Test and evaluation method for impact dynamic performance of composite structure of cement-based material of ballastless track
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- RAILWAY CONSTR RES INST OF CHINA ACAD OF RAILWAY SCI CO LTD
- Filing Date
- 2021-10-31
- Publication Date
- 2026-06-26
Smart Images
Figure CN116067805B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of performance testing of cement-based materials, specifically relating to the impact performance testing of cement-based materials. It is applicable to the dynamic performance evaluation of drop hammer impact of cement-based composite structures, and is particularly applicable to the dynamic impact performance evaluation of layered and embedded composite structures of cement-based materials for high-speed railway ballastless track. Background Technology
[0002] The track structure is a crucial component for transmitting train loads. All high-speed railways in my country with speeds exceeding 250 km / h utilize ballastless track structures. Ballastless track structures include slab track and twin-block track. Slab track is a layered composite structure consisting of steam-cured high-strength concrete track slabs and an emulsified asphalt mortar or self-compacting concrete filling layer. Twin-block track is an embedded composite structure consisting of steam-cured concrete sleepers and a cast-in-place concrete ballast bed. Research indicates that the cyclical impact loads from high-speed trains can easily lead to concrete cracking and delamination at the interfaces of layered and embedded composite structures, thus affecting the long-term durability and operational safety of the ballastless track. The impact resistance dynamic performance of cement-based composite structures is one of the key performance characteristics of ballastless tracks.
[0003] The drop hammer impact test is suitable for evaluating the impact performance of cement-based materials, and has the advantages of simple operation and intuitive results. ① The American Concrete Institute standard ACI 544.2R-1999 and industry standard CECS 13-2009 specify the drop hammer impact test method for fiber-reinforced concrete. However, the evaluation index of this method is mainly the cumulative impact energy, and the judgment is mainly based on the experience of the testers, which is highly subjective. ② The patent "A Fatigue Impact Test Device and Test Method for Concrete" (CN108051322B) proposes a fatigue impact test method for concrete materials, which can realize the automatic conduct of the drop hammer impact test. However, the termination criterion proposed by this method is the number of drop hammer impacts or the deformation of the strain gauge at the bottom of the concrete. This patent cannot obtain the changes in the surface morphology of the sample in real time during the drop hammer impact, and the method of judging the deformation by attaching strain gauges to the bottom of the sample is greatly affected by the impact test. ③ The patent "A Crack Detection Method in Bridge Images" (201910560712.1) proposes a crack detection method for bridge concrete. This method mainly analyzes existing bridge cracks through image processing. ④ Patent 201811168232.2, "A Method and Apparatus for Dynamic Non-destructive Testing of Joints in CRTSⅡ Type Slab Ballastless Track," proposes a method for detecting joints in ballastless track using ultrasonic pulse signals. This method achieves efficient and non-destructive testing of joints, but it cannot capture the dynamic damage process of cement-based materials during impact. It can be seen that existing standards and patents have the following drawbacks: the test objects are mostly single cement-based materials, lacking a method for evaluating the impact performance of special composite structures like ballastless tracks; existing methods often rely on manual observation to determine the presence of cracks, depending mainly on the experience of the test personnel, resulting in significant subjectivity; existing methods often use the cumulative impact energy at the initial crack as the evaluation standard, resulting in a single evaluation index and failing to comprehensively evaluate the dynamic impact performance of cement-based materials.
[0004] The purpose of this invention is to propose a method for evaluating the impact dynamic performance of layered and embedded composite structures of cement-based materials for ballastless track. This method not only calculates the cumulative impact energy at impact failure but also automatically records the sample surface state throughout the entire impact damage process. By capturing the sample surface morphology after each drop hammer impact using a high-definition camera, the method automatically analyzes the magnitude of lateral deformation and the number and total area of cracks and separations on the upper surface and interlayer interfaces. It also automatically calculates the cumulative impact energy and impact propagation coefficient, and uses multiple indicators to comprehensively evaluate the impact dynamic performance of the cement-based composite structure for ballastless track. Summary of the Invention
[0005] This invention addresses the impact resistance of composite structures for ballastless tracks in high-speed railways. It employs a drop hammer impact test combined with digital image analysis, overcoming the shortcomings of traditional methods such as complex operation, large result dispersion, strong subjectivity, and single evaluation index. It is particularly suitable for the impact dynamic performance testing and evaluation of layered and embedded composite structures of cement-based ballastless tracks in high-speed railways.
[0006] The method for testing and evaluating the impact dynamic performance of a cement-based composite structure for ballastless track is characterized by the following: test method.
[0007] The test steps are as follows: 1) A cement-based composite structure sample with a certain appearance size is obtained by casting or cutting; 2) The sample is taken out one day before the test and placed in the test room to air dry naturally. The appearance size of the sample is measured to an accuracy of 0.1 mm; 3) The sample is placed on the bracket, the clip is used to fix the position of the sample, and the sample is moved upward by the control system until it contacts the top support; 4) The analysis system is automatically turned on; 5) The control system selects the test mode and starts the drop hammer impact test; 6) The analysis system automatically records and analyzes the cracks and gaps on the sample surface based on the high-definition images captured; 7) When the test stop condition set in the corresponding test mode in step 5) is reached, the test is automatically stopped.
[0008] The method for testing and evaluating the impact dynamic performance of a cement-based composite structure for ballastless track is characterized by a drop hammer impact testing device.
[0009] The test setup consists of: 1) The drop hammer impact testing machine mainly consists of a bracket, motor, stranded wire, drop hammer, and sample chamber; 2) The ballastless track cement-based composite material specimen is fixed by clamps on the bracket platform, and the control system adjusts the vertical height of the specimen until it contacts the upper support; 3) The sample chamber is 600 mm × 400 mm × 400 mm in size, and six high-definition cameras are installed on the inner wall of the chamber; 4) The drop hammer is a stainless steel hemisphere of different diameters, and the counterweight can be adjusted by adding / removing weights to adjust the hammer head size and impact energy.
[0010] The method for testing and evaluating the impact dynamic performance of a cement-based composite structure for ballastless track is characterized by the sample structure and dimensions.
[0011] The sample structure and dimensions are as follows: 1) The test samples include two types: layered cement-based materials and embedded composite structures; 2) Type 1: Layered composite structure, with the upper layer being steam-cured high-strength concrete and the lower layer being C40 self-compacting concrete or emulsified asphalt mortar. The external dimensions of both the upper and lower cement-based materials are 400 mm × 200 mm × 100 mm; 3) Type 2: Embedded composite structure, with the embedded part being steam-cured high-strength concrete, with dimensions of 100 mm × 100 mm × 100 mm, and the outer part being cast-in-place concrete, with outer dimensions of 400 mm × 200 mm × 200 mm. The top surface of the embedded steam-cured concrete extends beyond the top of the cast-in-place concrete by a certain distance.
[0012] The method for testing and evaluating the impact dynamic performance of a cement-based composite structure for ballastless track is characterized by a digital image analysis method.
[0013] 1. The testing and analysis method is as follows: 1) Digital image analysis is used to capture the morphology of the upper surface and interlayer interface area of the sample after the drop hammer impact using a high-definition camera; 2) Based on the photos of the upper surface of the sample after each drop hammer impact captured by the high-definition camera, the lateral deformation of the sample in two directions is calculated by a self-written program in combination with the initial size of the sample; 3) The images captured by the high-definition camera are automatically converted into grayscale images, and after noise reduction processing, the cement-based materials, upper surface cracks and interface separations of each part of the sample are identified. When the grayscale value of a pixel is 0~50 and the distance in one direction exceeds 0.3 mm, it is judged as an upper surface crack or interface separation. The program automatically calculates the number and total area of upper surface cracks and interface separations; 4) When the first crack appears on the upper surface of the sample and no cracks are observed on the side, it is judged as the initial crack of the sample; 5) When the sample is identified as having a connected crack on the upper surface and side, it is considered that the sample has a whole through crack.
[0014] The method for testing and evaluating the impact dynamic performance of a cement-based composite structure for ballastless track is characterized by a drop hammer impact test mode.
[0015] The test modes are as follows: 1) Three modes can be adopted, all of which are automatically controlled by computer programs; 2) Mode 1: The test stops when the number of drop hammer impact tests reaches the set value; 3) Mode 2: The test stops when the composite structure initially cracks; 3) Mode 3: The critical value of impact damage of the composite structure is set, and the test stops when the composite structure develops a through crack or the total area of the interface gap reaches the critical value.
[0016] The method for testing and evaluating the impact dynamic performance of a cement-based composite structure for ballastless track is characterized by: evaluation indexes for the drop hammer impact performance of the sample.
[0017] The evaluation indicators are as follows: 1) The dynamic performance of the sample under drop hammer impact is evaluated by using multiple indicators, including cumulative drop hammer impact energy, impact expansion coefficient, lateral deformation magnitude, number and total area of cracks on the upper surface, and interface gap length and total area; 2) The cumulative drop hammer impact energy is calculated by E = m × g × h × N; 3) The number of impacts when the sample initially cracks is N1, and the number of impacts when a through crack occurs is N2. The impact expansion coefficient P = N1 / N2 is used to evaluate the impact expansion performance of the cement-based composite structure of ballastless track.
[0018] This invention conducts automated drop hammer impact tests on layered and embedded composite structures of cement-based materials for ballastless railway tracks. A high-definition camera captures the surface morphology of the sample after each impact, and a self-developed computer program automatically calculates the lateral deformation, surface cracks, number of interlayer gaps, and total area of the sample. It innovatively employs multiple indicators, including cumulative drop hammer impact energy, impact propagation coefficient, lateral deformation magnitude, number of surface cracks and interlayer gaps, and total area, to jointly evaluate the dynamic impact resistance of cement-based composite structures for ballastless railway tracks. This method boasts significant advantages, including the ability to accurately reproduce the physical structure of ballastless tracks, high intelligence, high accuracy of evaluation indicators, and strong comprehensiveness. It is particularly suitable for evaluating the dynamic impact resistance of high-speed railway ballastless track structures. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the experimental setup. In the diagram: 1: Motor 1; 2: Stranded wire; 3: Support platform; 4: Shadowless lamp; 5: Drop hammer; 6: Weight; 7: Column; 8: Guide tube; 9: Upper cover; 10: Pulley; 11: Guide tube door; 12: Support; 13: Sample chamber; 14: Cameras (6 in total) and control console; 15: Sample; 16: Clamp; 17: Bracket; 18: Motor 2; 19: Control console; 20: Computer. Detailed Implementation
[0020] The technical solution of the present invention will be further illustrated through embodiments and in conjunction with the accompanying drawings.
[0021] Example 1
[0022] This invention discloses a method for testing and evaluating the impact dynamic performance of cement-based composite structures for ballastless railway tracks. The specific implementation steps are as follows:
[0023] 1. Test specimens of cement-based composite structures for ballastless track were formed. The specimens were layered composite structures, with the upper layer being steam-cured high-strength concrete and the lower layer being emulsified asphalt mortar. The well-mixed emulsified asphalt mortar was poured into a 400 mm × 200 mm × 200 mm mold, with the emulsified asphalt mortar layer being 100 mm high. The steam-cured high-strength concrete specimen was then placed in the mold. After one day, the mold was removed, and the specimens were placed under standard conditions for further curing for 26 days.
[0024] 2. Remove the sample from the standard curing room and allow it to air dry naturally for 1 day. Use vernier calipers to measure the profile of the composite structure sample. The dimensions of the upper concrete layer are 401.5 mm × 199.3 mm × 99.1 mm, and the dimensions of the lower emulsified asphalt mortar layer are 401.1 mm × 201.3 mm × 100.8 mm.
[0025] 3. Place the sample on bracket 17 and secure it with clips 16. Use console 19 to lift the sample until it contacts the top support 12. At this point, the analysis system automatically activates, and the high-definition camera 14 acquires an image of the sample surface, autonomously identifying the upper high-strength concrete and the lower emulsified asphalt mortar.
[0026] 4. Open the duct 11 door, add two weights, each with a mass of 1 kg. The total mass of the drop hammer, weight 6, and connecting rod is 5 kg. Then close the duct 11 door.
[0027] 5. On the 19 control panel, set the drop hammer height to 500 mm, select test mode two: stop the test when the composite structure first cracks, and click the start button to start the drop hammer impact test.
[0028] 6. The computer analysis software automatically analyzes the photos of the upper surface and interface after each drop hammer impact, automatically calculates the size of the lateral deformation of the sample, the number of cracks on the upper surface and the number of interlayer gaps after each impact test, and displays the test results on the screen in real time.
[0029] 7. After 29 drops of the drop hammer impact test, the analysis system determined that the first crack appeared on the upper surface of the composite structure. At this point, the drop hammer impact test was stopped, and the single test ended. The cumulative drop hammer impact energy was 725 J. The maximum deformation of the sample in the x-direction was 0.7 mm, and there was no significant deformation in the y-direction. The total area of the cracks on the upper surface was 12.5 mm², and two delamination cracks appeared on the four sides, with a total area of 30.9 mm². The evaluation showed that the layered composite structure of the ballastless track cement-based material had good resistance to drop hammer impact.
[0030] Example 2
[0031] This invention discloses a method for testing and evaluating the impact dynamic performance of cement-based composite structures for ballastless railway tracks. The specific implementation steps are as follows:
[0032] 1. Test specimens of cement-based composite structures for ballastless track were formed. The specimens were layered composite structures, with the upper layer being steam-cured high-strength concrete and the lower layer being C40 self-compacting concrete. The well-mixed C40 self-compacting concrete was poured into a 400 mm × 200 mm × 200 mm mold, with the C40 self-compacting concrete layer being 100 mm high. The steam-cured high-strength concrete specimen was then placed in the mold. After one day, the mold was removed, and the specimens were placed under standard conditions for further curing for 26 days.
[0033] 2. Remove the samples from the standard curing room and allow them to air dry naturally for 1 day. Use vernier calipers to measure the profile of the composite structure samples. The dimensions of the upper layer of steam-cured high-strength concrete are 399.5 mm × 198.7 mm × 99.7 mm, and the dimensions of the lower layer of self-compacting concrete are 401.4 mm × 200.8 mm × 99.6 mm.
[0034] 3. Place the sample on bracket 17 and secure it with clips 16. Use console 19 to lift the sample until it contacts the top support 12. At this point, the analysis system automatically activates, and the high-definition camera 14 acquires an image of the sample surface, autonomously identifying the upper high-strength concrete and the lower self-compacting concrete.
[0035] 4. Open the duct 11 door, add two weights, each with a mass of 1 kg. The total mass of the drop hammer, weight 6, and connecting rod is 5 kg. Then close the duct 11 door.
[0036] 5. On the 19 control panel, set the drop hammer height to 500 mm, select test mode one: stop the test after 20 drop hammer impacts, and click the start button to start the drop hammer impact test.
[0037] 6. The computer analysis software automatically analyzes the photos of the upper surface and interface after each drop hammer impact, automatically calculates the size of the lateral deformation of the sample, the number of cracks on the upper surface and the number of interlayer gaps after each impact test, and displays the test results on the screen in real time.
[0038] 7. The drop hammer impact test automatically stops after reaching the set number of cycles. The cumulative drop hammer impact energy is 500 J. The sample shows no significant deformation in the x-direction, the maximum deformation in the y-direction is 0.6 mm, the total area of cracks on the upper surface is 5.8 mm², and one separation crack with a total area of 10.1 mm² is produced on the side. Evaluation shows that this layered composite structure of cement-based ballastless track exhibits excellent resistance to drop hammer impacts.
[0039] Example 3
[0040] This invention discloses a method for testing and evaluating the impact dynamic performance of cement-based composite structures for ballastless railway tracks. The specific implementation steps are as follows:
[0041] 1. Test specimens of cement-based composite structures for ballastless track. The specimens are embedded composite structures, with steam-cured high-strength concrete in the center and cast-in-place concrete around the perimeter. The well-mixed concrete was poured into a 400 mm × 200 mm × 200 mm mold, with a concrete layer height of 100 mm. After the concrete had slightly set, the steam-cured high-strength concrete specimens were placed in the molds. The molds were removed after one day, and the specimens were placed under standard conditions for further curing for 26 days.
[0042] 2. Remove the sample from the standard curing room and allow it to air dry naturally for 1 day. Use vernier calipers to measure the profile of the composite structure sample. The top surface dimensions of the central steam-cured high-strength concrete are 98.8 mm × 101.1 mm, the bottom surface dimensions of the lower concrete layer are 400.3 mm × 200.5 mm, and the overall height of the sample is 152.5 mm.
[0043] 3. Place the sample on bracket 17 and secure it with clips 16. Use console 19 to lift the sample until it contacts the top support 12. At this point, the analysis system automatically activates, and the high-definition camera 14 acquires an image of the sample surface, autonomously identifying the upper high-strength concrete and the lower self-compacting concrete.
[0044] 4. Open the duct 11 door, add two weights, each with a mass of 1 kg. The total mass of the drop hammer, weight 6, and connecting rod is 5 kg. Then close the duct 11 door.
[0045] 5. On the 19 control panel, set the drop hammer height to 500 mm, select test mode three: stop the test when the composite structure produces a through crack, and click the start button to start the drop hammer impact test.
[0046] 6. The computer analysis software automatically analyzes the photos of the upper surface and interface after each drop hammer impact, automatically calculates the size of the lateral deformation of the sample, the number of cracks on the upper surface and the number of interlayer gaps after each impact test, and displays the test results on the screen in real time.
[0047] 7. After 13 drops of the drop hammer impact test, the analysis software identified a through crack in the sample, at which point the drop hammer impact test stopped, and the single test ended. The cumulative drop hammer impact energy was 325 J. The maximum deformation of the sample in the x-direction was 3.3 mm, and there was no significant deformation in the y-direction. Three large cracks appeared on the upper surface of the sample, with a total area of 180.3 mm2. Three separation cracks appeared on the four contact surfaces, with a total area of 103.9 mm2. The evaluation concluded that the embedded composite structure of the ballastless track cement-based material has poor resistance to drop hammer impact.
[0048] The above description of the embodiments is provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the embodiments described herein, and any improvements and modifications made to the present invention by those skilled in the art based on the disclosure thereof should be within the scope of protection of the present invention.
Claims
1. A method for testing and evaluating the impact dynamic performance of cement-based composite structures for ballastless railway tracks, characterized in that: The test setup consists of a drop hammer impact testing machine, a control system, and an analysis system. The drop hammer impact testing machine automatically completes the impact test under program control. The control system is used to select different drop hammer impact test modes. The analysis system uses image processing technology to automatically calculate the lateral deformation and sample surface state of the cement-based composite structure during the drop hammer impact. The test subjects were cement-based composite structures for ballastless tracks, including two types: layered composite structures and embedded composite structures. The evaluation method involves using multiple indicators to jointly evaluate the impact resistance dynamic performance of the cement-based composite structure for ballastless track. The specific steps are as follows: 1) Using digital image analysis, a high-definition camera is used to capture the morphology of the upper surface and interlayer interface area of the sample after a drop hammer impact; 2) Based on the photos of the upper surface of the sample after each drop hammer impact captured by the high-definition camera, combined with the initial size of the sample, a self-written program is used to calculate the lateral deformation of the sample in two directions; 3) The images captured by the high-definition camera are automatically converted into grayscale images, and after noise reduction processing, the cement-based materials, upper surface cracks, and interface separations of each part of the sample are identified. When the grayscale value of a pixel is 0~50 and the distance in one direction exceeds 0.3mm, it is judged as an upper surface crack or interface separation. The program automatically calculates the number and total area of upper surface cracks and interface separations; 4) When the first crack appears on the upper surface of the sample and no cracks are observed on the side, it is judged as an initial crack in the sample; 5) When the sample is identified as having a connected crack on the upper surface and side, it is considered that the sample has a whole through crack.
2. The method for testing and evaluating the impact dynamic performance of a cement-based composite structure for ballastless track according to claim 1, characterized in that: The drop hammer impact testing machine consists of a bracket, a motor, stranded wire, a drop hammer, and a sample chamber; The specimen of the ballastless track cement-based composite material is fixed by a clamp on the bracket platform, and the control system adjusts the vertical height of the specimen until it contacts the upper support. The sample chamber measures 600mm × 400mm × 400mm, and six high-definition cameras are installed on the inner wall of the chamber. The drop hammer is a stainless steel hemisphere of different diameters, and the counterweight can be adjusted by adding or removing weights to adjust the hammer head size and impact energy.
3. The method for testing and evaluating the impact dynamic performance of a cement-based composite structure for ballastless track according to claim 1, characterized in that: The test objects include two types: layered composite structures and embedded composite structures; The layered composite structure consists of an upper layer of steam-cured high-strength concrete and a lower layer of C40 self-compacting concrete or emulsified asphalt mortar, with both layers of cement-based materials having external dimensions of 400mm×200mm×100mm. The embedded composite structure consists of an embedded layer of steam-cured high-strength concrete with dimensions of 100mm×100mm×100mm, and an outer layer of cast-in-place concrete with external dimensions of 400mm×200mm×200mm. The top surface of the embedded steam-cured concrete extends beyond the top of the cast-in-place concrete by a certain distance.
4. The method for testing and evaluating the impact dynamic performance of a cement-based composite structure for ballastless track according to claim 1, characterized in that: The drop hammer impact test can be conducted in three modes, all of which are automatically controlled by a computer program. Mode 1: The test stops when the number of drop hammer impact tests reaches a set value. Mode 2: The test stops when the composite structure shows initial cracks. Mode 3: A critical value for impact damage to the composite structure is set, and the test stops when the composite structure develops a through crack or the total area of the interface gap reaches the critical value.
5. The method for testing and evaluating the impact dynamic performance of a cement-based composite structure for ballastless track according to claim 1, characterized in that: The evaluation method is to use multiple indicators, such as cumulative drop hammer impact energy, impact expansion coefficient, lateral deformation magnitude, number and total area of cracks on the upper surface, and interface gap length and total area, to jointly evaluate the dynamic performance of the sample under drop hammer impact. The cumulative impact energy of the drop hammer is calculated using E=m×g×h×N; the number of impacts when the sample initially cracks is N1, and the number of impacts when a through crack occurs is N2. The impact propagation coefficient P=N1 / N2 is used to evaluate the impact propagation performance of the cement-based composite structure for ballastless track.