A load-carrying device

Abstract

This invention proposes a load-holding device, comprising a clamping mechanism, a coarse-adjustment lifting mechanism, a first strain gauge, and a fine-adjustment lifting mechanism. The clamping mechanism includes an upper clamping member and a lower clamping member for fixing both ends of the sample to be tested. The ends of the upper and lower clamping members facing away from the loaded sample are connected to a fatigue tensile testing instrument. The coarse-adjustment lifting mechanism and the fine-adjustment lifting mechanism are both disposed between the upper and lower clamping members, and are used to apply a force to the upper clamping member to drive it to move away from the lower clamping member. The first strain gauge is mounted on the sample for detecting the strain value of the sample. This device can achieve an equivalent replacement of the clamping force in the fatigue tensile testing instrument, ensuring that the sample remains under load throughout the disassembly and crack observation process, avoiding the influence of crack closure effects, and improving the accuracy of life prediction.

Description

[Technical Field]

[0001] This invention relates to the technical field of vehicle component life prediction, and in particular to a load-bearing device. [Background Technology]

[0002] Because traditional vehicle durability design and testing requirements do not favor life prediction experiments, users are often unaware of the accurate remaining lifespan of components during vehicle service. When faced with components exhibiting a clear tendency to fail, to prevent these components from becoming unusable during service, usable components with acceptable remaining lifespans are often directly replaced, resulting in significant unnecessary waste and increased manufacturing costs. Therefore, accurately predicting the remaining lifespan of vehicle components has high theoretical and practical value.

[0003] The key to accurate lifespan measurement lies in the accurate determination of the threshold value. Currently, there are three main methods for determining the threshold value:

[0004] 1. The first method is to use an in-situ machine independently developed by the Tonglu High Temperature Alloy Laboratory of Zhejiang University for observation. This machine can observe and record the evolution of the microstructure and failure fracture process of the sample in real time. This method can improve the accuracy of crack testing and make the test threshold value closer to the true value. However, since this in-situ machine places the tensile device under a scanning electron microscope for experimentation and observation, this method has the following drawbacks: First, to protect the electron microscope, the in-situ machine can only conduct fatigue tests at lower loading frequencies, and the tensile waveform that this in-situ tensile machine can currently load is only an approximate sine wave, which cannot simulate actual working conditions and cannot meet the testing requirements of actual working conditions; Second, due to the spatial limitations of the device design, the in-situ machine has high requirements for sample size, that is, it can only test the threshold value of small-sized samples and cannot realize the performance testing of engineering structural components; Third, since the in-situ machine requires the entire test to be conducted in an absolute vacuum environment, the test cannot simulate actual engineering environments such as corrosion, vibration, and swaying, and cannot be truly integrated into engineering application scenarios; Fourth, because the in-situ machine design is relatively complex, the experimental requirements during testing are relatively high, and the electron microscope needs to be repaired and maintained regularly, the human and material costs of developing and using the in-situ machine are relatively high.

[0005] 2. The second method involves measuring the crack length of the sample directly on the tensile instrument using a low-power microscope while the instrument is under load (i.e., the sample is clamped). (The high-power microscope cannot adjust the eyepiece to align with the tensile instrument for observation.) However, due to the low observation accuracy of the low-power microscope, it is difficult to capture points where the crack lengths are very close together (i.e., the threshold value) when the number of experiments is small. Generally, it takes many cycles of experiments to see the change in crack length. This directly leads to a large difference between the threshold value obtained from the test and the actual threshold value, resulting in inaccurate life prediction results. Furthermore, conducting experiments in this way increases the number of experimental cycles and increases time costs.

[0006] 3. The third method involves disassembling the test specimen under unloaded force (i.e., without clamping the specimen) and observing the crack length under an electron microscope. However, the stress state of the specimen changes before and after disassembly. The crack tip is unsupported by external forces after unloading. At this time, the elastic zone near the crack tip will constrain the plastic deformation of the plastic zone, causing the upper and lower surfaces of the crack to tend to close. At the same time, the shape of the crack tip undergoes irreversible changes, and the specimen cannot be used in the next crack test. To ensure the accuracy of crack length measurement, the tester usually discards the specimen after disassembling and measuring its crack length and selects a new specimen to reload the test. Although this slightly improves the accuracy of the measurement results, it consumes a lot of specimens, manpower, and time, which does not meet the requirements of sustainable development and violates the concept of green manufacturing.

[0007] In summary, existing experimental methods all involve directly clamping both ends of the sample in a tensile testing machine. If the sample is to be in a state of load retention, i.e., crack not closing, it must be clamped on the tensile testing machine. However, this method cannot simultaneously solve the problems of low measurement accuracy, severe sample wear, and inability to simulate real experimental conditions. In other words, the existing methods of conducting fatigue tests cannot meet the needs of actual engineering applications and cannot achieve the goal of accurately replacing failed parts during vehicle service. [Summary of the Invention]

[0008] The purpose of this invention is to solve the problems existing in the prior art and to propose a load-holding device that can achieve an equivalent replacement of the clamping force in the fatigue tensile instrument, ensuring that the sample is always in a load-holding state during disassembly and crack observation, avoiding the influence of crack closure effect, and improving the accuracy of life prediction.

[0009] To achieve the above objectives, the present invention proposes a load-holding device, comprising a clamping mechanism, a coarse adjustment lifting mechanism, a first strain gauge, and a fine adjustment lifting mechanism. The clamping mechanism includes an upper clamping member and a lower clamping member for fixing the two ends of the sample to be tested, respectively. The ends of the upper clamping member and the lower clamping member facing away from the loaded sample are respectively connected to a fatigue tensile instrument. The coarse adjustment lifting mechanism and the fine adjustment lifting mechanism are both disposed between the upper clamping member and the lower clamping member, and are used to apply a force to the upper clamping member to drive it to move away from the lower clamping member. The first strain gauge is mounted on the sample and is used to detect the strain value of the sample.

[0010] Preferably, the sample is positioned at the exact center of the clamping mechanism.

[0011] Preferably, when the coarse adjustment lifting mechanism and the fine adjustment lifting mechanism are not raised, no force is applied to the upper clamping member.

[0012] Preferably, the coarse adjustment lifting mechanism is mounted on the lower clamping member and includes two hydraulic jacks that can be raised and lowered synchronously, with the two hydraulic jacks symmetrically arranged on both sides of the sample to be tested.

[0013] Preferably, the two hydraulic jacks are controlled by a single hydraulic pump, so that the lifting and lowering amplitude of the two hydraulic jacks is the same each time.

[0014] Preferably, when the hydraulic jack's push rod is not raised, there is a gap between the end of the push rod and the upper clamping member.

[0015] Preferably, the first strain gauge is placed against the center of the side of the sample.

[0016] Preferably, the fine-tuning lifting mechanism includes two nut lifting assemblies, which are symmetrically arranged on both sides of the sample to be tested. Each nut lifting assembly includes a screw mounted on the lower clamping member and a lifting nut sleeved on the screw.

[0017] Preferably, a second strain gauge is installed on the screw of each of the two nut lifting assemblies.

[0018] Preferably, the second strain gauge is placed against the center of the side of the screw.

[0019] Preferably, the upper clamping member and the lower clamping member are respectively provided with mounting seats at opposite ends, and the two ends of the sample are respectively fixed on the mounting seats.

[0020] Preferably, the mounting base has several mounting holes, and the sample is connected to the mounting base by several bolts.

[0021] The beneficial effects of this invention are as follows: The load-bearing device of this invention ensures that the sample remains under load throughout the disassembly and crack observation process, thereby maintaining the shape and length of the crack tip. Furthermore, this device eliminates the crack closure effect caused by the sample being unloaded after disassembly, reducing experimental costs while improving the accuracy of lifespan prediction. This allows users to accurately determine whether parts need replacement based on their remaining lifespan during vehicle operation, significantly reducing manufacturing costs and aligning with the concept of sustainable development.

[0022] First, the load-bearing device can keep the sample under constant force before and after the fatigue tensile instrument is disassembled, so that the shape and length of the crack tip remain unchanged. This eliminates the crack closure effect caused by the sample being disassembled and no longer subjected to external force. Therefore, using this device will make the threshold value measurement results more accurate, reduce the experimental cost and improve the accuracy of life prediction, so that users can make a judgment on whether the parts need to be replaced based on the accurate remaining life value of the parts during the operation of the vehicle.

[0023] Secondly, testers can remove the load-bearing device containing the sample at any time to observe the failure propagation process of the microstructure in real time, obtain high-resolution, high-magnification real-time sequential SEM images, clarify the crack initiation and propagation laws, which is of great significance for studying the micro-mechanism of fatigue failure of various structural materials and provides an important and new experimental method for the study of fatigue crack initiation and propagation.

[0024] Third, it breaks away from the traditional mindset that samples can only be tested using tensile testing machines. It cleverly uses a mechanical device to achieve an equivalent replacement of the clamping force in fatigue tensile testing instruments, thereby achieving a load-bearing function for the sample. This ensures that the sample remains under load throughout disassembly and crack observation, while also having lower requirements for experimental space and sample size. The device's mechanical structure is ingenious and streamlined, and its operation is simple, significantly reducing both equipment and experimental costs. Furthermore, the entire experiment can be completed using only one sample, eliminating sample waste and aligning with the requirements of sustainable development and the concept of green manufacturing.

[0025] The features and advantages of the present invention will be described in detail through embodiments and in conjunction with the accompanying drawings. [Attached Image Description]

[0026] Figure 1 This is a schematic diagram of the structure of a load-carrying device according to the present invention;

[0027] Figure 2 yes Figure 1 Front view diagram.

Detailed Implementation Methods

[0028] See Figure 1 and Figure 2 The present invention provides a load-bearing device, including a clamping mechanism 1, a coarse adjustment lifting mechanism 2, a first strain gauge 3, and a fine adjustment lifting mechanism 5. The clamping mechanism 1 includes an upper clamping member 11 and a lower clamping member 12 for fixing the two ends of the sample 4 to be tested, respectively. The ends of the upper clamping member 11 and the lower clamping member 12 facing away from the loaded sample 4 are respectively connected to a fatigue tensile instrument. The coarse adjustment lifting mechanism 2 and the fine adjustment lifting mechanism 5 are both disposed between the upper clamping member 11 and the lower clamping member 12, and are used to apply a force to the upper clamping member 11 to drive it to move away from the lower clamping member 12. The first strain gauge 3 is installed on the sample 4 and is used to detect the strain value of the sample 4.

[0029] Furthermore, the sample 4 is positioned at the exact center of the clamping mechanism 1 to ensure that the sample 4 being tested is not affected by eccentric force.

[0030] Furthermore, when the coarse adjustment lifting mechanism 2 and the fine adjustment lifting mechanism 5 are not raised, no force is applied to the upper clamping member 11.

[0031] Furthermore, the coarse adjustment lifting mechanism 2 is mounted on the lower clamping member 12 and includes two hydraulic jacks that can be raised and lowered synchronously. The two hydraulic jacks are symmetrically arranged on both sides of the sample 4 to be tested. In this embodiment, the two hydraulic jacks are controlled simultaneously by a single hydraulic pump, so that the two hydraulic jacks raise and lower by the same amount each time. This achieves the effect that pressing one hydraulic pump can raise both hydraulic jacks to the same height simultaneously, ensuring that the sample 4 under test is not affected by eccentric force.

[0032] Furthermore, in this embodiment, the lower clamping member 12 has a U-shaped structure, with two concave mounting grooves symmetrically provided on the upper surfaces of both sides, and the bottoms of the two hydraulic jacks are fixedly installed in the mounting grooves.

[0033] Furthermore, when the hydraulic jack's push rod is not raised, there is a gap between the end of the push rod and the upper clamping member 11 to ensure that no force is applied to the upper clamping member 11, and the push rod surfaces of the two hydraulic jacks are arranged parallel to ensure that the sample 4 being tested is not affected by eccentric force. Specifically, in this embodiment, when the hydraulic jack's push rod is not raised, the upper surface of the push rod and the lower surface of the upper clamping member 11 maintain a reserved gap of 1-3 mm.

[0034] Furthermore, the first strain gauge 3 is attached to the center of the side of the sample 4 to ensure the accuracy of the test.

[0035] Furthermore, the fine-tuning lifting mechanism 5 includes two nut lifting assemblies, which are symmetrically arranged on both sides of the sample 4 to be tested. Each nut lifting assembly includes a screw mounted on the lower clamping member 12 and a lifting nut sleeved on the screw facing the upper clamping member 11. Before the lifting nuts are used to provide a lifting force to the upper clamping member 11, the upper surfaces of the two nut lifting assemblies maintain a 1-3mm clearance with the lower surface of the upper clamping member 11, and the upper surfaces of the two lifting nuts are parallel. Further, second strain gauges 50 are respectively installed on the screws of the two nut lifting assemblies. When adjusting the position of the lifting nuts, the changes of the second strain gauges 50 attached to the two screws are always the same, so that both provide the same lifting force to the upper clamping member 11, avoiding the influence of eccentric force. In addition, the second strain gauges 50 are attached to the center of the side of the screw to ensure the accuracy of the test. The lifting action of the lifting nuts can be adjusted and controlled by a digitally adjustable high-precision wrench.

[0036] Furthermore, each of the upper clamping member 11 and the lower clamping member 12 has a mounting base 10 at one of its opposite ends, and both ends of the sample 4 are fixed to the mounting base 10. In this embodiment, the mounting base 10 is provided at the middle position of the opposite ends of the upper clamping member 11 and the lower clamping member 12. A fixing end for connecting a fatigue tensile testing instrument is provided at the middle position of the opposite ends of the upper clamping member 11 and the lower clamping member 12.

[0037] Furthermore, the mounting base 10 is provided with a plurality of mounting holes, and the sample 4 is connected to the mounting base 10 by a plurality of bolts.

[0038] During the experiment, the upper clamping member 11 and the lower clamping member 12 were first fixed using a fatigue tensile instrument (not shown in the figure), and the sample 4 was installed on the mounting base 10 of the two clamping members by bolts. Then, the first strain gauge 3 was attached to the center of the side of the sample 4, and the two second strain gauges 50 were attached to the center of the side of the two screws respectively. When it is necessary to observe the crack length, first maintain the tensile force value of the fatigue tensile instrument at this crack length and record the strain value 'a' at this time; then begin unloading the tensile force of the fatigue tensile instrument, and press the hydraulic pump multiple times during the unloading process. When the lifting height exceeds the reserved height between the hydraulic jack and the upper clamp 11, the two hydraulic jacks will provide a lifting force to the upper clamp 11 together. At this time, the sample 4 under test is subjected to the combined action of the tensile force of the fatigue tensile instrument and the lifting force added to the upper clamp 11 by the hydraulic jack. Observe the value change of the second strain gauge 50 at all times, so that the strain value of the sample is always about 5 μm lower than the value 'a', until the tensile force of the fatigue tensile instrument is completely unloaded (by coarsely adjusting the lifting mechanism 2). The clamping mechanism 1 applies force, achieving a significant equivalent replacement of the tensile force of the fatigue tensile instrument. Then, by adjusting the lifting nut on the fine-tuning lifting mechanism 5, a lifting force is applied to the upper clamping part 11 to finely adjust the strain value. When the adjusted value is exactly the same as the initial strain value a and remains stable, the holding device can be removed from the fatigue tensile instrument (by applying force to the clamping mechanism 1 through the fine-tuning lifting mechanism 5, a small adjustment is achieved to replace the tensile force of the fatigue tensile instrument). Then, the holding device is placed under an electron microscope for observation, and the crack length of the sample 4 is observed and recorded. After the value is recorded, the device is placed back on the fatigue testing instrument, and this operation is repeated when the crack length needs to be observed again.

[0039] The load-holding device of this invention maintains the tested sample under load throughout the tensile test and crack observation process through strain equivalence. This avoids the crack closure effect that occurs after the sample is removed from the fatigue tensile instrument and no longer subjected to external force, thus ensuring that the crack condition of the sample remains unchanged before and after removal. In other words, a sample used in one experiment can still be used in the next experiment; all tensile tests can be completed using a single sample. This enables real-time and accurate determination of the threshold value, improving the accuracy of life prediction. Furthermore, it allows for the analysis of the microscopic mechanisms of crack initiation and propagation, significantly reducing experimental costs and providing a reference for subsequent life prediction experiments.

[0040] Implementation Case 1

[0041] Experiments have verified that this experimental device is feasible under various experimental conditions such as 1kN, 2kN, and 3kN. The following is an implementation case of the load-bearing device of the present invention when the maximum value is 1000N, the waveform is a square wave, the stress ratio is 0, and the load application frequency is 20Hz.

[0042] Using a universal tensile testing machine to clamp the bearing device of this invention, the strain value was recorded as 0 μm without any applied force. A constant tensile force of 1000 N was applied, and after the strain value detected by the first strain gauge 3 attached to the sample tended to stabilize, the strain value was recorded as 40 μm. At this time, the force of the universal tensile testing machine was unloaded, and the hydraulic pump was pressed repeatedly to keep the strain value as stable as possible. During this process, the strain value of the first strain gauge 3 was kept within the range of (a-10 μm) to (a-5 μm). After the force of the tensile testing machine was unloaded, the change in the strain gauge value was observed. The pressing was stopped when the strain value stabilized at 35 μm. At this time, the position of the lifting nut on the fine-tuning lifting mechanism 5 was adjusted to provide a lifting force to the upper clamping member 11. After the strain value stabilized at 40 μm, the device was removed from the tensile testing machine and placed flat on the table. It was found that the value of the first strain gauge did not change significantly.

[0043] Table 1. Variation of strain values ​​of the sample during the experiment.

[0044] Stress conditions of the device No force 1000N tensile force Hydraulic jack lifting force Hydraulic jack jacking force + jacking nut jacking force Strain value (μm) 0 40 35 40

[0045] This invention compares with three existing methods for determining threshold values:

[0046] The existing first method for determining the threshold value (i.e., using the in-situ machine independently developed by the Tonglu High-Temperature Alloy Laboratory of Zhejiang University) has the following problems when measured under the conditions of the above implementation case: (1) a load of this frequency cannot be applied; (2) a sample of this size cannot be clamped; and (3) a load of this waveform cannot be applied. Therefore, it can be seen that this method for determining the threshold value will not be feasible under the same experimental conditions.

[0047] Compared with the first method of determining the threshold value, this invention has the following advantages: Since the device is used to conduct the test on a standard universal testing machine, and then the device containing the sample is disassembled and placed under an electron microscope to observe the crack length and microstructure evolution process, the device has lower requirements for experimental space and sample size. It can achieve the same testing accuracy as an in-situ tensile testing machine, and can arbitrarily select the applied load frequency and waveform. It can use real-world samples to simulate the actual test conditions. Furthermore, the operation of this device is simple, and the device cost and experimental testing cost are low. It can fundamentally solve the problems that in-situ machines cannot simulate actual working conditions and that the machine equipment and experimental operation costs are high.

[0048] The existing second method for determining the threshold value (i.e., directly observing the crack using a low-magnification microscope while the tensile test is under load) has the following problems when measured under the conditions of the above implementation case: Measuring crack length using a low-magnification microscope results in low accuracy, the threshold value cannot be accurately determined, and the lifespan cannot be accurately predicted. Furthermore, this method for determining the threshold value, tested under the same experimental conditions, yielded results with low accuracy.

[0049] Compared with the second method of determining the threshold value, this invention has the following advantages: First, the tester can immediately remove the support device containing the sample at any time and measure the crack propagation length under an electron microscope, improving the accuracy of crack length observation. This allows for the observation of minute changes in crack length within a shorter cycle, significantly reducing the number of cycles and making the measured threshold value closer to the true threshold value. Second, since the device can be disassembled, the crack length on both sides of the sample can be observed under an electron microscope and averaged, greatly improving the accuracy of the crack length measurement data. Third, because the device can be disassembled and observed under an electron microscope in real time, changes in the crack tip structure can be observed at a microscopic level, allowing for further research into the mechanism of crack initiation and propagation.

[0050] The existing third method for determining the threshold value (i.e., directly observing the cracks in the disassembled sample using an electron microscope) has the following problems when measured under the conditions of the above implementation example: After testing the crack size of the sample once, since the sample is no longer under stress, it will be discarded, and a new sample will be needed to test the crack length again. This method of determining the threshold value, when tested under the same experimental conditions, will waste a large number of samples, significantly increasing the experimental cost.

[0051] Compared with the third method of determining the threshold value, this invention has the following advantages: This device can ensure that the sample is always under load during disassembly and crack observation, avoiding the crack closure effect caused by the sample being unloaded after disassembly. This ensures that the crack condition of the sample remains unchanged before and after disassembly, and the sample after one experiment can still be used for the next experiment. Only one sample is needed for the whole process, eliminating the need to repeatedly replace the sample, saving the time and cost of replacing the sample. It also avoids the experimental cost of starting fatigue testing on a new sample from 0, greatly reducing the manpower and material resources of the experiment.

[0052] In summary, this invention breaks away from the traditional mindset that testing can only be done by stretching samples using a tensile machine. It cleverly utilizes a streamlined mechanical structure to achieve precise determination of threshold values ​​with extremely low device and experimental operation costs and a simple experimental procedure. This improves the accuracy of lifespan prediction while enabling real-time observation of crack initiation and propagation, thereby facilitating the analysis of microscopic crack failure mechanisms. With accurate lifespan prediction values, users can accurately determine whether to replace components in scenarios with obvious failure tendencies. This reduces service costs and fundamentally lowers component manufacturing costs, truly achieving resource and energy conservation, improving resource utilization, and reducing energy consumption.

[0053] The above embodiments are illustrative of the present invention and are not intended to limit the present invention. Any simple modifications to the present invention are within the scope of protection of the present invention.

Claims

1. A load-carrying device, characterized in that: The device includes a clamping mechanism (1), a coarse adjustment lifting mechanism (2), a first strain gauge (3), and a fine adjustment lifting mechanism (5). The clamping mechanism (1) includes an upper clamping member (11) and a lower clamping member (12) for fixing the two ends of the sample (4) to be tested. The ends of the upper clamping member (11) and the lower clamping member (12) facing away from the loaded sample (4) are respectively connected to a fatigue tensile instrument. The coarse adjustment lifting mechanism (2) and the fine adjustment lifting mechanism (5) are both arranged between the upper clamping member (11) and the lower clamping member (12) for applying a force to the upper clamping member (11) to drive it to move away from the lower clamping member (12). The first strain gauge (3) is installed on the sample (4) for detecting the strain value of the sample (4).

2. The load-carrying device as described in claim 1, characterized in that: The sample (4) is positioned at the center of the clamping mechanism (1).

3. The load-carrying device as described in claim 1, characterized in that: When the coarse adjustment lifting mechanism (2) and the fine adjustment lifting mechanism (5) are not raised, no force is applied to the upper clamping member (11).

4. The load-carrying device as described in claim 1, characterized in that: The coarse adjustment lifting mechanism (2) is installed on the lower clamping member (12) and includes two hydraulic jacks that can be raised and lowered synchronously. The two hydraulic jacks are symmetrically arranged on both sides of the sample (4) to be tested.

5. A load-carrying device as described in claim 4, characterized in that: The two hydraulic jacks are controlled by a single hydraulic pump, ensuring that the lifting and lowering amplitude of the two hydraulic jacks is the same each time.

6. A load-carrying device as described in claim 5, characterized in that: When the hydraulic jack's push rod is not raised, there is a gap between the end of the push rod and the upper clamping member (11).

7. A load-carrying device as described in claim 1, characterized in that: The first strain gauge (3) is attached to the center of the side of the sample (4).

8. A load-carrying device as described in claim 1, characterized in that: The fine-tuning lifting mechanism (5) includes two nut lifting assemblies, and the two nut lifting assemblies are symmetrically arranged on both sides of the sample (4) to be tested. The nut lifting assembly includes a screw installed on the lower clamp (12) and a lifting nut sleeved on the screw.

9. A load-carrying device as described in claim 8, characterized in that: The two nut lifting assemblies each have a second strain gauge (50) installed on their screws.

10. A load-carrying device as described in claim 9, characterized in that: The second strain gauge (50) is attached to the center of the side of the screw.

11. A load-carrying device as described in claim 1, characterized in that: The upper clamping member (11) and the lower clamping member (12) are respectively provided with mounting bases (10) at their opposite ends, and the two ends of the sample (4) are respectively fixed on the mounting bases (10).

12. A load-carrying device as described in claim 11, characterized in that: The mounting base (10) has several mounting holes, and the sample (4) is connected to the mounting base (10) by several bolts.

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