Rubber aging acceleration rate analysis method based on time-temperature equivalent factor

Abstract

The invention discloses a rubber aging acceleration rate analysis method based on a time-temperature equivalent factor, which adopts a DMA dynamic thermal analysis test and dynamic temperature scanning to research viscoelastic mechanical properties of a rubber material, and comprises the following steps: firstly, obtaining a dynamic modulus and time relation curve at different temperatures according to the test; the method comprises the following steps: drawing a dynamic modulus relaxation main curve of a rubber material at a reference temperature by combining a time-temperature equivalence principle, calculating activation energy and a time-temperature equivalence factor of rubber based on an Arrhenius equation, and establishing a quantitative relationship among the reference temperature, different temperatures and the time-temperature equivalence factor so as to quantitatively determine the acceleration multiplying power of the rubber. By adopting the analysis method, the increased temperature required by the acceleration test can be calculated according to the acceleration rate required at the reference temperature, so that the accuracy of the material aging test is improved, the aging efficiency of the material is improved, and the method is suitable for analyzing and predicting the service life of the sealing material in the aging environment.

Description

Technical Field

[0001] The invention relates to the field of rubber materials, and in particular to an aging acceleration rate analysis method of rubber as a sealing material in an environment. Background Art

[0002] Rubber materials are widely used in seals of pressure vessels as an important component of pressure boundaries due to their good elasticity and rebound properties.

[0003] When rubber serves for a long time under long-term load conditions, stress relaxation will occur. Stress relaxation will reduce the rebound characteristics of the rubber, thereby reducing the sealing force between the sealing interfaces, which is insufficient to achieve the sealing effect and may damage the integrity of the pressure vessel, causing sealing failure.

[0004] Like all polymers, when rubber is exposed to high temperature, radiation and other working environments, it will age. Aging will promote the process of stress relaxation and cause the rubber seal to fail prematurely.

[0005] Currently, the failure time of rubber is mainly determined through experiments. During the test, the test temperature is often increased to promote rubber aging, thereby reducing the test time. However, a theoretical system has not been established to quantitatively analyze the acceleration rate of rubber aging after increasing the temperature and predict the service life of rubber. Summary of the invention

[0006] In order to quantitatively analyze the accelerated rate of rubber aging, the present invention provides a method for quantitatively analyzing the accelerated rate of rubber aging based on a time-temperature equivalent factor.

[0007] The technical solution adopted by the present invention to solve the technical problem is: a rubber aging acceleration rate analysis method based on a time-temperature equivalent factor, the steps are as follows:

[0008] S1, based on DMA dynamic thermal analysis test and dynamic temperature scanning, according to the viscoelastic mechanical properties of different rubber samples studied, the relationship curve between dynamic modulus and time at different temperatures is constructed. This curve can reflect the corresponding relationship between temperature, dynamic modulus and time;

[0009] S2, based on the viscoelastic mechanical characteristic curve and the time-temperature equivalence principle, the dynamic modulus relaxation master curve of rubber under different rubber samples is drawn to construct the functional relationship E=f(t,T);

[0010] S3, according to the dynamic modulus relaxation master curve, based on the Arrhenius equation, the activation energy of rubber and the time-temperature equivalent factor Log(α T ), it can be found that the acceleration rate of the current temperature T relative to the reference temperature T0 depends on the time-temperature equivalent factor Log(α T );

[0011] S4, establish reference temperature T0, different temperatures T and Log(α T ) to determine the accelerated aging rate of rubber and analyze and predict the life of sealing materials.

[0012] Further, the DMA dynamic thermal analysis test steps in step S1 are as follows:

[0013] (11) Sample preparation: A total of 6 groups of cylindrical samples with a size of Φ28×3 mm were selected, including 1 group of unirradiated (0 kGy) and 5 groups of irradiated with different cumulative doses (150 kGy, 300 kGy, 400 kGy, 500 kGy and 650 kGy), with 3 identical samples in each group;

[0014] (12) Fixture installation: Use a compression fixture to clamp the cylindrical specimen in the instrument compression fixture, making sure that the fixture can apply the required stress;

[0015] (13) Temperature setting: The temperature range is set to -20°C to 120°C, and the heating rate is 1°C / min;

[0016] (14) Frequency setting: Fixed frequencies of 0.1 Hz, 0.2 Hz, and 0.4 Hz were set for sinusoidal periodic stress loading, and the change of storage modulus E' with temperature under different frequency loading was measured.

[0017] Further, in step S2, T0 is selected as the reference temperature, and the dynamic modulus relaxation curve at other temperatures T is translated along the horizontal axis to a position where it coincides with the dynamic modulus relaxation curve at the reference temperature T0, and the translated distance is recorded as log(α T ), the relationship between dynamic modulus and time at different temperatures is expressed as the following formula:

[0018] E(log(t),T)=E(log(t)-log(α T ), T0),

[0019] E(t, T) = E(t / α T , T0),

[0020] Then the dynamic modulus relaxation master curve at the reference temperature is drawn, so as to realize the prediction of long-term stress relaxation behavior at the reference temperature T0, where the modulus at time t at temperature T is equal to t / α at temperature T0. T The modulus of the moment is the same, where log(α T ) is the time-temperature equivalent factor, T is the current temperature, and T0 is the reference temperature.

[0021] Furthermore, based on the dynamic modulus relaxation curves at different temperatures, the application of the time-temperature displacement principle should include the following steps:

[0022] (21) The time-dependent isothermal dynamic modulus relaxation curves were determined by DMA dynamic thermal analysis tests at different temperatures T and within a limited time range;

[0023] (22) Based on the dynamic modulus relaxation curve at reference temperature T0, the time-temperature equivalent factor at different temperatures T is calculated. Where log is the logarithm with base 10; C1 and C2 are positive constants, which depend on the material and the reference temperature, and the dynamic modulus relaxation curve at different temperatures T is translated along the abscissa to a position where it coincides with the dynamic modulus relaxation curve at the reference temperature T0;

[0024] (23) The dynamic modulus relaxation master curve at the reference temperature T0 is plotted to show the relaxation modulus changes over a wide range of time.

[0025] Furthermore, the aging equation based on the Arrhenius equation in step S3 is: The Arenius activation energy E a is a constant that has nothing to do with temperature, R is the ideal gas constant (8.314 J / K*mol), T ref is the reference temperature.

[0026] The beneficial effect of the present invention is that the analysis method of the present invention can calculate the elevated temperature required for the accelerated test based on the acceleration ratio required at the reference temperature, thereby improving the accuracy of the material aging test and improving the material aging efficiency, and is suitable for life analysis and prediction of sealing materials in an aging environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the working principle of the dynamic thermomechanical analyzer;

[0028] Figure 2 is the relationship between temperature and storage modulus under non-irradiation dose;

[0029] Figure 3 It is the relationship diagram between dynamic modulus and time at different temperatures;

[0030] Figure 4 Dynamic modulus relaxation curves of non-irradiated samples at different temperatures;

[0031] Figure 5 is the master curve of dynamic modulus relaxation of the unirradiated sample at the reference temperature;

[0032] Figure 6 It is the main curve of dynamic modulus relaxation at reference temperature after different irradiation doses;

[0033] Figure 7is the fitting curve of the time-temperature equivalent factor. DETAILED DESCRIPTION

[0034] The present invention is further described in detail with reference to the accompanying drawings and embodiments as follows.

[0035] The technical route adopted by the present invention to solve its technical problem is: the stress relaxation of rubber is mainly reflected by the viscoelastic mechanical properties of rubber. The viscoelastic mechanical properties of different rubber samples are studied based on DMA dynamic thermal analysis test and dynamic temperature scanning. According to the viscoelastic mechanical property curve and combined with the time-temperature equivalence principle, the dynamic modulus relaxation master curve of rubber under different rubber samples is drawn. The activation energy and time-temperature equivalent factor Log(α T ), thereby determining the accelerated aging rate of rubber and predicting the life of rubber materials.

[0036] This embodiment takes the commonly used rubber sealing material EPDM (ethylene propylene diene monomer rubber) as an example, selects rubber samples after being irradiated with different radiation doses, studies its mechanical properties through DMA dynamic thermal analysis test, determines the time-temperature equivalent factor of rubber by establishing a dynamic modulus relaxation master curve, and constructs a rubber aging acceleration rate analysis method based on the time-temperature equivalent factor. The specific steps are as follows.

[0037] S1, based on DMA dynamic thermal analysis test and dynamic temperature scanning, according to the viscoelastic mechanical properties of different rubber samples studied, construct the relationship curve between dynamic modulus and time at different temperatures. This curve can reflect the corresponding relationship between temperature, dynamic modulus and time.

[0038] DMA (Dynamic mechanical analysis) is mainly used to measure the mechanical behavior of materials at different temperatures and frequencies. Under alternating stress of a fixed frequency, the test is carried out at a certain heating rate to obtain the storage modulus E' versus temperature curve.

[0039] The experimental instrument for DMA dynamic thermal analysis is DMAQ800 dynamic thermal mechanical analyzer, the schematic diagram is as follows Figure 1 The main test steps are as follows:

[0040] (11) Sample preparation: There are 6 groups of samples, including those without irradiation (0 kGy) and those after irradiation with different cumulative doses (150 kGy, 300 kGy, 400 kGy, 500 kGy and 650 kGy), with 3 identical samples in each group. The sample shape is cylindrical and the size is Φ28×3 mm.

[0041] (12) Fixture installation: Use a compression fixture and clamp the cylindrical specimen in the instrument compression fixture, making sure that the fixture can apply the required stress.

[0042] (13) Temperature setting: The temperature range is set to -20℃~120℃, and the heating rate is 1℃ / min.

[0043] (14) Frequency setting: Fixed frequencies of 0.1 Hz, 0.2 Hz, and 0.4 Hz were set for sinusoidal periodic stress loading, and the change of storage modulus E' with temperature under different frequency loading was measured.

[0044] The test results of the storage modulus E' under different loading frequencies with temperature are as follows: Figure 2 As shown, the unirradiated sample is taken as an example. The dynamic modulus relaxation master curves under different irradiation doses are plotted.

[0045] The Time-Temperature Equivalence Principle is a principle often used in materials science and engineering to predict material properties and conduct accelerated aging experiments. That is, within a certain range, increasing temperature and extending time have the same effect on material aging. Therefore, the long-term mechanical behavior of a material at room temperature can be predicted by measuring the short-term mechanical behavior of a material at high temperature.

[0046] S2, based on the viscoelastic mechanical characteristic curve and combined with the time-temperature equivalence principle, the dynamic modulus relaxation master curve of rubber under different rubber samples is drawn to construct the functional relationship E=f(t,T).

[0047] For the mechanical behavior of rubber materials, the curve of the relationship between the dynamic modulus and time does not change shape with the change of temperature. The relationship between the dynamic modulus and time at different temperatures is as follows: Figure 3 shown.

[0048] Select T0 as the reference temperature, and translate the dynamic modulus relaxation curves at other temperatures T along the horizontal axis to the position where they coincide with the dynamic modulus relaxation curves at the reference temperature T0. The translation distance is recorded as log(α T ), and then draw the dynamic modulus relaxation master curve at the reference temperature T0, so as to realize the prediction of long-term stress relaxation behavior at the reference temperature. The relationship between dynamic modulus and time at different temperatures is expressed as the following formula:

[0049] E(log(t),T)=E(log(t)-log(α T ), T0),

[0050] E(t, T) = E(t / α T , T0),

[0051] Where the modulus at time t at temperature T is equal to t / α at temperature T0 T The modulus of the moment is the same, where log(α T) is the time-temperature equivalent factor, T is the current temperature, and T0 is the reference temperature.

[0052] Based on the dynamic modulus relaxation curves at different temperatures mentioned above, the application of the time-temperature displacement principle should include the following steps.

[0053] (21) The time-dependent isothermal dynamic modulus relaxation curves were determined by DMA dynamic thermal analysis experiments at different temperatures T and within a limited time range.

[0054] (22) Based on the dynamic modulus relaxation curve at reference temperature T0, the time-temperature equivalent factor log(α T ), and translate the dynamic modulus relaxation curves at different temperatures T along the abscissa to a position where they coincide with the dynamic modulus relaxation curves at the reference temperature T0.

[0055] (23) The dynamic modulus relaxation master curve at the reference temperature T0 is plotted to show the relaxation modulus changes over a wide range of time.

[0056] The time-temperature equivalent factor log(α T ) can be determined by the Williams-Landel-Ferry (WLF) model, which expresses the variation of the displacement factor with temperature in the following form: Where log is the logarithm to base 10; C1, C2 are positive constants that depend on the material and the reference temperature.

[0057] According to the above DMA dynamic thermal analysis test results, the dynamic modulus relaxation curves of rubber samples at different temperatures after different irradiation doses can be obtained in logarithmic coordinates, such as Figure 4 shown.

[0058] Select reference temperature T0 = 30 °C, according to the above time-temperature equivalent factor log(α T ), C1 and C2 in the WLF model at the reference temperature T0 can be calculated. It should be noted that C1 and C2 in the WLF model are positive constants and depend on the reference temperature T0. Their values ​​are shown in the following table.

[0059] Taking the reference temperature T0 = 30℃ as the main curve, the results of translating the dynamic modulus relaxation curves at other different temperatures to the main curve are as follows: Figure 5 shown.

[0060] Figure 5 The dynamic modulus relaxation master curve at the reference temperature after translation is shown. The results show that when the dynamic modulus relaxation master curve time of EPDM rubber is t>1s, its dynamic modulus and relaxation time show a linear relationship in logarithmic coordinates, and can be expressed by the formula log 10 E(t)=log 10 E1sec +k D ·log 10 t is used to represent the change of dynamic modulus with relaxation time, where E 1sec is the dynamic modulus at relaxation time t = 1s, k D is the slope of the linear fit in logarithmic coordinates, reflecting the relaxation rate of the material.

[0061] By processing the DMA test results of the remaining samples in turn, the dynamic modulus relaxation master curves at the reference temperature after different irradiation doses can be obtained. The results are shown in Figure 6 shown.

[0062] S3, according to the dynamic modulus relaxation master curve, based on the Arrhenius equation, the activation energy of rubber and the time-temperature equivalent factor Log(α T ), it can be found that the acceleration rate of the current temperature T relative to the reference temperature T0 depends on the time-temperature equivalent factor Log(α T ).

[0063] The Arrhenius equation describes the relationship between chemical reaction rate and temperature. Within a certain temperature range, the activation energy E in the equation a Is a constant that has nothing to do with temperature. The aging equation at different temperatures satisfies: Where E a is the Arenius activation energy, R is the ideal gas constant (8.314 J / K*mol), T ref is the reference temperature.

[0064] The following table shows C1 and C2 of non-irradiated samples at a reference temperature of 30°C.

[0065] <![CDATA[C1]]> <![CDATA[C2]]> Reference temperature 4.5 212.6 30℃ .

[0066] Taking the unirradiated sample as an example, according to C1 and C2 and the aging equation proposed in Table 1, it can be calculated that at the reference temperature T ref = Log(α corresponding to different temperatures T at 30℃ T ), the calculation results are as follows Figure 7 shown.

[0067] As can be seen from the figure, the temperature displacement factor Log(α T ) and 1 / T are in accordance with the linear distribution, and a linear fit is performed on them, and the fitting result is: Goodness of fit R 2 =0.998, the slope of the fitting curve is E a / R is 1.90, and E is calculated aFor unirradiated EPDM rubber, the time-temperature displacement factor Log(α T ), when T = 150 ° C, the time-temperature displacement factor Log(α T ) is -1.79.

[0068] S4, establish reference temperature T0, different temperatures T and Log(α T ) to determine the accelerated aging rate of rubber and analyze and predict the life of sealing materials.

[0069] According to the time-temperature equivalence principle and Figure 4 It can be seen that for 150℃ and reference temperature 30℃, if the same mechanical properties are to be achieved, the aging time satisfies the following relationship log(t0)=log(t)-log(α T ), where t0 is the aging time required at a reference temperature of 30°C, and t is the aging time at 150°C. That is, the aging rate at 150°C is 61.7 times that at a reference temperature of 30°C, i.e., 1 / (10^log(α T )).

[0070] Based on the test results of DMA dynamic thermal analysis, the activation energy of EPDM rubber under different irradiation doses was calculated. According to the time-temperature equivalence principle, the activation energy can be used to further calculate the aging acceleration rate of EPDM rubber at different temperatures relative to the reference temperature.

[0071] Taking unirradiated EPDM rubber as an example, the activation energy E a The size is 15.85 kJ / mol, and the aging acceleration rate at 150°C is 61.7 times that of the reference temperature of 30°C.

[0072] The above embodiments are only illustrative of the principles and effects of the present invention, as well as some embodiments of its application. For those skilled in the art, several modifications and improvements may be made without departing from the creative concept of the present invention, and all of these belong to the protection scope of the present invention.

Claims

1. A rubber aging acceleration rate analysis method based on time-temperature equivalent factor, characterized in that: The steps are as follows S1, based on DMA dynamic thermal analysis test and dynamic temperature scanning, according to the viscoelastic mechanical properties of different rubber samples, the relationship curve between dynamic modulus and time at different temperatures is constructed; S2, draw the dynamic modulus relaxation master curve of rubber and construct the functional relationship E=f(t,T); S3, according to the dynamic modulus relaxation master curve, based on the Arrhenius equation, the activation energy of rubber and the time-temperature equivalent factor Log(α T ); S4, establish reference temperature T0, different temperatures T and Log(α T ) to determine the accelerated aging rate of rubber.

2. The rubber aging acceleration rate analysis method based on time-temperature equivalent factor according to claim 1 is characterized in that: The DMA dynamic thermal analysis test steps in step S1 are as follows: (11) Select one group of unirradiated and five groups of cylindrical samples irradiated with different cumulative doses with a size of Φ28×3mm, with three identical samples in each group; (12) Select a compression fixture and clamp the cylindrical specimen in the instrument compression fixture; (13) The temperature range is set to -20°C to 120°C, and the heating rate is 1°C / min; (14) Fixed frequencies of 0.1 Hz, 0.2 Hz, and 0.4 Hz were set for sinusoidal periodic stress loading, and the variation of storage modulus E' with temperature under different loading frequencies was measured.

3. The rubber aging acceleration rate analysis method based on time-temperature equivalent factor according to claim 2 is characterized in that: In the step S2, T0 is selected as the reference temperature, and the dynamic modulus relaxation curves at other temperatures T are translated along the horizontal axis until they coincide with the dynamic modulus relaxation curves at the reference temperature T0, and the translation distance is recorded as log(α T ), the relationship between dynamic modulus and time at different temperatures is expressed as: E(log(t),T)=E(log(t)-log(α T ),T0), E(t,T)=E(t / α T ,T0), The dynamic modulus relaxation master curve at the reference temperature is drawn to predict the long-term stress relaxation behavior at the reference temperature T0, where the modulus at time t at temperature T is equal to t / α at temperature T0. T The modulus of the moment is the same, where log(α T ) is the time-temperature equivalent factor, T is the current temperature, and T0 is the reference temperature.

4. The rubber aging acceleration rate analysis method based on time-temperature equivalent factor according to claim 3 is characterized in that: The steps to calculate the time-temperature equivalent factor are as follows: (21) The time-dependent isothermal dynamic modulus relaxation curves were determined by DMA dynamic thermal analysis tests at different temperatures T and within a limited time range; (22) Based on the dynamic modulus relaxation curve at reference temperature T0, the time-temperature equivalent factor at different temperatures T is calculated. Where log is the logarithm with base 10; C1 and C2 are positive constants, which depend on the material and the reference temperature, and the dynamic modulus relaxation curve at different temperatures T is translated along the abscissa to a position where it coincides with the dynamic modulus relaxation curve at the reference temperature T0; (23) The dynamic modulus relaxation master curve at the reference temperature T0 is plotted to show the relaxation modulus changes over a wide range of time.

5. The rubber aging acceleration rate analysis method based on time-temperature equivalent factor according to claim 1, 2, 3 or 4, characterized in that: The aging equation based on the Arrhenius equation in step S3 is: The Arenius activation energy E a is a constant that has nothing to do with temperature, R is the ideal gas constant, T ref is the reference temperature.

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