A test method for low cycle fatigue performance of seamless expansion joint mixture

Abstract

The application discloses a kind of low-cycle fatigue performance test methods of seamless expansion joint mixture, including S1, preparation, installation beam component and normal temperature conservation;S2, low-temperature pretreatment;S3, low-cycle fatigue loading;S4, real-time acquisition beam component in low-cycle fatigue loading stress and strain data;S5, extract each maximum tensile deformation rate under initial peak stress and each cycle under peak stress, and curve under different maximum tensile deformation rate is fitted;S6, is substituted into corresponding curve, and the low-cycle fatigue life prediction value is obtained.The application simulates the expansion deformation process of bridge structure under the action of temperature change by applying displacement control cyclic tensile loading to seamless expansion joint mixture specimen under low-temperature environment, and quantitatively evaluates the low-cycle fatigue life of seamless expansion joint mixture by combining peak stress attenuation law with cumulative dissipation energy analysis.

Description

Technical Field

[0001] This invention relates to the field of road engineering materials, and in particular to a method for testing the low-cycle fatigue performance of seamless expansion joint mixtures. Background Technology

[0002] Seamless expansion joints are an important structural element in bridges used to absorb beam deformation. Due to their advantages such as good integrity, high driving comfort, and low maintenance, they are widely used in urban and highway bridges. Seamless expansion joints are typically filled with asphalt or polymer-modified mixtures with a certain degree of flexibility and ductility. During their service life, they must withstand repeated tensile deformation caused by changes in ambient temperature, especially at low temperatures where material deformation and damage are more significant. Therefore, comprehensive testing of the expansion joint materials is essential in engineering projects to ensure their long-term stable service.

[0003] Existing fatigue performance evaluation methods for road engineering materials mostly focus on conventional asphalt mixtures. Test methods primarily include four-point bending fatigue tests, indirect tensile fatigue tests, or compression fatigue tests. Test control methods are mainly stress-controlled or small-deformation strain-controlled, and the number of cycles is usually high, primarily used to simulate high-cycle or mid-cycle fatigue behavior under vehicle loads. However, seamless expansion joint asphalt mixtures in actual engineering are mainly subjected to periodic expansion and contraction deformation caused by temperature changes. Their deformation amplitude is relatively large, and the number of cycles is relatively low, exhibiting typical low-cycle fatigue characteristics. The aforementioned conventional fatigue test methods are insufficient to reflect their true mechanical response and damage evolution process under service conditions.

[0004] Furthermore, existing performance evaluations of seamless expansion joint composites primarily focus on indicators such as high-temperature stability, low-temperature crack resistance, or static tensile properties, with insufficient attention paid to their fatigue performance under low-temperature, large-deformation conditions. Regarding fatigue life determination, some studies use obvious fracture or complete failure of the specimen as the criterion, ignoring the evolutionary characteristics of the material's gradual decrease in load-bearing capacity and accumulation of internal damage during repeated tensile processes. This makes it difficult to achieve quantitative evaluation of fatigue performance and effective comparison between different materials.

[0005] Therefore, there is an urgent need for a low-cycle fatigue test method that can simulate the actual stress and deformation conditions of seamless expansion joint mixtures in low-temperature environments. By using reasonable loading control methods and life determination indicators, the mechanical property decay and damage evolution of materials during cyclic tensile processes can be characterized, providing a reliable test basis for the performance evaluation, material selection and engineering application of seamless expansion joint mixtures. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a low-cycle fatigue performance test method for seamless expansion joint mixtures. This test method simulates the expansion and contraction deformation process of bridge structures under temperature changes by applying displacement-controlled cyclic tensile loading to seamless expansion joint mixture specimens in a low-temperature environment, and quantitatively evaluates the low-cycle fatigue life of seamless expansion joint mixtures by combining the peak stress decay law and cumulative dissipated energy analysis.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for testing the low-cycle fatigue properties of seamless expansion joint mixtures includes the following steps.

[0009] S1. After preparing the beam-type component and installing both ends of it on the loading component of the cyclic tensile testing device, it is cured at room temperature.

[0010] S2. Place the cured beam-type component on the loading component into a set low-temperature environment for low-temperature pretreatment.

[0011] S3. In a set low-temperature constant temperature environment, apply cyclic tensile-recovery loads n times to the pre-treated beam members with different set maximum tensile deformation rates to achieve low-cycle fatigue loading.

[0012] S4. Real-time acquisition of stress and strain data of beam components under low-cycle fatigue loading.

[0013] S5. Based on stress and strain data, extract the initial peak stress at each maximum tensile deformation rate. Peak stress at each cycle number And the peak stress versus the number of cycles under different maximum tensile deformation rates was obtained by fitting. curve;

[0014] S6, will Substitute the corresponding The n value obtained from the curve is the predicted low-cycle fatigue life of the seamless expansion joint mixture under the corresponding maximum tensile deformation rate.

[0015] In S1, the beam-type component is prepared according to the engineering mix proportion of the seamless expansion joint mixture; the two ends of the beam-type component are bonded to the loading component of the cyclic tensile test device.

[0016] In S5, under different maximum tensile deformation rates The expression for the curve is:

[0017]

[0018] In the formula, is the single-cycle attenuation of peak stress, and is the fitting coefficient.

[0019] In S3, there are one or more sets of maximum tensile deformation rates ranging from 5% to 9%.

[0020] In S5, under different maximum tensile deformation rates α The specific expression for the curve is:

[0021] .

[0022] It also includes S7, which substitutes the predicted low-cycle fatigue life obtained from S6 into the cumulative dissipation energy analysis for verification. Only the predicted low-cycle fatigue life that has passed the verification can be used as the final low-cycle fatigue life; otherwise, repeat S3 to S7 until the cumulative dissipation energy verification is passed.

[0023] In S7, the cumulative energy dissipation The expression is:

[0024] .

[0025] In S7, the method for determining whether the cumulative energy dissipation verification is qualified is as follows: substitute the predicted low-cycle fatigue life value into the corresponding cumulative energy dissipation value. The expression yields the cumulative energy dissipated due to failure. This energy is then compared with the cumulative energy dissipated due to failure of the same seamless expansion joint mixture under different maximum tensile deformation rates. If it conforms to the expected pattern, the verification is successful.

[0026] In S1, the length of the beam specimen is 150–250 mm, and the cross-sectional dimensions are 30–50 mm × 30–50 mm; the curing time at room temperature is 24 h.

[0027] In S2 and S3, the low temperature environment is -10±1℃, and the low temperature pretreatment time is not less than 2 h; in S3, the tensile rate of low cycle fatigue loading is 2 mm / min.

[0028] The present invention has the following beneficial effects:

[0029] 1. Based on the actual stress and deformation characteristics of seamless expansion joint mixtures, this invention adopts a cyclic tensile loading method with displacement control under low temperature conditions, which can realistically simulate the expansion and contraction conditions caused by temperature changes in bridges.

[0030] 2. This invention determines the number of fatigue failure cycles by analyzing the peak stress decay law and combines it with the cumulative dissipated energy for verification.

[0031] This verification is beneficial for characterizing the performance degradation and damage accumulation features of materials during low-cycle fatigue, and improves the reliability of fatigue life evaluation.

[0032] 3. The experimental process of this invention is continuous and the parameters are clear, with good operability and repeatability. It is suitable for low-cycle fatigue performance testing and engineering application analysis of different types of seamless expansion joint mixtures. Detailed Implementation

[0033] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.

[0034] A method for testing the low-cycle fatigue properties of seamless expansion joint mixtures includes the following steps.

[0035] S1. After preparing the beam-type component and installing both ends of it on the loading component of the cyclic tensile testing device, cure it at room temperature for about 24 hours. The length of the beam-type specimen is preferably 150-250 mm, and the cross-sectional dimensions are preferably 30-50 mm × 30-50 mm.

[0036] S2. Place the cured beam-type component on the loading component into a set low-temperature environment of -10±1℃ for low-temperature pretreatment for no less than 2 hours.

[0037] S3. In a set low-temperature constant temperature environment, apply cyclic tensile-recovery loads n times to the pre-treated beam members with different set maximum tensile deformation rates to achieve low-cycle fatigue loading.

[0038] The maximum tensile deformation rate of the above different settings is preferably one or more of 5% to 9%, and the tensile rate of low cycle fatigue loading is preferably 2 mm / min.

[0039] S4. Real-time acquisition of stress and strain data of beam components under low-cycle fatigue loading.

[0040] S5. Based on stress and strain data, extract the initial peak stress at each maximum tensile deformation rate. Peak stress at each cycle number And the peak stress versus the number of cycles under different maximum tensile deformation rates was obtained by fitting. The curve, the general expression is:

[0041]

[0042] In the formula, is the single-cycle attenuation of peak stress, and is the fitting coefficient.

[0043] At α = 5%~9%, The preferred expression for the curve is:

[0044] .

[0045] S6, will Substitute the corresponding The n value obtained from the curve is the predicted low-cycle fatigue life of the seamless expansion joint mixture under the corresponding maximum tensile deformation rate.

[0046] S7. Substitute the predicted low-cycle fatigue life obtained in S6 into the cumulative dissipation energy analysis for verification. Only the predicted low-cycle fatigue life that passes the verification can be used as the final low-cycle fatigue life; otherwise, repeat S3 to S7 until the cumulative dissipation energy verification passes.

[0047] The above dissipated energy The preferred method is to calculate it using the following method:

[0048]

[0049] in:

[0050]

[0051] In the formula, E n — Energy dissipated in the nth cycle, kPa; σ — Stress during the test, MPa; ε — Strain during the test, με.

[0052] The above dissipation energy The relationship between the number of iterations and the number of iterations is approximately linear, and can be calculated using the following linear formula:

[0053]

[0054] in: For the experience of the first The total cumulative energy dissipation of materials after each cycle.

[0055] The cumulative energy dissipation under the initial state or the selected starting cycle, in kPa.

[0056] This represents the average increase in energy dissipation generated per unit cycle.

[0057] With α = 5%~9%, the cumulative energy dissipation The preferred expression is:

[0058] .

[0059] The preferred method for determining whether the above-mentioned cumulative energy dissipation verification is qualified is to substitute the predicted low-cycle fatigue life value into the corresponding cumulative energy dissipation value. The expression yields the cumulative energy dissipated due to failure. This energy is then compared with the cumulative energy dissipated due to failure of the same seamless expansion joint mixture under different maximum tensile deformation rates. If it conforms to the expected pattern, the verification is successful.

[0060] The present invention will be further described in detail with reference to the following two preferred embodiments.

[0061] Example 1

[0062] S1. In this embodiment, a seamless expansion joint mixture commonly used in a certain engineering project is selected as the research object. Rutting plate specimens are prepared using a rutting test molding method according to the bridge engineering mix proportions, and beam-type specimens are obtained by cutting from the rutting plate specimens. The specimens are 200 mm long and have a cross-sectional dimension of 40 mm × 40 mm.

[0063] The two ends of the small beam specimen were bonded and fixed to the steel plate loading member using an epoxy adhesive, and cured at 25 ℃ for 24 h.

[0064] S2. After curing, place the fixed specimen in a constant temperature incubator at −10 ℃±0.5 ℃ for low temperature pretreatment for no less than 2 hours to ensure uniform temperature distribution inside the specimen.

[0065] S3. After completing the low-temperature pretreatment, a low-cycle fatigue tensile test was conducted on the specimen under a constant temperature of −10℃. The test adopted a displacement-controlled cyclic tensile-recovery loading method, and the tensile deformation rate was set to 2 mm / min. When the specimen was stretched to the preset maximum tensile deformation rate, it was unloaded at the same rate to return to the initial state, completing one cycle of tensile loading.

[0066] In this embodiment, two maximum tensile deformation rates of 5% and 8% are set. Ten cycles of tensile testing are carried out under each deformation rate condition to simulate the temperature-induced periodic expansion and contraction of seamless expansion joint mixture during actual service.

[0067] S4. During the test, the tensile force, tensile displacement and corresponding stress-strain data of the specimen are collected and recorded in real time to obtain a complete cyclic stress-strain curve.

[0068] The test results show that after 10 cycles of loading, the peak stress of the specimen under the condition of 5% maximum tensile deformation rate is about 0.80 MPa, and the residual stress rate is about 96%; under the condition of 8% maximum tensile deformation rate, the peak stress of the specimen is about 1.11 MPa, and the residual stress rate is about 87%.

[0069] S5. Based on the stress-strain data obtained from low-cycle fatigue tests, the peak stress corresponding to each cycle was extracted and statistically analyzed. The results show that under low-cycle fatigue tensile loading conditions, the peak stress of the seamless expansion joint mixture exhibits a significant monotonic decreasing trend with the increase of the number of cycles, and this decreasing process can be described by an approximately linear relationship.

[0070] Through linear regression analysis, peak stress attenuation models were established under different maximum tensile deformation rates (i.e., (curve), where:

[0071] The peak stress attenuation relationship under the condition of 5% maximum tensile deformation rate is as follows:

[0072]

[0073] The peak stress attenuation relationship under the condition of 8% maximum tensile deformation rate is as follows:

[0074]

[0075] S6. Using a peak stress attenuation to 50% of the initial peak stress as the filler for seamless expansion joints to achieve low-cycle fatigue failure.

[0076] The criteria for determining the fatigue failure state. Based on the peak stress decay model described above, the corresponding fatigue failure cycle count was calculated. Specifically, the low-cycle fatigue life under a 5% maximum tensile deformation rate condition was 129 cycles, and the fatigue life under an 8% maximum tensile deformation rate condition was...

[0077] The low-cycle fatigue life is 62 cycles.

[0078] Based on the stress-strain data obtained during the experiment, the single-cycle dissipation energy of the specimen during each cyclic loading process is calculated. The single-cycle dissipation energy is the area enclosed by the corresponding cyclic stress-strain curve. The single-cycle dissipation energy of each cycle is accumulated to obtain the cumulative dissipation energy of the specimen during the cyclic loading process.

[0079] Fitting analysis was performed on the relationship between cumulative energy dissipation and cycle number under different maximum tensile deformation rates. The results show that the cumulative energy dissipation exhibits a good linear growth trend with the increase of cycle number, and the relationship can be characterized by a linear model. The fitting results and corresponding energy parameters for each working condition are shown in the table below.

[0080] Table 1. Cumulative energy dissipation under different tensile deformation rates

[0081]

[0082] Substituting the fatigue failure cycle number determined based on the peak stress decay model into the above-mentioned cumulative dissipated energy fitting relationship, the cumulative dissipated energy at which the specimens reached fatigue failure under different loading conditions was calculated to be 602 kPa and 623 kPa, respectively, which are basically consistent. The results show that for the same seamless expansion joint mixture, under different maximum tensile deformation rates, its cumulative dissipated energy at failure is concentrated within a relatively stable range, indicating that the low-cycle fatigue life results determined based on the peak stress decay law have good rationality and consistency.

[0083] Example 2

[0084] S1. PTUR-40 seamless expansion joint compound rutting slab specimens were prepared using a rutting test molding method. The rutting slab specimens were cut into specimens with dimensions of 40mm×40mm×200mm. Before the test, the two ends of the specimens were bonded to a steel plate with a central opening size of 45mm×45mm×5mm using epoxy adhesive. The specimens were cured at room temperature (25℃) for 24 hours. After the epoxy adhesive was completely cured and the specimens were completely bonded to the steel plate, they were placed in an insulated box at -10℃±0.5℃ for 4 hours.

[0085] S2. After the heat preservation is completed, hang the two ends of the specimen on the customized tensile fixture with a size of 70mm×30mm on the UTM-25 testing machine, and conduct the test in a constant temperature chamber at -10℃.

[0086] S3. Displacement-controlled low-cycle fatigue tests were conducted on PTUR-40 composite specimens under constant temperature conditions of -10℃. The test adopted a cyclic tensile-recovery loading method, with the tensile deformation rate uniformly set to 2 mm / min. When the specimen was stretched to the preset maximum tensile deformation rate, it was unloaded at the same rate to restore it to the initial state, completing one complete cyclic tensile process.

[0087] In this embodiment, two maximum tensile deformation rate conditions were set: 6% and 9%. Under each deformation rate condition, the specimen was subjected to 10 cycles of tensile testing to simulate the deformation development and fatigue response process of seamless expansion joint mixture under multiple temperature cycles.

[0088] S4. Throughout the experiment, stress-strain data of the specimens were continuously collected and recorded to obtain complete stress-strain curves. The experimental results show that after 10 cycles of tensile testing, the peak stress under a 6% deformation rate was 1.40 MPa, with a residual stress rate of 91.0%; the peak stress under a 9% deformation rate was 1.54 MPa, with a residual stress rate of 83.0%, indicating that the degree of damage accumulation in the mixture significantly increases with the increase of the maximum tensile deformation rate.

[0089] S5. Based on the stress-strain curve data obtained during the low-cycle fatigue test, the corresponding stress peak value was extracted from each cycle of tensile testing, and its variation with the number of cycles was analyzed. The results show that under low-temperature low-cycle fatigue loading conditions, the stress peak value of PTUR-40 mixture exhibits a significant monotonic decay characteristic with the increase of the number of cycles, and this decay process can be approximately described by a linear relationship.

[0090] Through linear regression analysis, the stress peak attenuation equations under different maximum tensile deformation rates are obtained as follows:

[0091] Under the condition of 6% maximum tensile deformation rate:

[0092]

[0093] Under the condition of 9% maximum tensile deformation rate:

[0094]

[0095] S6. The criterion for PTUR-40 mixture to reach low-cycle fatigue failure state is the attenuation of the peak stress to 50% of the initial peak stress. By combining the above peak stress attenuation model with experimental data, the model parameters are calibrated, and the corresponding number of cycles n is solved as the predicted value of low-cycle fatigue life of the mixture under different deformation rate conditions.

[0096] The calculation results show that the predicted fatigue life of PTUR-40 mixture is 77 cycles under the condition of 6% maximum tensile deformation rate and 43 cycles under the condition of 9% maximum tensile deformation rate.

[0097] S7. To verify the rationality and stability of the low-cycle fatigue life prediction results based on stress peak decay, the cumulative dissipation energy index is further used to conduct a consistency analysis of the prediction results.

[0098] Statistical analysis of cyclic tensile test results of PTUR-40 mixture under different maximum tensile deformation rates revealed that the cumulative energy dissipation during each cycle exhibits an approximately linear growth trend with increasing cycle number. This variation can be characterized by a linear fitting relationship. The corresponding cumulative energy dissipation growth equation and calculation results are shown in the table below:

[0099] Table 2. Cumulative energy dissipation at different maximum tensile deformation rates

[0100]

[0101] The number of fatigue failure cycles predicted based on the stress peak decay model Substituting into the above cumulative dissipated energy growth equation, the cumulative dissipated energy of PTUR-40 mixture when it reaches fatigue failure under different deformation rates is calculated to be 779 kPa and 737 kPa, respectively. The difference between the two is about 5%, and the dissipated energy is basically the same.

[0102] The analysis results show that under different maximum tensile deformation rates, the cumulative energy dissipation of PTUR-40 mixtures during failure is concentrated within a relatively stable range, further verifying that the low-cycle fatigue life prediction method based on stress peak decay has good rationality and stability.

[0103] This invention prepares seamless expansion joint composite beam specimens and applies cyclic tensile-recovery loading using a displacement-controlled method under low-temperature conditions to simulate the expansion and contraction deformation process of bridge structures under temperature changes. Low-cycle fatigue tests are conducted by setting different maximum tensile deformation rates, and stress-strain data are collected during the tests. Based on the decay relationship of peak stress with the number of cycles, the fatigue failure cycle number of the material is determined, and the fatigue life is verified by combining the evolution law of cumulative dissipated energy, thereby obtaining the low-cycle fatigue life of the seamless expansion joint composite under different loading conditions. The method of this invention can realistically reflect the fatigue performance evolution characteristics of seamless expansion joint composite under low-temperature large deformation conditions and has good practicality.

[0104] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various equivalent transformations can be made to the technical solutions of the present invention, and these equivalent transformations all fall within the protection scope of the present invention.

Claims

1. A method for testing the low-cycle fatigue properties of seamless expansion joint mixtures, characterized in that: include: S1. After preparing the beam-type component and installing both ends of it on the loading component of the cyclic tensile testing device, cure it at room temperature. S2. Place the cured beam-type component on the loading component into a set low-temperature environment for low-temperature pretreatment. S3. In a set low-temperature constant temperature environment, apply cyclic tensile-recovery loads n times to the pre-treated beam members with different set maximum tensile deformation rates to achieve low-cycle fatigue loading. S4. Real-time acquisition of stress and strain data of beam components under low-cycle fatigue loading; S5. Based on stress and strain data, extract the initial peak stress at each maximum tensile deformation rate. Peak stress at each cycle number And the peak stress versus the number of cycles under different maximum tensile deformation rates was obtained by fitting. curve; S6, will Substitute the corresponding The n value obtained from the curve is the predicted low-cycle fatigue life of the seamless expansion joint mixture under the corresponding maximum tensile deformation rate.

2. The method for testing the low-cycle fatigue performance of seamless expansion joint mixtures according to claim 1, characterized in that: In S1, the beam-type component is prepared according to the engineering mix proportion of the seamless expansion joint mixture; the two ends of the beam-type component are bonded to the loading component of the cyclic tensile test device.

3. The method for testing the low-cycle fatigue performance of seamless expansion joint mixtures according to claim 1, characterized in that: In S5, under different maximum tensile deformation rates The expression for the curve is: ； In the formula, is the single-cycle attenuation of peak stress, and is the fitting coefficient.

4. The method for testing the low-cycle fatigue performance of seamless expansion joint mixture according to claim 3, characterized in that: In S3, there are one or more sets of maximum tensile deformation rates ranging from 5% to 9%.

5. The method for testing the low-cycle fatigue performance of seamless expansion joint mixture according to claim 4, characterized in that: In S5, under different maximum tensile deformation rates α The specific expression for the curve is: 。 6. The method for testing the low-cycle fatigue properties of seamless expansion joint mixtures according to claim 1 or 5, characterized in that: It also includes S7, which substitutes the predicted low-cycle fatigue life obtained from S6 into the cumulative dissipation energy analysis for verification. Only the predicted low-cycle fatigue life that has passed the verification can be used as the final low-cycle fatigue life; otherwise, repeat S3 to S7 until the cumulative dissipation energy verification is passed.

7. The method for testing the low-cycle fatigue performance of seamless expansion joint mixtures according to claim 6, characterized in that: In S7, the cumulative energy dissipation The expression is: 。 8. The method for testing the low-cycle fatigue performance of seamless expansion joint mixture according to claim 6, characterized in that: In S7, the method for determining whether the cumulative energy dissipation verification is qualified is as follows: substitute the predicted low-cycle fatigue life value into the corresponding cumulative energy dissipation value. The expression yields the cumulative energy dissipated due to failure. This energy is then compared with the cumulative energy dissipated due to failure of the same seamless expansion joint mixture under different maximum tensile deformation rates. If it conforms to the expected pattern, the verification is successful.

9. The method for testing the low-cycle fatigue properties of seamless expansion joint mixtures according to claim 1, characterized in that: In S1, the length of the beam specimen is 150–250 mm, and the cross-sectional dimensions are 30–50 mm × 30–50 mm; the curing time at room temperature is 24 h.

10. The method for testing the low-cycle fatigue performance of seamless expansion joint mixture according to claim 1, characterized in that: In S2 and S3, the low temperature environment is -10±1℃, and the low temperature pretreatment time is not less than 2 h; in S3, the tensile rate of low cycle fatigue loading is 2 mm / min.

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