Fatigue crack test method for turnout broken rail monitoring system

Abstract

The invention relates to a fatigue crack test of a turnout broken rail monitoring system, which takes a full-scale turnout assembly as a test object, preforms damage on a loading section to form a stress concentration point, performs vertical cyclic load loading by using a fatigue testing machine, and restores the process of a steel rail fatigue crack from initiation to expansion and fracture under a field working condition. The method is used for the fatigue crack monitoring test of the turnout broken rail monitoring system.

Description

Technical Field

[0001] The invention relates to the field of track detection and monitoring, and in particular to a fatigue crack test method for a turnout broken rail monitoring system. Background Art

[0002] The present invention relates to the field of rail transit safety monitoring technology, and in particular to a fatigue crack test method for a switch rail break monitoring system. As the weakest link in the line, the switch needs to be moved back and forth during service to realize the train lane changing function. However, during the frequent switching of the switch, movable components such as the point rail and the heart rail are subjected to large longitudinal cyclic forces, coupled with temperature forces and train cyclic loads, which pose a major structural safety hazard. In the process of analyzing on-road rail damage cases, it was found that most rail breakages were caused by the initiation of small cracks, which were mainly affected by vertical cyclic loads. Stress concentration was generated at the cracks and continued to expand until the rails broke.

[0003] Due to the sporadic and random nature of fatigue cracks in the field and the volume of system installations, it's difficult to evaluate the crack monitoring performance of existing turnout broken rail monitoring systems based on their ability to monitor cracks in the field. Existing evaluation systems are often based on the identification of simulated damage, but the relationship between simulated damage and fatigue cracks is difficult to quantify. Furthermore, small fatigue cracks are generally closed before propagation. The ability to identify simulated damage does not equate to the ability to monitor real fatigue cracks from initiation to propagation.

[0004] Therefore, a fatigue crack test method is needed to simulate the in-service working conditions of rails and reproduce the process of rail fatigue crack initiation and expansion from the stress concentration point, so as to verify the monitoring performance of the turnout broken rail monitoring system for fatigue cracks.

[0005] The paper "Study on the Vibration Fatigue Life of U71Mn Rails" uses long strip specimens with prefabricated damage and performs fatigue loading on a hydraulic vibration test bench until they fracture in order to study the vibration fatigue life of rails. In the paper "Study on the Fatigue Crack Propagation Characteristics of Rails", standard C(T) compact tensile specimens (40mm wide, 9.8mm thick, 8mm cut length) made by sampling from the rail head are fatigue loaded on an MTS fatigue loading machine to study the fatigue propagation life of rail cracks. This test method uses wire cutting to sample the rail head. The shape of the specimen and its stress state during fatigue testing are quite different from those of in-service rails. This test method is mostly used to verify the fatigue performance of the material itself. The test method and process cannot explain the consistency of its fatigue crack propagation law and fracture process with the laws related to in-service rails.

[0006] CN 115615779, "A method for opening the fracture surface of defects and damage in metal parts," proposes a method for opening the fracture surface of internal defects and damage in metal parts. The internal damage of the metal is located by ultrasonic positioning, and then the metal part with internal damage is accurately located and opened by adopting three-point bending and fatigue loading tests. This effectively and accurately opens the location of the damage, ensuring that the fracture penetrates the location of the crack source, which helps to find the crack source and conduct analysis. The test adopts a three-point bending method. The lower surface of the specimen is a support roller, and the contact relationship is line contact. The contact relationship of the lower surface of the specimen cannot be equivalent to the contact relationship between the slide bed and the bottom of the rail. Its stress state during fatigue testing is different from that of the in-service rail. The cross-section of the long strip specimen is regular, and the stress is simpler than that of the rail cross-section, and the fatigue expansion method is different. Summary of the Invention

[0007] Existing test methods for rail fatigue cracks are all based on tests using standard test blocks or homemade test blocks. Although the test blocks are all taken from rails, their structure is simple and the test process cannot restore the stress conditions of the rail under the influence of rail type and in-service conditions. These methods are limited to the study of fatigue cracks in the substrate itself and cannot be used to test and verify the fatigue crack monitoring capabilities of the switch broken rail monitoring system.

[0008] The purpose of the present invention is to provide a method for testing fatigue cracks in turnout rails. The turnout assembly section containing the test rails is used as the test object. Prefabricated damage is formed on the test rails to form stress concentration points. A fatigue testing machine is used to simulate the vertical load when a train passes, and fatigue cracks close to the on-site working conditions are created, so that the initiation and expansion of fatigue cracks can be monitored online by the turnout broken rail monitoring system.

[0009] To achieve the above objectives, the present invention adopts the following technical solutions: the test object is set as a turnout assembly section, the loaded rail is a component of the assembly, an artificial notch is prefabricated on the rail to form a stress concentration point, the assembly is laid on a full-scale test platform according to the on-site working conditions, the section where the notch is located is placed directly below the fatigue loading head to control the direction of crack propagation, and the load value, load ratio and loading frequency of the fatigue testing machine are set to simulate the fatigue load when a train passes, so that fatigue cracks initiate at the stress concentration point and propagate until the rail breaks.

[0010] The specific technical solutions are:

[0011] A turnout rail fatigue crack test system includes a test object, a fatigue test loading device, and a turnout rail breakage monitoring system. A full-scale turnout assembly is used as the test object, and a fatigue sample is a section of the full-scale turnout assembly. The test object is installed in a manner consistent with on-site working conditions and includes a test base rail, a point rail, a slide bed plate, a pad, and a turnout sleeper. The turnout rail breakage monitoring system is arranged near the test assembly, and a sensor is installed near one end face of the point rail and connected to the turnout rail breakage monitoring system via a signal cable.

[0012] Furthermore, the number of switch sleepers can be adjusted according to the test requirements and test site restrictions; the first nail hole, the second nail hole, the third nail hole and the fourth nail hole are distributed in the center of the switch sleeper in sequence, the distance between the first nail hole and the end face of the switch sleeper on the same side is L1, the distance between the fourth nail hole and the cross-section of the switch sleeper on the same side is L2, the distance between the first nail hole and the second nail hole is L3, and the distance between the third nail hole and the fourth nail hole is L4; the first nail hole, the second nail hole, the third nail hole and the fourth nail hole are symmetrically distributed along the longitudinal direction of the switch sleeper.

[0013] Furthermore, the distances L1 to L4 can be adjusted according to test requirements, and the number of nail holes can also be increased or decreased according to the design of the rail pad.

[0014] Furthermore, the full-size turnout assembly also includes a first short basic rail and a second short basic rail; through holes are opened on both sides of the rail head widening device, which is fixed to the rail heads of the first short basic rail and the second short basic rail through hexagonal bolts, flat washers, spring washers, and hexagonal nuts to prevent interference between the rail bottoms when the first short basic rail is in close contact with the second short basic rail and the point rail.

[0015] Furthermore, the full-size turnout assembly also includes a first short basic rail and a second short basic rail; one end of the rail head clamping device is close to the waist of the point rail, and the other end is tightly attached to the waist of the first short basic rail and the second short basic rail through a high-strength bolt and a nut welded on the clamping device, thereby achieving a close fit between the first short basic rail, the second short basic rail and the point rail.

[0016] Furthermore, the fatigue test loading device includes a loading head, the loading profile of the loading head adopts a contoured design, retains the contour direction of the rail head of the loading section, and has a built-in rail head of 1:40; during the test, the loading head is placed above the loading section, transmitting the loading load from the fatigue test loading device, and fatigue loading the point rail. The built-in rail head of 1:40 can prevent the loading head from moving during the loading process, so as to ensure the contact stability between the point rail and the loading head during the loading process.

[0017] Furthermore, the prefabricated damage is on the short limb side of the rail bottom of the loading section, and the prefabricated damage can also be set at any position of the rail head, rail waist and rail bottom according to the test requirements; the loading pressure head is aligned with the center of the loading section.

[0018] A fatigue crack test method for a turnout broken rail monitoring system, using the above-mentioned test system, is characterized by comprising the following steps:

[0019] S10: Set up pre-support defects and lay out test components;

[0020] S20: Install the switch broken rail monitoring system, debug the system signal, initialize the system parameters, and start signal acquisition;

[0021] S30: Initialize the fatigue test loading device and set loading parameters;

[0022] S40: Start fatigue loading;

[0023] S50: Pause loading periodically to observe the damage of the rails, perform flaw detection, and record the damage status;

[0024] S60: If the crack length L is ≥ 15 mm, proceed to step S70, otherwise return to step S40;

[0025] S70: Adjust the loading parameters and continue loading until the rail breaks.

[0026] Furthermore, in step S10, the loading head is vertically centered with the loading section during arrangement, and the fatigue loading device is located directly above the loading head; the effective test length is the distance from the sensor installation position to the loading section in the longitudinal direction of the test rail, and the lengths of the first short basic rail and the second short basic rail are appropriately adjusted with the effective test length to ensure that the loading section is centered between the two turnout sleepers.

[0027] Furthermore, in step S20, based on experience, the loading parameters are set as follows: the loading force is set to 100 kN to 300 kN, the loading frequency is controlled at 4 Hz to 5 Hz, the load ratio is 0.2, the load ratio is minimum load / maximum load, and the loading mode is sinusoidal loading.

[0028] Furthermore, the three loading parameters are set according to specific test requirements and working conditions.

[0029] Furthermore, in step S50, the pause timing is generally based on the number of cyclic loading times and the state of the rail crack propagation.

[0030] Furthermore, the alarm situation of the turnout broken rail monitoring system during the loading process is used as a reference.

[0031] Furthermore, in step S60, the crack length of 15 mm is an empirical value obtained after analyzing the fatigue crack section and can be adjusted according to test requirements.

[0032] Furthermore, there are two ways to adjust the loading parameters: increase the loading force, generally no longer adjusting the loading frequency; reduce the loading force, the loading force setting should not be lower than 100kN, and the loading frequency can be appropriately increased according to the performance of the fatigue testing machine.

[0033] The present invention has the following advantages due to the adoption of the above technical solution:

[0034] This invention is a fatigue crack test for a turnout rail breakage monitoring system. Using full-scale turnout components as test objects, the test involves prefabricating damage in the loading section to form stress concentration points. A fatigue testing machine is then used to apply vertical cyclic loads, recreating the process of rail fatigue crack initiation, expansion, and fracture under field conditions. This test is used for fatigue crack monitoring tests of turnout rail breakage monitoring systems. The main features are as follows:

[0035] 1. A fatigue crack monitoring method for a switch broken rail monitoring system uses full-scale switch components as the test object.

[0036] 2. The fatigue specimen is a full-scale turnout assembly section, and the installation method is consistent with the on-site working conditions, including the test base rail, point rail and slide bed plate, pad, turnout sleeper and other sub-rail foundations.

[0037] 3. The distance between the switch tie nail holes is symmetrically distributed along the longitudinal center of the switch tie, and two test components can be installed symmetrically at the same time. It is possible to carry out fatigue crack tests on both the component point rails and the single basic rails.

[0038] 4. During the component test, use the rail head clamping device to fix the base rail and the point rail laterally to prevent the point rail from moving laterally. A rail head widening device is installed in between to prevent interference from the rail bottom during loading.

[0039] 5. In order to facilitate the detection of crack propagation on the short limb side of the point rail, two short basic rails are used to replace the entire rail during the component point rail test, so that there is sufficient operating space on the short limb side of the loading section for flaw detection operations.

[0040] 6. Test rails with preset defects. Use a fatigue testing machine to conduct fatigue tests on rails with prefabricated defects. The prefabricated defects control the direction of crack propagation in the fatigue loading section.

[0041] 7. The fatigue crack test method can be applied to the initiation and propagation of fatigue cracks in rails required for the performance verification of most turnout broken rail monitoring systems. It is also applicable to broken rail monitoring systems for section lines. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 It is a layout diagram of the test assembly of the present invention;

[0043] Figure 2 This is a diagram of the nail holes of the switch sleeper of the present invention;

[0044] Figure 3 It is a schematic diagram of the rail head widening device of the present invention;

[0045] Figure 4 is a schematic diagram of the rail head clamping device of the present invention;

[0046] Figure 5 Schematic diagram of the loading head of the present invention;

[0047] Figure 6 It is a schematic diagram of the loading section and prefabricated damage of the present invention;

[0048] Figure 7 It is a test system diagram of the present invention;

[0049] Figure 8 It is a diagram of the steps of implementing the experiment of the present invention. DETAILED DESCRIPTION

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field are within the scope of protection of the present invention.

[0051] The present invention provides a fatigue crack testing method for a turnout rail breakage monitoring system, reproducing the entire process of crack initiation and propagation on an in-service rail from a stress concentration point. To achieve this objective, the test object is set as a turnout assembly section, with the loaded rail as a component of the assembly. A prefabricated artificial notch in the rail forms a stress concentration point. The assembly is laid on a full-scale test platform according to on-site working conditions, with the section containing the notch positioned directly below the fatigue loading head to control the direction of crack propagation. The fatigue testing machine load value, load ratio, and loading frequency are set to simulate the fatigue load of a passing train, and the rail is loaded, causing fatigue cracks to initiate at the stress concentration point and propagate until the rail breaks.

[0052] The turnout assembly section includes a stock rail 1, a point rail 2, a first short stock rail 3, a second short stock rail 4, a slide bed plate 7, and a vulcanized pad 8, which are fixed on the switch sleeper 9 according to the on-site working conditions.

[0053] Optionally, if there is no requirement for testing such as flaw detection, the first section of stock rail 3 and the second section of stock rail 4 may also be replaced by the stock rail 1 .

[0054] Optionally, the point rail 2 can be a point rail raw material for processing, and can also be processed into a point rail section with a specific cross-section according to test requirements.

[0055] In particular, the number of switch sleepers 9 can be adjusted according to the test requirements and test site limitations. The first nail hole 901, the second nail hole 902, the third nail hole 903 and the fourth nail hole 904 are distributed in the center of the switch sleeper 9 in the horizontal direction. The distance between the first nail hole 901 and the end face of the switch sleeper on the same side is L1, the distance between the fourth nail hole 90 and the cross-section of the switch sleeper on the same side is L2, the distance between the first nail hole 901 and the second nail hole 902 is L3, and the distance between the third nail hole 903 and the fourth nail hole 904 is L4. Generally, the first nail hole 901, the second nail hole 902 and the third nail hole 903 and the fourth nail hole 904 are symmetrically distributed along the longitudinal direction of the switch sleeper 9. Optionally, L1 to L4 can be increased or decreased according to test requirements or the special design of the rail pad.

[0056] The rail head widening device 5 has through holes 501 on both sides, and is fixed to the rail head of the stock rail 30 by means of hexagonal bolts 502, flat washers 503, spring washers 504, and hexagonal nuts 505 to prevent interference between the rail bottoms when the first short stock rail 3 is in close contact with the second short stock rail 4 and the point rail 2.

[0057] One end of the rail head clamping device 6 is close to the waist of the point rail 2, and the other end is tightly attached to the waists of the first short basic rail 3 and the second short basic rail 4 through a high-strength bolt 601 and a nut 602 welded on the clamping device 6, thereby achieving a close fit between the first short basic rail 3, the second short basic rail 4 and the point rail 2.

[0058] In particular, the loading profile 1102 of the loading ram 11 adopts a contoured design, retaining the rail head contour direction of the loading section 202, and a built-in rail head 1:40 (1101). During the test, the loading ram 11 is placed above the loading section 202, transmitting the loading load from the fatigue test loading device 10 to fatigue load the point rail 2. The built-in rail head 1:40 (1101) can prevent the loading ram 11 from moving during the loading process to ensure the contact stability between the point rail 2 and the loading ram 11 during the loading process. The loading load of the fatigue testing machine 10 should be able to set the loading force, loading frequency, and load ratio separately to meet the test requirements of different test stages.

[0059] The prefabricated damage 201 is located on the short side of the rail bottom of the loading section 202. Optionally, the prefabricated damage 201 can be placed at any position on the rail head, rail waist, or rail bottom according to test requirements. The indenter 11 and the loading head 90 are aligned with the loading section 202 in the center.

[0060] The switch rail monitoring system 12 is located near the test assembly, with sensor 1201 installed near the end face of the switch rail 2 and connected to the switch rail monitoring system 12 via a signal cable 1202. The sensor installation location and number can be adjusted appropriately based on the technical principles and methods used by the test switch rail monitoring system 12.

[0061] The test implementation steps are shown in the figure and include the following steps:

[0062] S10: Set up pre-support defects and lay out test components;

[0063] S20: Install the switch broken rail monitoring system 12, debug the system signal, initialize the system parameters, and start signal acquisition;

[0064] S30: Initialize the fatigue test loading device and set loading parameters;

[0065] S40: Start fatigue loading;

[0066] S50: Pause loading periodically to observe the damage of the rails, perform flaw detection, and record the damage status;

[0067] S60: If the crack length L is ≥ 15 mm, proceed to step S70, otherwise return to step S40;

[0068] S70: Adjust the loading parameters and continue loading until the rail breaks.

[0069] in,

[0070] S10: During placement, the loading ram 11 should be centered perpendicular to the loading section 202. The fatigue loading device should be located directly above the loading ram to prevent tilting during loading. The effective test length is the distance from the sensor installation location to the loading section in the longitudinal direction of the test rail. The lengths of the first short stock rail 3 and the second short stock rail 4 should be adjusted appropriately to the effective test length to ensure that the loading section 202 is centered between the two turnout sleepers.

[0071] S20: Based on experience, set the loading parameters: the loading force is set to 100 kN to 300 kN, the loading frequency is controlled at 4 Hz to 5 Hz, the load ratio (minimum load / maximum load) is 0.2, and the loading method is sinusoidal loading. Optionally, the above three loading parameters can be set according to the specific test requirements and working conditions.

[0072] S50: The pause time is generally based on the number of cyclic loading cycles and the state of rail crack expansion. Optionally, the alarm status of the switch rail break monitoring system during loading can be used as a reference. Ultrasonic testing can be used for flaw detection.

[0073] S60: The crack length of 15 mm is an empirical value obtained based on fatigue crack section analysis and can be adjusted according to test requirements;

[0074] S70: There are two ways to adjust the loading parameters. Optionally, increase the loading force, and generally no longer adjust the loading frequency, which can accelerate the rail fracture process and thus achieve the purpose of shortening the test time. Optionally, reduce the loading force. The loading force setting should not be lower than 100kN. According to the performance of the fatigue testing machine, the loading frequency can be appropriately increased to reduce the test time and shorten the test time as much as possible. By controlling the loading force, the expansion rate of fatigue cracks at a specific length can be purposefully increased or decreased, thereby obtaining more test data and different test samples, providing a basis for more comprehensive verification of the performance of the turnout rail break monitoring system.

[0075] The present invention is a fatigue crack test for a turnout rail breakage monitoring system. A full-scale turnout assembly is used as the test object. By prefabricating damage on the loading section to form a stress concentration point, a fatigue testing machine is used to perform vertical cyclic load loading. The process of rail fatigue crack initiation, expansion, and fracture under on-site working conditions is restored for use in the fatigue crack monitoring test of the turnout rail breakage monitoring system.

[0076] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A turnout rail fatigue crack test system, comprising a test object, a fatigue test loading device (10), and a turnout rail breakage monitoring system (12), characterized in that: A full-scale turnout assembly is used as the test object, and a fatigue sample is a section of the full-scale turnout assembly. The installation method is consistent with the on-site working conditions, and the turnout assembly includes a test base rail (1), a point rail (2), a slide bed plate (7), a pad (8), and a turnout sleeper (9). The turnout broken rail monitoring system (12) is arranged near the test assembly, and a sensor (1201) is installed near one end face of the point rail (2) and is connected to the turnout broken rail monitoring system (12) via a signal cable (1202).

2. The turnout rail fatigue crack testing system according to claim 1, characterized in that: The number of the switch sleepers (9) can be adjusted according to the test requirements and the test site restrictions; the nail holes of the switch sleeper (9) are distributed in the middle of the horizontal direction, namely the first nail hole (901), the second nail hole (902), the third nail hole (903) and the fourth nail hole (904); the distance between the first nail hole (901) and the end face of the switch sleeper on the same side is L1, the distance between the fourth nail hole (90) and the cross-section of the switch sleeper on the same side is L2, the distance between the first nail hole (901) and the second nail hole (902) is L3, and the distance between the third nail hole (903) and the fourth nail hole (904) is L4; the first nail hole (901), the second nail hole (902), the third nail hole (903) and the fourth nail hole (904) are symmetrically distributed along the longitudinal direction of the switch sleeper (9).

3. The turnout rail fatigue crack testing system according to claim 2, characterized in that: The distances L1 to L4 can be adjusted according to test requirements, or the number of nail holes can be increased or decreased according to the design of the rail pad.

4. The turnout rail fatigue crack testing system according to claim 1, characterized in that: The full-size turnout assembly further comprises a first short basic rail (3) and a second short basic rail (4); through holes (501) are opened on both sides of the rail head widening device (5), which is fixed to the rail heads of the first short basic rail (3) and the second short basic rail (4) by means of hexagonal bolts (502), flat washers (503), spring washers (504), and hexagonal nuts (505), so as to prevent interference between the rail bottoms when the first short basic rail (3) is in a state of close contact with the second short basic rail (4) and the point rail (2).

5. The turnout rail fatigue crack testing system according to claim 1, characterized in that: The full-size turnout assembly further comprises a first short basic rail (3) and a second short basic rail (4); one end of a rail head clamping device (6) is close to the waist of the point rail (2), and the other end thereof is tightly attached to the waists of the first short basic rail (3) and the second short basic rail (4) through a high-strength bolt (601) and a nut (602) welded on the clamping device (6), thereby achieving a close-fitting state between the first short basic rail (3), the second short basic rail (4) and the point rail (2).

6. The turnout rail fatigue crack testing system according to claim 1, characterized in that: The fatigue test loading device (10) is connected to a loading pressure head (11); the loading profile (1102) of the loading pressure head (11) adopts a contoured design, retains the rail head profile direction of the loading section (202), and has a built-in rail head (1101); during the test, the loading pressure head (11) is placed above the loading section (202), transmits the loading load from the fatigue test loading device (10), and performs fatigue loading on the point rail (2); the built-in rail head (1101) can prevent the loading pressure head (11) from moving during the loading process, thereby ensuring the contact stability between the point rail (2) and the loading pressure head (11) during the loading process.

7. The turnout rail fatigue crack testing system according to claim 6, characterized in that: The prefabricated damage (201) is located on the short limb side of the rail bottom of the loading section (202). The prefabricated damage (201) can also be located at any position of the rail head, rail waist and rail bottom according to test requirements. The loading pressure head (11) is aligned with the loading section (202) in the center.

8. A fatigue crack test method for a switch broken rail monitoring system, using the test system according to claims 1-8, characterized in that: The steps include: S10: Set up pre-support defects and lay out test components; S20: Install the switch rail breakage monitoring system (12), debug the system signal, initialize the system parameters, and start signal acquisition; S30: Initialize the fatigue test loading device and set loading parameters; S40: Start fatigue loading; S50: Pause loading periodically to observe the damage of the rails, perform flaw detection, and record the damage status; S60: If the crack length L is ≥ 15 mm, proceed to step S70, otherwise return to step S40; S70: Adjust the loading parameters and continue loading until the rail breaks.

9. The test method according to claim 8, wherein In the step S10, the loading pressure head (11) and the loading cross section (202) are vertically centered during arrangement, and the fatigue loading device (10) is located directly above the loading pressure head (11); the effective test length is the distance from the installation position of the sensor (1201) to the loading cross section (202) in the longitudinal direction of the test rail, and the lengths of the first short basic rail (3) and the second short basic rail (4) are appropriately adjusted with the effective test length to ensure that the loading cross section (202) is located in the center between the two turnout sleepers.

10. The test method according to claim 8, wherein In step S20, based on experience, the loading parameters are set as follows: the loading force is set to 100 kN to 300 kN, the loading frequency is controlled at 4 Hz to 5 Hz, the load ratio is 0.2, the load ratio is minimum load / maximum load, and the loading mode is sinusoidal loading.

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