Interlaminar stress measurement device, method and contact stress characterization method
By placing sensors outside the sealed structure and measuring contact resistance using the DC potential method system and preload sensor, the problem of non-destructive stress measurement within the sealed structure is solved, and a simple and high-sensitivity measurement effect is achieved.
Patent Information
- Application Number
- CN202410550817.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-05-07
- Publication Date
- 2025-02-25
- Estimated Expiration
- 2044-05-07
AI Technical Summary
The prior art is difficult to measure interlayer stresses inside sealed structures without loss, and requires implantable force sensors, which are complicated to operate.
The direct current potential method system and preload sensor are used to measure the contact resistance to obtain the contact stress by placing the sensor outside the sealed structure, thereby obtaining the internal interlayer stress.
The non-destructive measurement of interlayer stress in the sealed structure is achieved, which simplifies operation and avoids the use of implantable sensors. The system is simple to build and has high sensitivity.
Smart Images
Figure CN118329239B_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the technical field of interlayer stress measurement, and in particular to an interlayer stress measurement device and method and a contact stress characterization method. Background Art
[0002] The DC potential method is one of the most commonly used methods for measuring material resistance, especially for measuring small resistances, including contact resistance. The four-terminal method is currently the main method for measuring contact resistance. The DC potential method has the advantages of easy system construction, simple operation, high sensitivity and short measurement time.
[0003] The contact resistance is caused by the fact that all solid surfaces are rough and uneven at the microscopic level. After the conductor is in contact, the actual contact area of the surface is much smaller than the nominal contact area. The current can only flow through the actual contact point, which leads to contact resistance on the conductor contact surface. In theoretical research, it is usually assumed that the roughness on the contact surface is a hemispherical micro-convex body in contact with the rigid plane, and a circular conductive area is formed after the micro-convex body contacts. The contact stress directly affects the contact resistance. When the contact stress increases, on the one hand, the area of the original conductive contact circle expands, and on the other hand, a new conductive contact circle is generated, which will reduce the contact resistance. Therefore, the contact stress can be characterized by the measurement of contact resistance.
[0004] For a single contact circle, according to the Holm formula of electrical contact theory, we have:
[0005]
[0006] Where ρ is the conductivity of the conductor and a is the radius of the contact circle.
[0007] When there are multiple conductive contact circles in the contact surface, the total contact resistance is the parallel resistance of each conductive contact circle. Assuming that there are n conductive contact circles, the total contact resistance can be calculated by the following formula:
[0008]
[0009] Therefore, the difficulty lies in finding the contact radius a of the contact circle. When a single micro-convex body contacts a plane, according to mechanical analysis, in the elastic stage of the micro-convex body:
[0010]
[0011] In the micro-convex body shaping stage:
[0012] FWf a 2
[0013] Therefore, it can be concluded that: a∝F^m, in the elastic stage Shaping stage Substituting this relationship into the formula, it can be determined that the contact resistance is exponentially related to the contact force:
[0014] R@@KF@ n '
[0015] In engineering, the values of K and m are usually determined based on experience. However, since the factors affecting contact resistance are relatively complex and there are large differences in experimental data under different experimental conditions, engineering empirical formulas can only be used to estimate the range of contact resistance. A more accurate study of the relationship between contact resistance and contact force currently relies on experimental measurements.
[0016] The multi-layer spherical structure includes two layers of hollow stainless steel shells, with a polymer adhesive tape between the inner and outer stainless steel shells. Each hollow shell is composed of two upper and lower hemisphere shells, and the upper and lower outermost hemisphere shells are assembled by bolts. The multi-layer spherical structure needs to ensure the airtightness and stability of the structure. Due to the aging of the polymer, the polymer adhesive tape will experience stress relaxation, which will cause the airtightness and stability of the structure to deteriorate. Therefore, it is very important to detect the interlayer stress of the spherical structure. Considering that the outermost spherical shell structure is mainly affected by interlayer stress, contact force and preload, the interlayer stress can be characterized based on the measured contact stress and preload. Summary of the invention
[0017] The purpose of the present invention is to provide an interlayer stress measurement device, method and contact stress characterization method to solve the problems existing in the above-mentioned prior art. There is no need to use an implantable force sensor. By placing a sensor outside a closed structure, the interlayer stress inside the structure can be measured. The present invention has strong innovation and broad application prospects.
[0018] To achieve the above object, the present invention provides the following solutions:
[0019] The present invention provides an interlayer stress measuring device, comprising:
[0020] A DC potentiometric system, the DC potentiometric system comprising a constant current source, a voltmeter, a four-terminal probe device and a data acquisition device, the four-terminal probe device comprising a first probe, a second probe, a third probe and a fourth probe; wherein the constant current source is connected to the first probe and the fourth probe, and is used to apply a constant current to the first probe and the fourth probe, the voltmeter is connected to the second probe and the third probe, and is used to measure the voltage between the second probe and the third probe, and the data acquisition device is connected to the voltmeter;
[0021] A preload force sensor is used to measure the preload force between an outer upper spherical shell and an outer lower spherical shell of a multi-layer spherical structure.
[0022] The present invention also provides a contact stress characterization method, using the interlayer stress measurement device as described above, comprising the following steps:
[0023] S1, measuring the preload force between the outer upper spherical shell and the outer lower spherical shell by the preload force sensor, and measuring the voltage between the second probe and the third probe by the voltmeter;
[0024] S2, adjusting the preload force between the outer upper spherical shell and the outer lower spherical shell, and repeating step S1, collecting different preload forces and corresponding voltages, and establishing a relationship curve between voltage and preload force;
[0025] S3, calculating the average contact stress between the outer upper spherical shell and the outer lower spherical shell, the average contact stress is σ,
[0026]
[0027] Wherein, A is the contact area between the outer upper spherical shell and the outer lower spherical shell, and F is the preload force;
[0028] In combination with the relationship curve between voltage and preload force in step S2, a relationship curve between average contact stress and voltage is established;
[0029] S4. Taking the difference between the measured voltage and the reference voltage to obtain a difference voltage, wherein the reference voltage is a voltage value corresponding to a certain specific contact stress; calculating the relationship curve between the difference voltage and the contact stress through the relationship curve between the average contact stress and the voltage in step S2, and using it to characterize the contact stress.
[0030] Preferably, before step S1, the method further comprises the following steps:
[0031] S11, constructing the interlaminar stress measuring device.
[0032] Preferably, after step S11 and before step S1, the following steps are further included:
[0033] S12, assembling the outer upper spherical shell and the outer lower spherical shell.
[0034] Preferably, the outer upper spherical shell and the outer lower spherical shell are connected by bolts and nuts, and in step S2, the preload force between the outer upper spherical shell and the outer lower spherical shell is adjusted by adjusting the nuts.
[0035] The present invention also provides a method for measuring interlayer stress, using the interlayer stress measuring device as described above, comprising the following steps:
[0036] S1, measuring the preload force between the outer upper spherical shell and the outer lower spherical shell by the preload force sensor, adjusting the preload force between the outer upper spherical shell and the outer lower spherical shell to a specific value, applying a constant current to the first probe and the fourth probe by the constant current source, and measuring the voltage between the second probe and the third probe by the voltmeter as a reference voltage;
[0037] S2. When the polymer adhesive tape of the multilayer spherical structure is aged, the voltage between the second probe and the third probe is measured, and the voltage is subtracted from the reference voltage to obtain a difference voltage, and the contact stress is calculated based on the relationship curve between the difference voltage and the contact stress established by the contact stress characterization method as described above;
[0038] S3. Based on the preload force measured by the preload force sensor and the contact stress calculated in step S2, the internal interlayer stress of the multilayer spherical structure is obtained through mechanical analysis.
[0039] Preferably, before step S1, the method further comprises the following steps:
[0040] S11, constructing the interlaminar stress measuring device.
[0041] Preferably, after step S11 and before step S1, the following steps are further included:
[0042] S12, assembling the multi-layer spherical structure, connecting the outer upper spherical shell and the outer lower spherical shell by bolts and nuts, and providing a polymer adhesive tape between the inner sphere and the outer spherical shell.
[0043] Preferably, in the step S1, the preload force between the outer upper spherical shell and the outer lower spherical shell is adjusted to a specific value by adjusting the nut.
[0044] Compared with the prior art, the present invention has achieved the following technical effects:
[0045] The present invention can measure the internal interlayer stress of a closed structure and realize non-destructive measurement; and compared with the traditional stress testing method, the present invention does not need to use an implantable sensor, but only needs to place a sensor outside the structure and measure the contact resistance to obtain the contact stress, thereby calculating the internal interlayer stress. The experimental system of the present invention is easy to build and operate, the internal interlayer stress characterization relationship is clear, the electrical signal has strong stability and high sensitivity, and has strong innovation and broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS
[0046] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.
[0047] Figure 1 It is a schematic structural diagram of an interlayer stress measuring device in an embodiment of the present invention;
[0048] Figure 2 Schematic diagram of the structure of the outer spherical shell of the multi-layer spherical structure in an embodiment of the present invention;
[0049] Figure 3 for Figure 2 Schematic diagram of the forces acting on the middle and outer spherical shells;
[0050] Figure 4 This is a schematic diagram of the structure of a multi-layer sphere in an embodiment of the present invention;
[0051] Figure 5 for Figure 4 Schematic diagram of the forces acting on the middle and outer spherical shells.
[0052] In the figure: 1-constant current source, 2-voltmeter, 3-data acquisition device, 4-preload sensor, 5-multilayer spherical structure, 6-four-terminal probe device, 601-first probe, 602-second probe, 603-third probe, 604-fourth probe, 701-outer upper spherical shell, 702-outer lower spherical shell, 703-polymer adhesive tape, 704-inner sphere. DETAILED DESCRIPTION
[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. 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.
[0054] The purpose of the present invention is to provide an interlayer stress measurement device, method and contact stress characterization method to solve the problems existing in the above-mentioned prior art. There is no need to use an implantable force sensor. By placing a sensor outside a closed structure, the interlayer stress inside the structure can be measured. The present invention has strong innovation and broad application prospects.
[0055] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.
[0056] Embodiment 1
[0057] like Figure 1 As shown, in this embodiment, an interlayer stress measurement device is provided, which is mainly composed of a DC potential method system and a preload force sensor. The DC potential method system is composed of a constant current source 1, a voltmeter 2, a four-terminal probe device 6 and a data acquisition device 3. The four probes of the four-terminal probe device 6 are respectively a first probe 601, a second probe 602, a third probe 603 and a fourth probe 604. The four probes are used to be arranged on the outside of the multilayer spherical structure 5; wherein the constant current source 1 is connected to the first probe 601 and the fourth probe 604 to apply a constant current thereto, the voltmeter 2 is connected to the second probe 602 and the third probe 603 to measure the voltage therebetween, and the data acquisition device 3 is connected to the voltmeter 2.
[0058] In this embodiment, the multi-layer spherical structure 5 mainly includes an outer spherical shell and an inner sphere 704, a polymer adhesive tape 703 is arranged between the inner sphere 704 and the outer spherical shell, and the outer spherical shell includes an outer upper spherical shell 701 and an outer lower spherical shell 702, the outer upper spherical shell 701 and the outer lower spherical shell 702 are assembled by four bolts, the bolts and nuts provide preload force for the entire structure, and the preload force provided by the four bolts is measured respectively by four preload force sensors 4.
[0059] Embodiment 2
[0060] like Figure 2 and Figure 3 As shown, this embodiment provides a contact stress characterization method, which mainly includes the following steps:
[0061] Step 1: Build the interlaminar stress measurement device in Example 1.
[0062] Step 2: Assemble a single-layer spherical shell structure, which is the outer spherical shell of the multi-layer spherical structure 5. A preload force is applied between the outer upper spherical shell 701 and the outer lower spherical shell 702 through bolts and nuts; the magnitude of the preload force F is measured by the preload force sensor 4, and the voltage U between the second probe 602 and the third probe 603 is measured using the voltmeter 2.
[0063] The preload force F of the structure can be changed by adjusting the nut. The difference in preload force will change the contact resistance between the outer upper spherical shell 701 and the outer lower spherical shell 702, and then change the voltage U accordingly. Therefore, by collecting different preload forces and their corresponding voltage signals, a relationship curve between U and F can be established.
[0064] The mechanism of the contact resistance between the outer upper spherical shell 701 and the outer lower spherical shell 702 being changed by different contact forces is as follows: the generation of contact resistance is caused by the fact that all solid surfaces are rough and uneven at the microscopic level. After the conductor is in contact, the actual contact area of the surface is much smaller than the nominal contact area; the current can only flow through the actual contact point, thus causing contact resistance on the conductor contact surface. In theoretical research, it is usually assumed that the roughness on the contact surface is a hemispherical micro-convex body in contact with a rigid plane, and a circular conductive area is formed after the micro-convex body contacts. The contact stress directly affects the contact resistance. When the contact stress increases, on the one hand, the area of the original conductive contact circle expands, and on the other hand, a new conductive contact circle is generated, which will reduce the contact resistance.
[0065] Step 3: The single-layer spherical shell structure does not contain the polymer adhesive tape 703 and has no interlayer stress. Therefore, the average contact stress σ between the outer upper spherical shell 701 and the outer lower spherical shell 702 can be calculated by the following formula:
[0066]
[0067] Wherein, A is the contact area between the outer upper spherical shell 701 and the outer lower spherical shell 702.
[0068] Combined with the relationship curve between U and F obtained in step 2, a relationship curve between σ and U can be established; by plotting with the measured voltage U as the vertical axis and the contact stress σ as the horizontal axis, a U-σ curve can be obtained.
[0069] Step 4: Through repeated experiments, it is found that the randomness of the rough surface condition and the resistance between the two voltage probes will cause the starting point of the established U-σ curve to also have strong randomness. In this embodiment, the method of taking the difference between the measured voltage signal and the reference voltage signal is adopted to reduce this randomness. The reference voltage signal is the voltage value corresponding to a certain contact stress. The voltage signal after the difference with the reference voltage signal (difference voltage, ΔU) has a strong correlation with the change of contact stress, so it can stably characterize the contact stress between the outer upper spherical shell 701 and the outer lower spherical shell 702.
[0070] Based on the above theory, the ΔU-σ curve can be calculated through the U-σ curve, and the contact force can be characterized by the ΔU-σ curve, which provides support for the measurement of the internal interlayer stress of the multi-layer spherical structure 5.
[0071] Embodiment 2
[0072] like Figure 4 and Figure 5 As shown, this embodiment provides a method for measuring interlayer stress, which mainly includes the following steps:
[0073] Step 1: Build the interlaminar stress measurement device in Example 1.
[0074] Step 2: Assemble the multi-layer spherical structure 5. The preload sensor 4 is used to measure the preload provided by the four bolts. By tightening the nuts, the combined preload force at the four bolts reaches a certain value F. 0 , assembly is completed; at this time, a constant current source 1 is used to apply a constant current to the first probe 601 and the fourth probe 604, and a voltmeter 2 is used to measure the voltage U between the second probe 602 and the third probe 603, and the voltage value at this time is recorded as the reference voltage U 0 .
[0075] Step 3: After the assembled multilayer spherical structure 5 has been in service for a long time, the internal polymer adhesive tape 703 will gradually age, thereby causing interlayer stress relaxation; the voltage signal U of the aged polymer adhesive tape 703 is measured by a four-terminal DC potential method, and the reference voltage U is subtracted from U. 0 , the difference voltage ΔU can be obtained; according to the ΔU-σ curve of the contact stress characterization method established in the second embodiment, the contact stress σ is calculated.
[0076] Step 4: Based on the preload force measured by the preload force sensor 4 and the contact stress σ calculated in step 3, the interlayer stress of the multi-layer spherical structure is obtained through mechanical analysis.
[0077] In addition, since the polymer adhesive tape may age unevenly, the distribution of interlayer stress may also be uneven, which in turn may lead to uneven distribution of contact stress. Therefore, based on the measurement method already implemented in the present invention, the array DC potential method technology can be further developed, and the DC potential method four-terminal probe can be designed 360 degrees in annularly to invert the conductive properties of the contact surface and its conductivity distribution. Combining the array DC potential method with the method developed in the present invention can achieve high-precision measurement under uneven distribution of contact stress, thereby solving the measurement of unevenly distributed interlayer stress.
[0078] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.
Claims
1. An interlaminar stress measuring device, characterized in that: include: A DC potentiometric system, the DC potentiometric system comprising a constant current source, a voltmeter, a four-terminal probe device and a data acquisition device, the four-terminal probe device comprising a first probe, a second probe, a third probe and a fourth probe arranged in sequence; wherein the constant current source is connected to the first probe and the fourth probe, and is used to apply a constant current to the first probe and the fourth probe, the voltmeter is connected to the second probe and the third probe, and is used to measure the voltage between the second probe and the third probe, and the data acquisition device is connected to the voltmeter; A preload sensor, the preload sensor is used to measure the preload force between the outer upper spherical shell and the outer lower spherical shell of a multi-layer spherical structure; wherein the multi-layer spherical structure includes an outer spherical shell and an inner sphere, a polymer adhesive tape is arranged between the inner sphere and the outer spherical shell, and the outer spherical shell includes the outer upper spherical shell and the outer lower spherical shell, the outer upper spherical shell and the outer lower spherical shell are assembled by bolts, and the preload force provided by the bolts is measured by the preload sensor.
2. A contact stress characterization method, characterized in that: The interlaminar stress measuring device according to claim 1 comprises the following steps: S1, measuring the preload force between the outer upper spherical shell and the outer lower spherical shell by the preload force sensor, and measuring the voltage between the second probe and the third probe by the voltmeter; S2, adjusting the preload force between the outer upper spherical shell and the outer lower spherical shell, and repeating step S1, collecting different preload forces and corresponding voltages, and establishing a relationship curve between voltage and preload force; S3, calculating the average contact stress between the outer upper spherical shell and the outer lower spherical shell, the average contact stress is σ, Wherein, A is the contact area between the outer upper spherical shell and the outer lower spherical shell, and F is the preload force; In combination with the relationship curve between voltage and preload force in step S2, a relationship curve between average contact stress and voltage is established; S4. Taking the difference between the measured voltage and the reference voltage to obtain a difference voltage, wherein the reference voltage is a voltage value corresponding to a certain specific contact stress; calculating the relationship curve between the difference voltage and the contact stress through the relationship curve between the average contact stress and the voltage in step S2, and using it to characterize the contact stress.
3. The contact stress characterization method according to claim 2, characterized in that: Before step S1, the method further includes the following steps: S11, constructing the interlaminar stress measuring device.
4. The contact stress characterization method according to claim 3, characterized in that: After step S11 and before step S1, the following steps are also included: S12, assembling the outer upper spherical shell and the outer lower spherical shell.
5. The contact stress characterization method according to claim 4, characterized in that: The outer upper spherical shell and the outer lower spherical shell are connected by bolts and nuts. In the step S2, the preload force between the outer upper spherical shell and the outer lower spherical shell is adjusted by adjusting the nuts.
6. A method for measuring interlaminar stress, characterized in that: The interlaminar stress measuring device according to claim 1 comprises the following steps: S1, measuring the preload force between the outer upper spherical shell and the outer lower spherical shell by the preload force sensor, adjusting the preload force between the outer upper spherical shell and the outer lower spherical shell to a specific value, applying a constant current to the first probe and the fourth probe by the constant current source, and measuring the voltage between the second probe and the third probe by the voltmeter as a reference voltage; S2. When the polymer adhesive tape of the multilayer spherical structure is aged, the voltage between the second probe and the third probe is measured, and the voltage is subtracted from the reference voltage to obtain the difference voltage, and the contact stress is calculated based on the relationship curve between the difference voltage and the contact stress established by the contact stress characterization method according to any one of claims 2 to 5; S3. Based on the preload force measured by the preload force sensor and the contact stress calculated in step S2, the internal interlayer stress of the multilayer spherical structure is obtained through mechanical analysis.
7. The interlaminar stress measurement method according to claim 6, characterized in that: Before step S1, the method further includes the following steps: S11, constructing the interlaminar stress measuring device.
8. The interlaminar stress measurement method according to claim 7, characterized in that: After step S11 and before step S1, the following steps are also included: S12, assembling the multi-layer spherical structure, connecting the outer upper spherical shell and the outer lower spherical shell by bolts and nuts, and providing a polymer adhesive tape between the inner sphere and the outer spherical shell.
9. The interlaminar stress measurement method according to claim 8, characterized in that: In the step S1, the preload force between the outer upper spherical shell and the outer lower spherical shell is adjusted to a specific value by adjusting the nut.
Citation Information
Patent Citations
Device and method for reckoning fatigue crack propagation rate of flat alloy by AC potentiometry
CN101832970A
Conformal method of curved surfaces of aircraft formation lights
CN105299567A