A test method for direct shear acoustic emission characteristics of UHPC key-stem joints

Abstract

The present invention discloses a direct shear acoustic emission characteristic test method for UHPC key tooth stem joints, belonging to the field of UHPC test technology, comprising S1, designing and preparing a UHPC specimen; S2, building a test system, including a loading device, an acoustic emission monitoring device, and a displacement and strain monitoring device; S3, testing the specimen through the test system and collecting corresponding data; S4, analyzing the data and revealing the shear stress behavior and damage failure mechanism of the stem joint under different parameter settings of the specimen in combination with acoustic emission characteristic parameters. The direct shear acoustic emission characteristic test method for UHPC key tooth stem joints provided by the present invention breaks through the limitations of traditional load-displacement curves, crack observation and other methods, realizes real-time, continuous, multi-stage monitoring, and comprehensively grasps the damage evolution dynamics.

Description

Technical Field

[0001] The present invention relates to the field of UHPC testing technology, and in particular to a method for testing direct shear acoustic emission characteristics of UHPC key-stem joints. Background Art

[0002] In the field of bridge engineering, UHPC (ultra-high performance concrete) is increasingly being used in segmental bridge structures due to its excellent mechanical properties. Key transportation facilities such as airport boarding bridges, connecting terminals to aircraft, often utilize UHPC segmental bridges. However, the key-stem joint, a critical structural force transmission point, becomes a weak link in shear resistance due to discontinuous reinforcement and discontinuous steel fiber distribution. During service, bridges must withstand complex forces such as vehicle loads and environmental vibrations. Key-stem joints are susceptible to micro-damage initiation and progressive development, threatening structural safety.

[0003] The key-stem joints of UHPC segmental bridges are weak links in shear resistance due to discontinuous reinforcement and intermittent steel fiber distribution. Traditional detection methods (such as load-displacement curves and crack observation) struggle to capture the evolution of internal microdamage in real time. However, acoustic emission technology can monitor the material's cracking process through elastic wave signals. Existing research shows that the shear performance of UHPC key-stem joints is significantly affected by factors such as lateral stress, key parameters (such as depth-to-height ratio and spacing-to-height ratio), and fiber content. However, a quantitative correlation model between acoustic emission characteristic parameters and mechanical response is lacking. Therefore, a full-process damage monitoring method integrating acoustic emission technology is urgently needed. Summary of the Invention

[0004] The purpose of the present invention is to provide a direct shear acoustic emission characteristic test method for UHPC key-tooth joints. By synchronously collecting acoustic emission characteristic parameters and mechanical data, the entire process of damage initiation, expansion and failure in the shear process of the joint can be monitored, providing a theoretical basis for optimizing joint design and bearing capacity calculation.

[0005] To achieve the above object, the present invention provides a method for testing the direct shear acoustic emission characteristics of UHPC key-tooth joints, comprising the following steps:

[0006] S1. Design and prepare UHPC specimens;

[0007] S2. Build the test system, including the loading device, acoustic emission monitoring device, and displacement and strain monitoring device;

[0008] S3. Test the specimen through the test system and collect corresponding data;

[0009] S4. Analyze the data and combine it with the acoustic emission characteristic parameters to reveal the shear stress behavior and damage failure mechanism of the dry joint under different parameter settings of the specimen.

[0010] Preferably, the loading device in step S2 adopts an electro-hydraulic servo press, which is equipped with a prestressed screw to apply lateral stress; the acoustic emission monitoring device adopts several sensors to respectively collect acoustic emission characteristic parameters, including amplitude, energy, count, duration, rise time and average frequency; the displacement and strain monitoring device adopts a micrometer to measure vertical slip, and a strain gauge is attached to the root of the key tooth to monitor stress concentration.

[0011] Preferably, in step S3, a loading control method is used, which is divided into two stages: preloading and formal loading. The same load level is used in the two stages, and the acoustic emission signal, load-displacement data and strain data are recorded respectively. Before the test, The shear bearing capacity of the specimen is estimated, where is the area of ​​the plane interface, is the lateral compressive stress on the joint, is the friction coefficient of the joint; at the same time, the shear bearing capacity of the key joint specimen is estimated using the following formula:

[0012] ;

[0013] in, is the joint surface area; is the ultimate tensile strength of the specimen.

[0014] Preferably, step S4 specifically includes the following steps:

[0015] S41. Analyze the characteristic parameters of acoustic emission to clarify the development trend from microcracks to damage cracks, and provide data information for the final failure mode and failure mechanism;

[0016] S42. Construct a mechanical-acoustic emission coupling model that correlates mechanical response with acoustic emission characteristics to understand the damage and failure process of the specimen;

[0017] S43. Considering the lateral compressive stress, key tooth geometric parameters, and fiber content, a bearing capacity prediction model is established in combination with the acoustic emission characteristic parameters. Thus, a quantitative relationship between the above parameters and the bearing capacity of the UHPC key tooth joint is established to achieve the prediction of the bearing capacity.

[0018] Preferably, step S41 specifically includes:

[0019] Microcrack identification: Amplitude <40dB, corresponding to early damage inside the key teeth, the calculation formula is:

[0020] ;

[0021] in, For the The amplitude of the acoustic emission event, is the indicator function;

[0022] Macro crack expansion: 40dB≤amplitude≤60dB, corresponding to the crack expansion at the root of the key tooth, the energy release rate formula is: ;in, is the energy of a single event, is the time interval;

[0023] Destruction crack determination: Amplitude > 60dB, corresponding to key tooth shear failure, sound source coordinate calculation based on time difference positioning method:

[0024] ;

[0025] in, is the sensor coordinate, is the signal arrival time, is the elastic wave velocity.

[0026] Preferably, the mechanical-acoustic emission coupling model in step S42 is based on the following association:

[0027] Cracking threshold determination correlation: a sudden increase in acoustic emission time rate corresponds to the cracking load , combined with the Mohr stress circle criterion formula , determine the critical state of the specimen starting to damage and crack from the perspectives of mechanics and acoustics;

[0028] Correlation between the ultimate failure point and the peak value of acoustic emission energy Corresponding limit load , based on the shear strength criterion formula , the moment when the specimen reaches the bearing limit and is destroyed is judged by combining the acoustic emission characteristics and mechanical theory, among which, is the key tooth area; 、 is the coefficient;

[0029] Failure mode association: The failure mode is determined based on the frequency of the acoustic emission signal. In the case of ductile failure, the low-frequency signal is dominant, corresponding to the steel fiber bridging effect, and there is a residual load formula. In the case of brittle failure, high-frequency signals dominate, corresponding to the shearing of the key teeth, and the damage factor formula is: ,in, The residual energy is determined by correlating the acoustic emission signal frequency with the mechanical properties to determine the specimen failure mode and performance status after failure.

[0030] Preferably, step S43 integrates the influence of the single factors of lateral compressive stress, key tooth geometric parameters and fiber content on the performance of the specimen to establish a bearing capacity prediction model, wherein the influence of the single factor is as follows:

[0031] Lateral compressive stress: Increasing will delay the peak of acoustic emission event rate and increase the energy corresponding to the ultimate load. The fitting formula is: ;

[0032] Key tooth depth ratio :when = 0.5, the acoustic emission events are concentrated at the root and the failure mode is ductile; when When <0.3, the failure mode is brittle, and the formula is: ,in, is the damage uniformity coefficient;

[0033] The formula for steel fiber dosage is: ,in, is the fiber volume content; is the base energy density.

[0034] Preferably, the expression of the bearing capacity prediction model is:

[0035] ;

[0036] in, is a constant term; 、 、 、 、 、 are the regression coefficients of the corresponding variables; is the acoustic emission energy; Counting acoustic emission events; is the average frequency.

[0037] Therefore, the present invention adopts the above-mentioned UHPC key-stem joint direct shear acoustic emission characteristic test method, which has the following beneficial effects:

[0038] (1) Multi-stage monitoring from microcrack initiation to macroscopic damage, achieving dynamic correlation between stress, damage and acoustic signals;

[0039] (2) By integrating parameters such as lateral compressive stress, key tooth geometry, and fiber content, a bearing capacity prediction model based on acoustic emission characteristics is established, thereby establishing a quantitative relationship between the above parameters and the bearing capacity of the UHPC key tooth joint, and realizing the prediction of the bearing capacity.

[0040] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 This is a flow chart of a direct shear acoustic emission characteristic test method for UHPC key-stem joints according to the present invention;

[0042] Figure 2A specific flow chart of data analysis according to an embodiment of the present invention;

[0043] Figure 3 This is a superposition diagram of the load-slip curve and the acoustic emission energy rate of an embodiment of the present invention. DETAILED DESCRIPTION

[0044] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort shall fall within the scope of protection of the present invention.

[0045] In bridge construction and maintenance, UHPC segmental bridges are widely used due to their excellent mechanical properties. This is particularly true in facilities such as airport boarding bridges, which place stringent demands on structural safety and durability. As a critical force transmission site, the shear performance and damage evolution of the key-stem joint directly impact the overall service safety of the bridge. This test was conducted to accurately investigate the acoustic emission characteristics of UHPC key-stem joints under direct shear stress, clarify the damage development patterns, and support the development of a full-lifecycle health monitoring and safety assessment system for bridge structures. The following details the specific implementation process of the direct shear acoustic emission characteristics test method for UHPC key-stem joints, taking into account the actual service environment and stress characteristics of bridges.

[0046] See also Figure 1-Figure 3 A direct shear acoustic emission characteristic test method for UHPC key-teeth joints comprises the following steps:

[0047] S1. Design and prepare UHPC specimens;

[0048] S2. Build the test system, including the loading device, acoustic emission monitoring device, and displacement and strain monitoring device;

[0049] The loading device uses an electro-hydraulic servo press with a prestressed screw to apply lateral stress. The loading rate is 0.5 kN / s in the elastic stage and 0.1 mm / min after cracking.

[0050] The acoustic emission monitoring device uses several sensors (frequency 100kHz-1MHz, threshold 40dB) to collect acoustic emission characteristic parameters, including amplitude, energy, count, duration, rise time and average frequency;

[0051] The displacement and strain monitoring device uses a micrometer to measure vertical slip (accuracy 0.001mm), and a strain gauge (grid length 5mm) is attached to the root of the key teeth to monitor stress concentration.

[0052] S3. Test the specimens through the test system and collect the corresponding data; adopt the loading control method, which is divided into two stages: preloading and formal loading. The same load level is used in the two stages, and the acoustic emission signal, load-displacement data and strain data are recorded respectively. Preloading: 10% of the estimated ultimate load is preloaded and the equipment is calibrated for 5 minutes. Formal loading: force control stage: 20kN / level, each level is held for 2 minutes, and the initial acoustic emission signal is recorded; displacement control stage: after cracking, switch to 0.1mm / min until the load drops to 50% of the ultimate load or the slip reaches 5.5mm. Before the test, use The shear bearing capacity of the specimen is estimated, where is the area of ​​the plane interface, is the lateral compressive stress on the joint, is the friction coefficient of the joint; at the same time, the shear bearing capacity of the key joint specimen is estimated using the following formula:

[0053] ;

[0054] in, is the joint surface area; is the ultimate tensile strength of the specimen.

[0055] S4. Analyze the data and combine the acoustic emission characteristic parameters to reveal the shear stress behavior and damage failure mechanism of the dry joint under different parameter settings of the specimen. The specific steps include:

[0056] S41. Analyze the characteristic parameters of acoustic emission to clarify the development trend from microcracks to damage cracks, and provide data information for the final failure mode and failure mechanism, including:

[0057] Microcrack identification: Amplitude <40dB, corresponding to early damage inside the key teeth, the calculation formula is:

[0058] ;

[0059] in, For the The amplitude of the acoustic emission event, is the indicator function;

[0060] Macro crack expansion: 40dB≤amplitude≤60dB, corresponding to the crack expansion at the root of the key tooth, the energy release rate formula is: ;in, is the energy of a single event, is the time interval;

[0061] Destruction crack determination: Amplitude > 60dB, corresponding to key tooth shear failure, sound source coordinate calculation based on time difference positioning method:

[0062] ;

[0063] in, is the sensor coordinate, is the signal arrival time, is the elastic wave velocity.

[0064] S42. Construct a mechanical-acoustic emission coupling model that correlates mechanical response with acoustic emission characteristics to understand the damage and failure process of the specimen. The mechanical-acoustic emission coupling model is based on the following correlation:

[0065] Cracking threshold determination correlation: a sudden increase in acoustic emission time rate corresponds to the cracking load , combined with the Mohr stress circle criterion formula , determine the critical state of the specimen starting to damage and crack from the perspectives of mechanics and acoustics;

[0066] Correlation between the ultimate failure point and the peak value of acoustic emission energy Corresponding limit load , based on the shear strength criterion formula , the moment when the specimen reaches the bearing limit and is destroyed is judged by combining the acoustic emission characteristics and mechanical theory, among which, is the key tooth area; 、 is the coefficient;

[0067] Failure mode association: The failure mode is determined based on the frequency of the acoustic emission signal. In the case of ductile failure, the low-frequency signal is dominant, corresponding to the steel fiber bridging effect, and there is a residual load formula. In the case of brittle failure, high-frequency signals dominate, corresponding to the shearing of the key teeth, and the damage factor formula is: ,in, The residual energy is determined by correlating the acoustic emission signal frequency with the mechanical properties to determine the specimen failure mode and performance status after failure.

[0068] S43. Considering the lateral compressive stress, key tooth geometry, and fiber content, a bearing capacity prediction model was established in combination with acoustic emission characteristic parameters. A quantitative relationship between these parameters and the bearing capacity of the UHPC key tooth joint was established to predict the bearing capacity. The influence of the single factors of lateral compressive stress, key tooth geometry, and fiber content on the specimen performance was then integrated to establish a bearing capacity prediction model. The influence of the single factors is as follows:

[0069] Lateral compressive stress: Increasing will delay the peak of acoustic emission event rate and increase the energy corresponding to the ultimate load. The fitting formula is: ;

[0070] Key tooth depth ratio :when = 0.5, the acoustic emission events are concentrated at the root and the failure mode is ductile; when When <0.3, the failure mode is brittle, and the formula is: ,in, is the damage uniformity coefficient;

[0071] The formula for steel fiber dosage is: ,in, is the fiber volume content; is the base energy density.

[0072] The expression of the bearing capacity prediction model is:

[0073] ;

[0074] in, is a constant term; 、 、 、 、 、 are the regression coefficients of the corresponding variables; is the acoustic emission energy; Counting acoustic emission events; is the average frequency.

[0075] Therefore, the present invention adopts the above-mentioned UHPC key-stem joint direct shear acoustic emission characteristic test method to break through the limitations of traditional load-displacement curves, crack observation and other methods, realize real-time, continuous, multi-stage monitoring, and fully grasp the damage evolution dynamics.

[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 the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A test method for direct shear acoustic emission characteristics of UHPC key-tooth joints, characterized in that: The following steps are involved: S1. Design and prepare UHPC specimens; S2. Build the test system, including the loading device, acoustic emission monitoring device, and displacement and strain monitoring device; S3. Test the specimen through the test system and collect corresponding data; S4. Analyze the data and combine the acoustic emission characteristic parameters to reveal the shear stress behavior and damage failure mechanism of the dry joint under different parameter settings of the specimen. The specific steps include: S41. Analyze the characteristic parameters of acoustic emission to clarify the development trend from microcracks to damage cracks, and provide data information for the final failure mode and failure mechanism; S42. Construct a mechanical-acoustic emission coupling model that correlates mechanical response with acoustic emission characteristics to understand the damage and failure process of the specimen; S43. Considering the lateral compressive stress, key tooth geometry parameters, and fiber content, a bearing capacity prediction model is established in combination with acoustic emission characteristic parameters. This establishes a quantitative relationship between the above parameters and the bearing capacity of the UHPC key tooth joint, thus achieving the prediction of the bearing capacity. Step S41 specifically includes: Microcrack identification: Amplitude <40dB, corresponding to early damage inside the key teeth, the calculation formula is: ； in, For the The amplitude of the acoustic emission event, is the indicator function; Macro crack expansion: 40dB≤amplitude≤60dB, corresponding to the crack expansion at the root of the key tooth, the energy release rate formula is: ;in, is the energy of a single event, is the time interval; Destruction crack determination: Amplitude > 60dB, corresponding to key tooth shear failure, sound source coordinate calculation based on time difference positioning method: ； in, is the sensor coordinate, is the signal arrival time, is the elastic wave velocity; The mechanical-acoustic emission coupling model in step S42 is based on the following association: Cracking threshold determination correlation: a sudden increase in acoustic emission event rate corresponds to a cracking load , combined with the Mohr stress circle criterion formula , the critical state of the specimen starting to damage and crack is determined from the perspectives of mechanics and acoustics; is the lateral compressive stress on the joint, is the ultimate tensile strength of the specimen; Correlation between the ultimate failure point and the peak value of acoustic emission energy Corresponding limit load , based on the shear strength criterion formula , the moment when the specimen reaches the bearing limit and is destroyed is judged by combining the acoustic emission characteristics and mechanical theory, among which, is the key tooth area; 、 is the coefficient; is the area of ​​the flat surface; is the friction coefficient of the joint; Failure mode association: The failure mode is determined based on the frequency of the acoustic emission signal. In the case of ductile failure, the low-frequency signal is dominant, corresponding to the steel fiber bridging effect, and there is a residual load formula. In the case of brittle failure, high-frequency signals dominate, corresponding to the shearing of the key teeth, and the damage factor formula is: ,in, The residual energy is determined by correlating the acoustic emission signal frequency with the mechanical properties to clarify the specimen failure mode and performance status after failure. The expression of the bearing capacity prediction model is: ； in, is a constant term; 、 、 、 、 、 are the regression coefficients of the corresponding variables; is the acoustic emission energy; Counting acoustic emission events; is the average frequency; is the key tooth depth-to-height ratio; is the fiber volume content.

2. A direct shear acoustic emission characteristics test method for UHPC key-tooth joints according to claim 1, characterized in that: The loading device in step S2 uses an electro-hydraulic servo press with a prestressed screw to apply lateral stress; the acoustic emission monitoring device uses several sensors to collect acoustic emission characteristic parameters, including amplitude, energy, count, duration, rise time and average frequency; the displacement and strain monitoring device uses a micrometer to measure vertical slip, and a strain gauge is attached to the root of the key tooth to monitor stress concentration.

3. The direct shear acoustic emission characteristics test method for UHPC key-teeth joints according to claim 1 is characterized by: In step S3, the loading control method is used, which is divided into two stages: preloading and formal loading. The same load level is used in the two stages, and the acoustic emission signal, load-displacement data and strain data are recorded respectively. Before the test, the The shear bearing capacity of the specimen is estimated, where is the area of ​​the plane interface, is the lateral compressive stress on the joint, is the friction coefficient of the joint; at the same time, the shear bearing capacity of the key joint specimen is estimated using the following formula: ； in, is the joint surface area; is the ultimate tensile strength of the specimen.

4. A UHPC key-teeth joint direct shear acoustic emission characteristics test method according to claim 1, characterized in that: Step S43 integrates the influence of the single factors of lateral compressive stress, key tooth geometric parameters and fiber content on the performance of the specimen to establish a bearing capacity prediction model. The influence of the single factor is as follows: Lateral compressive stress: Increasing will delay the peak of acoustic emission event rate and increase the energy corresponding to the ultimate load. The fitting formula is: ; Key tooth depth ratio :when = 0.5, the acoustic emission events are concentrated at the root and the failure mode is ductile; when When <0.3, the failure mode is brittle, and the formula is: ,in, is the damage uniformity coefficient; The formula for steel fiber dosage is: ,in, is the fiber volume content; is the base energy density.

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