A method for characterizing the strength of a laser shock processing process based on unilateral cantilever directional bending

Abstract

The present application relates to a kind of laser shock wave processing process intensity characterization method based on unilateral cantilever directional bending, belong to material laser shock reinforcement technical field.The directional bending degree of free cantilever metal plate is measured to quantify the strengthening effect of laser shock on material.This method is based on the side fixed clamping of sample, the other side free suspension, plastic deformation is formed by the impact of pulsed laser on the edge of free cantilever, bending is generated, by quantifying the bending amplitude, the influence of different process parameters on material strengthening can be reflected.The present application has the advantages of standardization and high precision, high efficiency and convenience, adaptability and practicality.

Description

Technical Field

[0001] This invention relates to a method for characterizing the intensity of laser shock wave treatment process based on unilateral cantilever directional bending, belonging to the field of laser shock strengthening technology for materials. Background Technology

[0002] Mechanical shot peening is a mature and widely used plastic deformation technique for strengthening metal surfaces. To accurately characterize the processing strength of mechanical shot peening, engineers have used the change in arc height based on Almen specimens to quantify the shot peening intensity. Almen specimens are standardized metal sheets with specific geometric shapes. By measuring the bending (arc height) produced after shot peening impact, the degree of strengthening during the shot peening process can be determined. Almen strength, as a quantitative indicator of shot peening strengthening processes, not only provides a scientific basis for comparing strength under different shot peening conditions but also lays the foundation for the selection, optimization, and standardization of shot peening parameters.

[0003] In contrast, laser shock peening (LSP) is an advanced surface strengthening technology that utilizes a high-energy pulsed laser beam to instantly generate extremely high pressure and temperature on the material surface, thereby inducing localized plastic deformation. Although LSP offers significant advantages in improving material surface hardness, ductility, and corrosion resistance, its processing intensity remains in the experimental stage. Currently, the processing intensity of LSP mainly depends on the adjustment of process parameters such as laser energy, pulse width, and spot size. However, due to the complex relationships between these parameters and the lack of a unified standardized reference for the impact of different parameter combinations on materials, the intensity characterization of LSP lacks a universally applicable quantitative standard. Furthermore, the strengthening requirements of LSP vary depending on the processing scenario (such as surface strengthening of aerospace parts and surface treatment of medical implant materials), which prevents the existing process parameters from forming a standardized system, limiting its application in a wider range of fields.

[0004] Unlike mechanical shot peening, which uses arc height to characterize process intensity, laser impact peening, if using the deformation of the center of the Almen sample for intensity characterization, suffers from the peculiar convex or concave deformation induced by laser impact in the center of the sample, making a linear change in process intensity impossible. In other words, the center of a mechanically shot-peened metal sample tends to convexly, allowing for the characterization of increasing or decreasing process intensity based on changes in deformation height; however, with laser impact peening, the deformation direction of the metal sample is not uniform, making it impossible to determine the increase or decrease in process intensity based on changes in deformation height in the same direction. Therefore, finding a more uniform method to determine the process intensification changes of laser impact peening has become a problem that engineers need to solve.

[0005] Therefore, establishing quantitative standards for the process strength of laser shock peening (LSP) surface strengthening technology has become a key focus and challenge in current research. This is not only crucial for improving the application and engineering level of LSP technology, but also of great significance for precisely controlling the strengthening effect, improving processing efficiency, and enhancing product quality. By establishing a strength characterization method based on standardized test pieces, LSP strengthening technology is expected to achieve more precise and controllable surface strengthening effects, and provide a scientific basis for different materials and strengthening scenarios. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for characterizing the strength of laser shockwave treatment processes based on directional bending of a single-sided cantilever. This method quantifies the strengthening effect of laser shock on materials by measuring the degree of directional bending of a free-hanging metal plate. Based on a sample fixed and clamped on one side while freely suspended on the other, this method utilizes the impact of a pulsed laser at the edge of the free cantilever to induce plastic deformation and bending. By quantifying the bending amplitude, the influence of different process parameters on material strengthening can be reflected.

[0007] The present invention adopts the following technical solution:

[0008] A method for characterizing the intensity of laser shock wave processing based on unilateral cantilever directional bending includes the following steps:

[0009] S1, Sample preparation and fixing: The sample is a rectangular metal sheet, with one end fixed and the other end being a free cantilever end;

[0010] S2, Laser Shock: Set the energy, pulse width, and spot size of the laser device. The laser shock position is centered in the width direction of the rectangular metal sheet, and the edge of the free cantilever end is the center of the outermost spot in the shock area.

[0011] S3, Measurement of bending degree: The sample after laser shock will produce a certain degree of bending. The degree of bending is measured. The magnitude of the bending degree is proportional to the laser shock intensity. Under different combinations of laser parameters, the maximum degree of bending of the sample is recorded as a characterization of the strengthening effect.

[0012] S4, Adjustment and optimization of process parameters;

[0013] S5, Establish standardized characterization: After determining different combinations of process parameters and performing surface treatment on the samples, establish the correspondence between the combination of process parameters and the degree of bending of the obtained samples, and characterize the processing strength of different combinations of process parameters with different corresponding degrees of bending.

[0014] In this invention, one side of the specimen is clamped and fixed, while the other side is freely suspended. Plastic deformation is induced at the edge of the free cantilever by a pulsed laser, resulting in bending. The direction perpendicular to the impact area at the edge of the cantilever is the deformation direction of the specimen, and the incident direction of the laser beam is the positive direction. Under unilateral edge impact conditions, the specimen maintains a fixed impact deformation direction. Without reverse deformation, a larger bending amplitude indicates a stronger strengthening effect, and the surface hardness and fatigue resistance of the material are improved.

[0015] Preferably, in step S1, the rectangular metal sheet is made of pure iron, aluminum alloy or titanium alloy, etc., and the sample thickness is 1.2mm to 4mm. The size is determined according to the strengthening requirements and impact range, and the sample thickness increases with the increase of the cantilever length.

[0016] Preferably, in step S1, the free cantilever length of the sample should be no less than 1.5 times its width to ensure that the laser impact can produce a significant bending effect.

[0017] When the sample thickness is at the lower limit of 1.2mm, the cantilever length should be 40mm-80mm; when the sample thickness is at the upper limit of 4mm, the cantilever length should be 80mm-200mm; based on this, when the sample thickness is between 1.2mm and 4mm, the cantilever length should be between 40mm and 200mm, depending on the actual working conditions.

[0018] Preferably, in step S2, the laser shock parameters include energy, pulse width, and spot size, which are adjusted according to different material properties and strengthening requirements. The energy range is 1J to 5J, the pulse width is 10ns to 30ns, and when the spot size is less than 3mm, the impact area size is 20mm×6mm; when the spot size is greater than 3mm, the impact area size is greater than 20mm×6mm.

[0019] Preferably, the number of laser impacts is selected such that a single laser impact is suitable for strengthening thin plates, while thicker plates are strengthened by multiple impacts, with an overlap rate ranging from 30% to 70%.

[0020] Preferably, in step S3, the degree of bending is measured by a displacement sensor or a digital dial gauge, and the maximum degree of bending of the sample under different laser parameters is recorded as a characterization of the strengthening effect.

[0021] Preferably, in step S5, during the same batch or a strength characterization process as needed, based on the fact that the size and thickness of the test piece have been standardized, the principles for determining the standardized characterization method include: longitudinal displacement of the cantilever and test piece material. The direction of the longitudinal displacement of the cantilever is the vertical direction of the laser beam relative to the impact area at the edge of the cantilever, and the incident direction of the laser beam is positive. The test piece material is a metal material selected by the technician as needed.

[0022] This invention requires a pre-configured single-sided cantilever structure of standard test material, where the free cantilever portion is subjected to pulsed laser impact. The laser beam is focused on the unclamped edge of the sheet, inducing plastic deformation through localized high pressure, thereby causing the sheet to bend. Under different process parameters such as impact energy, pulse width, or spot size, the degree of plastic deformation on the material surface varies, resulting in different degrees of bending. The effect of laser impact on material strengthening is characterized by measuring the degree of bending of the single-sided cantilever plate. A larger bending amplitude indicates a stronger impact strengthening effect, and improved surface hardness and fatigue resistance of the material. Conversely, a smaller bending amplitude indicates a weaker strengthening effect.

[0023] This method characterizes process strength without relying on the change in arc height caused by laser shock treatment of the sample's center position. This eliminates the adverse effects of insignificant and difficult-to-quantify changes in arc height, and avoids characterization defects caused by changes in the laser-induced bending deformation mechanism. When characterizing process strength through directional bending of a single-sided cantilever, the more significant bending deformation improves the distinguishability of process strength and simplifies the precision requirements of process strength characterization.

[0024] For any details not covered in this invention, please refer to the prior art.

[0025] The beneficial effects of this invention are as follows:

[0026] Standardization and High Precision: Compared to traditional laser shock peening (LSP) characterization methods, the single-sided cantilever bending test provides a standardized quantitative basis, greatly improving the comparability of test results. By standardizing the bending degree variation, the impact of different LSP parameters on material strengthening can be objectively evaluated, avoiding the bias of subjective judgment in traditional methods.

[0027] Efficiency and Convenience: This method is simple to operate; the material's strengthening strength data can be obtained by measuring the bending degree of a single cantilever, greatly simplifying the testing process. It eliminates the need for complex hardness tests or microstructural analyses, enabling rapid and effective strength characterization of materials.

[0028] Adaptability and practicality: This method is applicable to a variety of metallic materials, including pure iron and aluminum alloys. Especially in the fields of high-performance materials such as aerospace, automotive and nuclear energy, it can provide a scientific basis for optimizing process parameters for surface strengthening of materials. Attached Figure Description

[0029] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0030] Figure 1 This is a schematic diagram of the specimen structure of the present invention;

[0031] Figure 2 This is a technical schematic diagram of the present invention, wherein A to E are schematic diagrams of rectangular pure iron sheet → single-sided clamping → impact on the edge of the unclamped side → impact on the edge area of ​​the unclamped side → bending of the pure iron sheet, respectively.

[0032] Figure 3 This diagram illustrates how different impact energies or overlap rates lead to changes in process strength under the same single impact size. A→B→C represents the improvement of process strength by increasing laser energy, and D→B→E represents the improvement of process strength by increasing the laser spot overlap rate.

[0033] Figure 4 This diagram illustrates how to maintain constant process strength by changing the impact energy or overlap rate under different single impact sizes. A, B, and C have different combinations of laser energy and spot overlap rate, achieving the same process strength: the spot overlap rate decreases sequentially from A to B to C, while the laser energy increases sequentially.

[0034] Figure 5 The principle for adjusting the impact zone range corresponding to different single impact sizes. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solutions in this specification, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. However, this is not the only description; all aspects not described in detail herein are based on conventional techniques in the art.

[0036] The technical principle of this invention is as follows:

[0037] By quantifying the degree of bending under different process parameters, a standardized characterization of pulsed laser shock intensity is provided. This method relies on the unilateral cantilever bending effect. Specifically, when one side of a rectangular metal specimen is fixed while the other side is freely suspended, a pulsed laser applied to the edge of the freely suspended side causes localized plastic deformation of the material surface through high-energy impact, leading to bending of the entire specimen. The change in the degree of bending directly reflects the intensity and strengthening effect of the laser shock.

[0038] Figure 1 This demonstrates the basic configuration principle: a rectangular sheet of pure iron is clamped and fixed on one side, while the other side is exposed to laser shock. Parameters such as the laser pulse energy, pulse width, and spot size affect the depth and range of deformation on the material surface, causing the sample to bend to a certain degree. A greater degree of bending indicates a more significant strengthening effect, suggesting that the material surface has been subjected to a stronger laser shock.

[0039] This bend-based characterization method provides a new approach for the quantitative evaluation of laser shock strengthening, avoiding the limitations of traditional methods that rely on microstructure analysis and hardness testing, and can provide a relatively stable evaluation index under varying process conditions.

[0040] Example 1

[0041] A method for characterizing the intensity of laser shock wave processing based on unilateral cantilever directional bending includes the following steps:

[0042] S1, Sample preparation and fixing: The sample is a rectangular metal sheet, with one end fixed and the other end being a free cantilever end;

[0043] The rectangular metal sheet is made of pure iron, aluminum alloy, titanium alloy, etc., and the sample thickness ranges from 1.2 mm to 4 mm. The size is determined according to the strengthening requirements and impact range, and the sample thickness increases with the increase of the cantilever length. One side of the sample is fixed using a standard clamp, while the other side remains completely free to ensure that significant bending occurs during the impact.

[0044] Standard fixtures are not subject to specific limitations. Technicians can select clamping devices based on the working conditions to ensure the stability of the sample's fixed side. The stability of the sample's fixed side refers to the fact that the clamping part of the rectangular sheet does not slip or deform in any direction during the subsequent laser shock treatment. This requires that the width and pressure of the clamping part be uniformly calibrated before the test.

[0045] It should be noted that this invention does not limit the specific test piece material. Technicians can select more practical conventional metal materials according to process standard requirements or future industry standard requirements to improve the accuracy of strength characterization and the operability of process strength characterization. When the properties of the metal material test piece change, technicians can adjust the specific values ​​of relevant process variables such as test piece specifications and laser parameters used in subsequent steps based on process experience.

[0046] The free cantilever length of the specimen should be no less than 1.5 times its width to ensure that the laser impact can produce a significant bending effect.

[0047] When the sample thickness is at the lower limit of 1.2mm, the cantilever length should be 40mm-80mm; when the sample thickness is at the upper limit of 4mm, the cantilever length should be 80mm-200mm; based on this, when the sample thickness is between 1.2mm and 4mm, the cantilever length should be between 40mm and 200mm, depending on the actual working conditions.

[0048] S2, Laser Shock: Set the energy, pulse width, and spot size of the laser device. The laser shock position is centered in the width direction of the rectangular metal sheet, and the edge of the free cantilever end is the center of the outermost spot in the shock area.

[0049] The energy range is 1J (low energy) to 5J (high energy), and the pulse width is 10ns to 30ns. Shorter pulse widths are more suitable for strengthening outer surfaces, while longer pulse widths are more suitable for strengthening deep surfaces. Before each experiment, the laser's output power, spot size, and pulse width must be calibrated using standardized optical instruments to ensure parameter consistency.

[0050] It should be noted that the laser output power error should not exceed ±5%; the spot size (diameter of a circular spot) error should not exceed ±0.1mm.

[0051] It should be noted that the impact area of ​​the free cantilever should be centered in the width direction of the sheet, with the edge of the free cantilever's width at the center of the outermost laser spot in the impact area. Positioning the impact area at the outermost end of the cantilever avoids the singularity of laser-induced impact deformation and prevents the possibility of reverse bending of the test piece.

[0052] When the spot size changes, the range of the impact zone of the free cantilever should be selected accordingly. Figure 5 The principles for adjusting the impact region under different spot sizes are demonstrated. When the spot diameter is less than 3 mm, the size of the impact region is typically 20 mm × 6 mm, a size suitable for strengthening conventional materials. When the spot diameter exceeds 3 mm, it is recommended to appropriately increase the range of the impact region or adjust the size of the sample to ensure the uniformity of laser shock and the strengthening effect. When the spot size is large, the coverage area of ​​the impact region needs to be expanded to avoid uneven impact on the material surface, which could affect the strengthening effect.

[0053] Furthermore, regarding the number of impacts, a single impact is suitable for strengthening thin plates, where the thickness is ≤3-4mm, and the bending amplitude of the free cantilever after a single impact is mainly observed. Multiple impacts enhance the strengthening effect by changing the number of impacts (planar overlap rate or interlayer overlap rate 30%-70%), and are suitable for thicker plates (thickness >3-4mm). Planar overlap rate refers to the degree of overlap between adjacent light spots in a single layer plane, and interlayer overlap rate refers to the degree of overlap between adjacent light spots between adjacent single layers. The calculation method for the degree of overlap of the light spots is the percentage of the overlap area length to the diameter of a single light spot.

[0054] S3, Measurement of bending degree: The sample after laser shock will produce a certain degree of bending. The degree of bending is measured. The magnitude of the bending degree is proportional to the laser shock intensity. Under different combinations of laser parameters, the maximum degree of bending of the sample is recorded as a characterization of the strengthening effect.

[0055] The change in curvature is not only affected by laser energy, but also closely related to factors such as spot size, pulse width, and impact energy. Under different experimental conditions, the changes in curvature were recorded, and data analysis was performed to determine the strengthening effect under different process parameters.

[0056] S4, Adjustment and optimization of process parameters;

[0057] Variations in bending degree under different process parameters can be used to reflect the strengthening effect of laser shock. By adjusting the laser energy, pulse width, and spot size, the shock effect can be optimized to ensure that the strengthening of the material surface meets the expected requirements.

[0058] Figure 3 and Figure 4 The effects of different single-impact sizes and overlap rates are demonstrated. Under the same single-impact size conditions, adjusting the impact energy or overlap rate directly affects the strengthening effect: increasing the impact energy is suitable for scenarios where the strengthening effect is insufficient; increasing the overlap rate results in a more uniform surface treatment, suitable for aerospace components. At different single-impact sizes, the consistency of process strength can be maintained by adjusting the laser energy or overlap rate. For example, for small spot sizes, higher energy and a moderate overlap rate should be used; for large spot sizes, lower energy and a higher overlap rate should be used.

[0059] S5, Establish standardized characterization: After determining different combinations of process parameters and performing surface treatment on the samples, establish the correspondence between the combination of process parameters and the degree of bending of the obtained samples, and characterize the processing strength of different combinations of process parameters with different corresponding degrees of bending.

[0060] By testing multiple samples, the range of strengthening effects under the same process conditions was obtained, and by comparing the bending changes under different process parameter settings, process selection criteria were formulated.

[0061] After obtaining standardized evaluation results, appropriate combinations of process parameters can be selected based on the actual application scenario (such as low-load or high-load environment) to achieve optimal strengthening of the material surface.

[0062] In the same batch or a single strength characterization process as needed, based on the standardized specimen size and thickness, the principle for determining the standardized characterization method is: cantilever longitudinal displacement + specimen material. The direction of the cantilever longitudinal displacement is perpendicular to the laser beam relative to the impact area at the edge of the cantilever, and the incident direction of the laser beam is positive; the specimen material is a metal material selected by the technicians as needed.

[0063] Example 2

[0064] A laser shock wave treatment process intensity characterization method based on unilateral cantilever directional bending is described in Example 1, except that the sample material is industrial pure iron sheet with a thickness of 1.4 mm and a size of 50 mm × 30 mm, where 50 mm is the length of the free cantilever portion after removing the clamping part.

[0065] Laser parameters: laser energy is 1.2J, pulse width is 10ns, spot diameter is 2.5mm, and single impact size is 20mm×6mm.

[0066] The sample is fixed on a fixture, subjected to laser impact, and its degree of bending is measured and the data is recorded.

[0067] Under this combination of low energy and small spot size, the sample curvature was 0.4 mm (curvature refers to the vertical distance at the outermost edge of the cantilever end, i.e., the bending length in the incident direction of the laser beam), indicating that the impact strengthening effect was relatively mild. The surface hardness and fatigue strength of the material were improved, but the high-strength strengthening level was not achieved. Taking the strength type based on industrial pure iron sheet as Fe, the process strength determined by this laser shock process combination is denoted as 0.4 mm Fe.

[0068] This combination is suitable for materials with low surface hardness requirements and is mainly used for material strengthening under low load conditions.

[0069] Example 3

[0070] A laser shock wave processing intensity characterization method based on unilateral cantilever directional bending is described in Example 1, except that the sample material is pure aluminum alloy sheet with a thickness of 2.0 mm and a size of 60 mm × 40 mm, where 60 mm is the length of the free cantilever portion after removing the clamping part.

[0071] Laser parameters: laser energy is 2.8J, pulse width is 15ns, spot diameter is 5mm, and single impact size is 25mm×8mm.

[0072] Experimental procedure: Fix the sample, adjust the laser shock parameters, and record the curvature data.

[0073] Under this combination, the sample curvature was 2.0 mm, indicating that laser shock effectively improved the surface strengthening effect, and the fatigue resistance and hardness of the material were both improved. Taking the strength type based on pure aluminum alloy sheet as Al, the process strength determined by this laser shock process combination is denoted as 2 mm Al.

[0074] Suitable for medium-load applications such as aerospace and automotive industries, where high reinforcement effects are required.

[0075] Example 4

[0076] A laser shock wave processing intensity characterization method based on unilateral cantilever directional bending is described in Example 1, except that the sample material is pure titanium alloy sheet with a thickness of 3.0 mm and a size of 80 mm × 50 mm, where 80 mm is the length of the free cantilever portion after removing the clamping part.

[0077] Laser parameters: laser energy is 5.5J, pulse width is 25ns, spot diameter is 8mm, and single impact size is 30mm×10mm.

[0078] Experimental procedure: After the sample is fixed, a high-energy pulsed laser is applied, and the curvature is measured.

[0079] The curvature of 4.0 mm indicates that the high-energy combination produced a relatively strong impact effect, with significant surface strengthening. The material exhibits higher resistance to crack propagation and fatigue limit, making it suitable for material strengthening requirements under high-load environments. Taking the strength type of the pure titanium alloy sheet as Ti, the process strength determined by this laser shock blasting process combination is denoted as 4 mm Ti.

[0080] Suitable for applications requiring high strength and high reliability, such as aerospace and nuclear energy equipment.

[0081] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for characterizing the intensity of laser shock wave processing based on unilateral cantilever directional bending, characterized in that, Includes the following steps: S1, Sample preparation and fixing: The sample is a rectangular metal sheet, with one end fixed and the other end being a free cantilever end; S2, Laser Shock: Set the energy, pulse width, and spot size of the laser device. The laser shock position is centered in the width direction of the rectangular metal sheet, and the edge of the free cantilever end is the center of the outermost spot in the shock area. S3, Measurement of bending degree: The sample after laser shock will produce a certain degree of bending. The degree of bending is measured. The magnitude of the bending degree is proportional to the laser shock intensity. Under different combinations of laser parameters, the maximum degree of bending of the sample is recorded as a characterization of the strengthening effect. S4, Adjustment and optimization of process parameters; S5, Establish standardized characterization: After determining different combinations of process parameters and performing surface treatment on the samples, establish the correspondence between the combination of process parameters and the degree of bending of the obtained samples, and characterize the processing strength of different combinations of process parameters with different corresponding degrees of bending.

2. The method for characterizing the intensity of laser shock wave processing based on unilateral cantilever directional bending according to claim 1, characterized in that, In step S1, the rectangular metal sheet is made of pure iron, aluminum alloy or titanium alloy, and the sample thickness is 1.2 mm to 4 mm.

3. The method for characterizing the intensity of laser shock wave processing based on unilateral cantilever directional bending according to claim 2, characterized in that, In step S1, the length of the free cantilever of the sample is not less than 1.5 times its width to ensure that the laser impact can produce a significant bending effect.

4. The method for characterizing the intensity of laser shock wave processing based on unilateral cantilever directional bending according to claim 1, characterized in that, In step S2, the energy range is 1J to 5J, and the pulse width is 10ns to 30ns. When the spot size is less than 3mm, the impact area size is 20mm×6mm; when the spot size is greater than 3mm, the impact area size is greater than 20mm×6mm.

5. The method for characterizing the intensity of laser shock wave processing based on unilateral cantilever directional bending according to claim 4, characterized in that, Single laser impact is suitable for strengthening thin sheets, while thicker sheets are reinforced by multiple impacts, with an overlap rate ranging from 30% to 70%.

6. The method for characterizing the intensity of laser shock wave processing based on unilateral cantilever directional bending according to claim 5, characterized in that, In step S3, the degree of bending is measured using a displacement sensor or a digital dial indicator.

7. The method for characterizing the intensity of laser shock wave processing based on unilateral cantilever directional bending according to claim 6, characterized in that, In step S5, during a strength characterization process conducted in the same batch or as needed, based on the standardized size and thickness of the test piece, the principles for determining the standardized characterization method include: longitudinal displacement of the cantilever and test piece material. The direction of the longitudinal displacement of the cantilever is perpendicular to the laser beam relative to the impact area at the edge of the cantilever, and the incident direction of the laser beam is positive. The test piece material is a metal material selected by the technicians as needed.

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