Electromagnetic loading four-point bending stress device and its acoustoelastic coefficient measurement method

Abstract

This invention discloses an electromagnetically loaded four-point bending stress device and a method for measuring the acoustoelastic coefficient of multilayer structures. The device is an electromagnetically loaded four-point bending stress loading device. Based on the magnitude of the electromagnetic force and four-point bending theory, the internal stress magnitude and distribution of the multilayer structure are calculated. The method achieves the propagation of ultrasonic critically refracted longitudinal waves along the interface of the multilayer structure by adjusting the incident angle of the emitted sound wave. The change in sound velocity under stress is calculated by analyzing the propagation path and sound time. Finally, the acoustoelastic coefficient of the multilayer composite structure is calculated based on acoustoelastic theory. The stress loading device of this invention can reduce internal damage to the specimen and can measure the acoustoelastic coefficient of the internal materials of multilayer structures.

Description

Technical Field

[0001] This invention belongs to the field of ultrasonic testing technology, specifically a four-point bending stress device with electromagnetic loading and a method for measuring its acoustoelastic coefficient. Background Technology

[0002] Ultrasonic testing is a technique that utilizes the interaction between ultrasonic waves and the test specimen. By analyzing data from the ultrasonic testing instrument, such as changes in sound wave propagation time and amplitude, the internal state of the specimen can be obtained, thereby evaluating its specific applicability. According to Snell's law, when a beam of ultrasonic longitudinal wave is incident at a certain angle from solid medium I into solid medium II, part of the energy is reflected at the interface, with the reflection angle equal to the incident angle. The other part of the energy is refracted into medium II, and after wave mode conversion, refracted longitudinal waves and refracted transverse waves are formed in medium II. When the angle between the refracted longitudinal wave and the normal is 90°, the refracted longitudinal wave in medium II propagates along the interface between the two media, and is called the critical refracted longitudinal wave. The critical refracted longitudinal wave has the characteristics of fast propagation speed, simple signal analysis and localization, and sensitivity to stress changes in the material.

[0003] Electromagnetic loading is based on the principle of electromagnetic induction and Ampere's law. When an electric current flows through a conductor, a magnetic field is generated around the conductor. The direction of this magnetic field is perpendicular to the direction of the current and changes with the current. If another current or charge exists in this magnetic field, it will experience a force from the magnetic field. The magnitude of the loading force can be adjusted by changing the magnitude of the excitation current.

[0004] Current methods for testing the acoustoelastic coefficient of materials mainly involve applying tensile and compressive loads to the specimen and measuring the acoustoelastic coefficient using ultrasonic transmission. Typically, the specimen is a single material. For multi-layered specimens made of different materials, there is a lack of relevant methods for measuring the acoustoelastic coefficient. Furthermore, multi-layered materials may delaminate under tensile and compressive loads, which not only causes damage to the internal structure but also affects the accuracy of ultrasonic transmission testing to some extent. Summary of the Invention

[0005] The present invention addresses the shortcomings of the prior art by proposing an electromagnetically loaded four-point bending stress device and its acoustoelastic coefficient measurement method. This invention aims to utilize the easily adjustable critical refractive wave and its sensitivity to changes in interfacial stress to measure the acoustoelastic coefficient of the internal materials of a multilayer structure while reducing internal structural damage.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] The four-point bending stress device based on electromagnetic loading of the present invention is characterized by:

[0008] An electromagnetic loading device is installed on a base. The electromagnetic loading device includes a control system, a first loading head, and a second loading head. The first loading head and the second loading head are respectively in contact with one side of a multi-layered specimen, and the other side of the specimen is respectively in contact with a first stop and a second stop. The first stop and the second stop are respectively located in corresponding grooves in the base.

[0009] A movable first guide rod and a second guide rod are provided above the base. A first telescopic rod and a second telescopic rod are correspondingly provided on the first guide rod and the second telescopic rod. An acoustic emission probe and an acoustic receiving probe with wedges are correspondingly provided at the lower ends of the first telescopic rod and the second telescopic rod. The wedge of the acoustic emission probe is in contact with one side of the test piece, and the wedge of the acoustic receiving probe is in contact with the upper surface of the test piece.

[0010] The method for measuring the acoustoelastic coefficient of a four-point bending stress device based on electromagnetic loading, as described in this invention, is characterized by comprising the following steps:

[0011] Step 1. Place the specimen on the base, between the first loading head and the second loading head, and between the first stop and the second stop. Adjust the positions of the first stop and the second stop in the corresponding grooves to fix the specimen.

[0012] Step 2. The control system controls the first guide rod and the second guide rod to move toward the specimen, and after reaching the target position, controls the first telescopic rod and the second telescopic rod to extend and retract, so that the wedges of the acoustic emission probe and the acoustic receiving probe are in contact with the side and top surface of the specimen.

[0013] Step 3. The control system moves the acoustic receiving probe to the upper edge of the first layer structure of the specimen, and moves the acoustic emitting probe so that the vertical distance between the two probes is S0;

[0014] Step 4. After the control system controls the first loading head and the second loading head to apply a load force F to the specimen respectively, it then controls the acoustic emission probe to emit an incident angle of θ. 01 The first ultrasonic signal, and at the same time, the acoustic receiving probe receives the first ultrasonic signal at an acoustic time of t0;

[0015] Step 5. Define the current layer number of the specimen as i, and initialize i = 1; define the number of layers to be measured as n, and define n... max The total number of layers in the specimen;

[0016] Step 6: After the control system controls the acoustic receiving probe to move to the interface between the i-th layer and the (i+1)-th layer of the specimen, it then controls the acoustic emitting probe to emit at an incident angle of θ. 0iThe i-th ultrasonic signal, and simultaneously, the acoustic receiving probe receives the i-th ultrasonic signal at an acoustic time t. i ;

[0017] Step 7. After assigning i+1 to i, return to step 6 and execute sequentially until i>n;

[0018] Step 8. Based on the acoustic time and path, and combined with the acoustoelastic theory, calculate the acoustoelastic coefficient of the specimen through the correspondence between stress change and sound velocity change.

[0019] The method for measuring the acoustic elastic coefficient of the present invention is also characterized in that step 8 includes:

[0020] Step 8.1: Calculate the acoustic elastic coefficient k of the i-th layer using equation (1). n :

[0021]

[0022] In equation (1), σ (i-1)i Let σ be the stress on the upper surface of the i-th layer of the specimen, obtained from equation (2); i(i+1) v represents the stress on the upper surface of the (i+1)th layer of the specimen, obtained from equation (3); (i-1)i With v i(i+1) These are the propagation velocities of sound waves on the upper surfaces of the i-th and (i+1)-th layers of the specimen, respectively, and are obtained by solving equations (4) to (7) together.

[0023]

[0024]

[0025] In equations (2) and (3), a represents the overall thickness of the specimen, and I z This represents the numerical value of the moment of inertia, which is: L1 represents the distance between the first loading head (3) and the geometric center of the first stop block, d i This represents the thickness of the i-th structural material layer;

[0026]

[0027]

[0028]

[0029]

[0030] In equations (4) to (7), t 00Let d0 represent the total sound propagation within the wedges of the acoustic emitting probe and the acoustic receiving probe, and θ represent the thickness of the wedges of the acoustic emitting probe and the acoustic receiving probe, respectively. 0i θ represents the acoustic emission angle when measuring the acoustic elastic coefficient of the i-th layer structure. i The angle of sound wave propagation within the i-th layer of the structure when the acoustic elastic coefficient is measured is given by: v (i-1)i With v i(i+1) Let v represent the propagation velocities of sound waves on the upper surfaces of the i-th and (i+1)-th layers of the structure when the acoustic elastic coefficient of the i-th layer is measured. i(i+1) This represents the propagation speed of sound waves on the upper surface of the (i+1)th layer when the acoustic elastic coefficient of the i-th layer is measured.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1. This invention employs a four-point bending loading method based on electromagnetic loading. The magnitude of the electromagnetic loading force can be adjusted by a control system. Combined with the four-point bending principle, the stress magnitude of each layer surface inside the multi-layer structure specimen can be obtained through simple internal material stress analysis. This method can reduce the impact of uneven stress distribution inside the specimen material caused by tension and compression on sound wave propagation.

[0033] 2. This invention, by combining the characteristics of stress loading method, can be applied to specimen structures of different sizes within a certain range. By controlling the movement of the acoustic emission probe and acoustic receiving probe through the control system, the measurement error caused by the traditional need for manual probe movement is reduced.

[0034] 3. This invention utilizes Snell's law to excite ultrasonic critical refraction waves, that is, the incident angle of acoustic emission can be adjusted to excite different types of critical refraction waves, so that the sound waves can propagate along the interfaces of multi-layered structures, which facilitates the location and acquisition of sound wave signals. Attached Figure Description

[0035] Figure 1 This is a diagram of the device of the present invention;

[0036] Figure 2 Load distribution diagram applied to this invention;

[0037] Figure 3 This is a schematic cross-sectional view of the multi-layer structure of the present invention;

[0038] Figure 4 This is a schematic diagram of ultrasonic wave propagation according to the present invention. Detailed Implementation

[0039] In this embodiment, a four-point bending stress device based on electromagnetic loading is described, such as... Figure 1As shown, an electromagnetic loading device 2 is provided on a base 1. The electromagnetic loading device 2 is provided with a control system, a first loading head 3 and a second loading head 4. The first loading head 3 and the second loading head 4 are respectively in contact with one side of the multi-layered specimen 5, and the other side of the specimen 5 is respectively in contact with the first stop 8 and the second stop 9. The first stop 8 and the second stop 9 are respectively set in the corresponding sliding grooves of the base 1.

[0040] A movable first guide rod 12 and second guide rod 13 are provided above the base 1. A first telescopic rod 10 and a second telescopic rod 11 are provided on the first guide rod 12 and the second guide rod 13 respectively. A sound emission probe 6 with a wedge and a sound receiving probe 7 with a wedge are provided at the lower ends of the first telescopic rod 10 and the second telescopic rod 11 respectively. The wedge of the sound emission probe 6 is in contact with one side of the test piece 5, and the wedge of the sound receiving probe 7 is in contact with the upper surface of the test piece 5.

[0041] In this embodiment, the method for measuring the acoustoelastic coefficient of the electromagnetically loaded four-point bending stress device is to measure the acoustoelastic coefficient of the first layer material of a multilayer structure, including the following steps:

[0042] Step 1. Place the specimen 5 on the base 1, between the first loading head 3 and the second loading head 4, and between the first stop block 8 and the second stop block 9. Adjust the positions of the first stop block 8 and the second stop block 9 in the corresponding grooves to fix the specimen 5.

[0043] Step 2. The control system controls the first guide rod 12 and the second guide rod 13 to move toward the specimen 5 respectively, and after reaching the target position, controls the first telescopic rod 10 and the second telescopic rod 11 to extend and retract, so that the wedges of the acoustic emission probe 6 and the acoustic receiving probe 7 are in contact with the side and top surface of the specimen 5.

[0044] Step 3. The control system moves the acoustic receiving probe 7 to the upper edge of the first layer structure of the specimen 5, and moves the acoustic emitting probe 6 so that the vertical distance between the two probes is S0;

[0045] Step 4. After the control system controls the first loading head 3 and the second loading head 4 to apply load forces to the specimen 5 respectively, it then controls the acoustic emission probe 6 to emit at an incident angle of θ. 01 The first ultrasonic signal, and at the same time, the acoustic receiving probe 7 receives the first ultrasonic signal at a time t0;

[0046] Step 5. After the control system moves the acoustic receiving probe 7 to the interface between the first and second layers of the specimen 5, it then controls the acoustic emitting probe 6 to emit at an incident angle of θ. 02 The second ultrasonic signal, and at the same time, the acoustic receiving probe 7 receives the second ultrasonic signal at a time t1;

[0047] Step 6. Based on the acoustic time and path, and combined with the theory of acoustic elasticity, calculate the acoustic elastic coefficient of specimen 5 through the correspondence between stress change and sound velocity change.

[0048] Step 6.1: Apply load to specimen 5 using the electromagnetic loading device 2, with the load distribution as follows. Figure 2 As shown, based on the four-point bending theory, the stress σ on the upper surface of the first layer of specimen 5 can be obtained. 01 The stress σ on the upper surface of the second layer structure of specimen 5 12 , combined Figure 3 The schematic diagram of the cross-section of the multi-layer structure shown, σ 01 With σ 12 The values ​​can be obtained from equations (1) and (2) respectively;

[0049]

[0050]

[0051] Step 6.2, according to Snell's law as shown in equation (3):

[0052]

[0053] In equation (3), v0 is the propagation speed of the sound wave within the wedge, and v1 is the propagation speed of the sound wave in the first layer of the structure when no load is applied; to excite the critical refracted wave, θ1 = 90° is required, and the value of θ0 is adjusted to... The ultrasonic wave then propagates along the upper surface of material layer 1. Similarly, the value of θ0 is adjusted to... The ultrasonic wave then propagates along the upper surface of material layer 2, where v2 is the propagation speed of the sound wave in the second layer structure when no load is applied.

[0054] Step 6.3, as follows Figure 4 As shown, the propagation speed is obtained according to step 4.

[0055] Step 6.4, as follows Figure 4 As shown, according to step 5, it is thus segmented into t segments according to the propagation path. 00 t 11 and t 12 The relationship between them satisfies equation (4), t 00 The total sound wave propagation time in the wedges of the acoustic emitting probe 6 and the acoustic receiving probe 7 is represented by t, which is obtained from equation (5); 11 When the sound wave propagates inside the first layer of the structure, it is obtained from equation (6); t 12 When the sound wave propagates on the upper surface of the second layer structure, it is obtained from equation (7);

[0056] t 00 +t11 +t 12 =t1 (4)

[0057]

[0058]

[0059]

[0060] In equation (6), s1 is the propagation path of the sound wave inside the first layer of the structure, and is obtained from equation (8); in equation (7), s 12 The path length of the sound wave propagating on the upper surface of the second layer structure is given by equation (9);

[0061]

[0062] s 12 =s0-d1tanθ1 (9)

[0063] The θ1 mentioned above can be determined according to Snell's law. We obtain, and from equation (10):

[0064]

[0065] According to the acoustoelastic theory, the velocity difference between two ultrasonic shear waves along the principal stress direction is proportional to the difference between the two principal stresses. This proportionality coefficient is called the acoustoelastic coefficient. The acoustoelastic coefficient of the first layer of structural material of specimen 5 can be obtained by equation (11).

[0066]

[0067] Combining equations (1) to (11), we get:

[0068]

[0069] Using the method described above, the acoustic elastic coefficient of each layer in a multi-layered structure can be measured sequentially.

Claims

1. A method for measuring the acoustic elastic coefficient, characterized in that, This is applied to a four-point bending stress device with electromagnetic loading. The four-point bending stress device is an electromagnetic loading device (2) set on a base (1). The electromagnetic loading device (2) is equipped with a control system, a first loading head (3) and a second loading head (4). The first loading head (3) and the second loading head (4) are in contact with one side of a multi-layered specimen (5), and the other side of the specimen (5) is in contact with a first stop (8) and a second stop (9) respectively. The first stop (8) and the second stop (9) are respectively set in corresponding grooves of the base (1). A movable first guide rod (12) and a second guide rod (13) are provided above the base (1). A first telescopic rod (10) and a second telescopic rod (11) are provided on the first guide rod (12) and the second guide rod (13). A sound emission probe (6) with a wedge and a sound receiving probe (7) with a wedge are provided at the lower ends of the first telescopic rod (10) and the second telescopic rod (11). The wedge of the sound emission probe (6) contacts one side of the test piece (5), and the wedge of the sound receiving probe (7) contacts the upper surface of the test piece (5). The method for measuring the acoustoelastic coefficient includes the following steps: Step 1. Place the specimen (5) on the base (1) and between the first loading head (3) and the second loading head (4) and the first stop (8) and the second stop (9). Adjust the position of the first stop (8) and the second stop (9) in the corresponding grooves to fix the specimen (5). Step 2. The control system controls the first guide rod (12) and the second guide rod (13) to move toward the specimen (5) respectively, and after reaching the target position, controls the first telescopic rod (10) and the second telescopic rod (11) to extend and retract, so that the wedge of the acoustic emission probe (6) and the wedge of the acoustic receiving probe (7) are respectively attached to the side and the top surface of the specimen (5); Step 3. The control system moves the acoustic receiving probe (7) to the upper edge of the first layer structure of the specimen (5), and moves the acoustic emitting probe (6) so that the vertical distance between the two probes is [missing information]. ; Step 4. The control system controls the first loading head (3) and the second loading head (4) to apply load forces to the specimen (5) respectively. Then, the acoustic emission probe (6) is controlled to emit an incident angle of 100°. The ultrasonic signal, and at the same time, the acoustic receiving probe (7) receives the ultrasonic signal at an acoustic time of ; Step 5. Define the current layer number of the specimen (5) as... and initialize =1; Define the number of layers to be measured as Define n max The total number of layers in the specimen (5); Step 6: The control system controls the acoustic receiving probe (7) to move to the first position of the test piece (5). Layer structure and the first After the interface of the layered structure, the incident angle of the acoustic emission probe (6) is controlled to be... The Ultrasonic signals, and simultaneously, the acoustic receiving probe (7) receives the first... The acoustic time of the ultrasound signal is ; Step 7. Assign to Then, return to step 6 and execute sequentially until... until; Step 8. Based on the acoustic time and path, and combined with the acoustic elasticity theory, the stress change and sound velocity change correspondence are used to calculate the first step of the test piece (5) using equation (1). The acoustic elastic coefficient of the layered structure : (1) In equation (1), For specimen (5) The upper surface stress of the layered structure; For specimen (5) The upper surface stress of the layered structure; and The sound waves in specimen (5) are respectively Layer and first The propagation speed on the upper surface of the layered structure.

2. The method for measuring the acoustic elastic coefficient according to claim 1, characterized in that, In step 8, the specimen (5) is obtained from equation (2). upper surface stress of layered structure The first result of the test piece (5) is obtained from equation (3). upper surface stress of layered structure The acoustic wave in specimen (5) is solved by combining equations (4) to (7). Propagation speed on the upper surface of the layered structure and the Propagation speed on the upper surface of the layered structure ; (2) (3) In equations (2) and (3), This indicates the overall thickness of specimen (5). This represents the numerical value of the moment of inertia, which is: , This represents the distance between the geometric centers of the first loading head (3) and the first stop (8). Indicates the first The thickness of the layered structural material; (4) (5) (6) (7) In equations (4) to (7), This indicates the total sound propagation time in the wedge of the acoustic emitting probe (6) and the wedge of the acoustic receiving probe (7). The thickness of the wedges representing the acoustic emission probe (6) and the acoustic receiving probe (7) is indicated. Indicates the measurement of the first The acoustic elastic coefficient of the layered structure is the acoustic emission angle. Indicates the measurement of the first The acoustoelastic coefficient of the layered structure is the sound wave at the th... The propagation angle within the layer structure, its value is ， and They represent the measurement of the first The acoustoelastic coefficient of the layered structure is the sound wave at the th... Layer and First The propagation speed on the upper surface of the layered structure, This indicates the speed at which sound waves propagate within the wedge.

Images