constraint of the edge of the impact area that has completed elastic recovery both make the elastic deformation release of the sub-surface at the center of the impact area weak, which is easy to cause the significant non-monotonic stress field distribution in the sub-surface of the material with the maximum residual compressive stress; on the contrary, when the circular shot is introduced into a small depth, the difference between the deformation time at the center of the impact area and the deformation time at the edge of the impact area is not obvious, the elastic deformation release of the sub-surface at the center of the impact area is strong, and the non-monotonicity of the residual stress distribution is relatively insignificant or the residual stress distribution is monotonic.

[0090] The above is a situation where the residual stress distribution trend corresponding to the different depths of the round projectile pressed into the material surface under specific process conditions presents different states.

[0091] The relevant process conditions that lead to the difference in deformation time between the inner and outer positions of the impact zone on the surface of the material also include but are not limited to the following aspects: (1) When the surface strengthening process technology to be adopted is changed, the contact deformation is changed to non-contact free deformation, such as changing mechanical shot peening to laser shock; (2) When the surface strengthening process technology to be adopted is changed, the duration of the process that directly determines the strain rate is changed, such as changing mechanical shot peening to laser shock; (3) When the surface strengthening process technology to be adopted does not change, the shot size in the mechanical shot peening process is changed, causing the curvature diameter of the direct deformation area to change; (4) When the surface strengthening process technology to be adopted does not change, the beam energy distribution in the laser shock process is changed, such as the transition from flat-top distribution to Gaussian distribution.

[0092] It should be pointed out that, regardless of whether the surface strengthening process technology is changed, when the residual stress distribution state proposed by the present invention is changed through regulation, the change of the residual compressive stress field strength and its main influencing indexes should not have a negative effect on the long-life service of the structural material to be strengthened, or the negative effect of the change of the residual compressive stress field strength and its main influencing indexes on the long-life service of the structural material to be strengthened should be lower than the positive effect brought about by the change of the residual stress distribution state. The main influencing indexes of the residual compressive stress field strength include surface residual compressive stress, maximum residual compressive stress, residual compressive stress depth, etc.

[0093] Specifically, when the residual stress distribution state plays a key role in the long service life of structural materials, when the stress distribution state is regulated according to the technical solution proposed in the present invention, the principle to be followed in changing the surface strengthening process technology or the established surface strengthening process parameters is that the residual compressive stress field intensity introduced into the material surface layer and its main influencing indicators do not change significantly, and the basis for judging the significant change is that the service life of the structural material subjected to surface processing by the final surface strengthening process technology must be improved.

[0094] S3: The surface strengthening process technology and its parameters are used to perform surface strengthening treatment on the structural material to be strengthened, so as to obtain a strengthening effect that meets the requirements of the residual compressive stress distribution trend.

[0095] According to the determined surface strengthening process technology and its parameter settings, the surface strengthening treatment of the structural material to be strengthened is performed to obtain a strengthening effect that meets the requirements of the residual compressive stress distribution trend. After completing this step, the structural material to be strengthened obtains the residual stress distribution state to be obtained, or compared with the state in which the surface processing is not performed according to the technical solution, the residual stress distribution state of the surface layer of the structural material to be strengthened is closer to the residual stress distribution state to be obtained.

[0096] Example 2

[0097] A method for regulating the monotonicity and non-monotonicity distribution trend of residual compressive stress field in a surface layer of a structural material, comprising:

[0098] This embodiment takes the 20Cr gear steel used in a certain field as an example of the structural material to be strengthened. In a specific scenario in the application field, failure analysis shows that the failure crack originates from the sub-surface of the material, and the analysis conclusion points out that the life extension method includes enhancing the residual compressive stress in the sub-surface. The most economical and applicable surface strengthening process needs to be selected under the hardware conditions. After preliminary evaluation, the processing equipment has the conditions for mechanical shot peening and ultrasonic shot peening, but considering the cost-effectiveness and process maturity, mechanical shot peening technology is preferred.

[0099] S1: According to the hardware conditions and economic requirements, it is clear that the residual compressive stress field distribution state to be introduced is non-monotonic. Since there is no requirement for feature surface integrity or residual stress depth, the parameter optimization is performed based on the conventional mechanical shot peening process by default.

[0100] S2: Determine to use mechanical shot peening as the surface strengthening process technology. Low-cost round cast steel projectiles (diameter 0.4mm, hardness HRC45) are selected, the shot peening flow rate is set to 6kg / min, and the shot peening gas pressure is 1.5MPa. Preliminary experimental verification shows that this parameter combination can introduce a surface residual stress of -150MPa, a maximum residual compressive stress of -180MPa (located at a depth of 50μm in the surface layer), and a residual compressive stress depth of 400μm, which meets the non-monotonic characteristics of the residual compressive stress field and the conventional service requirements of the target material.

[0101] S3: The surface of the gear steel component to be strengthened was treated using the optimal mechanical shot peening process parameters. The test results after treatment showed that the residual compressive stress field on the surface of the component showed a non-monotonic distribution trend, which corresponds to the cracking failure characteristics of the target surface.

[0102] Example 3

[0103] A method for regulating the monotonicity and non-monotonicity distribution trend of residual compressive stress field in a surface layer of a structural material, comprising:

[0104] This embodiment takes the austenitic stainless steel material to be strengthened as an example in a certain field. In a specific scenario in the application field, failure analysis shows that the failure crack originates from the surface of the material, and the analysis conclusion points out that the life extension method includes enhancing the residual compressive stress on its surface. The established surface strengthening process technology of the austenitic stainless steel material is mechanical shot peening. The established mechanical shot peening process conditions can introduce a relatively high-intensity residual compressive stress field on the surface of the material. The stress field is a non-monotonic distribution state in which the maximum residual compressive stress is located in the sub-surface layer. The surface residual stress is -120MPa, the maximum residual compressive stress and its depth are -200MPa, 200μm, and the residual compressive stress depth is 600μm.

[0105] S1: Corresponding to the cracking failure mechanism of the target surface, the residual stress distribution state is introduced as monotonicity. Based on the processing equipment resource conditions, the surface strengthening method is changed to laser shock process technology.

[0106] S2: Corresponding to the residual compressive stress field intensity introduced by mechanical shot peening, the laser shock process conditions (Nd: YAG laser laser energy 3J, pulse width 10ns, circular beam with a diameter of 3mm, black tape absorption layer, deionized water curtain constraint layer) were determined by multiple optimizations. The introduced residual stress field was in a monotonic distribution state, with a surface residual stress of -220MPa and a residual compressive stress depth of 610μm.

[0107] S3: The target material is surface processed by using the optimally determined laser shock process technology and parameter conditions to obtain a monotonic residual stress distribution state with a maximum residual compressive stress located on the outermost surface of the target material and having sufficient residual compressive stress field intensity.

[0108] Example 4

[0109] A method for regulating the monotonicity and non-monotonicity distribution trend of residual compressive stress field in a surface layer of a structural material, comprising:

[0110] This embodiment takes the austenitic stainless steel material to be strengthened as an example in a certain field. In a specific scenario in the application field, failure analysis shows that the failure crack originates from the surface of the material, and the analysis conclusion points out that the life extension method includes enhancing the residual compressive stress on its surface. The established surface strengthening process technology of the austenitic stainless steel material is mechanical shot peening. The established mechanical shot peening process conditions can introduce a relatively high-intensity residual compressive stress field on the surface of the material. The stress field is a non-monotonic distribution state in which the maximum residual compressive stress is located in the sub-surface layer. The surface residual stress is -120MPa, the maximum residual compressive stress and its depth are -200MPa, 200μm, and the residual compressive stress depth is 600μm.

[0111] S1: Corresponding to the cracking failure mechanism of the target surface, the residual stress distribution state to be introduced is monotonic. In the absence of other processing equipment such as laser shock, mechanical shot peening is still selected as the surface processing method of the target. The existing mechanical shot peening process uses round 0.6mm diameter S230 stainless steel projectiles, shot peening flow rate 8kg / min, and shot peening gas pressure 2MPa.

[0112] S2: Based on the principle of reducing the penetration depth of round shot, the mechanical shot peening process conditions were adjusted to use round 0.8mm diameter S280 stainless steel shot, shot peening flow rate of 8kg / min, and shot peening gas pressure of 2.2MPa. This process condition introduced a surface residual stress of -140MPa in the residual stress field, the maximum residual compressive stress and its depth were -180MPa, 60μm, and the residual compressive stress depth was 580μm.

[0113] S3: The target material is surface processed by using the optimally determined mechanical shot peening process technology and parameter conditions to obtain a residual stress distribution state that is further close to "monotonicity" and has sufficient residual compressive stress field intensity.

[0114] Example 5

[0115] A method for regulating the monotonicity and non-monotonicity distribution trend of residual compressive stress field in a surface layer of a structural material, comprising:

[0116] This embodiment takes the 20Cr gear steel used in a certain field as an example of the structural material to be strengthened. In a specific scenario in the application field, failure analysis shows that the failure crack originates from the surface of the material, and the analysis conclusion points out that the life extension method includes enhancing the residual compressive stress on its surface. The established surface strengthening process technology of the 20Cr gear steel material is laser shock. The established laser shock process conditions can introduce a relatively high-intensity residual compressive stress field on the surface of the material. The stress field is a monotonic distribution state in which the maximum residual compressive stress is located on the surface, the surface residual stress is -220MPa, and the residual compressive stress depth is 800μm.

[0117] S1: Corresponding to the cracking failure mechanism of the target surface, the residual stress distribution state to be introduced is monotonic. Gears, tooth surfaces, tooth bottoms, etc. have hidden shielding structures, which are not suitable for mechanical shot peening. The residual stress distribution state to be introduced has no dependence on and demand for other surface processing technologies such as mechanical shot peening, so the established surface processing technology is laser shock unchanged.

[0118] S2: In order to further obtain the residual stress distribution state corresponding to the material failure mode, the energy distribution of the pulsed laser beam used in the laser shock is adjusted, that is, the Gaussian distribution is changed to the flat-top distribution. This process condition introduces a surface residual stress of -230MPa in the residual stress field, a residual compressive stress depth of 800μm, and a more uniform residual stress distribution on the target surface.

[0119] S3: The target material is surface processed by using the optimally determined laser shock process technology and parameter conditions to obtain a monotonic residual stress distribution state with a maximum residual compressive stress located on the outermost surface of the target material and having sufficient residual compressive stress field intensity.

[0120] Example 6

[0121] A method for regulating the monotonicity and non-monotonicity distribution trend of residual compressive stress field in a surface layer of a structural material, comprising:

[0122] This embodiment takes the 20Cr gear steel used in a certain field as an example of the structural material to be strengthened. In a specific scenario in the application field, failure analysis shows that the failure crack originates from the sub-surface of the material, and the analysis conclusion points out that the life extension method includes enhancing the residual compressive stress in the sub-surface. The established surface strengthening process technology of the 20Cr gear steel material is laser shock, and the established laser shock process conditions can introduce a relatively high-intensity residual compressive stress field on the surface of the material. The stress field is a monotonic distribution state in which the maximum residual compressive stress is located on the surface, the surface residual stress is -220MPa, and the residual compressive stress depth is 800μm.

[0123] S1: Corresponding to the cracking failure mechanism of the target surface, the residual stress distribution state is proposed to be non-monotonic. There are hidden shielding structures on the gear tooth surface and tooth bottom, which are not suitable for mechanical shot peening, so the established surface processing technology is kept unchanged as laser shock.

[0124] S2: In order to get closer to the residual stress distribution state corresponding to the material failure mode, the energy distribution of the pulsed laser beam used in the laser shock was adjusted, that is, the flat-top distribution was changed to the Gaussian distribution. This process condition introduced a surface residual stress of -210MPa in the residual stress field, a maximum residual compressive stress and its depth of -220MPa, 100μm, and a residual compressive stress depth of 800μm.

[0125] S3: The target material is surface processed by using the optimally determined laser shock process technology and parameter conditions to obtain a non-monotonic residual stress distribution state with sufficient residual compressive stress field intensity and the maximum residual compressive stress located in the sub-surface of the target material.

[0126] Example 7

[0127] A method for regulating the monotonicity and non-monotonicity distribution trend of residual compressive stress field in a surface layer of a structural material, comprising:

[0128] This embodiment takes the 20Cr gear steel used in a certain field as an example of the structural material to be strengthened. In a specific scenario in the application field, failure analysis shows that the failure crack originates from the sub-surface of the material, and the analysis conclusion points out that the life extension method includes enhancing the residual compressive stress in the sub-surface. The established surface strengthening process technology of the 20Cr gear steel material is mechanical shot peening. The established mechanical shot peening process conditions can introduce a relatively high-intensity residual compressive stress field on the surface of the material. The stress field is a non-monotonic distribution state in which the maximum residual compressive stress is located in the sub-surface, with a surface residual stress of -100MPa, a maximum residual compressive stress and its depth of -200MPa, 180μm, and a residual compressive stress depth of 600μm.

[0129] S1: Corresponding to the cracking failure mechanism of the target surface, the residual stress distribution state to be introduced is non-monotonic. In the absence of other processing equipment such as laser shock, mechanical shot peening is still selected as the surface processing method of the target. The existing mechanical shot peening process uses round 0.6mm diameter S230 stainless steel projectiles, shot peening flow rate 8kg / min, and shot peening gas pressure 2MPa.

[0130] S2: Under the constraints of the processing equipment and its parameter setting range, the established mechanical shot peening process is the optimal process.

[0131] S3: The target material is surface processed by using the initially established mechanical shot peening process technology and parameter conditions to obtain a non-monotonic residual stress distribution state with sufficient residual compressive stress field intensity and the maximum residual compressive stress located in the sub-surface of the target material.

[0132] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for regulating the monotonicity and non-monotonicity distribution trend of residual compressive stress field in the surface layer of a structural material, characterized in that: The following steps are involved: S1: Determine the target requirements for the distribution trend of residual compressive stress field to be introduced by surface strengthening; S2: According to the target requirements, select and determine the surface strengthening process technology and its parameters, and the parameter selection is based on the process conditions that cause the difference in deformation time between the inner and outer positions of the material surface impact area; When a monotonic residual compressive stress distribution is required, the process parameters are selected so that the deformation time difference between the inner and outer positions of the impact area is small; When a non-monotonic residual compressive stress distribution is required, the process parameters that result in a large difference in deformation time between positions inside and outside the impact area are selected; S3: The surface strengthening process technology and its parameters are used to perform surface strengthening treatment on the structural material to be strengthened, so as to obtain a strengthening effect that meets the requirements of the residual compressive stress distribution trend.

2. The method according to claim 1, characterized in that In step S1, if it is concluded through failure analysis that fatigue cracking of the structural material to be strengthened occurs in the sub-surface of the material, it is necessary to introduce a maximum residual compressive stress located on the sub-surface of the structural material to be strengthened; and if fatigue cracking occurs on the outermost surface of the material, it is necessary to introduce a maximum residual compressive stress located on the outermost surface of the material.

3. The method according to claim 1, characterized in that: In step S2, the surface strengthening process technology includes a contact surface strengthening process technology and a non-contact surface strengthening process technology; Preferably, the contact surface strengthening process technology includes mechanical shot peening and ultrasonic shot peening; Preferably, the non-contact surface strengthening process technology includes laser shock.

4. The method according to claim 1, characterized in that In step S2, the selection of the surface strengthening process technology is determined based on the influencing factors of the changeable surface strengthening process technology, specifically including: a: If there is no established surface strengthening process technology for the structural material to be strengthened, then if the hardware conditions permit, choose the surface strengthening process technology that is most likely to obtain the residual stress distribution trend of the current state; b: If there is an established surface strengthening process technology for the structural material to be strengthened, whether to change the surface strengthening process technology shall be determined based on the influencing factors that can change the surface strengthening process technology.

5. The method according to claim 4, characterized in that The influencing factors of the changeable surface strengthening process technology include hardware conditions, residual stress distribution trend control range and characteristic requirements of the structural material to be strengthened; Preferably, the hardware conditions include whether there are processing equipment, and whether the process condition setting range of the existing processing equipment is sufficient; Preferably, the characteristic requirements of the structural material to be strengthened include structural characteristics, mechanical properties and surface integrity characteristics of the structural material to be strengthened.

6. The method according to claim 4, characterized in that In step a, when hardware conditions permit, the surface strengthening process technology that is most likely to obtain the residual stress distribution trend of the current state is selected, including: if a monotonic residual compressive stress field is to be introduced, a non-contact surface strengthening process technology is preferably used, and a short-pulse laser shock surface strengthening technology with flat-top distribution laser energy is further preferably used; if a non-monotonic residual compressive stress field is to be introduced, a contact surface strengthening process technology is preferably used, and mechanical shot peening or ultrasonic shot peening is further preferably used; Or, in step b, under the premise of the existence of an established surface strengthening process technology, based on the influencing factors of the changeable surface strengthening process technology, within the scope permitted by conditions, change to a surface strengthening process technology that can obtain a target stress state; if conditions do not permit, maintain the established surface process technology, and perform a trend adjustment of the residual stress distribution state to be introduced within the adjustable range of the process parameters of the established surface strengthening process technology, or do not perform a trend adjustment within the adjustable range of the process parameters.

7. The method according to claim 6, characterized in that In step b, on the basis of determining the target requirements of the residual stress distribution state to be introduced, if the residual stress distribution trend introduced by the adopted surface strengthening process technology does not meet the target requirements, if other conditions permit, consider changing the surface processing technology; wherein the other conditions permit both the hardware conditions and the characteristic requirements of the structural material to be strengthened, or the hardware conditions permit, while the characteristic requirements of the structural material to be strengthened do not permit; Preferably, for structural materials that are to be treated for life extension using non-contact surface strengthening technology, if a non-monotonic residual stress distribution state is to be obtained, consideration is given to changing the non-contact surface strengthening technology that is difficult to obtain a non-monotonic residual stress state to a contact surface strengthening technology.

8. The method according to claim 6, characterized in that In step b, on the basis of determining the target requirements of the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the adopted surface strengthening process technology does not meet the target requirements, the characteristic requirements of the structural material to be strengthened do not allow the surface strengthening process technology to be changed, and the hardware conditions do not allow it, in this case, the trend of the residual stress distribution state to be introduced can only be adjusted within the adjustable range of the process parameters of the established surface strengthening process technology, so that the residual stress distribution state is as close to the required target state as possible; Or, in step b, on the basis of determining the target requirements for the residual stress distribution state to be introduced, if the residual compressive stress field distribution trend introduced by the adopted surface strengthening process technology meets the target requirements, and the characteristic requirements of the structural material to be strengthened also allow changes to the surface strengthening process technology, in this case, the original established surface process and the original process parameters are maintained, that is, the process is not changed, and there is no need to adjust the process parameters of the established surface strengthening process technology.

9. The method according to claim 1, characterized in that: In step S2, the time difference of deformation of the inner and outer positions of the impact region is small, which means that the height difference of the impact region is less than 20% of the plane width or diameter of the impact region; Preferably, the time difference of deformation of the inner and outer positions of the impact region being relatively large means that the height difference of the impact region is not less than 20% of the plane width or diameter of the impact region.

10. The method according to claim 1, characterized in that In step S2, the process conditions that lead to the difference in deformation time between the inner and outer positions of the impact region of the surface layer of the material include: When the surface strengthening process technology is changed, the contact deformation is changed to non-contact free deformation; preferably, the mechanical shot peening is changed to laser impact, and the ultrasonic shot peening is changed to laser impact; When the surface strengthening process technology is changed, the change directly determines the process time of the strain rate. It is preferred to change mechanical shot peening to laser impact, and ultrasonic shot peening to laser impact. When the surface strengthening process technology is unchanged, the size of the projectile in the variable contact surface strengthening process causes the curvature diameter of the direct deformation area to change; When the surface strengthening process technology is unchanged, the energy distribution of the beam in the non-contact surface strengthening process is preferably a transition between a flat-top distribution and a Gaussian distribution.

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