Full-field data inversion method for two-dimensional thermal response to laser irradiation

Abstract

The present invention provides a full-field data inversion method for two-dimensional thermal response to laser irradiation, relates to the field of solid physics, and solves the problems of difficulty in obtaining data from high-temperature measurement points in existing experiments, difficulty in measuring stress under laser irradiation, and difficulty in obtaining temperature and stress distribution near a light spot. The method comprises: obtaining temperature field data of a target under the action of laser, and extracting a corresponding pre-function; improving the temperature field data based on the extracted pre-function by a temperature field inversion method to obtain a temperature field distribution; performing a strain field inversion of a material based on the temperature field distribution to obtain a material strain function; combining the material strain function with the mechanical properties of the material to perform a stress field inversion of the material to obtain a material stress distribution; based on the material stress distribution, obtaining a damage function of a corresponding material by selecting different target materials under the action of laser, and completing damage assessment. The present invention effectively avoids a high-temperature zone and does not use strain gauges for measurement, so that the obtained thermal strain and thermal stress are more accurate.

Description

Technical Field

[0001] The invention relates to the field of solid state physics and is applied to the temperature and stress acquisition process of laser irradiation experiments, and specifically relates to a full-field data inversion method for two-dimensional thermal response of laser irradiation. Background Art

[0002] Due to its significant advantages such as high energy density, low operating cost, rapid response and precise positioning, high-power lasers have shown broad application prospects in many fields such as precision machining and scientific research. Although high-power lasers play an increasingly important role in industry and scientific research, their understanding of the mechanism of material action still faces major challenges, especially in the thermodynamic and mechanical responses when high-energy lasers interact with materials. This process involves complex nonlinear physical phenomena, including but not limited to solid heat transfer under local high heat flux conditions and the mechanical and thermal coupling characteristics of materials, which are difficult to accurately model in theory.

[0003] At present, data on the thermal response of materials under strong laser irradiation mainly rely on experimental means to obtain. The typical method is to use thermocouples and strain gauge sensors to monitor the temperature and stress changes on the back of the target. However, this method has the following key defects:

[0004] 1. Data acquisition location is limited: only local data on the back of the target can be measured, and information on the area on the front of the target that is directly irradiated by the laser cannot be directly obtained. For thin targets, the assumption that the back temperature is equivalent to the front temperature may not hold; for thick targets, there is a lack of effective inversion technology to determine the thermal state of the front.

[0005] 2. Insufficient spatial resolution of data: Existing point measurements can only provide limited point data and cannot depict the temperature and stress distribution of the entire surface of the target. Especially in the center of laser irradiation, the high temperature environment affects the working performance of the strain gauge, and increasing the number of thermocouples is limited by physical space and wire layout, and may interfere with the natural flow of the temperature field.

[0006] 3. Limitations of data fusion and verification: Experimental measurement data and numerical simulation results are usually evaluated in isolation, lacking a systematic framework that can comprehensively consider the correlation between measurement errors and model accuracy. This separate processing method fails to give full play to the complementary advantages of the two, limiting the in-depth understanding of the thermal process of materials under laser irradiation.

[0007] The above defects not only hinder the comprehensive analysis of the thermal process mechanism of materials under laser action, but also directly affect the scientificity and reliability of laser damage assessment and protection design. Therefore, it is urgent to develop an innovative technical solution to overcome the limitations of existing technologies, achieve comprehensive and high-precision measurement and analysis of the thermal response of laser irradiated materials, and lay a solid scientific foundation for the optimized design and safe application of laser technology in materials engineering. Summary of the invention

[0008] Based on the current status of the background technology, the purpose of the present invention is to solve the problems of difficulty in obtaining data from existing high-temperature measurement points in experiments, difficulty in measuring laser irradiation stress, and difficulty in obtaining temperature and stress distribution near the light spot. Therefore, a full-field data inversion method for two-dimensional thermal response of laser irradiation is proposed as a new way to fuse experimental measurement point data and simulation data. The present invention combines numerical simulation with limited experimental data to complete the temperature distribution reconstruction of the target under laser irradiation, and then realizes target stress inversion and damage assessment; the measurement point arrangement of the present invention is more flexible, effectively avoiding the high temperature zone and not using strain gauges to measure strain, and the calculated thermal strain and thermal stress are more accurate.

[0009] The present invention adopts the following technical solutions to achieve the purpose:

[0010] A method for full-field data inversion of two-dimensional thermal response to laser irradiation, the method comprising the following steps:

[0011] S1, obtaining the temperature field data of the target under the action of laser and extracting the corresponding prediction function;

[0012] S2. By using the temperature field inversion method, the temperature field data is improved based on the extracted pre-function to obtain the temperature field distribution;

[0013] S3, performing material strain field inversion based on temperature field distribution to obtain material strain function;

[0014] S4. Combining the material strain function with the material mechanical properties, inverting the material stress field, and obtaining the material stress distribution;

[0015] S5. Based on the material stress distribution, different target materials are selected under the action of laser to obtain the damage function of the corresponding material and complete the damage assessment.

[0016] Specifically, step S1 is based on laser irradiation of the target. When the power of the laser is lower than a preset power threshold, or the thickness of the target is higher than a preset thickness threshold, the target is in thermal equilibrium without melting through. The thermal equilibrium state of the target is used to characterize the comprehensive ability of laser irradiation and heat transfer of the target material, and is applied to the temperature field inversion process of step S2.

[0017] Preferably, the thermal equilibrium state of the target is determined by: detecting the temperature of the target material under laser irradiation in real time to obtain a temperature time series curve; taking the difference between the average value of the last five detection points and the first five detection points at any time in the temperature time series curve as the slope of the temperature time series curve; during the real-time detection process, when the slope reaches a maximum value and then begins to decrease, taking the detection point corresponding to 90% of the maximum value of the slope decrease as the temperature equilibrium point, and determining whether the target reaches a thermal equilibrium state at the time of the temperature equilibrium point.

[0018] Preferably, in step S1, under the action of laser, the laser irradiation spot on the target is equivalent to a heat source with a Gaussian distribution, and the heat source is simplified to a temperature heat source distributed in concentric rings and applied to the target surface based on the principle of equivalent energy; based on the temperature heat source, a finite element method is used to calculate the heat flow in the target to obtain the temperature field data of the target under the action of laser, and the temperature field data is fitted into a function expression of a corresponding form as a pre-function for extraction.

[0019] Preferably, in step S2, a plurality of thermocouples are arranged on the back of the target to obtain the back temperature during laser irradiation, thereby calibrating the distribution function, and after perfecting the undetermined coefficients in the temperature field data, the temperature field distribution is obtained; in the arrangement of the thermocouples, the coordinates of the temperature measurement point corresponding to each thermocouple are fixed, and the coordinates are The direction range is -30 to 30, The direction range is -10 to 10.

[0020] In summary, due to the adoption of this technical solution, the beneficial effects of the present invention are as follows:

[0021] By using the strategy of combining pre-distributed functions with free parameters, the present invention can efficiently extract key information from simulations, realize the two-dimensional distribution reconstruction of the temperature field through the constraints of experimental measurement point data, and then accurately evaluate material damage. Compared with traditional methods, the present invention overcomes the limitation of only obtaining limited measurement point data, provides comprehensive temperature distribution characteristics, and can enhance the understanding of the thermal process of materials under laser action.

[0022] The present invention allows for a more flexible arrangement of measuring points, avoiding direct interference from high temperature areas, thereby ensuring the accuracy and completeness of data collection, and obtaining reliable information even under extreme conditions. By introducing a local point heat source model to simplify the solid thermal stress equation, there is no need to rely on strain gauges for strain measurement, especially in high temperature environments, which avoids the problem of strain gauge performance degradation and improves the accuracy and stability of stress distribution calculations. After rigorous ground experimental verification, the temperature field reconstruction results of the present invention performed well and were highly consistent with the strain distribution measured in the experiment, demonstrating the effectiveness and practical application value of the method of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the overall process of the method of the present invention;

[0024] Figure 2 is a schematic diagram of an equivalent surface heat source spot;

[0025] Figure 3 Schematic diagram of simulated temperature field distribution;

[0026] Figure 4 Schematic diagram of the arrangement scheme for strain measurement;

[0027] Figure 5 This is a schematic diagram of the inverted temperature cloud map effect;

[0028] Figure 6 It is a schematic diagram for comparing the inverted temperature cloud map and the measured value distribution;

[0029] Figure 7 It is the material strain cloud diagram corresponding to the radial deformation of the material;

[0030] Figure 8 It is the material strain cloud diagram corresponding to the circumferential deformation of the material;

[0031] Fig. 9 Schematic diagram of heat balance calculation. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0033] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] Example 1

[0035] A full-field data inversion method for two-dimensional thermal response to laser irradiation. Figure 1 The overall steps of the method are shown and can be summarized as follows:

[0036] S1, obtaining the temperature field data of the target under the action of laser and extracting the corresponding prediction function;

[0037] S2. By using the temperature field inversion method, the temperature field data is improved based on the extracted pre-function to obtain the temperature field distribution;

[0038] S3, performing material strain field inversion based on temperature field distribution to obtain material strain function;

[0039] S4. Combining the material strain function with the material mechanical properties, inverting the material stress field, and obtaining the material stress distribution;

[0040] S5. Based on the material stress distribution, different target materials are selected under the action of laser to obtain the damage function of the corresponding material and complete the damage assessment.

[0041] This embodiment will introduce the details of each step in detail according to the above step sequence.

[0042] In step S1, under the action of laser, the laser irradiation spot on the target is equivalent to a heat source with Gaussian distribution. For example, for a typical Gaussian distribution spot type heat source, it is simplified to a temperature heat source distributed in concentric rings applied to the target surface according to the equivalent energy principle, such as Figure 2 Then, based on the temperature heat source, the finite element method is used to calculate the heat flow in the target, and the temperature field data of the target under the action of the laser is obtained. The temperature field data involves the temperature value , the polar diameter of the temperature measurement point in the polar coordinate system , polar angle ,time wait.

[0043] According to the finite element analysis, the temperature distribution is generally similar to the Gaussian distribution, that is, Figure 3 As shown; Figure 3 In the figure, the vertical axis represents temperature in °C; the horizontal axes Z and Y are the corresponding coordinate axes of the two-dimensional coordinate system in the Z direction and the Y direction, respectively, and the coordinate units are in millimeters (mm). The two-dimensional coordinate system is the coordinate system formed by each point on the target with the center of the target as the origin, and the coordinate value corresponds to the distance from the origin. Figure 3 It can be seen that the target temperature presents a ring distribution with the origin as the center, the temperature at and near the origin is high, and the corresponding temperature in the direction away from the origin decreases rapidly. Therefore, the temperature field data can be fitted into a function expression of the corresponding form as a pre-function for extraction. In this embodiment, the temperature field data conforms to the two-dimensional Gaussian distribution function, and the fitting method mentioned above is universal. When the temperature distribution is in other forms, it can be fitted into a function expression of the corresponding form.

[0044] In this embodiment, the temperature field data conforms to the function expression of the two-dimensional Gaussian distribution function:

[0045]

[0046] In the formula, is an exponential function, Indicates the temperature value, represents the geometric coordinates of the measurement domain, represents the geometric coordinates of the laser action point, , , , , All are unknown coefficients; each unknown coefficient is obtained by solving the measured values.

[0047] Enter step S2. In order to invert the temperature field, several thermocouples are arranged on the back of the target to obtain the back temperature during laser irradiation, so as to calibrate the distribution function and obtain the temperature field distribution after perfecting the undetermined coefficients in the temperature field data. Figure 4 The hint, Figure 4 The strain measurement points are also marked; the coordinates of the temperature measurement points corresponding to each thermocouple are fixed. The direction range is -30 to 30, The direction range is -10 to 10.

[0048] According to the above measurement method, example data measured at 9 temperature measurement points in this embodiment are shown in Table 1 below.

[0049] Table 1 Example data table of temperature measurement points

[0050]

[0051] Based on the data of 9 measurement points measured every second, this embodiment fits the distribution function of the temperature field every second in Matlab code. Taking the first second as an example, the coefficients to be determined obtained by fitting are:

[0052]

[0053]

[0054]

[0055]

[0056]

[0057] The distribution diagram obtained from the 1st second data can be found in for Draw within the plane range, that is, Figure 5 As shown; when the reconstructed temperature and the thermocouple measurement value are plotted in the figure, the following is obtained: Figure 6 From Figure 6 It can be seen that the distribution function and the measured value are checked against each other to obtain a smoother distribution. At this time, the temperature field data is improved and the corresponding temperature field distribution is obtained.

[0058] Entering step S3, after obtaining the temperature field distribution, the material strain function is calculated according to the solid mechanics theory. According to the function expression fitted by the improved temperature field data, let , , ,in and All are intermediate parameters. is the polar diameter of the temperature measuring point in the polar coordinate system; set The constraint that the displacement is not singular at is:

[0059]

[0060] In the formula, is the intermediate parameter, is the thermal expansion coefficient of the material, is the Poisson's ratio of the material; at the same time, the boundary condition constraints are set, and the displacement caused by the temperature at the edge of the target is preset to 0, that is, , is the polar diameter corresponding to the edge of the target, is the displacement caused by temperature, then:

[0061]

[0062] In the formula, It is also an intermediate parameter; according to the intermediate parameter , , calculate the strain functions of two types of materials, and obtain two types of material strain cloud diagrams, which correspond to the radial deformation of the material and the circumferential deformation of the material respectively.

[0063] In this embodiment, the formulas for calculating the strain functions of the two types of materials are as follows:

[0064]

[0065]

[0066]

[0067] In the formula, Also an intermediate parameter, Represents the material strain function corresponding to the radial deformation of the material, Represents the material strain function corresponding to the circumferential deformation of the material.

[0068] This embodiment uses common aviation aluminum alloy materials as an example at this step, and takes the following example parameters: , , , , , , , , we can calculate:

[0069]

[0070]

[0071] Based on the above sample data, the strain cloud corresponding to the radial deformation of the material is drawn as follows Figure 7 As shown, the strain cloud corresponding to the circumferential deformation of the material is as follows Figure 8 shown.

[0072] Enter step S4, and obtain the radial deformation strain field of the material according to the strain functions of the two types of materials and the circumferential deformation strain field , from which the material stress distribution can be obtained. In this step of this embodiment, three common materials are first given, namely aluminum alloy, titanium alloy, and T700 carbon fiber / epoxy composite material, and their respective material mechanical properties are as follows:

[0073] Aluminum Alloy:

[0074] Standard thermal expansion coefficient , which is used when calculating strain contours;

[0075] Temperature-dependent elastic modulus , which is used in calculating stress distribution;

[0076] Temperature-dependent strength values , which is used when calculating the damage function.

[0077] Titanium Alloy:

[0078] Standard thermal expansion coefficient ;

[0079] Temperature-dependent elastic modulus ;

[0080] Temperature-dependent strength values .

[0081] T700 Carbon Fiber / Epoxy Composite:

[0082] Standard thermal expansion coefficient ;

[0083] Temperature-dependent elastic modulus ;

[0084] Temperature-dependent strength values .

[0085] The elastic modulus of the material's mechanical properties that changes with temperature As material properties , combined with the radial deformation strain field and the circumferential deformation strain field After that, the material stress distribution is calculated as follows:

[0086]

[0087]

[0088] In the formula, Represents the material stress distribution corresponding to the radial deformation of the material, Represents the material stress distribution corresponding to the circumferential deformation of the material.

[0089] Enter step S5, according to different target material selections, obtain the strength value of the selected target material as it changes with temperature from the corresponding material mechanical properties , calculate the damage function of the corresponding material.

[0090] When the target material is selected as aluminum alloy or titanium alloy, the corresponding damage function is as follows:

[0091]

[0092] When the target material is selected as T700 carbon fiber / epoxy composite material, the corresponding damage function is as follows:

[0093]

[0094] This completes the damage assessment of the selected target material.

[0095] Example 2

[0096] Based on Example 1, this example describes in some detail the thermal equilibrium state involved in the application process of the method. In step S1, based on the irradiation of the target by the laser, when the power of the laser is lower than the preset power threshold, or the thickness of the target is higher than the preset thickness threshold, the laser energy is relatively insufficient, and the target is in a thermal equilibrium state without being melted through.

[0097] The time when this thermal equilibrium state appears is an important indicator of concern during the research process. It represents the comprehensive ability of laser irradiation and target material heat transfer, and is used in the temperature field inversion process of step S2. Therefore, this embodiment proposes a method for automatically determining this state, as follows:

[0098] Real-time detection of the temperature of the target material under laser irradiation, such as Fig. 9 The temperature time series curve shown in the figure; the difference between the average value of the last five detection points and the first five detection points at any time in the temperature time series curve is taken as the slope of the temperature time series curve; in the real-time detection process, when the slope reaches the maximum value, it begins to decrease, and the detection point corresponding to 90% of the maximum value of the slope decrease is taken as the temperature equilibrium point to determine whether the target reaches thermal equilibrium at the temperature equilibrium point. Fig. 9 The temperature-time curve of the example shows that the temperature sequence reaches thermal equilibrium at 44 seconds.

[0099] In summary, the present invention greatly improves the measurement and analysis of the thermal response of laser irradiated materials through an innovative full-field data inversion method, provides strong technical support for the optimization design, damage prediction and protection in the field of laser technology and materials, and has significant academic significance and broad application prospects.

Claims

1. A method for full-field data inversion of two-dimensional thermal response to laser irradiation, characterized in that: The method comprises the following steps: S1, obtaining the temperature field data of the target under the action of laser and extracting the corresponding prediction function; S2. By using the temperature field inversion method, the temperature field data is improved based on the extracted pre-function to obtain the temperature field distribution; S3, performing material strain field inversion based on temperature field distribution to obtain material strain function; S4. Combining the material strain function with the material mechanical properties, inverting the material stress field, and obtaining the material stress distribution; S5. Based on the material stress distribution, by selecting different target materials under the action of laser, the damage function of the corresponding material is obtained to complete the damage assessment; In step S1, the temperature field data is fitted into a function expression of a corresponding form as a pre-function for extraction. When the temperature field data conforms to a two-dimensional Gaussian distribution function, the fitted function expression is: In the formula, is an exponential function, Indicates the temperature value, represents the geometric coordinates of the measurement domain, represents the geometric coordinates of the laser action point, , , , , All are undetermined coefficients; each undetermined coefficient is obtained by solving the measured values; In step S3, after obtaining the temperature field distribution, the material strain function is calculated according to the solid mechanics theory; according to the function expression fitted by the improved temperature field data, let , , ,in and These are all intermediate parameters. is the polar diameter of the temperature measuring point in the polar coordinate system; set The constraint that the displacement is not singular at is: In the formula, is the intermediate parameter, is the thermal expansion coefficient of the material, is the Poisson's ratio of the material; at the same time, the boundary condition constraints are set, and the displacement caused by the temperature at the edge of the target is preset to 0, that is, , is the polar diameter corresponding to the edge of the target, is the displacement caused by temperature, then: In the formula, It is also an intermediate parameter; according to the intermediate parameter , , calculate the strain functions of two types of materials and obtain two types of material strain cloud diagrams, corresponding to the radial deformation of the material and the circumferential deformation of the material respectively; The formulas for calculating the strain functions of the two types of materials are as follows: In the formula, Also an intermediate parameter, Represents the material strain function corresponding to the radial deformation of the material, Represents the material strain function corresponding to the circumferential deformation of the material; In step S4, the radial deformation strain field of the material is obtained according to the strain functions of the two types of materials. and the circumferential deformation strain field ; Combine the material properties in the mechanical properties of materials , calculate the material stress distribution as follows: In the formula, Represents the material stress distribution corresponding to the radial deformation of the material, Represents the material stress distribution corresponding to the circumferential deformation of the material.

2. The laser irradiation two-dimensional thermal response full-field data inversion method according to claim 1 is characterized in that: Step S1 is based on laser irradiation of the target. When the power of the laser is lower than a preset power threshold, or the thickness of the target is higher than a preset thickness threshold, the target is in thermal equilibrium without melting through. The thermal equilibrium state of the target is used to characterize the comprehensive ability of laser irradiation and heat transfer of the target material, and is applied to the temperature field inversion process of step S2.

3. The laser irradiation two-dimensional thermal response full-field data inversion method according to claim 2 is characterized in that: The method for judging the thermal equilibrium state of the target is as follows: the temperature of the target material under laser irradiation is detected in real time to obtain a temperature time series curve; the difference between the average value of the last five detection points and the first five detection points at any time in the temperature time series curve is taken as the slope of the temperature time series curve; during the real-time detection process, when the slope reaches a maximum value and then begins to decrease, the detection point corresponding to 90% of the maximum value of the slope decrease is taken as the temperature equilibrium point, and it is judged that the target reaches a thermal equilibrium state at the time of the temperature equilibrium point.

4. The laser irradiation two-dimensional thermal response full-field data inversion method according to claim 1 is characterized in that: In step S1, under the action of laser, the laser irradiation spot on the target is equivalent to a heat source with Gaussian distribution, and the heat source is simplified to a temperature heat source distributed in concentric rings and applied to the target surface according to the principle of equivalent energy; based on the temperature heat source, the finite element method is used to calculate the conduction of heat flux in the target to obtain the temperature field data of the target under the action of laser, and the temperature field data is fitted into a function expression of the corresponding form as a pre-function for extraction.

5. The laser irradiation two-dimensional thermal response full-field data inversion method according to claim 1, characterized in that: In step S2, several thermocouples are arranged on the back of the target to obtain the back temperature during laser irradiation, so as to calibrate the distribution function, and after perfecting the undetermined coefficients in the temperature field data, the temperature field distribution is obtained; in the arrangement of the thermocouples, the coordinates of the temperature measurement point corresponding to each thermocouple are fixed, and the coordinates are The direction range is -30 to 30, The direction range is -10 to 10.

6. The laser irradiation two-dimensional thermal response full-field data inversion method according to claim 1, characterized in that: According to different target material selections, the strength value of the selected target material changing with temperature is obtained from the corresponding material mechanical properties. , calculate the damage function of the corresponding material; When the target material is selected as aluminum alloy or titanium alloy, the corresponding damage function is as follows: When the target material is selected as T700 carbon fiber / epoxy composite material, the corresponding damage function is as follows: This completes the damage assessment of the selected target material.

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