A method for determining laser shock induced spalling damage

Abstract

The present invention belongs to the field of laser processing technology, and in particular relates to a method for judging laser shock-induced spalling damage. A local characteristic sample is processed by using the material properties and geometric characteristics of a real part; the characteristic sample is impacted by using a proposed laser parameter; the depth of the impact pit is measured; a characteristic sample model is established; the finite element analysis parameters are solved according to the proposed laser parameters; the solved finite element analysis parameters are numerically simulated and calculated to extract the pit depth of the impact area; the two pit depths are compared to obtain a relative error; the laser shock parameters are adjusted according to the comparison result, and the above steps are repeated until the error between the two does not exceed the error threshold; the maximum strain is extracted from the numerical simulation visualization cloud map result that meets the relative error requirement; the maximum strain obtained by the finite element simulation is compared with the critical strain of material damage, and then it is determined whether the proposed parameters will cause spalling damage, thereby effectively improving the application reliability of the laser shock strengthening process on thin-walled parts.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser processing, and in particular relates to a method for determining laser shock induced spalling damage. Background Art

[0002] Laser shock peening is an advanced material surface modification technology. It uses a beam of high-energy, short-pulse laser to periodically bombard the surface of a metal material covered with an absorption layer and a constraint layer according to a preset trajectory (the absorption layer is usually special aluminum foil or black paint, and the constraint layer is deionized water or special transparent glass), forming a high-temperature, high-pressure plasma shock wave, and undergoing non-equilibrium interaction in the surface material, inducing high-amplitude and large-depth residual compressive stress, thereby improving the metal's surface properties such as fatigue resistance and wear resistance. It is widely used to increase the fatigue life of thin-walled aviation structural components such as aircraft engine compressor blades and aircraft fuselage skins.

[0003] However, improper configuration of parameters during the strengthening process can lead to a decrease in the impact strengthening effect, such as excessive deformation of components and spallation damage within them. Spallation damage occurs when a high strain rate load acts on the surface of a metal material. Due to interface reflection, two sparse waves propagate in opposite directions at a certain location within the material. When these two waves meet, tensile stress is generated at the corresponding location. When this tensile stress exceeds the spallation limit of the metal material, localized tearing occurs within the material. This layered tearing is called spallation damage.

[0004] Because spallation damage occurs internally in the material, it cannot be detected by conventional visual inspection. If a component with internal spallation damage is put into service, this location can easily become a fatigue source, leading to rapid failure of the component and adversely affecting the service life of the equipment.

[0005] Existing laser shock peening of thin-walled components primarily determines whether spallation has occurred based on whether a bulge forms on the back of the impacted component. If a bulge forms on the back of the impacted component, spallation is assumed to have occurred within the impacted area; if no bulge forms on the back of the impacted component, spallation is assumed to have not occurred. This judgment method is somewhat subjective and cannot accurately determine if spallation has occurred within the component despite no bulge forming on the back. Summary of the Invention

[0006] (1) Technical issues to be solved

[0007] The present invention mainly addresses the above problems and proposes a method for determining laser shock induced spallation damage, the purpose of which is to solve the problem of how to determine whether spallation defects will occur inside the impacted part under specific laser parameters.

[0008] (2) Technical solution

[0009] To achieve the above object, the present invention provides a method for determining laser shock induced spallation damage, comprising the following steps:

[0010] S1. Process local area characteristic specimens according to the material properties and geometric characteristics of real parts;

[0011] S2. impacting the characteristic sample using the proposed laser parameters;

[0012] S3, measuring the impacted characteristic sample to obtain the impact pit depth of the characteristic sample;

[0013] S4. Use finite element software to establish a characteristic specimen model;

[0014] S5. solving finite element analysis parameters according to the proposed laser parameters;

[0015] S6. Performing numerical simulation calculation on the solved finite element analysis parameters to extract the pit depth of the impact area;

[0016] S7. Comparing the impact pit depth of the characteristic sample obtained by the test with the pit depth of the impact area extracted to obtain a relative error;

[0017] S8, adjusting the laser shock parameters according to the comparison result, and repeating steps S5 to S7 until the error between the two does not exceed a certain error threshold;

[0018] S9, extracting the maximum strain on the finite element calculation model from the numerical simulation visualization cloud map result that meets the relative error requirement in step S8;

[0019] S10. Compare the maximum strain obtained by the finite element simulation with the critical strain of material damage, and determine whether the proposed parameters will cause spalling damage.

[0020] Furthermore, the proposed laser parameters include at least: laser energy, number of impacts, spot type, and spot size.

[0021] Furthermore, in step S3, the tool for measuring the impact pit depth of the characteristic sample is a white light interferometer or a confocal microscope.

[0022] Furthermore, the specific contents of step S4 include:

[0023] S41. Based on the modeling function of ABAQUS finite element software, a three-dimensional model is established according to the geometric dimensions of the characteristic sample;

[0024] S42, setting the material properties of the established three-dimensional model according to the physical properties of the characteristic sample;

[0025] S43. Define the same material elastic-plastic parameters as those of the characteristic specimen, divide the mesh, create analysis steps, and define constraint conditions.

[0026] Furthermore, the step S42 specifically includes: the material properties of the three-dimensional model set according to the physical properties of the characteristic sample include: material parameters density, elastic modulus, Poisson's ratio, and dynamic yield strength.

[0027] Furthermore, the specific contents of step S5 include:

[0028] S51. Equivalent the laser shock parameters to a pressure load distributed in time and space, and create the expression:

[0029]

[0030]

[0031] Where I0 is the laser power density, E0 is the input laser energy, and d l is the spot diameter, τ is the pulse width, P max is the equivalent peak pressure;

[0032] S52, the proposed laser parameters are substituted into the expression, and the equivalent peak pressure (P) is solved by combining equations 1) and 2). max ).

[0033] Furthermore, in step S7, the calculation formula for obtaining the relative error is:

[0034]

[0035] In Equation 3), δ is the relative error, d sim is the extracted pit depth of the impact area, d exp is the impact pit depth of the characteristic sample obtained in the test.

[0036] Furthermore, before step S2, the method further includes sticking aluminum foil tape on the characteristic sample as an absorption layer and arranging deionized water as a constraint layer.

[0037] (3) Beneficial effects

[0038] The above technical solution of the present invention has the following advantages: processing local area characteristic samples through the material properties and geometric characteristics of real parts; using the proposed laser parameters to impact the characteristic samples; measuring the impact pit depth of the characteristic samples; using finite element software to establish a characteristic sample model; solving the finite element analysis parameters according to the proposed laser parameters; performing numerical simulation calculations on the solved finite element analysis parameters to extract the pit depth of the impact area; then comparing the two pit depths to obtain a relative error; adjusting the laser impact parameters according to the comparison results, and repeating the above steps until the error between the two does not exceed a certain error threshold; extracting the maximum strain on the finite element calculation model from the numerical simulation visualization cloud map results that meet the relative error requirements; comparing the maximum strain obtained by the finite element simulation with the critical strain of material damage, and then judging whether the proposed parameters will cause spalling damage, thereby effectively improving the application reliability of the laser shock strengthening process on thin-walled parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 An exemplary flow chart of a method for determining laser shock induced spallation damage according to an embodiment of the present disclosure is shown.

[0040] Figure 2 A 3D finite element analysis model of spallation damage is shown.

[0041] Figure 3 A strain photograph of an impact specimen with magnified deformation is shown. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present disclosure, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present disclosure without making any creative efforts are also within the scope of protection of the present disclosure.

[0043] As used in this application and the claims, unless the context clearly indicates otherwise, the words "a," "an," "an," and / or "the" are not intended to refer to the singular but may include the plural. Generally speaking, the terms "comprises" and "include" only indicate the inclusion of the steps and elements specifically identified, and these steps and elements do not constitute an exclusive list. A method or apparatus may also include other steps or elements.

[0044] Although the present application makes various references to certain modules in the system according to embodiments of the present application, any number of different modules can be used and run on the user terminal and / or server. The modules are illustrative only, and different aspects of the system and method can use different modules.

[0045] Flowcharts are used in this application to illustrate the operations performed by the systems according to the embodiments of the present application. It should be understood that the preceding or following operations are not necessarily performed in exact order. Instead, the various steps may be processed in reverse order or simultaneously, as needed. Furthermore, other operations may be added to these processes, or one or more operations may be removed from these processes.

[0046] Figure 1 An exemplary flow chart of a method for determining laser shock induced spallation damage according to an embodiment of the present disclosure is shown.

[0047] First, in step S1, a local area feature sample is processed according to the material properties and geometric characteristics of the real part.

[0048] Among them, characteristic samples with the same geometric shape and surface state are processed from the same material as the real parts, or samples are taken from scrap parts that are the same as the real parts to obtain characteristic samples.

[0049] In step S2, the characteristic sample is impacted using the proposed laser parameters.

[0050] Specifically, the proposed laser parameters include at least: laser energy, number of impacts, spot type, and spot size. The characteristic specimen is impacted using these set laser shock peening parameters, and the pre-impact absorption layer and constrained layer are consistent with the actual part strengthening process.

[0051] In step S3, the characteristic sample after impact is measured to obtain the impact pit depth of the characteristic sample.

[0052] Specifically, the depth of the impact pit on the characteristic specimen can be measured using surface testing instruments such as white light interferometer and confocal microscope, and the obtained depth value is recorded as d exp .

[0053] In step S4, a characteristic sample model is established using finite element software.

[0054] The specific contents of step S4 include:

[0055] S41. Based on the modeling function of ABAQUS finite element software, a three-dimensional model is established according to the geometric dimensions of the characteristic sample;

[0056] S42, setting the material properties of the established three-dimensional model according to the physical properties of the characteristic sample;

[0057] S43. Define the same material elastic-plastic parameters as those of the characteristic specimen, divide the mesh, create analysis steps, and define constraint conditions.

[0058] It should be noted that the parameters of the material of the established three-dimensional model are set according to the parameters of the characteristic sample. That is to say, the geometric dimensions and all physical parameters of the material of the constructed three-dimensional model are consistent with the characteristic sample of the actual experiment, avoiding large errors between the simulation results and the actual results.

[0059] In step S5, finite element analysis parameters are solved according to the proposed laser parameters.

[0060] Specifically, the time limit of the finite element numerical simulation of laser shock peening is to convert the laser shock parameters into a pressure load distributed in time and space, and then apply it to the action surface. max ) can be obtained by formula 1) and 2):

[0061]

[0062]

[0063] I0 is the laser power density, E0 is the input laser energy, d l is the spot diameter and τ is the pulse width.

[0064] In step S6, the solved finite element analysis parameters are subjected to numerical simulation calculation to extract the pit depth of the impact area.

[0065] In this step, the equivalent peak pressure calculated in step 5 is used for numerical simulation calculation, and the maximum pit depth in the impact area is measured on the calculated cloud map result and recorded as d sim .

[0066] In step S7, the impact pit depth of the characteristic sample obtained by the test is compared with the pit depth of the extracted impact area to obtain a relative error.

[0067] The relative error δ between the maximum pit depth measured experimentally and the maximum pit depth obtained by finite element extraction is calculated according to Equation 3).

[0068]

[0069] In step S8, the laser shock parameters are adjusted according to the comparison result, and steps S5 to S7 are repeated until the error between the two does not exceed a certain error threshold.

[0070] Specifically, a certain error threshold is recorded as δ0. If δ≤δ0, the finite element model accuracy meets the standard and step S9 can be performed. If δ>δ0, the accuracy does not meet the standard and the equivalent pressure value needs to be adjusted (increase or decrease by a certain percentage). Steps S5, S6, and S7 are repeated to solve for the new δ' until δ'≤δ0.

[0071] In step S9, the maximum strain on the finite element calculation model is extracted from the numerical simulation visualization cloud map result that meets the relative error requirement in step S8.

[0072] Extract the maximum equivalent plastic strain ε from the numerical simulation visualization cloud map results that meet the relative error requirements in step S8 PEEQ .

[0073] In step S10, the maximum strain obtained by the finite element simulation is compared with the critical strain of material damage, and it is determined whether the proposed parameters will cause spalling damage.

[0074] The maximum equivalent plastic strain ε extracted from the finite element model PEEQ The critical strain ε of material damage f Compare. If ε PEEQ <ε f , then no spalling defects will occur inside the material under this parameter impact. If ε PEEQ ≥ε f , then under the impact of this parameter, spalling defects will occur inside the material.

[0075] In the above method of the present invention, through this embodiment, it is possible to determine whether spallation defects will occur inside the impacted part under specific laser parameters, thereby effectively improving the application reliability of the laser shock peening process on thin-walled parts.

[0076] Next, refer to the attached Figure 1 , the method for determining laser shock induced spallation damage of the present invention is further described with specific examples.

[0077] Example 1

[0078] Taking a single pulse energy of 25J and a 4mm square spot impacting a 0.25mm thick TC4 titanium alloy as an example, the test includes the following steps:

[0079] Step 1: Process a localized feature specimen based on the material properties and geometric characteristics of the actual part. A thin-walled feature specimen with dimensions of 30mm × 20mm × 0.25mm is machined based on the actual part. Based on the surface roughness of the actual part, mechanical grinding and polishing are used to achieve a surface roughness of Ra0.8.

[0080] Step 2: Impact the characteristic sample using the proposed laser parameters. Specific laser shock peening parameters (single pulse energy 25J, pulse width 15ns, square spot type, spot side length 4mm, and number of impacts 1) were used to impact the characteristic sample. Before impact, aluminum foil tape was applied as an absorption layer, deionized water was placed as a restraining layer, and the impact was completed.

[0081] Step 3: Measure the depth of the impact pit on the characteristic sample. Use white light interferometer to measure the maximum depth of the center of the pit in the impact area. The result d exp It is 23.2μm.

[0082] Step 4: Use finite element software to establish a characteristic specimen model. Use the commercial finite element numerical simulation software ABAQUS to establish a 30mm×20mm×0.25mm three-dimensional model, set the material parameters density: 4.5g / cm3, elastic modulus: 110GPa, Poisson's ratio: 0.342, dynamic yield strength 1345GPa, and define the damage definition criterion (and spallation criterion): critical damage strain ε f is 0.115. Then meshing is performed and analysis steps are created to obtain the following Figure 2 Model shown.

[0083] Step 5: Solve the finite element analysis parameters according to the laser parameters formulated in the experiment. According to the laser shock peening parameters (single pulse energy 25J, pulse width 15ns, spot type square, spot side length 4mm, number of shocks 1), the equivalent peak pressure P is solved by equations 1) and 2). max It is 3292MPa.

[0084] Step 6: Finite element numerical simulation analysis and extraction of the pit depth in the impact area. The equivalent peak pressure P obtained in step 5 is used. max (3292MPa) to perform numerical simulation calculations, obtain a visual result cloud map, and measure the maximum depth d of the pit sim It is 18.54μm.

[0085] Step 7: Compare the experimental and finite element impact zone pit depths and calculate the relative error δ. Substituting the experimentally measured maximum pit depth of 23.2 μm and the finite element-derived maximum pit depth of 19.53 μm into Equation 3, the relative error δ is 15.8%.

[0086] Step 8: Adjust the laser shock parameters according to the comparison results and repeat step 5 until the error between the two does not exceed a certain threshold δ0. Assume that the threshold δ0 is 5%. Since δ>δ0, and d sim <d exp , so the equivalent peak pressure P in step 5 is max Increase the pressure by 10% to 3621 MPa and repeat steps 6 and 7 to obtain a new relative error of 4.6%.

[0087] Step 9: Extract the maximum strain on the finite element calculation model. Extract the maximum equivalent plastic strain ε from the numerical simulation visualization cloud map results that meet the relative error requirements in step 8. PEEQ =0.115, Figure 3This is the strain distribution result after the surface deformation is magnified 100 times.

[0088] Step 10: Compare the strain obtained by finite element simulation with the critical strain of material damage, and determine whether the proposed parameters will cause spalling damage. PEEQ The critical strain ε of material damage f For comparison. Since ε PEEQ =ε f =0.115. Under the proposed laser shock parameters, spalling will occur inside the thin-walled TC4 titanium alloy component.

[0089] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for determining laser shock induced spalling damage, characterized in that: The following steps are involved: S1. Process local area characteristic specimens according to the material properties and geometric characteristics of real parts; S2. impacting the characteristic sample using the proposed laser parameters; S3, measuring the impacted characteristic sample to obtain the impact pit depth of the characteristic sample; S4. Use finite element software to establish a characteristic specimen model; S5. solving finite element analysis parameters according to the proposed laser parameters; S6. Performing numerical simulation calculation on the solved finite element analysis parameters to extract the pit depth of the impact area; S7. Comparing the impact pit depth of the characteristic sample obtained by the test with the pit depth of the impact area extracted to obtain a relative error; S8, adjusting the laser shock parameters according to the comparison result, and repeating steps S5 to S7 until the error between the two does not exceed the error threshold; S9, extracting the maximum strain on the finite element calculation model from the numerical simulation visualization cloud map result that meets the relative error requirement in step S8; S10, comparing the maximum strain obtained by the finite element simulation with the critical strain of material damage, and determining whether the proposed parameters will cause spalling damage; The specific contents of step S4 include: S41. Based on the modeling function of ABAQUS finite element software, a three-dimensional model is established according to the geometric dimensions of the characteristic sample; S42, setting the material properties of the established three-dimensional model according to the physical properties of the characteristic sample; S43, defining the same material elastic-plastic parameters as those of the characteristic specimen, dividing the mesh, creating analysis steps, and defining constraint conditions; The specific contents of step S5 include: S51. Equivalent the laser shock parameters to a pressure load distributed in time and space, and create the expression: Formula 1) Formula 2) In the formula, I 0 is the laser power density, E 0 is the input laser energy, d l is the spot diameter, τ is the pulse width, P max is the equivalent peak pressure; S52. Substitute the proposed laser parameters into the expression, and solve the equivalent peak pressure by combining equations 1) and 2). P max ; In step S7, the calculation formula for obtaining the relative error is: Formula 3) In Equation 3), δ is the relative error, d sim is the extracted pit depth of the impact area, d exp is the impact pit depth of the characteristic sample obtained in the test.

2. The method for determining laser shock induced spallation damage according to claim 1, wherein: The proposed laser parameters include at least: laser energy, number of impacts, spot type, and spot size.

3. The method for determining laser shock induced spallation damage according to claim 1, wherein: In step S3, the tool for measuring the impact pit depth of the characteristic sample is a white light interferometer or a confocal microscope.

4. The method for determining laser shock induced spallation damage according to claim 1, wherein: The step S42 specifically includes: setting the material properties of the three-dimensional model according to the physical properties of the characteristic sample, including: material parameters density, elastic modulus, Poisson's ratio, and dynamic yield strength.

5. The method for determining laser shock induced spallation damage according to claim 1, wherein: Before step S2, the method further includes sticking aluminum foil tape to the characteristic sample as an absorption layer and arranging deionized water as a constraint layer.

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