Method and device for measuring viscoelastic mechanical properties of polymers in high and low temperature environments

Abstract

This invention discloses a method and apparatus for measuring the viscoelastic mechanical properties of polymers under high and low temperature environments, belonging to the field of mechanical property testing. This invention collects the admittance curves of the nth-order vibration of a resonant unit consisting of a spacer bar and a test sample, obtains the resonant frequency and anti-resonant frequency of the nth-order vibration, constructs the vibration characteristic equation and loss factor solution equation, and solves the equations to obtain the mechanical property parameters. This invention can accurately measure the viscoelastic mechanical properties of polymer materials at different temperatures. The apparatus of this invention is simple to manufacture, provides reliable measurement results, and is fast. Compared with the most commonly used methods for measuring the viscoelastic mechanical properties of polymers, whose measurement frequency range is usually below tens of Hz, this invention can obtain results at frequencies from several kHz to tens of kHz. This invention is of great significance for characterizing the mid-frequency viscoelastic mechanical properties of polymer materials and has broad application prospects.

Description

Technical Field

[0001] This invention relates to mechanical property testing, specifically to a method and apparatus for measuring the viscoelastic mechanical properties of polymer materials under high and low temperature environments. Background Technology

[0002] Polymer materials, as important engineering materials, have wide applications in electronic packaging, acoustic devices, and vibration and noise reduction. Compared with conventional hard materials, polymers have lower stiffness and lower sound velocity. These materials exhibit dual characteristics of elastic deformation and viscous flow, i.e., viscoelastic behavior. Their mechanical response can be characterized by complex moduli (including storage modulus E' and loss modulus E''), with the loss factor tanδ (tanδ=E'' / E') serving as a core indicator of the material's internal friction or damping characteristics. The viscoelastic parameters of polymers directly affect their energy dissipation performance and dynamic response characteristics in vibration environments. Therefore, accurately characterizing the viscoelastic parameters of polymers in the high and low temperature range (from the brittle glassy state at extremely low temperatures to the highly elastic state and even the fluid dynamic state at high temperatures) is of crucial academic and engineering value for engineering design, life prediction, and structural vibration control.

[0003] Currently, commonly used polymer viscoelasticity testing methods both domestically and internationally include: 1) Dynamic Mechanical Analysis (DMA), which calculates storage modulus and loss factor by applying sinusoidal alternating stress to the sample and measuring its strain response; the test frequency is typically limited to below tens of Hz; 2) Ultrasonic pulse-echo method, which uses a piezoelectric transducer to emit ultrasonic pulses into the material and measures the time difference and amplitude attenuation of the incident wave and the reflected echo to invert the modulus and loss factor; this method typically operates at frequencies in the MHz range, but the pulse signal is weak due to the strong absorption of ultrasonic waves by polymers. Polymer materials are often used for mechanical vibration damping, therefore their viscoelastic mechanical properties in the mid-frequency band (hundreds of Hz to tens of kHz) are also very important; however, there are currently no good methods for measuring the high and low temperature mechanical properties of polymers in this frequency band.

[0004] Existing technologies utilize piezoelectric transducers to excite longitudinal and torsional vibrations in cylindrical metal or ceramic samples to measure elastic modulus and loss factor (internal friction). The sample is a hard material. Adding a heat-insulating rod between the sample and the piezoelectric transducer allows this technology to be applied to high and low temperature measurements (see Chinese Patent CN 110987595 A). Vibration measurement methods are related to sound velocity, requiring the sample diameter to be much smaller than the wavelength of the vibrating system. However, polymers, being soft materials, have extremely low sound velocities compared to hard materials. When testing polymer materials, if polymer samples are prepared according to the previous frequency matching requirements, the sample length will be on the same order of magnitude as the diameter, clearly not satisfying the one-dimensional slender rod vibration assumption, thus causing errors in the calculation of modulus and loss factor. Therefore, existing measurement methods are not suitable for polymer measurements. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a measuring device and method for measuring the viscoelastic mechanical properties of polymer materials under high and low temperature environments.

[0006] One object of the present invention is to provide a device for measuring the viscoelastic mechanical properties of polymer materials under high temperature and low temperature environments.

[0007] The measuring device for the viscoelastic mechanical properties of polymer materials under high and low temperature environments of the present invention includes: a piezoelectric transducer, a spacer bar, an impedance analyzer, a temperature sensor, and a temperature control device; wherein, the test sample is a polymer; the stiffness and sound velocity of the spacer bar are both greater than those of the test sample; one end of the spacer bar is connected to the test sample to form an integral resonant unit; the other end of the spacer bar is equipped with a piezoelectric transducer; the piezoelectric transducer is connected to the impedance analyzer; the test sample is placed in the temperature control device; the temperature sensor is placed next to the test sample; the piezoelectric transducer generates an excitation wave to excite the resonant unit to generate n-order vibration modes, at which point there are a total of n half-wavelengths distributed between the test sample and the spacer bar. In the integrated resonant unit composed of spacers, the spacers provide acoustic length compensation for the test specimen at the end, which indirectly increases the effective vibration length of the test specimen and reduces the radial effect caused by the short resonant wavelength of the test specimen. The piezoelectric transducer converts the vibration into a current signal and transmits it to the impedance analyzer. The impedance analyzer extracts the admittance curve of the nth order vibration of the resonant unit, obtains the resonant frequency and anti-resonant frequency of the nth order vibration from the admittance curve of the nth order vibration, constructs the implicit vibration characteristic equation and establishes the loss factor solution equation, and solves the equation to obtain the longitudinal mechanical performance parameters and torsional mechanical performance parameters of the test specimen, where n is a natural number ≥1.

[0008] Young's modulus and the loss factor of the longitudinal vibration mode are collectively referred to as longitudinal mechanical performance parameters, while shear modulus and the loss factor of the torsional vibration mode are collectively referred to as torsional mechanical performance parameters.

[0009] Piezoelectric transducers are divided into longitudinal vibration type piezoelectric transducers and torsional vibration type piezoelectric transducers, which are used to measure the longitudinal mechanical property parameters and torsional mechanical property parameters of test specimens, respectively.

[0010] The temperature sensor uses a thermocouple. The temperature control device includes a high-temperature furnace and a low-temperature chamber, and the test sample is placed in the constant temperature zone of the high-temperature furnace or the low-temperature chamber.

[0011] The spacer bar is made of alumina ceramic. During high-temperature or low-temperature measurements, the spacer bar isolates the high-temperature or low-temperature region from the piezoelectric transducer. Thanks to the excellent thermal insulation properties of alumina ceramic, the temperature of the piezoelectric transducer remains within its normal operating temperature range. The outer diameter of the spacer bar is equal to the outer diameter of the test specimen, which is a cylinder or a cylindrical shell with an internal through-hole. d is the inner diameter of the test specimen. For a cylindrical shell with an internal through-hole, d is greater than 0; for a cylinder, d = 0.

[0012] The length l of the test specimen M and the length l of the spacer S The total outer diameter D of the test specimen is greater than 5n times, meaning that the one-dimensional vibration assumption is satisfied within each half-wavelength. Based on the response of the piezoelectric transducer, the theoretical test frequency range of the vibration system composed of the piezoelectric transducer and resonant unit is from several hundred Hz to several hundred kHz. However, considering the length limitations of the actual test specimen and spacer, the recommended frequency range of the excitation wave is 2 kHz to 50 kHz. The total length of the resonant unit is equal to n times the half-wavelength, i.e., l M +l S =nλ / 2.

[0013] The operating temperature range of the measuring device of the present invention is not limited by the temperature limit of the piezoelectric transducer (such as the Curie temperature), but mainly depends on the temperature limit of the spacer bar, the heat-resistant adhesive and the test sample itself.

[0014] Another objective of this invention is to provide a method for measuring the viscoelastic mechanical properties of polymer materials under high and low temperature environments.

[0015] The method for measuring the viscoelastic mechanical properties of polymer materials under high and low temperature environments according to the present invention includes the following steps:

[0016] 1) One end of the spacer is connected to the test sample to form a resonant unit; a piezoelectric transducer is installed at the other end of the spacer;

[0017] The piezoelectric transducer is connected to the impedance analyzer; the test sample is placed in the temperature control device; the temperature sensor is placed next to the test sample.

[0018] 2) Set the temperature control device to the set temperature, and the temperature sensor measures and records the temperature;

[0019] The impedance analyzer applies a voltage signal to the piezoelectric transducer, which converts the voltage signal into mechanical vibration, generating an excitation wave that excites the resonant unit to vibrate, producing an nth-order vibration mode. At this time, there are n half-wavelengths distributed in the integrated resonant unit composed of the test specimen and the spacer. The spacer provides acoustic length compensation for the test specimen at the end, which indirectly increases the effective vibration length of the test specimen and reduces the radial effect caused by the short resonant wavelength of the test specimen.

[0020] The impedance analyzer performs frequency sweep within a set frequency band; the piezoelectric transducer converts vibration into current signals and transmits them to the impedance analyzer.

[0021] The impedance analyzer extracts the admittance curve of the nth-order vibration of the resonant unit at the current temperature;

[0022] 3) Obtain the resonant frequency and anti-resonant frequency of the nth-order vibration at the current temperature from the admittance curve of the nth-order vibration of the resonant unit at the previous temperature.

[0023] 4) Based on the resonant frequency and anti-resonant frequency of the nth-order vibration at the current temperature, an implicit vibration characteristic equation is constructed according to the vibration mode, and a loss factor solution equation is established according to the strain energy distribution. The vibration characteristic equation and the loss factor solution equation are solved numerically, and the longitudinal mechanical property parameters and torsional mechanical property parameters of the test specimen at the current temperature are calculated.

[0024] In step 1), when measuring the longitudinal mechanical properties of the test specimen, a longitudinal vibration type piezoelectric transducer is used; when measuring the torsional mechanical properties of the test specimen, a torsional vibration type piezoelectric transducer is used.

[0025] In step 2), when measuring the longitudinal mechanical performance parameters, the impedance analyzer applies a voltage signal to the longitudinal vibration piezoelectric transducer. The longitudinal vibration piezoelectric transducer converts the voltage signal into longitudinal mechanical vibration, generating an excitation wave that drives the resonant unit to vibrate longitudinally, producing an nth-order longitudinal vibration mode. The impedance analyzer performs frequency sweep within the set frequency band. The longitudinal vibration piezoelectric transducer senses the nth-order longitudinal vibration signal of the resonant unit and converts it into an internal current, transmitting the current signal to the impedance analyzer. The impedance analyzer obtains the admittance curve of the nth-order vibration of the resonant unit at the current temperature based on the ratio of the returned current signal to the output voltage signal. When measuring torsional mechanical properties, an impedance analyzer applies a voltage signal to a torsional vibration piezoelectric transducer. The torsional vibration piezoelectric transducer converts the voltage signal into torsional mechanical vibration, which drives the resonant unit to torsional vibration, generating an nth-order torsional vibration mode. The impedance analyzer performs frequency sweep within a set frequency band. The torsional vibration piezoelectric transducer senses the nth-order torsional vibration signal of the resonant unit and converts it into an internal current, transmitting the current signal to the impedance analyzer. The impedance analyzer obtains the admittance curve of the nth-order vibration of the resonant unit at the current temperature based on the ratio of the returned current signal to the output voltage signal.

[0026] In step 3), the imaginary part of the admittance is the susceptance, and the real part of the admittance is the conductance. When measuring the longitudinal mechanical performance parameters, the resonant and anti-resonant frequencies of the nth-order vibration during longitudinal vibration are obtained from the admittance curve of the nth-order vibration during longitudinal vibration. The peak and valley values ​​are obtained by flattening the susceptance curve of the nth-order vibration during longitudinal vibration, and the two half-power points are obtained by flattening the conductance curve. The resonant frequencies of the nth-order vibration during longitudinal vibration of the piezoelectric transducer and resonant unit are then extracted. and anti-resonant frequency .

[0027] When measuring torsional mechanical performance parameters, the resonant and anti-resonant frequencies of the nth-order vibration during torsional vibration are obtained from the admittance curve during torsional vibration. The peak and valley values ​​are obtained by flattening the susceptance curve of the nth-order vibration during torsional vibration, and the two half-power points are obtained by flattening the conductivity curve. The resonant frequencies of the nth-order vibration during torsional vibration of the piezoelectric transducer and resonant unit are then extracted. and anti-resonant frequency .

[0028] In step 4), when measuring the longitudinal mechanical performance parameters, the longitudinal vibration characteristic equation of the resonant element is constructed based on the resonant frequency and anti-resonant frequency of the nth order vibration during longitudinal vibration:

[0029]

[0030] Where h is the thickness of the piezoelectric transducer, and D PD is the outer diameter of the piezoelectric transducer, D is the outer diameter of the spacer bar and the test specimen, d is the inner diameter of the test specimen, and l is the outer diameter of the piezoelectric transducer. M To measure the length of the test specimen, l S The length of the spacer bar It is to test the density of the sample. It refers to the density of the piezoelectric transducer. It is the density of the spacer bars. It is the open-circuit elastic stiffness constant of a longitudinal vibration type piezoelectric transducer. It is the Young's modulus of the spacer bar. It is the wavenumber of the test specimen during longitudinal vibration. It is the wave number of a longitudinally vibrating piezoelectric transducer during longitudinal vibration. This represents the wave number of the spacer during longitudinal vibration. Because the spacer has excellent thermal stability, the Young's modulus of the spacer changes negligibly with temperature. The characteristic equation for longitudinal vibration is implicit; by numerically solving the characteristic equation, the Young's modulus of the test specimen can be calculated. .

[0031] After obtaining the Young's modulus, since the strain energy in the longitudinal vibration piezoelectric transducer and the spacer is much smaller than the strain energy in the test specimen, their contribution to the overall component loss is ignored. The longitudinal vibration loss factor tanδ of the test specimen is then calculated. ML The equation is obtained by solving the longitudinal vibration loss factor:

[0032]

[0033]

[0034]

[0035] Among them, W SL and W ML A represents the strain energy of the spacer and the test specimen at resonance during longitudinal vibration, respectively. L and B L These are the first and second parameters used to calculate the longitudinal vibration loss factor, respectively.

[0036] When measuring torsional mechanical properties, the characteristic equation of torsional vibration of the resonant element is constructed based on the resonant frequency and anti-resonant frequency of the nth-order vibration during torsional vibration:

[0037]

[0038] Where, d P The inner diameter of the torsional vibration type piezoelectric transducer. G is the short-circuit elastic compliance constant of a torsional vibration type piezoelectric transducer. M To test the shear modulus of the sample. It is the shear modulus of the spacer bar. It is the wavenumber of the test specimen during torsional vibration. It is the wave number of a torsional vibration type piezoelectric transducer during torsional vibration. The wave number of the spacer during torsional vibration is given; the characteristic equation of torsional vibration is solved numerically to calculate the shear modulus of the test specimen. .

[0039] Torsional vibration loss factor The equation is obtained by solving the torsional vibration loss factor:

[0040]

[0041]

[0042]

[0043] Among them, W ST and W MT A represents the strain energy of the spacer bar and the test specimen at resonance during torsional vibration, respectively. T and B T These are the first and second parameters used to calculate the torsional vibration loss factor, respectively.

[0044] Further, in step 2), the set temperature is changed, and steps 2 to 4 are repeated. The impedance analyzer obtains the admittance curves of the nth-order vibration of the resonant unit at different temperatures, and the resonant frequency and anti-resonant frequency of the nth-order vibration at different temperatures are obtained accordingly. The vibration characteristic equation and the loss factor equation are solved numerically to calculate the longitudinal mechanical property parameters and torsional mechanical property parameters of the test specimen at different temperatures.

[0045] Advantages of this invention:

[0046] This invention can accurately measure the viscoelastic mechanical properties of polymer materials at different temperatures, including elastic modulus and loss factor. The device of this invention is simple to manufacture, the measurement results are reliable and fast. Compared with the most commonly used method for measuring the viscoelastic mechanical properties of polymers, namely the DMA measurement method, whose measurement frequency range is usually below tens of Hz, this invention can measure results at frequencies of several kHz to tens of kHz. This invention is of great significance for characterizing the mid-frequency viscoelastic mechanical properties of polymer materials and has broad application prospects. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the connection relationship of test specimens in an embodiment of the measuring device for the viscoelastic mechanical properties of polymer materials under high and low temperature environments of the present invention.

[0048] Figure 2 This is a schematic diagram showing the vibration waveform distribution of a piezoelectric transducer and a resonant unit in a resonant state.

[0049] Figure 3 This is a schematic diagram of an embodiment of the measuring device for the viscoelastic mechanical properties of polymer materials under high and low temperature environments according to the present invention.

[0050] Figure 4 The conductivity curve is obtained from an embodiment of the method for measuring the viscoelastic mechanical properties of polymer materials under high and low temperature environments according to the present invention. Detailed Implementation

[0051] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0052] like Figure 1 and 3 As shown, the measuring device for the viscoelastic mechanical properties of polymer materials under high and low temperature environments in this embodiment includes: a piezoelectric transducer 1, a spacer 2, an impedance analyzer 4, a temperature sensor 6, and a temperature control device 5; wherein, the test sample 3 is a polymer; the stiffness and sound velocity of the spacer 2 are both greater than those of the test sample 3; one end of the spacer 2 is connected to the test sample 3 to form an integral resonant unit; the other end of the spacer 2 is provided with the piezoelectric transducer 1; the piezoelectric transducer 1 is connected to the impedance analyzer 4; the test sample 3 is placed in the temperature control device 5; and the temperature sensor 6 is placed next to the test sample 3.

[0053] Piezoelectric transducers are classified into longitudinal vibration type piezoelectric transducers and torsional vibration type piezoelectric transducers, used to measure the longitudinal and torsional mechanical properties of test specimens, respectively. The longitudinal vibration type piezoelectric transducer is a piezoelectric ceramic disk polarized along the thickness direction, with an outer diameter of D. P The thickness is h, and its two circular end faces are coated with electrode layers; the torsional vibration type piezoelectric transducer includes two identical semicircular rings with an outer diameter of D. P The inner diameter is d P The thickness is h; both semicircular rings are polarized along the thickness direction, the electrode surfaces of the two semicircular rings face each other, and the polarization directions are opposite. They are fixed together by conductive silver paste to form a ring; D P ≤D.

[0054] Figure 2 The vibration waveform distribution of the piezoelectric transducer and resonant unit in the resonant state is shown. The curve represents the strain energy density distribution along the axial direction (the length direction of the test specimen), i.e., the Z-axis, during first-order vibration. This invention utilizes a spacer bar as a waveguide medium, adjusting the length l of the test specimen... M and the length l of the spacer SThe sum of these factors ensures that the entire three-component system (transducer-spacer-sample) satisfies the one-dimensional slender rod vibration assumption at the test frequency. At the resonant frequency, the antinodes and nodes of the standing wave are distributed throughout the entire composite rod. By using the admittance curves measured by an impedance analyzer and combining them with the implicit equations, the mechanical properties of the test sample can be decoupled from the overall vibration response.

[0055] In this embodiment, the temperature sensor 6 is a thermocouple. The temperature control device 5 includes a high-temperature furnace and a low-temperature chamber. The test sample 3 is placed in the constant temperature zone of the high-temperature furnace or the low-temperature chamber, such as... Figure 3 As shown.

[0056] Example 1

[0057] This embodiment measures longitudinal mechanical properties. The method for measuring the viscoelastic mechanical properties of polymer materials under high and low temperature environments includes the following steps:

[0058] 1) One end of the spacer is bonded to the test specimen to form a whole resonant unit; the other end of the spacer is bonded to a longitudinal vibration type piezoelectric transducer; fast-drying adhesive is used to bond the piezoelectric transducer, and inorganic ceramic high-temperature adhesive is used to bond the test specimen.

[0059] A longitudinal vibration type piezoelectric transducer is connected to an impedance analyzer; such as Figure 3 As shown, the longitudinal vibration type piezoelectric transducer can be located outside the high-temperature furnace or low-temperature chamber, while the test sample is accurately placed in the constant temperature area and a thermocouple is set next to the test sample.

[0060] 2) Set the temperature control device to the set temperature, and the temperature sensor measures and records the temperature;

[0061] An impedance analyzer applies a voltage signal to a longitudinally vibrating piezoelectric transducer, which converts the voltage signal into longitudinal mechanical vibration, generating an excitation wave that drives the resonant unit to vibrate longitudinally, producing the nth order longitudinal vibration mode. The impedance analyzer performs frequency sweep measurements from low to high frequency within a set frequency band of 2 kHz to 50 kHz. On the acquired admittance curve, the main conductance peaks that appear sequentially correspond to the first, second, and up to the nth order longitudinal vibration modes of the resonant system, respectively.

[0062] The longitudinal vibration type piezoelectric transducer senses the nth order longitudinal vibration signal of the resonant unit and converts it into an internal current, which is then transmitted to the impedance analyzer.

[0063] The impedance analyzer obtains the admittance curve of the resonant unit during longitudinal vibration at the current temperature based on the ratio of the returned current signal to the output voltage signal.

[0064] 3) Flatten the susceptance curve of the nth-order vibration of the resonant unit under longitudinal vibration at the current temperature to obtain the peak and valley values, and flatten the conductivity curve to obtain two half-power points. Extract the resonant frequency of the nth-order vibration of the piezoelectric transducer and the resonant unit under longitudinal vibration at the current temperature. and anti-resonant frequency ;

[0065] 4) Based on the resonant frequency and anti-resonant frequency of the nth-order vibration during longitudinal vibration, construct the characteristic equation of longitudinal vibration of the resonant element:

[0066]

[0067] Where h is the thickness of the piezoelectric transducer, and D P D is the outer diameter of the piezoelectric transducer, D is the outer diameter of the spacer bar and the test specimen, d is the inner diameter of the test specimen, and l is the outer diameter of the piezoelectric transducer. M To measure the length of the test specimen, l S The length of the spacer bar It is to test the density of the sample. It refers to the density of the piezoelectric transducer. It is the density of the spacer bars. It is the open-circuit elastic stiffness constant of a longitudinal vibration type piezoelectric transducer. It is the Young's modulus of the spacer bar. It is the wavenumber of the test specimen during longitudinal vibration. It is the wave number of a longitudinally vibrating piezoelectric transducer during longitudinal vibration. The longitudinal vibration time interval is the wave number of the spacer. The longitudinal vibration characteristic equation is an implicit equation. The Young's modulus of the test specimen is calculated by numerically solving the longitudinal vibration characteristic equation. ;

[0068] After obtaining the Young's modulus, since the strain energy in the longitudinal vibration piezoelectric transducer and the spacer is much smaller than the strain energy in the test specimen, their contribution to the overall component loss is ignored. The longitudinal vibration loss factor tanδ of the test specimen is then calculated. ML The equation is obtained by solving the longitudinal vibration loss factor:

[0069]

[0070]

[0071]

[0072] Among them, W SL and W ML A represents the strain energy of the spacer and the test specimen at resonance during longitudinal vibration, respectively. L and B LThese are the first and second parameters for calculating the longitudinal vibration loss factor, respectively.

[0073] 5) Change the temperature set in step 2) to a range of 0~125℃ and repeat steps 2~4). Obtain the admittance curves of the nth order vibration of the resonant unit under different temperatures using the impedance analyzer. Accordingly, obtain the resonant frequency and anti-resonant frequency of the nth order vibration under different temperatures. Solve the longitudinal vibration characteristic equation and the longitudinal vibration loss factor equation numerically to calculate the longitudinal mechanical performance parameters of the test sample under different temperatures.

[0074] In this embodiment, polyvinylidene fluoride (PVDF) was selected as the test sample for measuring its viscoelastic parameters at room temperature. The experimental parameters were set as follows: the spacer was made of alumina ceramic, and the length of the spacer... Approximately 20 mm in diameter and 10 mm in outer diameter; the test specimen is a cylinder with a length of... The piezoelectric transducer has a diameter of approximately 40 mm, an outer diameter D of 10 mm, an inner diameter d=0, a thickness h of 2 mm, and an outer diameter D of approximately 40 mm. P The value is 10 mm. n=1. Figure 4 The measured conductivity amplitude-frequency curve is shown. A clear conductivity peak appears near a frequency of approximately 9.9 kHz, which corresponds to the first-order longitudinal vibration mode of the test component. Based on the peak frequency and half-power bandwidth of the conductivity curve in the figure, the viscoelastic mechanical properties of the PVDF material at room temperature and a frequency of approximately 10 kHz are calculated using the longitudinal vibration characteristic equation and loss factor solution equation proposed in this invention: Young's modulus 2.89 GPa, longitudinal vibration loss factor 0.0316.

[0075] Example 2

[0076] This embodiment measures torsional mechanical properties. The method for measuring the viscoelastic mechanical properties of polymer materials under high and low temperature environments includes the following steps:

[0077] 1) One end of the spacer is connected to the test specimen to form a resonant unit; the other end of the spacer is equipped with a torsional vibration type piezoelectric transducer;

[0078] The torsional vibration type piezoelectric transducer is connected to the impedance analyzer; the torsional vibration type piezoelectric transducer is located outside the high temperature furnace or low temperature chamber, and the test sample is accurately placed in the constant temperature area, with a thermocouple placed next to the test sample.

[0079] 2) Set the temperature control device to the set temperature, and the temperature sensor measures and records the temperature;

[0080] An impedance analyzer applies a voltage signal to a torsional vibration piezoelectric transducer, which converts the voltage signal into torsional mechanical vibration, driving the resonant unit to torsional vibration and generating an nth-order torsional vibration mode.

[0081] The impedance analyzer performs frequency sweep within the set frequency band; the torsional vibration type piezoelectric transducer senses the nth order torsional vibration signal of the resonant unit and converts it into internal current, which is then transmitted to the impedance analyzer; on the acquired admittance curve, the main conductance peaks that appear in sequence correspond to the first, second and up to the nth order torsional vibration modes of the resonant system, respectively.

[0082] The impedance analyzer obtains the admittance curve of the resonant unit during torsional vibration at the current temperature based on the ratio of the returned current signal to the output voltage signal.

[0083] 3) Flatten the susceptance curve of the nth-order vibration of the resonant unit under torsional vibration at the current temperature to obtain the peak and valley values. Flatten the conductivity curve to obtain two half-power points. Extract the resonant frequency of the nth-order vibration of the piezoelectric transducer and the resonant unit under torsional vibration at the current temperature. and anti-resonant frequency ;

[0084] 4) Based on the resonant frequency and anti-resonant frequency of the nth-order vibration during torsional vibration, construct the characteristic equation of torsional vibration of the resonant element:

[0085]

[0086] Where, d P The inner diameter of the torsional vibration type piezoelectric transducer. G is the short-circuit elastic compliance constant of a torsional vibration type piezoelectric transducer. M To test the shear modulus of the sample. It is the shear modulus of the spacer bar. It is the wavenumber of the test specimen during torsional vibration. It is the wave number of a torsional vibration type piezoelectric transducer during torsional vibration. The wave number of the spacer during torsional vibration is given; the characteristic equation of torsional vibration is solved numerically to calculate the shear modulus of the test specimen. ;

[0087] Torsional vibration loss factor The equation is obtained by solving the torsional vibration loss factor:

[0088]

[0089]

[0090]

[0091] Among them, W ST and W MT A represents the strain energy of the spacer bar and the test specimen at resonance during torsional vibration, respectively. T and B T These are the first and second parameters for calculating the torsional vibration loss factor, respectively;

[0092] 5) Change the temperature set in step 2) and repeat steps 2 to 4). Obtain the admittance curves of the nth order vibration of the resonant unit under torsional vibration at different temperatures using an impedance analyzer. Accordingly, obtain the resonant frequency and anti-resonant frequency of the nth order vibration under torsional vibration at different temperatures. Solve the characteristic equation of torsional vibration and the equation for solving the loss factor of torsional vibration numerically to calculate the torsional mechanical properties parameters of the test specimen at different temperatures.

[0093] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art will understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection of the present invention is defined by the claims.

Claims

1. A method for measuring the viscoelastic mechanical properties of polymer materials under high and low temperature environments, characterized in that, The measurement method includes the following steps: 1) One end of the spacer is connected to the test sample to form a resonant unit; a piezoelectric transducer is installed at the other end of the spacer; The piezoelectric transducer is connected to the impedance analyzer; the test sample is placed in the temperature control device; the temperature sensor is placed next to the test sample. 2) Set the temperature control device to the set temperature, and the temperature sensor measures and records the temperature; The impedance analyzer applies a voltage signal to the piezoelectric transducer, which converts the voltage signal into mechanical vibration, generating an excitation wave that excites the resonant unit to vibrate, producing an nth-order vibration mode. At this time, there are n half-wavelengths distributed in the integrated resonant unit composed of the test specimen and the spacer bar. The spacer bar provides acoustic length compensation for the test specimen, increasing the effective vibration length of the test specimen. The impedance analyzer performs frequency sweep within a set frequency band; the piezoelectric transducer converts vibration into current signals and transmits them to the impedance analyzer. The impedance analyzer extracts the admittance curve of the nth-order vibration of the resonant unit at the current temperature; 3) Obtain the resonant frequency and anti-resonant frequency of the nth-order vibration at the current temperature from the admittance curve of the nth-order vibration of the resonant unit at the previous temperature. 4) Based on the resonant frequency and anti-resonant frequency of the nth-order vibration at the current temperature, an implicit vibration characteristic equation is constructed according to the vibration mode, and a loss factor solution equation is established according to the strain energy distribution. The vibration characteristic equation and the loss factor solution equation are solved numerically, and the longitudinal mechanical property parameters and torsional mechanical property parameters of the test specimen at the current temperature are calculated.

2. The measurement method according to claim 1, characterized in that, In step 1), when measuring the longitudinal mechanical properties of the test specimen, a longitudinal vibration type piezoelectric transducer is used; when measuring the torsional mechanical properties of the test specimen, a torsional vibration type piezoelectric transducer is used.

3. The measurement method according to claim 2, characterized in that, In step 2), the impedance analyzer applies a voltage signal to the longitudinal or torsional vibration type piezoelectric transducer. The longitudinal or torsional vibration type piezoelectric transducer converts the voltage signal into longitudinal or torsional mechanical vibration, generating an excitation wave that drives the resonant unit to vibrate longitudinally or torsionally, generating an nth-order longitudinal or torsional vibration mode. The impedance analyzer performs frequency sweep within the set frequency band. The longitudinal or torsional vibration type piezoelectric transducer senses the nth-order longitudinal or torsional vibration signal of the resonant unit and converts it into an internal current, transmitting the current signal to the impedance analyzer. The impedance analyzer obtains the admittance curve of the nth-order vibration of the resonant unit at the current temperature based on the ratio of the returned current signal to the output voltage signal.

4. The measurement method according to claim 3, characterized in that, The peak and trough values ​​of the susceptance curve for the nth-order vibration under longitudinal or torsional vibration are obtained by flattening the susceptance curve, and the two half-power points are obtained by flattening the conductivity curve. The resonant frequencies of the nth-order vibration under longitudinal vibration of the piezoelectric transducer and the resonant unit are then extracted. and anti-resonant frequency And the resonant frequency of the nth order vibration during torsional vibration. and anti-resonant frequency .

5. The measurement method according to claim 4, characterized in that, In step 4), based on the resonant frequency and anti-resonant frequency of the nth-order vibration during longitudinal vibration, the characteristic equation of longitudinal vibration of the resonant element is constructed: Where h is the thickness of the piezoelectric transducer, and D P D is the outer diameter of the piezoelectric transducer, D is the outer diameter of the spacer bar and the test specimen, d is the inner diameter of the test specimen, and l is the outer diameter of the piezoelectric transducer. M To measure the length of the test specimen, l S The length of the spacer bar It is to test the density of the sample. It refers to the density of the piezoelectric transducer. It is the density of the spacer bars. It is the open-circuit elastic stiffness constant of a longitudinal vibration type piezoelectric transducer. To test the Young's modulus of the sample. It is the Young's modulus of the spacer bar. It is the wavenumber of the test specimen during longitudinal vibration. It is the wave number of a longitudinally vibrating piezoelectric transducer during longitudinal vibration. The wave number of the spacer during longitudinal vibration is used to numerically solve the characteristic equation of longitudinal vibration and calculate the Young's modulus of the test specimen. .

6. The measurement method according to claim 5, characterized in that, The longitudinal vibration loss factor tan delta of the test sample is solved according to the following formula ML : where W SL and W ML are the strain energies of the spacer bar and test specimen, respectively, at resonance of the longitudinal vibration, A L and B L are first and second parameters, respectively, for calculating the longitudinal vibration loss factor.

7. The measurement method according to claim 4, characterized in that, In step 4), based on the resonant frequency and anti-resonant frequency of the nth-order vibration during torsional vibration, the characteristic equation of torsional vibration of the resonant element is constructed: Where h is the thickness of the piezoelectric transducer, and D P D is the outer diameter of the piezoelectric transducer, D is the outer diameter of the spacer bar and the test specimen, d is the inner diameter of the test specimen, and l is the outer diameter of the piezoelectric transducer. M To measure the length of the test specimen, l S The length of the spacer bar It is to test the density of the sample. It refers to the density of the piezoelectric transducer. It is the density of the spacer bars, d P The inner diameter of the torsional vibration type piezoelectric transducer. G is the short-circuit elastic compliance constant of a torsional vibration type piezoelectric transducer. M To test the shear modulus of the sample. It is the shear modulus of the spacer bar. It is the wavenumber of the test specimen during torsional vibration. It is the wave number of a torsional vibration type piezoelectric transducer during torsional vibration. The wave number of the spacer during torsional vibration is given; the characteristic equation of torsional vibration is solved numerically to calculate the shear modulus of the test specimen. .

8. The measurement method according to claim 7, characterized in that, In step 4), the torsional vibration loss factor of the test specimen is calculated according to the following formula. : Among them, W ST and W MT A represents the strain energy of the spacer bar and the test specimen at resonance during torsional vibration, respectively. T and B T These are the first and second parameters used to calculate the torsional vibration loss factor, respectively.

9. A measuring device for the viscoelastic mechanical properties of polymer materials under high and low temperature environments, used to implement the measuring method according to any one of claims 1 to 8, characterized in that, The measuring device includes: a piezoelectric transducer, a spacer, an impedance analyzer, a temperature sensor, and a temperature control device; wherein, the test sample is a polymer; the stiffness and sound velocity of the spacer are greater than those of the test sample; one end of the spacer is connected to the test sample to form an integral resonant unit; the other end of the spacer is equipped with a piezoelectric transducer; the piezoelectric transducer is connected to the impedance analyzer; the test sample is placed in the temperature control device; the temperature sensor is placed next to the test sample; the piezoelectric transducer generates an excitation wave to excite the resonant unit to generate an nth-order vibration mode, at which point a total of n half-wavelengths are distributed in the integral resonant unit composed of the test sample and the spacer; the test sample provides acoustic length compensation for the spacer, increasing the effective vibration length of the test sample; the piezoelectric transducer converts the vibration into a current signal and transmits it to the impedance analyzer; the impedance analyzer extracts the admittance curve of the nth-order vibration of the resonant unit, obtains the resonant frequency and anti-resonant frequency of the nth-order vibration from the admittance curve of the nth-order vibration, constructs an implicit vibration characteristic equation and establishes a loss factor solution equation, and solves the equation to obtain the longitudinal mechanical performance parameters and torsional mechanical performance parameters of the test sample, where n is a natural number ≥ 1.

10. The measuring device according to claim 9, characterized in that, The length l of the test sample M and the length l of the spacer S The total outer diameter D of the test specimen is greater than 5n times.

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