A method of testing compression properties by a testing machine

Abstract

The application discloses a method for testing compression performance by a testing machine, and specific steps thereof comprise placing a sample on the upper end surface of a compression main body, making the two end surfaces of the sample parallel; after fixing is completed by an extensometer, the testing machine is zeroed, and the extensometer is zeroed; the testing machine is started to compress, the extensometer synchronously collects sample load data and average deformation data on both sides, and the above data are transmitted to the testing machine, and a stress-strain curve is generated by the testing machine, and compression yield strength, compression elastic modulus and compression strength are read from the curve. By directly hanging the double-side extensometer between the upper cover and the compression main body, a closed symmetrical measurement chain is formed, the two knife edges are located in the same rigid frame, the bending deformation is offset to each other, the reading difference is reduced to one tenth of the original, the load line and the measurement line are overlapped, the secondary force transmission path is avoided, the frame flexibility only affects the overall displacement and does not change the relative deformation in the extensometer gauge length, and therefore the elasticity modulus repeatability is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of material performance testing technology, and more specifically, to a method for testing compressive properties using a testing machine. Background Technology

[0002] Compression performance is a test performed on metallic materials using a specialized compression testing machine. During the test, the specimen deforms under axial static pressure until it reaches its compressive strength or fails. By recording the stress-strain relationship during the test, mechanical properties such as the material's elastic modulus, yield strength, and compressive strength can be analyzed.

[0003] The compressive properties of metallic materials are affected by a variety of factors, including the material's chemical composition, microstructure, and processing techniques. For example, the addition of alloying elements can significantly affect the material's hardness, strength, and toughness; while heat treatment processes can alter the material's microstructure, thereby affecting its mechanical properties.

[0004] In practical applications, the compressibility of metallic materials is crucial to their performance in various engineering applications. For example, in the aerospace field, materials need to withstand extremely high pressure and temperature, thus requiring excellent compressive strength and high-temperature stability; in automobile manufacturing, the compressibility of materials directly affects the crashworthiness and safety of the vehicle body.

[0005] The original compression test method used a dual-platform approach, placing the sample in the middle and fixing a dial indicator to one platform with a magnetic base, while the dial indicator's pointer rested on the other platform. This method lacked the ability to handle coaxiality, and the dial indicator required manual reading and recording, making the operation cumbersome, inefficient, and requiring multiple people to work together. Furthermore, interference factors were prone to occur during the test. Summary of the Invention

[0006] In order to overcome the above-mentioned defects of the prior art, the present invention provides a method for testing compression performance using a testing machine, so as to solve at least some of the technical problems mentioned in the background art.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for testing compression performance using a testing machine. The testing machine includes a testing body, a base, a compression body, and a top cover. The base is disposed on the testing body, and the compression body is disposed on the base. The testing body has a testing platform disposed opposite to the top cover, and the top cover is movable relative to the testing platform. The specific steps for testing compression performance using the testing machine are as follows:

[0008] Place the sample on the upper end face of the compression body, making the two end faces of the sample parallel; Extensometers are arranged on both sides of the sample, with one end of the extensometer fixed to the upper cover and the other end fixed to the compression body; After the extensometer is fixed, the testing machine is zeroed, and the extensometer is also zeroed. The testing machine is started to compress the sample. The extensometer simultaneously collects the sample load data and the average deformation data on both sides, and transmits the above data to the testing machine. The testing machine generates a stress-strain curve and reads the compressive yield strength, compressive elastic modulus and compressive strength from the curve.

[0009] The specific technical effects of this embodiment are as follows: By directly hanging the double-sided extensometers between the top cover and the compression body, a closed symmetrical measurement chain is formed, so that the blades on both sides are located within the same rigid frame, the bending deformation cancels each other out, the reading difference is reduced to one-tenth of the original, and the load line coincides with the measurement line, avoiding secondary force transmission paths. The frame flexibility only affects the overall displacement without changing the relative deformation within the extensometer gauge length, thereby significantly improving the repeatability of the elastic modulus. This structure also shortens the measurement chain length by about 30%, reduces the cumulative gap, and reduces the coaxiality error from 0.05 mm to below 0.02 mm. Moreover, the installation height is determined only by the screw depth of the top cover thread, which can accommodate samples of different heights without moving the base. Positioning, pre-tightening, and measurement are completed in one step, reducing the operation steps from four steps to two steps, which can be completed by one person. It provides a rigid, symmetrical, and short-chain mechanical platform for subsequent advanced functions such as rate jump and zero drift calibration.

[0010] Optionally, the specific steps for starting the testing machine to perform compression are as follows: The upper cover compresses the specimen downward at a first rate until the specimen is compressed to 40%-60% of the expected yield load F; The compression rate of the top cover is switched to the second rate to compress the sample downwards, and this is continued for a first predetermined time before the compression rate of the top cover is switched back to the first rate until the sample is compressed to the expected yield load F. The second rate is greater than the first rate.

[0011] The specific technical advantages of this implementation method are as follows: A rate jump is inserted into the elastic segment, and the elastic modulus is calculated in real time using transient stress and strain differences. Reasoning: In traditional single-rate loading, slow-varying errors such as frame flexibility and micro-slippage of the fixture can be introduced into the elastic segment, leading to a dispersion of the elastic modulus. At the instant of the rate jump, the stress state of the sample has not yet been redistributed; the stress and strain differences read at this time only reflect the elastic response of the material itself, eliminating slow-varying errors. The same sample can be used for both calibration and formal testing without additional standard samples, the process remains uninterrupted, and the total test time only increases by two seconds, yet the accuracy of the elastic modulus measurement is improved by one level.

[0012] Optionally, the second rate is at least five times the first rate.

[0013] The specific technical effects of this implementation are as follows: the larger the rate ratio, the more obvious the transient stress difference signal and the higher the signal-to-noise ratio. When the rate ratio reaches five times, the signal-to-noise ratio of the transient stress difference signal exceeds 20 decibels, and the standard deviation of the elastic modulus further decreases. At the same time, the stroke in the high-rate section is extremely short, and the elastic deformation of the locking ring only utilizes a small portion of its linear region, eliminating the risk of loosening and maintaining the reliability of the equipment.

[0014] Optionally, the first rate is 0.15-0.25 mm / min; And / or, the second rate is 1-3 mm / min; And / or, the first predetermined duration is 0.5-2 seconds.

[0015] The specific technical effects of this implementation are as follows: the first rate is low enough to ensure slow stress growth in the elastic segment, avoiding micro-yielding before the jump; the second rate is high enough to ensure that the strain readings during the switching time meet the ADC resolution requirements; the dwell time eliminates the rate build-up lag of the hydraulic testing machine, ensuring synchronous acquisition of stress and strain. These parameter ranges have been experimentally verified to obtain clear transient signals without damaging the specimen.

[0016] Optionally, the testing machine further includes an extension rod; the top end of the extension rod is fixedly connected to the upper cover, and the lower end of the extension rod is slidably mounted on the compression body; one end of the extensometer is fixed to the extension rod, and the other end is fixed to the compression body.

[0017] The specific technical advantages of this embodiment are as follows: the extension rod is rigidly connected to the upper cover by a thread, and the lower end is guided by a linear bearing, forming a closed chain of "hanging up and sliding down". The installation height of the extensometer can be continuously adjusted according to the sample thickness. Compared with the original base boss scheme, the length of the measuring chain is adjustable, compatible with samples of different heights, and the sliding guide eliminates lateral clearance, further reducing the probability of off-center loading.

[0018] Optionally, the testing machine further includes a locking ring; the locking ring is sleeved on the extension rod and elastically abuts against the upper cover to allow the extension rod to spring back upward.

[0019] The specific technical effects of this embodiment are as follows: the locking ring provides preload while retaining elastic compression margin. During speed jumps or micro-motion calibration, the locking ring can absorb micron-level displacement, preventing thread loosening; the preload ensures no relative slippage between the extension rod and the top cover, maintaining constant stiffness of the measuring chain during long-term testing, and reducing zero drift by more than half.

[0020] Optionally, the compression body has mounting ears protruding in all directions; the mounting ears are provided with vertical through holes and linear bearings located in the vertical through holes; the extension rod passes through the vertical through holes via the linear bearings.

[0021] The specific technical effects of this embodiment are as follows: the linear bearing transforms the sliding friction of the extension rod into rolling friction, reducing the coefficient of friction by two orders of magnitude, decreasing the thrust required for fine-motion calibration, and making the impact on the axial stress of the sample negligible. Simultaneously, the bearing eliminates lateral clearance, allowing the extension rod to move only axially, reducing the reading difference caused by off-center loading to one-tenth of its original value.

[0022] Optionally, during the compression process of the testing machine, after each second preset time period, the upper cover rises at a third rate and continues for a third preset time period before immediately descending to its initial position during the rise, and then continues to descend at the first rate to recompress the sample.

[0023] The specific technical effects of this embodiment are as follows: periodic micro-motion allows the extensometer to obtain an "in-situ calibration" opportunity during the test. The bearing-locking ring combination ensures that micro-motion only causes elastic deformation and does not loosen the specimen; the difference between the micro-motion start and end point readings directly reflects the current zero drift, without the need to disassemble the extensometer. In long-term tests, zero drift is subtracted in real time, and the fluctuation in yield strength determination is reduced by an order of magnitude.

[0024] Optionally, the first rate is at least twice the third rate.

[0025] The specific technical effects of this embodiment are as follows: the micro-motion rate is slow enough that the stress change caused by micro-motion is much smaller than the normal loading stress, avoiding additional damage to the sample; at the same time, the slow micro-motion provides the ADC with enough sampling points to ensure zero-drift reading resolution. When the rate ratio is greater than twice, the influence of micro-motion on the stress curve is minimized and cannot be distinguished by the naked eye, ensuring smooth original data.

[0026] Optionally, the second preset duration is 1-3 minutes; And / or, the third rate is 0.8-1.2 mm / min; And / or, the third preset duration is 0.2-0.4 mm.

[0027] The specific technical advantages of this implementation method are as follows: the 1-3 minute interval balances the timeliness of drift capture with system overhead; the 0.8-1.2 mm / min speed combined with the 0.2-0.4 mm stroke allows the micro-motion to be completed within 10-20 seconds, with minimal impact on the overall test rhythm. This parameter range has been verified over a long period of time and can control zero drift within 2 micro-strains without introducing additional hardware, significantly improving the repeatability of yield point determination. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of a testing machine according to the present invention; Figure 2This is a flowchart illustrating a method for testing compression performance using a testing machine according to the present invention.

[0029] The attached figures are labeled as follows: 1. Top cover; 2. Locking ring; 3. Through hole; 4. Extensometer; 5. Extension rod; 6. Compression body; 7. Base; 8. Sample. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] like Figure 1 The test machine shown includes a test body, a base 7, a compression body 6 and an upper cover 1. The base 7 is disposed on the test body and the compression body 6 is disposed on the base 7. The test body is provided with a test platform disposed opposite to the upper cover 1, and the upper cover 1 can be raised and lowered relative to the test platform.

[0032] As an optional implementation, the testing machine also includes an extension rod 5; the top end of the extension rod 5 is fixedly connected to the upper cover 1, and the lower end of the extension rod 5 is slidably mounted on the compression body 6; one end of the extensometer 4 is fixed to the extension rod 5, and the other end is fixed to the compression body 6. The extension rod 5 is rigidly connected to the upper cover 1 by threads, and the lower end is guided by a linear bearing to form a closed chain of "upward hanging and downward sliding". The installation height of the extensometer 4 can be continuously adjusted according to the sample thickness. Compared with the original base 7 boss scheme, the measuring chain length is adjustable, compatible with samples of different heights, and the sliding guide eliminates lateral clearance, further reducing the probability of off-center loading.

[0033] As an optional implementation, the testing machine also includes a locking ring 2; the locking ring 2 is fitted onto the extension rod 5 and elastically abuts against the upper cover 1 to allow the extension rod 5 to spring upward. The locking ring 2 provides preload while retaining elastic compression allowance. During rate jumps or micro-motion calibration, the locking ring 2 can absorb micron-level displacement, preventing thread loosening; the preload ensures no relative slippage between the extension rod 5 and the upper cover 1, maintaining constant stiffness of the measuring chain during long-term testing, and reducing zero drift by more than half.

[0034] As an optional implementation, the compression body 6 has mounting ears protruding in all directions; the mounting ears are provided with vertical through holes 3 and linear bearings located within the vertical through holes 3; the extension rod 5 passes through the vertical through holes 3 via the linear bearings. The linear bearings change the sliding friction of the extension rod 5 into rolling friction, reducing the coefficient of friction by two orders of magnitude, reducing the thrust required for fine-motion calibration, and making the effect on the axial stress of the sample negligible. At the same time, the bearings eliminate lateral clearance, allowing the extension rod 5 to move only axially, reducing the reading difference caused by off-center loading to one-tenth of its original value.

[0035] like Figure 2 As shown, the specific steps for testing compression performance using a testing machine are as follows: Place an aluminum alloy cylindrical sample with a diameter of 10 mm and a height of 15 mm on the upper end face of the compression body 6, and grind both ends of the sample flat to a parallelism of 0.01 mm to keep the two end faces parallel. Extensometers 4 are arranged on both sides of the sample. One end of the extensometer 4 is fixed to the upper cover 1, and the other end is fixed to the compression body 6. After the extensometer 4 is fixed, the testing machine is zeroed, and the extensometer 4 is also zeroed. The testing machine is started to compress the sample. The extensometer 4 simultaneously collects the sample load data and the average deformation data on both sides, and transmits the above data to the testing machine. The testing machine generates a stress-strain curve and reads the compressive yield strength, compressive elastic modulus and compressive strength from the curve.

[0036] By directly hanging the double-sided extensometers 4 between the upper cover 1 and the compression body 6, a closed symmetrical measurement chain is formed, so that the knife edges on both sides are located within the same rigid frame, the bending deformation cancels each other out, and the reading difference is reduced to one-tenth of the original. At the same time, the load line and the measurement line coincide, avoiding secondary force transmission paths. The frame flexibility only affects the overall displacement without changing the relative deformation within the gauge length of the extensometers 4, thereby significantly improving the repeatability of the elastic modulus. This structure also shortens the measurement chain length by about 30%, reduces the cumulative gap, and reduces the coaxiality error from 0.05 mm to less than 0.02 mm. Moreover, the installation height is determined only by the screw depth of the upper cover 1, and it can accommodate samples of different heights without moving the base 7. Positioning, pre-tightening, and measurement are completed in one step, reducing the operation steps from four steps to two steps, which can be completed by one person. It provides a rigid, symmetrical, and short-chain mechanical platform for subsequent advanced functions such as rate jump and zero drift calibration.

[0037] Example 1: The specific steps for starting the testing machine for compression are as follows: The compression program is initiated. The upper cover 1 descends at a first rate of 0.2 mm / min, loading to 50% of the expected yield load. The load is then stabilized, and the rate is instantly switched to a second rate of 2 mm / min and maintained for 1 second. It then descends back to 0.2 mm / min, continuing loading until the specimen yields. The stress and strain differences before and after the switch are recorded by the same clock and used to calculate the elastic modulus. The entire jump stroke is only 33 µm. The locking ring 2 absorbs the displacement through elastic deformation, resulting in no additional damage to the specimen. During subsequent loading, a micro-motion calibration is inserted every 2 minutes. The upper cover 1 rises 0.3 mm at a rate of 1 mm / min, immediately descends back to its original position, and continues compression at 0.2 mm / min. The entire micro-motion cycle is 20 seconds. The peak load change is less than 1% of the maximum load. The linear bearing ensures no lateral component of displacement. The difference between the extensometer 4 readings at the micro-motion start and end points is the current zero drift, which is subtracted in real time by the software. The testing machine synchronously acquires the load and the average deformation on both sides, generating a stress-strain curve. The compressive yield strength, compressive elastic modulus, and compressive strength are directly read from the curve.

[0038] The test results of 10 samples in the same batch in this embodiment are as follows: the average elastic modulus is 69.4 GPa, the relative standard deviation is 0.8%, the yield strength fluctuation is less than 1 MPa, the long-term zero drift is controlled within 2 µε, the total test time is the same as that of the conventional single-rate method, no additional hardware is required, and one person can complete the clamping test and calibration.

[0039] Example 2: The structure of the testing machine is exactly the same as that of Example 1, and the parameters are adjusted as follows: the first speed is 0.15 mm / min, the second speed is 1 mm / min, the second speed is 6.7 times the first speed, and lasts for 0.5 s; the micro-motion calibration is inserted once every 1 min, the third speed is 0.8 mm / min, the rise is 0.2 mm, and the cycle is 15 s.

[0040] Tests on 10 aluminum alloy samples from the same batch showed the following results: average elastic modulus 69.2 GPa, relative standard deviation 0.9%, long-term zero drift ≤2µε, and yield strength fluctuation <1MPa. Even with a rate ratio of 6.7 times, the transient signal-to-noise ratio remained >18dB, the micro-motion cycle was shortened to 1 minute, and zero drift was captured more frequently, making it suitable for test scenarios with rapid environmental temperature changes.

[0041] Example 3: The structure of the testing machine is exactly the same as that of Example 1, and the parameters are adjusted as follows: the first speed is 0.25 mm / min, the second speed is 3 mm / min, the second speed is 12 times the first speed, and lasts for 2 seconds; the micro-motion calibration is inserted once every 3 minutes, the third speed is 1.2 mm / min, the rise is 0.4 mm, and the cycle is 25 seconds.

[0042] Tests on 10 aluminum alloy samples from the same batch showed: average elastic modulus 69.5 GPa, relative standard deviation 0.7%, long-term zero drift ≤2µε, and yield strength fluctuation <1MPa. A 12x rate ratio resulted in a larger transient stress increment and a signal-to-noise ratio >22dB; a 3-minute micro-motion interval reduced the number of calibrations, making it suitable for ultra-long-duration tests (>4h); the utilization rate of the locking ring's elastic zone remained <10%, with no risk of loosening.

[0043] To verify long-term stability, the same sample was continuously loaded at a constant temperature of 22℃ for 4 hours, with a rate jump performed every 30 minutes and a micro-motion calibration performed every 2 minutes. The results showed that the elastic modulus fluctuated within the range of 69.3 to 69.5 GPa, with a relative change of less than 0.3%, and the yield strength reading drift did not exceed 0.5 MPa, proving that the closed symmetry chain and bearing guide structure can maintain micron-level repeatability during long-term operation. During the micro-motion calibration, the locking ring 2 provided a 50µm elastic stroke, but only 5µm was actually used, remaining within the linear elastic region. After 1000 cycles, the preload decayed by less than 2%, with no loosening. Under full dry lubrication conditions, the linear bearing's friction remained stable within 0.05 N, ensuring that the influence of the micro-motion thrust on the axial stress of the sample was below the detection limit. Within the rate jump segment, the second rate of 2 mm / min and the first rate of 0.2 mm / min form a 10-fold speed difference, making the transient stress increment clearly discernible. The signal-to-noise ratio remains above 20 dB, further reducing the uncertainty in the elastic modulus calculation. Throughout the entire test, the coaxiality deviation between the upper cover 1 and the compression body 6 remains within 0.02 mm, verifying the closed measurement chain's ability to suppress off-center loading. Ultimately, this embodiment achieves high-precision elastic modulus measurement, online zero-drift correction, and real-time off-center loading suppression using the original structure itself without adding any external sensors. The test efficiency is the same as the conventional single-rate method, but the repeatability of the elastic modulus is reduced from the industry-common 3% to 0.8%, and the fluctuation in yield strength determination is reduced from 3 MPa to less than 1 MPa.

[0044] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for testing compression performance using a testing machine, characterized in that: The testing machine includes a testing body, a base, a compression body, and a top cover. The base is disposed on the testing body, and the compression body is disposed on the base. The testing body has a testing platform opposite to the top cover, and the top cover can be raised and lowered relative to the testing platform. The specific steps for testing the compression performance using the testing machine are as follows: Place the sample on the upper end face of the compression body, making the two end faces of the sample parallel; arrange extensometers on both sides of the sample, with one end of the extensometer fixed to the top cover and the other end fixed to the compression body; after the extensometers are fixed, the testing machine is zeroed, and the extensometers are also zeroed; start the testing machine for compression, and the extensometers simultaneously collect the sample load data and the average deformation data on both sides, and transmit the above data to the testing machine, which generates a stress-strain curve and reads the compressive yield strength, compressive elastic modulus, and compressive strength from the curve; the specific steps for starting the testing machine for compression are as follows: The top cover compresses the sample downward at a first rate until the sample is compressed to 40%-60% of the expected yield load F; the compression speed of the top cover is increased. The compression rate of the upper cover is switched to a second rate to compress the sample downwards, and after a first predetermined time, the compression rate of the upper cover is switched back to the first rate until the sample is compressed to the expected yield load F; wherein, the second rate is greater than the first rate; during the compression process of the testing machine, after each second predetermined time, the upper cover rises at a third rate, and after a third predetermined time, it immediately descends to the initial position when it rose, and then continues to descend at the first rate to recompress the sample; wherein, the testing machine also includes an extension rod; the top end of the extension rod is fixedly connected to the upper cover, and the lower end of the extension rod is slidably mounted on the compression body; one end of the extensometer is fixed to the extension rod, and the other end is fixed to the compression body; the testing machine also includes a locking ring; the locking ring is sleeved on the extension rod and elastically abuts against the upper cover to allow the extension rod to rebound upwards; the compression body has mounting ears protruding in all directions; the mounting ears are provided with vertical through holes and linear bearings located in the vertical through holes; the extension rod passes through the vertical through holes through the linear bearings.

2. The method for testing compression performance using a testing machine according to claim 1, characterized in that: The second rate is at least five times the first rate.

3. The method for testing compression performance using a testing machine according to claim 1, characterized in that: The first rate is 0.15-0.25 mm / min; and / or, the second rate is 1-3 mm / min; and / or, the first predetermined duration is 0.5-2 s.

4. The method for testing compression performance using a testing machine according to claim 1, characterized in that: The first rate is at least twice the third rate.

5. The method for testing compression performance using a testing machine according to claim 1, characterized in that: The second preset duration is 1-3 min; and / or, the third rate is 0.8-1.2 mm / min; And / or, the third preset duration is 0.2-0.4 mm.

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