A polymer elastomer tensile testing system and analysis method resistant to wall slip

Abstract

This invention belongs to the field of precision scientific instrument manufacturing and polymer material characterization technology. Specifically, it discloses a tensile testing system and analysis method for polymer elastomers with resistance to wall slip. The method includes the following steps: S1, preparing a defect-free annular polymer elastomer sample; S2, fitting the sample onto two parallel fixed rods of the tensile testing system in a floating contact fit without mechanical clamping; S3, placing the sample in a vacuum chamber; S4, applying periodic tensile deformation to the annular polymer elastomer sample; S5, acquiring the stress response signal of the annular polymer elastomer sample and performing spectral analysis to obtain even-order harmonic signals. This invention, employing the aforementioned tensile testing system and analysis method for polymer elastomers with resistance to wall slip, eliminates measurement artifacts introduced by geometric mismatch in hardware construction and overcomes the defect of misjudging even-order harmonics, providing a new high-sensitivity detection dimension for the characterization of the microstructure of polymer materials.

Description

Technical Field

[0001] This invention relates to the fields of precision scientific instrument manufacturing and polymer material characterization technology, and in particular to a tensile testing system and analysis method for polymer elastomers with resistance to wall slippage. Background Technology

[0002] In the field of polymer material mechanical property testing and rheological characterization, general-purpose equipment such as tensile testing machines are mainly used. A typical structure includes a main frame, force sensors, displacement sensors, and two sets of rigid clamps (commonly such as mechanical wedge clamps, pneumatic clamps, or threaded locking clamps). During standard tensile testing, operators typically prepare dumbbell-shaped or elongated rubber / elastomer specimens, placing both ends in the metal jaws of the upper and lower clamps, using mechanical clamping force or friction to physically fix the specimen ends. Subsequently, the drive beam moves to apply an axial load to the specimen, and the force and displacement signals are recorded by the sensors to obtain a stress-strain curve.

[0003] In the existing technology, the above-mentioned technology has proven mature in testing metals or rigid plastics, but when conducting large deformation tests on soft elastomers such as rubber and hydrogels, the following long-standing technical defects remain unresolved: 1) Wall slippage caused by structural defects. Polymer elastomers are incompressible materials with a Poisson's ratio (ν) close to 0.5. This means that when the stretch ratio (λ) is large (λ>1.5), the specimen will experience drastic shrinkage in both width and thickness as it elongates axially. However, rigid clamps (metal jaws) cannot adaptively adjust to the thickness shrinkage of the specimen. This geometric mismatch between the "rigid clamp" and the "flexible specimen" at the interface inevitably leads to the specimen gradually losing effective contact pressure at the clamping point, resulting in microscopic debonding or interface slippage. Furthermore, attempts to increase friction by applying sandpaper or strong adhesive to the interface often induce localized stress concentration, even causing the specimen to tear at the clamping edges, and cannot fundamentally eliminate slippage in the later stages of large deformation.

[0004] 2) Distortion and error in measurement data. Wall slippage directly disrupts the benchmark for displacement measurement and introduces uncontrollable frictional noise. This results in the force-displacement curves measured by researchers containing numerous artifacts, severely obscuring the true intrinsic properties of the material.

[0005] 3) Misinterpretation of Nonlinear Signals (Even Harmonics). In nonlinear rheology research, ideal symmetrical stretching should produce a symmetrical stress response (containing only odd harmonics). However, the aforementioned wall slip disrupts the physical symmetry of the testing system, causing the sensor-acquired signals to be mixed with random even harmonics. Because existing equipment cannot distinguish between "false signals caused by slip" and "true signals caused by intrinsic material nonlinearity" from the hardware structure, equipment manufacturers and researchers often treat all even harmonics as "systematic errors" or "background noise" and filter or ignore them. This approach leads to the loss of crucial information. In fact, after eliminating slip interference, even harmonics are an important characteristic for characterizing the strain hardening properties of materials. The limitations of current technology prevent the industry from using this highly sensitive indicator to accurately characterize the microscopic physical picture of materials.

[0006] In summary, the tensile testing technique using a "dumbbell-shaped specimen + rigid fixture" is limited by its physical structure, making it unable to overcome the wall slippage problem under large deformation, resulting in distorted measurement data, and it cannot accurately acquire and utilize even harmonics for material characterization. Summary of the Invention

[0007] The purpose of this invention is to provide a tensile testing system and analysis method for polymer elastomers with anti-wall slippage, which eliminates measurement artifacts introduced by geometric mismatch from the hardware construction, and overcomes the misjudgment defect of dual harmonics, providing a new high-sensitivity detection dimension for the characterization of the microstructure of polymer materials.

[0008] To achieve the above objectives, the present invention provides a method for tensile testing and analysis of polymeric elastomers with resistance to wall slippage, comprising the following steps: S1. Prepare defect-free cyclic polymer elastomer samples; S2. The annular polymer elastomer sample obtained in S1 is placed on the two parallel fixed rods of the tensile testing system. The annular polymer elastomer sample and the fixed rods are in a floating contact fit without mechanical clamping. S3. Place the tensile testing system in a vacuum environment chamber; S4. Control the relative movement of the two parallel fixed rods to apply periodic tensile deformation to the annular polymer elastomer sample. During the stretching process, the annular polymer elastomer sample uses the floating contact fit to adaptively adjust on the surface of the parallel fixed rods according to the Poisson contraction of its own thickness, so as to maintain interface contact and eliminate wall slippage. S5. Collect the stress response signal of the annular polymer elastomer sample and perform spectrum analysis to obtain the even harmonic signal.

[0009] Preferably, in S1, the defect-free cyclic polymer elastomer sample is prepared by a mold polymerization process.

[0010] Preferably, the defect-free annular polymer elastomer sample is made of PM2E, or one of natural rubber or hydrogel soft materials.

[0011] Preferably, the mold polymerization process specifically includes: Using c-M2E as a monomer, ring-opening polymerization was performed under the action of TBD catalyst and water initiator to synthesize Đ Monodisperse and vinyl-terminated PM2E prepolymers with a concentration ≤1.10; PM2E prepolymer was mixed with crosslinking agent and platinum catalyst, injected into a ring mold, cured by hydrosilylation and demolded to obtain a seamless, internally homogeneous defect-free ring rubber sample.

[0012] Among them, TBD catalyst is a highly efficient organic base catalyst, with the Chinese name 1,5,7-triazabicyclo[4.4.0]dec-5-ene and the English name 1,5,7-Triazabicyclo[4.4.0]dec-5-ene.

[0013] PM2E prepolymer is an organosilicon polymer with a precise molecular weight, its Chinese name is poly(1-ethyl-1,1-(3-methoxy-1,5-dimethyl)pentasiloxane), and its English name is Poly(1-ethyl-1,1-(3-methoxy-1,5-dimethyl)pentasiloxane).

[0014] Preferably, the crosslinking agent is tetra(dimethylsiloxy)silane, and the platinum catalyst is Ossko platinum catalyst, which is a highly active platinum catalyst for hydrosilylation reactions.

[0015] Preferably, it also includes system linearity control and verification: At least one standard linear elastic element is connected in parallel with a ring-shaped polymer elastomer sample between two parallel fixed rods. As the number of parallel standard linear elastic elements increases, the variation trend of even harmonic amplitude in the stress response signal is detected; when the proportion of even harmonics is observed to decrease with the increase of system linearity, it is confirmed that the even harmonics originate from the intrinsic nonlinearity of the annular polymer elastomer sample.

[0016] Preferably, a mathematical algorithm is used to perform a Fast Fourier Transform (FFT) on the acquired stress response signal to convert the time-domain signal into a frequency-domain signal, and to extract the fundamental frequency and amplitude of each harmonic.

[0017] Preferably, in S4, the periodic deformation is specifically a sawtooth wave with a stretching rate of 0.67 s. -1 .

[0018] The present invention also provides a tensile testing system for polymeric elastomers with resistance to wall slippage, comprising: The double-rod floating fixture includes two rigid parallel fixed rods for passing through and supporting the annular specimen. The parallel fixed rods have a smooth surface design and are used for adaptive fine adjustment of the annular specimen along the circumference of the rods when it is deformed under stress. A vacuum environment cavity is used to house the dual-rod floating fixture, with a working air pressure below 10 Pa, to eliminate the interference of air convection resistance on weak harmonic signals; A periodic deformation application and detection assembly is used to drive the dual-bar floating fixture to perform relative motion and acquire the stress response signal of the annular specimen.

[0019] Preferably, the surface smooth design specifically includes: Low-friction coefficient engineering ceramics or Teflon-coated metals are used to meet the testing requirements of ultrasoft materials.

[0020] Therefore, the present invention employs the above-mentioned tensile testing system and analysis method for polymeric elastomers with anti-wall slippage, and the beneficial effects are as follows: Significantly improved measurement accuracy: Through the adaptive contact design of "defect-free ring specimen + double-rod floating fixture", interface debonding caused by geometric mismatch is eliminated, the measurement error of tensile test is greatly reduced, the true force curve is provided, and the data reliability is improved.

[0021] Improved signal-to-noise ratio and resolution: By combining a vacuum testing environment with a slip-free floating contact mechanism, air convection disturbances and interface "stick-slip" friction noise are eliminated, and weak high-order harmonic signals that traditional stretching machines cannot identify can be captured.

[0022] New application of even harmonics: The first experiment confirms that even harmonics are an intrinsic manifestation of strain hardening in materials. Their strength increases with the stretch ratio and is independent of the stretching rate, providing a new dimension for characterizing the microstructure of materials.

[0023] It has system self-testing and calibration capabilities: by introducing a parallel verification mechanism of linear springs, the relative nonlinearity of the system can be precisely controlled within the range of 5% to 100%, which proves that the nonlinear signal measured comes from the material itself, thereby enhancing the commercial value of the instrument.

[0024] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the double-rod floating fixture in Example 1 of the present invention, which describes a tensile testing system and analysis method for polymer elastomers that resists wall slippage. Figure 2This is a schematic diagram of the supporting standard linear elastic element in Embodiment 1 of the present invention, which describes a tensile testing system and analysis method for polymeric elastomers that resists wall slippage. Figure 3 This is a schematic diagram of the annular mold in Example 2 of the present invention, which describes a tensile testing system and analysis method for polymer elastomers that resist wall slippage. Figure 4 This is a periodic strain diagram of a polymer elastomer tensile testing system and analysis method for resisting wall slippage according to Example 3 of the present invention, under controlled tensile rates and different tensile ratios. Figure 5 This is a periodic strain diagram of a polymer elastomer tensile testing system and analysis method for resisting wall slippage according to Example 3 of the present invention, showing the controlled tensile ratio and different tensile rates. Figure 6 This is the FFT transform spectrum of Example 3 of the tensile testing system and analysis method for a polymer elastomer with anti-wall slippage according to the present invention; Figure 7 This is a graph showing the even harmonics as a function of stretching ratio in Example 3 of the present invention, which describes a tensile testing system and analysis method for a polymer elastomer with resistance to wall slippage. Figure 8 This is a graph showing the even harmonics as a function of tensile rate in Example 3 of the present invention, which describes a tensile testing system and analysis method for a polymer elastomer with resistance to wall slippage.

[0026] Figure Labels 1. Upper rod; 2. Rubber sample; 3. Standard linear elastic element; 4. Lower rod. Detailed Implementation

[0027] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0028] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0029] In this invention, funding support information is as follows: Funded by the Fundamental Research Funds for the Central Universities (Project No.: 226-2025-00200). This work was supported by the National Natural Science Foundation of China (Project Nos. 52503023 and 52541017).

[0030] Example 1 A tensile testing system for polymer elastomers with resistance to wall slippage includes a dual-bar floating fixture, a vacuum environment chamber for housing the dual-bar floating fixture, and a periodic deformation application assembly. The parallel fixed rods are made of smooth Teflon-coated metal. The working pressure of the vacuum environment chamber is below 10 Pa. The periodic deformation application assembly includes a high-precision force sensor and a drive motor. Figure 1 As shown, the double-rod floating fixture includes two rigid parallel fixed rods that pass through and support the rubber sample. The diameter of the parallel fixed rods is smaller than the inner diameter of the rubber sample. Each parallel fixed rod includes an upper rod and a lower rod. The upper rod is connected to a high-precision force sensor to collect the stress response signal of the rubber sample; the lower rod is connected to a drive motor to drive the double-rod floating fixture to perform relative movement. When an annular rubber film sample is fitted onto the two fixed rods, the rubber sample can adaptively adjust circumferentially along the rod surface during stretching, eliminating interface debonding and wall slippage. Figure 2 As shown, the parallel retaining rod is also used to pass through and support the standard linear elastic element.

[0031] Example 2 A defect-free annular PM2E rubber sample, specifically the rubber sample in Example 1, is prepared by in-situ molding polymerization and crosslinking to eliminate cutting defects. The preparation method is as follows: PM2E prepolymer synthesis: In a dry reaction vessel, cyclic monomer c-M2E is used as raw material, and TBD catalyst and water initiator are added to carry out ring-opening polymerization. The molecular weight is adjusted by controlling the molar ratio of monomer to initiator to prepare monodisperse bissilanol-terminated PM2E polymer. Excess vinyl dimethyl chlorosilane is added to carry out end-capping reaction to functionalize both ends of the polymer to vinyl groups.

[0032] The adjustment methods for the molar ratio corresponding to the target molecular weight in the monodisperse bissilanol-terminated PM2E polymer are shown in Table 1.

[0033] Table 1. Correspondence between target molecular weight and monomer:initiator (molar ratio)

[0034] Crosslinking and mixing: The vinyl-terminated PM2E prepolymer was mixed with tetra(dimethylsiloxy)silane in stoichiometric ratio, and Ossko platinum catalyst at 50 ppm of the total mass of PM2E prepolymer was added. The mixture was then degassed under vacuum.

[0035] Mold Forming and Curing: An aluminum alloy ring mold was fabricated using 3D printing technology. The structure of the aluminum alloy ring mold is as follows: Figure 3 As shown, the mixture is injected into an aluminum alloy ring mold to complete the curing process.

[0036] Demolding and finished product: After slowly cooling to room temperature, the product is demolded to obtain a transparent, homogeneous, and structurally defect-free annular rubber film sample with a circumference of 30 mm, a width of 5 mm, and a thickness of 1 mm.

[0037] Example 3 A tensile testing and analysis method for polymeric elastomers with resistance to wall slip, a high-precision vacuum tensile testing and analysis method for eliminating wall slip, using the testing system of Example 1 and the rubber sample of Example 2, includes the following steps: S1. Place the rubber sample on the upper and lower rods. During the stretching process, the rubber sample can be adaptively adjusted circumferentially along the surface of the rod to eliminate interface debonding and wall slippage.

[0038] S2. Environmental control: The double-rod floating fixture is enclosed in a vacuum environment chamber, and the vacuum is drawn to 10Pa to eliminate the interference of air convection resistance on weak harmonic signals.

[0039] S3. Deformation Application and Signal Acquisition: The drive motor is set to a constant stretching rate to drive the lower rod to move. In this embodiment, the stretching rate is 0.67s. -1 Periodic sawtooth wave deformation is applied to control the maximum tensile ratio; in this embodiment, λ=3.67. A force sensor collects stress response signals in real time, and the sampling frequency must meet the requirement of capturing higher harmonics; in this embodiment, 100 data points are collected per second.

[0040] S4. Data Analysis and Processing: Extract at least 10 complete cycles of the stabilized signal and perform FFT analysis. (At the base frequency...) even multiples of frequency ( , A clear harmonic peak appears at ( ), which is the signal characteristic of the intrinsic nonlinearity of the material.

[0041] To verify that the measured even harmonics originate from intrinsic material properties rather than instrument errors, a parallel linear spring verification method was employed: A standard linear elastic element (metal spring with a purely linear force response) is connected in parallel between the upper and lower rods, and periodic deformation (such as a sawtooth wave with a constant stretching rate of 0.67 s) is applied. -1 High signal-to-noise ratio stress response signals were acquired and subjected to Fast Fourier Transform (FFT) to extract the fundamental frequency and amplitudes of each harmonic. This was done while maintaining a constant tensile rate of 0.67 s. -1 When applying periodic deformation while changing the stretch ratio, the periodic strain is as follows: Figure 4 As shown; when a constant stretching ratio λ=3.67 is maintained, periodic deformation is applied while the stretching rate is changed, and the periodic strain is as follows. Figure 5 As shown; the FFT transform spectrum is as follows Figure 6As shown, the dependence of even-order harmonics in the stress response on the stretch ratio is illustrated. The variations of even-order harmonics with stretch ratio and with stretch rate are shown in the figures below. Figure 7 and Figure 8 As shown.

[0042] Verification shows that as the number of parallel springs increases (improving the overall linearity of the system), the proportion of even-order harmonics decreases significantly, and no even-order harmonics are detected when only springs are tested. This confirms that the even-order harmonics in pure rubber testing originate entirely from the material's nonlinearity. By connecting a standard linearization component, the relative nonlinearity of the system can be precisely controlled within the range of 5% to 100%. This function gives the equipment a "self-checking" capability, allowing it to demonstrate to the user that the measured nonlinear signal originates entirely from the material itself, rather than from equipment system errors. More importantly, it confirms for the first time that even-order harmonics are not instrument noise, but rather an intrinsic manifestation of material strain hardening. The intensity of even-order harmonics increases with the stretch ratio but is independent of the stretching rate, thus clarifying their physical origin.

[0043] Therefore, the present invention employs the above-mentioned tensile testing system and analysis method for polymer elastomers with anti-wall slippage, which eliminates the measurement artifacts introduced by geometric mismatch from the hardware construction perspective, and overcomes the misjudgment defect of dual harmonics, providing a new high-sensitivity detection dimension for the characterization of the microstructure of polymer materials.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for tensile testing and analysis of polymeric elastomers with resistance to wall slippage, characterized in that, Includes the following steps: S1. Prepare defect-free cyclic polymer elastomer samples; S2. The annular polymer elastomer sample obtained in S1 is placed on the two parallel fixed rods of the tensile testing system. The annular polymer elastomer sample and the fixed rods are in a floating contact fit without mechanical clamping. S3. Place the tensile testing system in a vacuum environment chamber; S4. Control the relative movement of the two parallel fixed rods to apply periodic tensile deformation to the annular polymer elastomer sample. During the stretching process, the annular polymer elastomer sample uses the floating contact fit to adaptively adjust on the surface of the parallel fixed rods according to the Poisson contraction of its own thickness, maintaining interface contact and eliminating wall slippage. S5. Collect the stress response signal of the annular polymer elastomer sample and perform spectrum analysis to obtain the even harmonic signal.

2. The method for tensile testing and analysis of polymeric elastomers with resistance to wall slippage according to claim 1, characterized in that, In S1, the defect-free cyclic polymer elastomer sample is prepared by a mold polymerization process.

3. The method for tensile testing and analysis of polymeric elastomers with resistance to wall slippage according to claim 2, characterized in that, The specific mold polymerization process is as follows: Using c-M2E as a monomer, ring-opening polymerization was performed under the action of TBD catalyst and water initiator to synthesize Đ Monodisperse and vinyl-terminated PM2E prepolymers with a concentration ≤1.10; PM2E prepolymer was mixed with crosslinking agent and platinum catalyst, injected into a ring mold, cured by hydrosilylation, and demolded to obtain a seamless, internally homogeneous, defect-free ring rubber sample.

4. The method for tensile testing and analysis of polymeric elastomers with resistance to wall slippage according to claim 3, characterized in that, The crosslinking agent is specifically tetra(dimethylsiloxy)silane, and the platinum catalyst is specifically Ossko platinum catalyst.

5. The method for tensile testing and analysis of polymeric elastomers with resistance to wall slippage according to claim 1, characterized in that, It also includes system linearity tuning and verification: At least one standard linear elastic element is connected in parallel with a ring-shaped polymer elastomer sample between two parallel fixed rods. As the number of parallel standard linear elastic elements increases, the variation trend of even harmonic amplitude in the stress response signal is detected; when the proportion of even harmonics is observed to decrease with the increase of system linearity, it is confirmed that the even harmonics originate from the intrinsic nonlinearity of the annular polymer elastomer sample.

6. The method for tensile testing and analysis of polymeric elastomers with resistance to wall slippage according to claim 5, characterized in that: The collected stress response signal was subjected to a fast Fourier transform to extract the fundamental frequency and the amplitude of each harmonic.

7. The method for tensile testing and analysis of polymeric elastomers with resistance to wall slippage according to claim 1, characterized in that, In S4, the periodic deformation is specifically a sawtooth wave with a stretching rate of 0.67 s. -1 .

8. A tensile testing system for a polymeric elastomer resisting wall slippage for implementing the method according to any one of claims 1-7, characterized in that, include: The double-rod floating fixture includes two rigid parallel fixed rods for passing through and supporting the annular specimen. The parallel fixed rods have a smooth surface design and are used for adaptive fine adjustment of the annular specimen along the circumference of the rods when it is deformed under stress. A vacuum environment chamber is used to house the dual-rod floating tooling, with a working air pressure below 10 Pa; A periodic deformation application and detection assembly is used to drive the dual-bar floating fixture to perform relative motion and acquire the stress response signal of the annular specimen.

9. The tensile testing system for a polymer elastomer with resistance to wall slippage according to claim 8, characterized in that, The surface smoothing design specifically refers to: Use engineering ceramics or Teflon-coated metals with low coefficient of friction.

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