Ultrasonic-based method, system, and media for detecting residual stress fields in aircraft engine forgings

Abstract

The application relates to an ultrasonic-based aero-engine forge piece residual stress field detection method, which comprises the following steps: determining a corresponding acoustic elasticity control equation based on a linear relationship between ultrasonic wave velocity and stress of a forge piece material; calibrating an acoustic elasticity coefficient of the forge piece material; performing accurate measurement on a cross-sectional size of a forge piece to reconstruct a geometric shape of the forge piece; determining an acoustic beam scanning scheme based on Snell's law; performing multi-angle scanning excitation and receiving position and direction calculation according to the acoustic beam scanning scheme to collect ultrasonic receiving signals; calculating ultrasonic wave transit time and velocity according to the collected ultrasonic receiving signals; performing stress reconstruction inversion calculation on the geometric shape of the forge piece to construct a corresponding residual stress field; and performing three-dimensional imaging based on the corresponding residual stress field.

Description

Technical Field

[0001] This invention relates to the field of residual stress detection in aero-engine forgings, and more specifically, to a non-destructive testing scheme for the three-dimensional residual stress field of the entire cross-section of aero-engine forgings based on ultrasound. Background Technology

[0002] Residual stress refers to the effects and influences that a component will experience during the manufacturing process from various technological factors. If these effects and influences do not completely disappear after these factors disappear, and some effects and influences remain in the component, then these residual effects and influences are called residual stress.

[0003] Residual stresses are generated in metallic materials during machining and hot working (castings, welding, forgings). The presence of residual stresses has a significant impact on the mechanical properties of the materials.

[0004] During the manufacturing of aero-engines, significant residual stress is generated during the forming process of high-temperature alloy forgings. Specifically, during part machining, the residual stress remaining in the forging is released as part of the material is removed. As a self-balancing internal stress, the residual stress redistributes after machining to achieve rebalancing, while simultaneously causing deformation of the forging in its post-machining free state, thus significantly affecting the shape and dimensional accuracy of the part. For example, to meet the weight reduction requirements of aero-engines, high-temperature alloy turbine disks pursue a thinner and lighter design, which makes the machining deformation problem caused by residual stress more prominent.

[0005] In particular, turbine disks, as core hot-end components in aero engines, have extremely high requirements for dimensional tolerances. Even minor machining deformations can cause parts to be scrapped or require multiple reworks to meet assembly requirements. Residual stresses retained in the parts will also be superimposed on service loads during subsequent use, changing the actual stress state of the forgings and thus affecting their dimensional stability and fatigue performance during service, which in turn has a significant impact on the overall performance, lifespan, and reliability of the engine.

[0006] In summary, the residual stress generated during the forging process evolves and is transmitted between different processes, ultimately having a significant impact on the machining and service life of high-temperature alloy forgings. Therefore, it is necessary to understand the distribution characteristics and evolution laws of residual stress in each process in order to predict its impact on subsequent machining deformation and service performance, and thus optimize the manufacturing process; this is also an important foundation for realizing the forward design and life prediction of aero-engines.

[0007] The only way to establish the actual level and spatial distribution of residual stress is through reliable measurement. Currently, the profile method is generally used to detect residual stress in the cross-section of forgings. This method requires cutting the entire forging in half and can only detect stress perpendicular to the cut section. This method can damage the forging and can only detect unidirectional residual stress, which cannot fully meet the requirements for strength and life assessment. Therefore, it is urgent to develop a non-destructive testing method for the three-dimensional residual stress field of the entire cross-section of aero-engine forgings. Summary of the Invention

[0008] This application, considering geometric and material nonlinearity, establishes an acoustoelastic theoretical model based on nonlinear theory to assess the influence of arbitrary triaxial stress on ultrasonic velocity. Furthermore, based on the theoretical results, an analytical relationship is established between the stress increment and the change in ultrasonic velocity.

[0009] According to a first aspect of this application, a method for detecting residual stress field in aero-engine forgings based on ultrasound is provided, comprising:

[0010] The corresponding acoustoelastic control equation is determined based on the linear relationship between ultrasonic velocity and stress in forging material.

[0011] Calibrated the acoustic elastic coefficient of the forging material;

[0012] Precise measurements are performed on the cross-sectional dimensions of the forging to reconstruct its geometry;

[0013] Determine the acoustic beam scanning scheme based on Snell's law;

[0014] According to the aforementioned acoustic beam scanning scheme, multi-angle scanning excitation and receiving position and direction calculations are performed to acquire ultrasonic received signals;

[0015] The transit time and velocity of the ultrasonic waves are calculated based on the collected ultrasonic received signals.

[0016] Stress reconstruction inversion calculations are performed on the geometry of the forging to construct the corresponding residual stress field;

[0017] Three-dimensional imaging is performed based on the corresponding residual stress field.

[0018] According to a second aspect of this application, a computer-readable storage medium storing instructions is provided that, when executed, cause a machine to perform a residual stress field detection method as described in the first invention.

[0019] According to a third aspect of this application, an ultrasonic-based residual stress field detection system for aero-engine forgings is provided, including means for performing the residual stress field detection method as described in the first aspect.

[0020] This overview is provided to introduce, in a simplified form, some of the concepts further described in the detailed description below. This overview is not intended to identify key or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. Attached Figure Description

[0021] To describe how the above and other advantages and features of the invention are obtained, a more detailed description of the invention, which has been briefly described above, will be presented with reference to specific embodiments of the invention shown in the accompanying drawings. It will be understood that these drawings depict only exemplary embodiments of the invention and are therefore not intended to limit its scope. The invention will be described and explained using the drawings and with the aid of additional features and details, in which:

[0022] Figure 1 A schematic flowchart of an ultrasonic-based method for detecting residual stress fields in aero-engine forgings according to an embodiment of this application is shown.

[0023] Figure 2 A coordinate system description (three states) of a deformable object according to an embodiment of this application is shown.

[0024] Figure 3 An illustration of stress settings and ultrasonic propagation direction according to an embodiment of this application is shown.

[0025] Figure 4 An experimental setup for calibrating the acoustoelastic coefficient curve of stress state and sensitive acoustic parameters according to an embodiment of this application is shown.

[0026] Figure 5 A schematic block diagram of a visual beam path setting GUI interface according to an embodiment of this application is shown.

[0027] Figure 6 A schematic diagram of the sound beam path design of a forging according to an embodiment of this application under different working conditions (three working conditions) is shown.

[0028] Figure 7 A schematic diagram of the general discretization of a reconstructed image and the projection area according to an embodiment of this application is shown. Detailed Implementation

[0029] Ultrasonic testing utilizes lasers to excite ultrasonic waves and leverages the propagation characteristics of these waves to invert information about the material's microstructure and structural features, achieving non-destructive testing. Initially used primarily for flaw detection, ultrasonic technology has since been applied to residual stress detection in materials. Ultrasonic stress detection applies the acoustoelastic principle of ultrasound, which states that changes in residual stress cause changes in the propagation speed of ultrasonic waves within the material. This principle, based on the inherent relationship between the propagation speed of ultrasonic waves and stress in the tested object, converts this characteristic into a digital signal representation for quantitative mechanical testing.

[0030] However, existing ultrasonic residual stress detection technology does not take into account the relationship between ultrasonic velocity and material stress in a comprehensive manner, and the acoustoelastic equation and its parameter settings used cannot accurately reflect the corresponding relationship.

[0031] On the other hand, when measuring the stress of forging sections of various shapes, the commonly used contour method requires cutting the entire forging in half and can only detect the stress perpendicular to the cut section. This method can damage the forging and can only detect unidirectional residual stress.

[0032] To overcome the aforementioned shortcomings in existing ultrasonic residual stress detection technologies, this application proposes a novel residual stress field detection scheme for aero-engine forgings.

[0033] In general, the scheme of this application is based on the acoustoelastic effect of materials. It calculates the acoustoelastic coefficient by solving the linear analytical expression between the change in longitudinal wave velocity and the change in stress, and by calibrating the acoustoelastic coefficient curve of stress state and sensitive acoustic parameters. Then, it establishes the relationship between the change in ultrasonic wave velocity and stress in any direction. Then, through reasonable sound beam path design, it uses dual probes to complete ultrasonic scanning of the entire cross section of the forging. Finally, it obtains the information of the three-dimensional residual stress field of the entire cross section by inverting the data collected by scanning.

[0034] The ultrasonic residual stress measurement scheme of this application is also based on the linear relationship between ultrasonic velocity and material stress. This relationship within the elastic limit is called the acoustoelastic effect, which reflects the linear change in ultrasonic propagation time with stress. Compared with existing technologies, this scheme further improves the acoustoelastic equation calibrating this relationship through in-depth analysis of the linear relationship between ultrasonic velocity and material stress, making it more accurate in reflecting the linear relationship between ultrasonic velocity and material stress. Furthermore, in determining the acoustic beam scanning scheme for the forging cross-section, this scheme employs a novel acoustic beam path design, making the acoustic beam path inside the structure more regular, while simultaneously obtaining the incident and exit conditions of the external acoustic beam.

[0035] Now for reference Figure 1Here is a schematic flowchart illustrating an ultrasonic-based method for detecting residual stress fields in aero-engine forgings according to an embodiment of this application.

[0036] As shown in the figure, firstly, at step 102, the corresponding acoustoelastic control equation is determined based on the linear relationship between ultrasonic velocity and forging material stress.

[0037] Research has shown that the propagation speed of elastic waves in stressed solid materials depends not only on the material's density and second-order elastic coefficients, but also on higher-order elastic coefficients and the initial stress state. This relationship between sound velocity and stress is known as the acoustoelastic effect.

[0038] To better reflect the relationship between ultrasonic velocity and forging material stress, and to derive the corresponding acoustoelastic control equations, this scheme first defines three states in the coordinate system to describe the object: the natural state, the initial state, and the final state, as follows: Figure 2 As shown:

[0039] The natural state is when an object is in an undeformed state with no stress or strain, and its position is represented by a vector ξ or a component ζ. α Represented by X. The initial state is the state of the object after deformation or under a certain load, and its position vector is represented by X or its component X. J The final state is represented by the state achieved when a small acoustic perturbation is superimposed on the deformable object, causing further deformation. Its position vector is represented by x or its component x. j The physical variables and material properties under the three states are represented by superscripts o, i, and f, respectively, where o represents the quantity in the natural state, i represents the quantity in the initial state, and f represents the quantity in the final state. The deformation from the natural state to the initial state, from the natural state to the final state, and from the initial state to the final state can be represented by the displacement vector u as follows: u i =X-ξ,u f =x-ξ and u=xX.

[0040] Therefore, the Lagrange strain of the initial and final states, described in natural coordinates, is as follows:

[0041]

[0042] Where α and β represent the x-coordinate and y-coordinate in the natural coordinate system, and E represents the Lagrange strain tensor.

[0043] Because the superimposed ultrasonic dynamic disturbance is very small, that is Therefore, the strain caused by the small ultrasonic disturbance from the initial state to the final state can be approximated as:

[0044]

[0045] Furthermore, the stress at a point can be represented by the Cauchy stress tensor t or the second Biora-Kirchhoff stress tensor T. From the definition, the relationship between the two is as follows:

[0046]

[0047] Since the object is continuous, the relationship between the three densities can be obtained by the law of conservation of mass as follows:

[0048]

[0049] Where ρ represents the material density.

[0050] Substituting equation (1.4) into equation (1.3), we can obtain:

[0051]

[0052] On the other hand, small ultrasonic disturbances from the initial state to the final state of an object will create a stress increment T = T f -T i This increment is represented in the natural coordinate system as

[0053] The transformation of an object from its initial state to its final state is a dynamic deformation, and its equation of motion is:

[0054]

[0055] Equation (1.6) can be expressed in natural coordinates as follows:

[0056]

[0057] Hyperelastic materials are materials that possess strain energy, which is greater than the Oula-Kirchhoff stress T. αβ With strain energy function W(E) αβ Satisfying between ) In the formula E aβ For finite deformation strain tensor.

[0058] This constitutive model, where the material strain energy function is nonlinear, can be expressed as:

[0059]

[0060] In the formula c αβγδ and c αβγδζη These are the second and third elastic moduli of the material, respectively.

[0061] Taking the partial derivative of equation (1.8) with respect to strain and neglecting higher-order terms, we can obtain the expressions for the Biora-Kirchhoff stress in the initial and final states:

[0062]

[0063] Assuming the initial prestrain is a small deformation, then:

[0064]

[0065] Where e represents the Cauchy stress tensor.

[0066] Subtracting equations (1.9) and (1.10), we obtain the small stress increment as:

[0067]

[0068] Substituting the small stress increments (1.11) induced by pre-strain and ultrasound into the equation of motion (1.7),

[0069] The change of an object from its natural state to its initial state is a static process, i.e., t i or T i Balance is required:

[0070]

[0071] The governing equations of the acoustic elastic wave expressed in natural coordinates can then be obtained as follows:

[0072]

[0073] in ρ 0 is the material density at zero stress, and u is the displacement increment from the initial state to the final state; It is a component of the second PK stress tensor measured under natural conditions. αβγδ and c αβγδζη These represent the second-order and third-order elastic coefficients, respectively; This represents the initial displacement from the natural state to the initial state; These are the components of the initial Cauchy stress tensor.

[0074] Similarly, the acoustic elastic control equation expressed in terms of the initial coordinates can be obtained as follows:

[0075]

[0076] in,

[0077] The equivalent stiffness is represented by the initial coordinates.

[0078] The theoretical derivation is based on a spatial coordinate system. Since the wave velocity change depends only on the magnitude of the stress and the angle θ between the ultrasonic propagation direction and the stress direction, this problem can be further solved through coordinate transformation. Assuming the stress is (σ1, σ2, σ3) in the spatial coordinate system and the ultrasonic propagation direction is (cosθ1, sinθ1, 0), these two directions can define a new plane. The stress (σ1, σ2, σ3) can be equivalent to a uniaxial stress σ in a certain direction on this plane. An orthogonal coordinate system is established in the new plane. The direction of the equivalent stress is taken as the y-axis direction in the new coordinate system, the direction perpendicular to it is taken as the x-axis direction, and the direction corresponding to the perpendicular plane vector following the right-hand rule is taken as the z-axis direction. In this coordinate system, the ultrasonic propagation direction is transformed into (cosθ, sinθ, 0), where θ is the angle between the ultrasonic longitudinal wave propagation direction and the x-axis. The specific settings of the stress and the ultrasonic propagation direction are as follows... Figure 3 As shown.

[0079] Using the Murnaghan material model, the ultrasonic wave propagates in the direction (cosθ, sinθ, 0). Based on the solution of ultrasonic wave propagation... (U and N are characteristic parameters in the characteristic solution, u is the displacement vector, V is the wave velocity, and t is the wave propagation time.) Substituting these into equation (1.15) yields the characteristic equation. The expansion is:

[0080]

[0081] in

[0082]

[0083] Where θ represents the angle between the direction of ultrasonic propagation and the direction of stress;

[0084] λ and μ are the ultrasonic second-order elastic moduli of the material.

[0085] l, m, and n are the ultrasonic third-order elastic moduli of the material.

[0086] σ represents the magnitude of the stress.

[0087] The above equation has three solutions, among which the solution for the longitudinal wave velocity corresponds to (D) 11 -ρ 0 V 2 (D) 22 -ρ 0 V 2 )-D 12 D 21 The larger solution is 0. Assume the P-wave velocity is V. L Solving the equation, we get:

[0088]

[0089] By omitting the linear term of σ inside the square root of expression (1.17), ρ can be analytically solved. 0 V L 2 The relationship between the velocity of sound and stress is expressed as a linear function. Since the change in sound velocity due to stress is smaller than the change in sound velocity under stress-free conditions, subsequent research focuses on the change in sound velocity caused by stress. Differentiating both sides of the equation yields a linear analytical expression for the relationship between the change in longitudinal wave velocity and the change in stress:

[0090]

[0091] Among them, dV L This represents the change in the longitudinal wave velocity of the ultrasound.

[0092] V L The longitudinal wave velocity of ultrasound;

[0093] V0 is the longitudinal wave velocity of ultrasound under zero stress.

[0094] dσ is the change in stress magnitude;

[0095] ρ 0 Material density at zero stress;

[0096] K and S are the corresponding variables obtained from simplification and summation. Furthermore, by differentiating both sides of Equation 1.17 with respect to Equation 1.18, we can obtain K and S as follows:

[0097] 8lμ-8λm-12λμ+λn+4mμ+24λ 2 sin(θ) 2 +48μ 2 sin(θ) 2 -8λ 2 +8μ 2

[0098]

[0099] Since the velocity change caused by stress is not significant, V can be approximated as... L If ≈V0, then equation (1.18) can be finally expressed analytically as:

[0100]

[0101] Thus, through the above deduction process, this scheme provides an improved acoustoelastic control equation to more accurately reflect the linear relationship between ultrasonic velocity and forging material stress.

[0102] It should be understood that the meanings of the letter symbols appearing in the above equation derivation are the same as those of the corresponding letter symbols used in various existing formulas relating ultrasonic velocity and stress. In other words, even if the meanings of the various letter symbols involved in equations (1.1)-(1.19) are not specifically explained in the above content, those skilled in the art can understand their meanings based on common sense in the field of materials stress research.

[0103] On the other hand, it should be understood that although the above embodiments are mainly based on Lagrange strain to derive the acoustoelastic control equations, this is not intended to limit the acoustoelastic control equations in this application to the Lagrange strain method. In fact, other methods such as Euler strain, Almancian strain tensor, etc., can be applied to the schemes in this application, and these all fall within the protection scope of this application.

[0104] After obtaining the improved acoustoelastic control equation, the process proceeds to step 104, where the acoustoelastic coefficient of the forging material is calibrated.

[0105] To accurately calculate the propagation state of ultrasound in metallic alloys (e.g., nickel-based alloys) for inversion, it is necessary to accurately determine the second-order elastic coefficients λ, μ and the third-order elastic coefficients l, m, n of the base material of the alloy. These elastic coefficients will be used to calculate the simplified summation variables K and S in the aforementioned acoustoelastic governing equation (1.19).

[0106] Therefore, it is necessary to perform acoustoelastic coefficient curve calibration calculations based on stress state and sensitive acoustic parameters to obtain the acoustoelastic coefficient. From this, the relationship between ultrasonic wave velocity variation along any direction and stress can be calculated. An example of the corresponding theoretical calculation formula for the acoustoelastic coefficient is as follows:

[0107]

[0108] Where V represents the longitudinal wave velocity of ultrasound, the first subscript is the wave propagation direction, the second subscript is the polarization direction of the particle, and the third subscript is the direction of uniaxial stress.

[0109] V 111 This indicates the wave velocity of the ultrasonic longitudinal wave propagating along the uniaxial stress direction (in the stress-free state);

[0110] V 113 This represents the wave velocity of ultrasonic longitudinal waves propagating perpendicular to the uniaxial stress direction (in a stress-free state).

[0111] V 133 This represents the wave velocity of an ultrasonic transverse wave propagating perpendicular to the uniaxial stress direction (in a stress-free state).

[0112] dV 111The differential represents the change in wave velocity (differential) of an ultrasonic longitudinal wave propagating along the uniaxial stress direction due to uniaxial stress.

[0113] dV 113 It represents the change in wave velocity (differential) of ultrasonic longitudinal waves propagating perpendicular to the direction of uniaxial stress due to uniaxial stress.

[0114] dV 133 The differential represents the change in wave velocity (differential) of an ultrasonic transverse wave propagating perpendicular to the direction of uniaxial stress due to uniaxial stress.

[0115] λ and μ represent the second-order elastic coefficients of the forging material;

[0116] l, m, and n represent the third-order elastic coefficients of the forging material;

[0117] σ represents the magnitude of the triaxial stress vector of the forging material;

[0118] dσ represents the change in the magnitude of the triaxial stress vector of the forging material.

[0119] Based on the calibrated acoustic elastic coefficient curve, the corresponding second-order elastic coefficients λ and μ, and the third-order elastic coefficients l, m, and n of the material can be calculated using the formula.

[0120] Specifically, the λ and μ of the material first need to be calibrated using destructive tensile tests to determine their values. Simultaneously, the stress range for the acoustoelastic coefficient calibration experiment is selected based on the experimental results. The acoustoelastic coefficient curve is calibrated using the Lcr wave detection method, ultrasonic longitudinal wave method, and ultrasonic transverse wave method. The specific experimental setup for calibrating the acoustoelastic coefficient curve with stress states and sensitive acoustic parameters is as follows: Figure 4 As shown.

[0121] After the acoustoelastic parameters of the required forging material are calibrated according to the acoustoelastic coefficient curve, the process proceeds to step 106, where the cross-sectional dimensions of the forging are precisely measured to reconstruct the geometry of the forging.

[0122] Sound velocity measurement requires precise transit time and propagation distance parameters, and determining the position of the ultrasonic transducer requires precise dimensional information. Therefore, precise dimensional measurements of the forging under test are necessary. These precise measurements may include referring to design drawings and using a coordinate measuring machine and related gauges to accurately measure the dimensions and angles of each side of the forging cross-section and reconstruct the geometry of the forging. The precise measurement of the forging cross-sectional dimensions can employ conventional techniques, which will not be detailed here.

[0123] The process then proceeds to step 108, in which the acoustic beam scanning scheme is determined based on Snell's law.

[0124] The ultrasound beam path within the cross-section of a structure is not the same as the initial incident beam path. This is because ultrasound is refracted at the structural boundaries, causing the beam path inside the structure to differ from the incident path. For stress field imaging, which requires a specific beam path, the presence of these boundaries presents a challenge to path scanning.

[0125] The ultrasound beam path inside the structure and the external incident path follow Snell's law as shown in equation (3), and the formula is as follows:

[0126]

[0127] Where θ1 represents the incident angle of the ultrasonic wave, θ2 represents the refraction angle of the ultrasonic wave, v1 represents the incident longitudinal wave velocity of the ultrasonic wave, and v2 represents the refraction velocity of the longitudinal wave of the ultrasonic wave.

[0128] Therefore, given the physical properties of the material, the external sound beam path can be deduced by specifying the internal sound beam path, thereby achieving sound beam path design, making the internal sound beam path of the structure more regular, and obtaining the incident and exit conditions of the external sound beam.

[0129] Specifically, the acoustic beam scanning scheme may include the following steps:

[0130] 1) After determining the starting position coordinates, input the geometric position coordinates and dimensions of the cross section of the structure to be measured, and draw the cross section in a two-dimensional coordinate system.

[0131] 2) Set the angle between the internal desired sound beam path and the x-axis and the y-axis intercept, and output the corresponding external sound beam path.

[0132] 3) Set the ultrasonic transducer moving path envelope to obtain the intersection point of the external sound beam path and the ultrasonic transducer moving path, which is the excitation receiving position coordinate.

[0133] 4) Based on the angle between the external sound beam path and the x-axis, the tilt direction of the excitation receiving probe is obtained.

[0134] 5) Based on the Snell's law and the aforementioned internal sound beam path, the external sound beam path is deduced.

[0135] By writing code based on the above scheme, a visual GUI interface for setting the acoustic beam path can be obtained, such as... Figure 5 As shown, the GUI interface can be divided into four parts: display interface, input settings, operating area, and input history.

[0136] After entering the geometric shape (in coordinate form in the front panel), the internal sound beam path and x-axis angle, and the internal sound beam path and y-axis intercept in the corresponding input setting boxes, the external sound beam path can be calculated by clicking the "Draw" button in the running area according to the above scheme, and the external sound beam path will be displayed in the display interface.

[0137] The following is based on Figure 6 The following example illustrates the design of the acoustic beam path under different working conditions, using three typical working conditions as an example of scanning a typical forging cross section shown in the figure.

[0138] Operating Condition 1: Internal 0° and 90° intersection path design;

[0139] Working Condition 2: Internal 45° and 135° intersecting path design;

[0140] Condition 3: Custom path (in this diagram, the incident angle is 60° and the coordinates of the incident point are -40).

[0141] In the first two operating conditions, the internal path has been preset through the pre-file, and the preset internal path can be changed through the pre-file. In operating condition 3, the internal sound beam setting angle and internal sound beam setting intercept need to be manually entered.

[0142] It should be understood that this acoustic beam scanning scheme is not limited to applications in... Figure 6 In the cross-section shown, in fact, any cross-section can be fully scanned and covered by adjusting the incident position, incident angle and scanning step of the sound beam.

[0143] After the acoustic beam scanning scheme is determined, the process proceeds to step 110. In this step, according to the acoustic beam scanning scheme, multi-angle scanning excitation and receiving position and direction calculations are performed to acquire ultrasound receiving signals. This step includes:

[0144] 1) Based on the reconstructed geometry and position of the forging (in step 106), set the required internal sound beam path angle and intercept;

[0145] 2) Based on the sound beam path design method in the sound beam scanning scheme, a series of excitation position x-coordinates, excitation position y-coordinates, excitation angles, receiving position x-coordinates, receiving position y-coordinates, and receiving angles are obtained, and a corresponding multi-axis control table is further formed.

[0146] 3) Input the multi-axis control table into the multi-axis controller to control the specific operation of the acoustic beam scanning accordingly.

[0147] In this way, the ultrasonic wave propagation excitation and reception along the corresponding path can be realized, and the original ultrasonic wave signal can be collected.

[0148] Next, the process proceeds to step 112. In this step, the transit time (i.e., "transit time") and velocity (i.e., wave velocity) of the ultrasonic wave are calculated based on the acquired ultrasonic received signal. Specifically, based on the acquired ultrasonic received signal and excitation signal, the transit time is calculated using a cross-correlation algorithm, and then the ultrasonic velocity along the corresponding ultrasonic path is calculated. The calculation can be implemented using techniques known in the art.

[0149] The process then proceeds to step 114, where stress reconstruction inversion calculations are performed on the reconstructed geometry of the forging to be tested to construct the corresponding residual stress field.

[0150] In this step, the (residual) stress field can be constructed in the form of a stress cloud map. The stress cloud map is described by a two-dimensional function f(x, y), where x and y are the coordinates of a point in space, and the value of the function f corresponds to the image value, i.e., the brightness of the image; in this scheme, it corresponds to the stress magnitude of the stress field in a known direction. Since the corresponding acoustoelastic control equations have been established and the ultrasonic wave velocity has been obtained in previous steps, the corresponding stress magnitude can be calculated based on the linear relationship between the ultrasonic wave velocity and the stress of the forging material in the acoustoelastic control equations.

[0151] It is understood that the reconstruction inversion can be performed on the entire geometry of the forging to be tested generated in step 106, or the reconstruction inversion can be limited to a selected region image within the geometry.

[0152] Because the stress field in the imaging exhibits both positive and negative stress modes (tensile and compressive stress), unlike general imaging where f can only be positive, f can be negative in this scheme, indicating that the stress field has compressive characteristics, corresponding to an increase in velocity. Assume the reconstructed region is square, and the origin of the reconstructed coordinate system coincides with the lower left corner of the square.

[0153] Specifically, the image of the region to be reconstructed is discretized into N = n × n square grids, each grid representing one pixel. The density of the discrete pixels determines the image accuracy. The stress field characterization image of the measured object is included within the reconstructed region. The general discretization of the reconstructed image and the projection region are as follows: Figure 7 As shown, the grid is numbered sequentially from left to right and from top to bottom to form the desired imaging area. Let ω be the path length of the i-th ray within the j-th pixel. ij Let L be the total number of rays, then the coefficient matrix is ​​formed by ω ij The resulting L×N dimensional matrix.

[0154] The image to be reconstructed is discretized into multiple grids, each grid representing a pixel and corresponding to a parameter value to be solved. For the image reconstruction problem, after data discretization, the essence is solving the equation p = Ax. Here, A is the coefficient matrix between the associated residual stress field and the projected data, i.e., the distance the hypothetical ultrasound travels through each grid point; x is the residual stress field to be reconstructed for each grid (pixel), and p is the measured projected data, i.e., the corresponding change in ultrasound velocity. The system of equations to be solved can be written in expanded form as follows:

[0155] ω 11 x1+ω 12 x2+ω 13 x3+…ω 1J x N =p1

[0156] ω 21 x1+ω 22 x2+ω 23 x3+…ω 2J x N =p2

[0157] …

[0158] ω L1 x1+ω L2 x2+ω L3 x3+…ω LJ x N =p L (4)

[0159] An N-dimensional image has n grids. An image is represented by (x1, x2, ..., x3) grids. 2， x3…,x N Let x be the corresponding point in N-dimensional space. Each equation corresponds to a hyperplane, and the solutions to these equations are the intersection points of all hyperplanes.

[0160] Therefore, this scheme adopts a structural residual stress characterization method that is not limited to neural network models. The inversion algorithm model is trained with the finite element simulation results and ultrasonic test results of the residual stress field of typical structures, so as to invert the triaxial stress inside the structure when the direction of the residual stress is unknown.

[0161] Finally, when all the grids (pixels) of the stress cloud image have reconstructed the corresponding residual stress field, the process proceeds to step 116. In this step, three-dimensional imaging is performed based on the residual stress field of all the grids (pixels) of the image, that is, the residual stress field distribution of the entire cross section of the forging is obtained by using the inversion algorithm of Equation (4) based on the obtained multi-angle multi-path ultrasonic speed, thereby completing the detection of the three-dimensional residual stress field of the entire cross section of the forging.

[0162] advantage:

[0163] This application can detect the three-dimensional residual stress field of the entire cross section of the forging without damaging it. The detection efficiency is high and the detection cost is greatly reduced. It can effectively support the process optimization in the manufacturing process of engine forgings, thereby improving the dimensional accuracy and stability of various engine parts. The detected residual stress data is an important input for strength and life assessment, which will effectively improve the fine design of key engine parts.

[0164] While different embodiments have been described above, it should be understood that they are merely examples and not limitations. Those skilled in the art will appreciate that various modifications in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims. Therefore, the breadth and scope of the invention disclosed herein should not be limited by the exemplary embodiments disclosed above, but should be defined solely by the appended claims and their equivalents.

Claims

1. A method for detecting residual stress field in aero-engine forgings based on ultrasound, comprising: The corresponding acoustoelastic control equation is determined based on the linear relationship between ultrasonic velocity and stress in forging material. Calibrated the acoustic elastic coefficient of the forging material; Precise measurements are performed on the cross-sectional dimensions of the forging to reconstruct its geometry; Determine the acoustic beam scanning scheme based on Snell's law; According to the aforementioned acoustic beam scanning scheme, multi-angle scanning excitation and receiving position and direction calculations are performed to acquire ultrasonic received signals; The transit time and velocity of the ultrasonic waves are calculated based on the collected ultrasonic received signals. Stress reconstruction inversion calculations are performed on the geometry of the forging to construct the corresponding residual stress field; Three-dimensional imaging is performed based on the corresponding residual stress field.

2. The residual stress field detection method as described in claim 1, characterized in that, The acoustoelastic control equation is: Among them, dV L This represents the change in the longitudinal wave velocity of the ultrasound. V L The longitudinal wave velocity of ultrasound; V0 is the longitudinal wave velocity of ultrasound under zero stress. dσ is the change in the magnitude of stress; ρ 0 Material density at zero stress; K and S are the corresponding variables obtained from the simplification and summarization, and where: 8lμ-8λm-12λμ+λn+4μμ+24λ 2 sin(θ) 2 +48m 2 sin(θ) 2 -8m 2 +8m 2 Where θ represents the angle between the direction of ultrasonic propagation and the direction of stress; λ and μ represent the second-order elastic coefficients of the forging material; l, m, and n represent the third-order elastic coefficients of the forging material.

3. The residual stress field detection method as described in claim 2, characterized in that, The acoustoelastic coefficient is calibrated based on a curve derived from the theoretical calculation formula for the acoustoelastic coefficient: Where V represents the longitudinal wave velocity of ultrasound, the first subscript is the wave propagation direction, the second subscript is the polarization direction of the particle, and the third subscript is the direction of uniaxial stress. V 111 This indicates the wave velocity of the ultrasonic longitudinal wave propagating along the uniaxial stress direction (in the stress-free state); V 113 This represents the wave velocity of ultrasonic longitudinal waves propagating perpendicular to the uniaxial stress direction (in a stress-free state). V 133 This represents the wave velocity of an ultrasonic transverse wave propagating perpendicular to the uniaxial stress direction (in a stress-free state). dV 111 The differential represents the change in wave velocity (differential) of an ultrasonic longitudinal wave propagating along the uniaxial stress direction due to uniaxial stress. dV 113 It represents the change in wave velocity (differential) of ultrasonic longitudinal waves propagating perpendicular to the direction of uniaxial stress due to uniaxial stress. dV 133 The differential represents the change in wave velocity (differential) of an ultrasonic transverse wave propagating perpendicular to the direction of uniaxial stress due to uniaxial stress. λ and μ represent the second-order elastic coefficients of the forging material; l, m, and n represent the third-order elastic coefficients of the forging material; σ represents the magnitude of the triaxial stress vector of the forging material; dσ represents the change in the magnitude of the triaxial stress vector of the forging material.

4. The residual stress field detection method as described in claim 1, characterized in that, The method for determining the acoustic beam scanning scheme based on Snell's law includes: 1) After determining the starting position coordinates, input the geometric position coordinates and dimensions of the structural section of the forging to be tested, and draw the section in a two-dimensional coordinate system; 2) Set the angle between the internal desired sound beam path and the x-axis and the y-intercept, and output the corresponding external sound beam path; 3) Set the ultrasonic transducer moving path envelope, and obtain the intersection point of the external sound beam path and the ultrasonic transducer moving path, which is the excitation receiving position coordinate. 4) Based on the angle between the external sound beam path and the x-axis, the tilt direction of the excitation receiving probe is obtained; 5) Based on the Snell's law and the set internal sound beam path, the external sound beam path is solved inversely; Snell's law is as follows: Where θ1 represents the incident angle of the ultrasonic wave, θ2 represents the refraction angle of the ultrasonic wave, v1 represents the incident longitudinal wave velocity of the ultrasonic wave, and v2 represents the refraction velocity of the longitudinal wave of the ultrasonic wave.

5. The residual stress field detection method as described in claim 4, characterized in that, The step of performing multi-angle scanning excitation and receiving position and direction calculation to acquire ultrasound receiving signals according to the acoustic beam scanning scheme includes: 1) Based on the reconstructed geometry and position of the forging, set the required angle and intercept of the internal sound beam path; 2) Based on the sound beam path design method in the sound beam scanning scheme, a series of excitation position x-coordinates, excitation position y-coordinates, excitation angles, receiving position x-coordinates, receiving position y-coordinates, and receiving angles are obtained, and corresponding multi-axis control tables are formed. 3) Input the multi-axis control table into the multi-axis controller to control the beam scanning operation accordingly.

6. The residual stress field detection method as described in claim 1, characterized in that, The stress reconstruction inversion calculation performed on the geometry of the forging to construct the corresponding residual stress field is constructed in the form of a stress cloud map, wherein the stress cloud map is described by a two-dimensional function f(x, y), where x and y are the coordinates of a spatial point, and the value of the function represents the stress magnitude of the stress field in a known direction.

7. The residual stress field detection method as described in claim 6, characterized in that, The process of performing stress reconstruction inversion calculations on the geometry of the forging to construct the corresponding residual stress field includes: The image to be reconstructed is discretized into N = n × n square grids, and the path length of the i-th ray within the j-th pixel is ω. ij Let L be the total number of rays, then the coefficient matrix A is formed by ω ij The resulting L×N dimensional matrix; The residual stress field is constructed by solving the equation p = Ax, where A is a coefficient matrix representing the distance the ultrasound travels through each grid point under each ray; x is the residual stress field to be reconstructed for each grid; and p is the change in ultrasound velocity. The expanded form of the equation p = Ax is as follows: oh 11 x1+ω 12 x2+ω 13 x3+…oh 1J x N =p1 oh 21 x1+ω 22 x2+ω 23 x3+…oh 2J x N =p2 … oh L1 x1+ω L2 x2+ω L3 x3+…oh LJ x N =p L (4)。 8. The residual stress field detection method as described in claim 7, characterized in that, The three-dimensional imaging based on the corresponding residual stress field includes: performing three-dimensional imaging based on the residual stress field of all grids in the image.

9. A computer-readable storage medium storing instructions that, when executed, cause a machine to perform the residual stress field detection method as described in any one of claims 1-8.

10. An ultrasonic-based residual stress field detection system for aero-engine forgings, comprising means for performing the residual stress field detection method as described in any one of claims 1-8.

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