A pulling device for detecting the cohesive strength of asphalt material

Abstract

The application discloses a pulling device for detecting the bonding strength of asphalt material, which comprises a base, a vertical column arranged on the base and a crossbeam horizontally arranged on the vertical column, wherein the free end of the crossbeam is provided with a tension sensor for detecting the tension signal generated in the pulling process of the bonding test piece, a pneumatic push rod is arranged below the tension sensor and can realize axial linear movement for providing controllable tension, a displacement sensor for testing the displacement of the pneumatic push rod is arranged on one side of the pneumatic push rod, a pulling head is connected to the end of the pneumatic push rod for connecting with the surface of the bonding test piece and realizing interface separation in the loading process of the pneumatic push rod. The application can realize stable and controllable loading process, accurate force value collection and efficient test process and is suitable for rapid evaluation of the bonding strength of asphalt material.

Description

Technical Field

[0001] This invention belongs to the field of asphalt material bond strength testing technology, specifically relating to a pull-out device for testing the bond strength of asphalt materials. Background Technology

[0002] With the development of road engineering technology, the bonding performance between asphalt pavement structural layers has a significant impact on the mechanical properties and service life of the overall road structure. In particular, insufficient bonding between the asphalt layer and the base course and surface course can easily lead to interlayer slippage, crack propagation, and even structural delamination, seriously affecting the road's service performance and maintenance cycle.

[0003] Currently, the main testing methods for the bonding properties of asphalt-based materials include splitting crack tests, shear tests, and pull-out tests. Among these, the pull-out method has become a commonly used method for evaluating bonding performance due to its simple testing process, clear loading direction, and ability to intuitively reflect interfacial tensile strength. However, most existing pull-out testing equipment relies on manual loading or static loading structures, which suffers from problems such as unstable loading, low data accuracy, and poor operational repeatability, making it difficult to meet the needs of precise testing of new materials.

[0004] Furthermore, with the increasing demand for rapid on-site testing, traditional pull-out testing equipment is bulky, cumbersome to operate, and uses a single data transmission method, making it unsuitable for testing bonded specimens in complex construction environments. Therefore, there is an urgent need for a compact, controllable loading, and real-time data acquisition and transmission device for asphalt material pull-out testing to improve the efficiency and accuracy of interfacial adhesion performance testing.

[0005] In pull-out tests, the peak tensile force at interface failure is the measured bond strength. Therefore, a stable and reproducible stress process must be achieved under the set loading rate, peak tensile force, and holding time. Otherwise, force overshoot, fluctuation, or rate instability will lead to peak identification deviation and reduced result repeatability. Summary of the Invention

[0006] This invention addresses the technical problems existing in the prior art by providing a pull-out device and its control method for testing the bond strength of asphalt materials. The pull-out device can achieve a stable and controllable loading process, accurate force value acquisition, and efficient testing process, and is suitable for rapid evaluation of the bond strength of asphalt materials.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a pull-out device for testing the bonding strength of asphalt materials, comprising a base, a vertically mounted column on the base, and a horizontally mounted beam on the column. A tension sensor is provided at the free end of the beam to detect the tension signal generated during the pull-out process of the bonded specimen under test. A pneumatic push rod is installed below the tension sensor and is capable of axial linear movement to provide controllable tension. A displacement sensor is provided on one side of the pneumatic push rod to test its displacement. A pull-out head is connected to the end of the pneumatic push rod and is used to connect with the surface of the bonded specimen under test. Interface separation is achieved during the loading process of the pneumatic push rod. During the test, the bonded specimen under test is mounted on the base, and the pull-out head is tightly fitted to the bonding surface of the bonded specimen or fixed by adhesive bonding. The pneumatic push rod is activated to drive the pull-out head to apply tension to the bonded specimen under test, thereby achieving the testing of the bonding strength of the asphalt materials.

[0008] This invention takes precise control of loading force as the core indicator. The host computer sets parameters such as loading speed, maximum tensile force and holding time in the test scheme, and uses them to constrain the mechanical trajectory of the pulling process.

[0009] In the pneumatic loading process, the compressibility of air reduces the equivalent stiffness of the actuator and introduces a time lag in the charging and discharging transmission. The flow-pressure difference relationship of the proportional valve / solenoid valve is nonlinear and accompanied by dead zones and hysteresis. The cylinder sealing pair has viscous-Coulomb compound friction and stick-slip. At the same time, factors such as air source pressure / temperature fluctuations, pipeline volume elasticity and micro-leakage, as well as abrupt changes in boundary conditions during the crack initiation to fracture of the specimen, all work together to make the output force prone to oscillation, overshoot and random fluctuations, and weaken repeatability. Against this background, positional PID relies on a single feedback and fixed parameters, making it difficult to maintain consistent dynamic quality under different operating points and rapid load change scenarios. It often exhibits integral saturation and abrupt changes in valve opening, resulting in long constant force tracking adjustment time, large overshoot, and insufficient disturbance rejection.

[0010] The control method for the pull-out device used for testing the bond strength of asphalt materials according to the present invention is as follows:

[0011] This invention constructs a model predictive control (MPC) closed-loop architecture, consisting of a pneumatic loading structure, a sensor feedback unit, a signal acquisition controller, and a host computer. The controller collects tension and displacement in real time as state inputs to the MPC, realizing predictive-optimized control of the electro-proportional pressure valve, so that the force trajectory smoothly tracks the set target.

[0012] Based on the discrete state-space model, the control algorithm predicts future outputs in a rolling manner and constructs a quadratic cost function with "minimizing tracking error + penalizing control increment". At the same time, it suppresses sudden changes in valve opening and overshoot by constraints such as output range, input amplitude and input increment. It only executes the first optimal control quantity of each cycle and iterates by shifting the window, thereby obtaining a shorter settling time and a smaller overshoot under disturbances and model uncertainties.

[0013] Thus, while meeting the predetermined test parameters, the system ensures stable stress and reliable data, effectively improving the accuracy and repeatability of bond strength testing;

[0014] (1) System Modeling

[0015] The signal acquisition controller first performs discretized state-space modeling of the loading system. Based on the dynamic response of the pneumatic cylinder under different control inputs, the following state-space model is established:

[0016] x(k+1)=Ax(k)+Bu(k), y(k)=Cx(k)

[0017] Wherein, the state variable x(k) represents the loading state of the system, the control input u(k) represents the input control quantity to the electro-proportional pressure valve, the output quantity y(k) is the current tension value of the system, and the system matrices A, B, and C are obtained through experimental identification or least squares modeling.

[0018] The state vector is selected in the following form:

[0019]

[0020] (2) Rolling forecasting mechanism

[0021] Within each control cycle, starting from the current state x(k), the system output at N future time points is predicted using the model.

[0022] The prediction recursion is as follows:

[0023]

[0024] The entire predicted output vector is:

[0025]

[0026] Where N is the prediction step size and M is the control step size, and M≤N;

[0027] (3) Cost function construction

[0028] The control objective is to make the predicted output trajectory as close as possible to the target trajectory y. ref To suppress drastic changes in the control variables, the following cost function is constructed:

[0029]

[0030] in

[0031] y ref (k+i): Expected loading trajectory;

[0032] Δu(k+i)=u(k+j)-u(k+j-1): control increment;

[0033] λ: Controller smoothing weighting factor, used to prevent control jumps;

[0034] This optimization problem is transformed into a standard quadratic optimization problem (QP) in the form of:

[0035]

[0036] (4) Constraint Design

[0037] To ensure the physical feasibility and system security of the loading process, the following constraints are introduced:

[0038] Loading range limitations:

[0039] Control input restrictions: u min ≤u(k+i)≤u max

[0040] Control increment limit: |Δu(k+i)|≤Δu max

[0041] The above inequality constraints are uniformly written into matrix form to construct G and h, and the open-source solver qpOASES is called to achieve fast solution;

[0042] (5) Online optimization solution and execution

[0043] Within each sampling period, the following optimization process is executed:

[0044] 1) Obtain the current system state x(k);

[0045] 2) Constructing the prediction model and inequality constraints;

[0046] 3) Construct the cost function and generate the QP problem;

[0047] 4) Use the solver to obtain the optimal control sequence U * ;

[0048] 5) Only execute the first control variable u of the optimal sequence. * (k) is used to drive an electro-proportional pressure valve;

[0049] 6) Repeat the above steps in the next cycle;

[0050] (6) State update and disturbance rejection mechanism

[0051] After each control cycle, the controller updates its state based on the actual load value y(k) fed back by the tension sensor.

[0052] If some states of the system are unmeasurable, a Kalman filter can be introduced for estimation.

[0053] If persistent bias exists, a perturbation observer can be used to correct the model error;

[0054] If the model error is large, a robust MPC control strategy can be constructed to improve the ability to resist disturbances.

[0055] Compared with the prior art, the present invention has the following advantages and beneficial effects: the present invention can realize a stable and controllable loading process, accurate force value acquisition and efficient testing process, and is suitable for rapid evaluation of the bonding strength of various road materials. Attached Figure Description

[0056] Figure 1 This is an overall structural diagram of the pulling device in this invention.

[0057] Figure 2 This is a schematic diagram of the pulling device in this invention.

[0058] Figure 3 This is a control principle diagram of the pneumatic loading system in this invention.

[0059] Figure 4 This is a control principle diagram of the signal acquisition, control unit, and host computer analysis system in this invention.

[0060] In the diagram: 1-base, 2-column, 3-beam, 4-tension sensor, 5-pneumatic push rod, 6-pull head. Detailed Implementation

[0061] 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.

[0062] like Figure 1-2 As shown, the present invention provides a pull-out device for testing the bond strength of asphalt, which mainly includes the following parts:

[0063] Base 1: Used to mount the bonded specimen under test. It features a rigid structure to stably support the entire system and ensure no displacement during testing. Column 2: Vertically mounted on base 1, providing support for the crossbeam 3 and allowing for height adjustment along the column axis. Crossbeam 3: Horizontally mounted on column 2, with one end fixed to the tension sensor 4 via screws, supporting the entire loading system. Tension sensor 4: Used to detect the tension signal generated during the pull-out process. Located below the crossbeam 3, its output is connected to a host computer for data acquisition. Pneumatic push rod 5: Installed below the tension sensor 4, enabling axial linear movement to provide controllable pull-out force. Pull-out head 6: Connected to the end of the pneumatic push rod 5, used to connect with the surface of the bonded specimen (such as an asphalt coating) under test, achieving interface separation during loading.

[0064] In practice, the operator installs the prepared bond test specimen onto the base, ensuring the pull-out head is tightly fitted to the bonding surface of the specimen or fixed by adhesive. After setting the loading parameters (e.g., maximum tensile force, loading rate) on the host computer, the pull-out instrument is started. The electric push rod begins to move downward, driving the pull-out head to apply tensile force to the bond test specimen. Throughout the pull-out process, the tensile force sensor records the change in tensile force over time in real time and transmits this data to the host computer for processing and display. When the bonding at the interface of the bond test specimen fails, the tensile force reaches its peak value, which is the maximum bond strength of the bond test specimen. The test then automatically ends, and the test data is automatically saved.

[0065] like Figure 3 and Figure 4 As shown, it includes a pneumatic loading system, a signal acquisition and control unit, and a host computer analysis system, which are used to achieve precise control of the mechanical response of asphalt specimens during the pull-out process and to acquire data on their bonding performance.

[0066] 1. Pneumatic loading system

[0067] like Figure 3 As shown, the pneumatic loading module includes:

[0068] The air source provides a stable supply of compressed air to the system;

[0069] The gas source regulating unit and the drying filter water separator are used to stabilize the gas source and remove moisture to ensure that the gas entering the system is clean and stable.

[0070] The electro-proportional pressure valve receives analog control signals (voltage) from the controller to continuously regulate the air pressure entering the actuator cylinder.

[0071] The electromagnetic reversing valve is controlled by a digital signal output from the controller to switch its state, thereby controlling the air intake and exhaust path of the cylinder and realizing the forward and backward movement of the cylinder piston.

[0072] The actuator cylinder (or pneumatic push rod) is connected at the front end to the pull head, which is used to connect with the asphalt specimen to be tested.

[0073] A tension sensor, installed on the fixed end of the actuator cylinder, is used to collect the axial tension generated during the pulling process in real time;

[0074] The displacement sensor is installed on the cylinder's moving axis to record the displacement of the drawing head.

[0075] During system operation, the user sets parameters such as the target loading rate and peak tension via a host computer. The controller sends an analog voltage signal to the electro-proportional valve based on the set parameters to adjust the intake pressure of the actuator cylinder, achieving continuous and adjustable pulling loading. The solenoid directional valve, in conjunction with the proportional valve, switches the intake and exhaust direction of the actuator cylinder, thereby extending or retracting the push rod.

[0076] 2. Signal Acquisition and Control System

[0077] like Figure 2 As shown, the system's control core is a signal acquisition controller, responsible for bidirectional processing of analog and digital signals. Its signal channels include:

[0078] Analog input channel A11: Connects to a tension sensor to acquire real-time tension signals;

[0079] Analog input channel A12: Connects to a displacement sensor to collect the displacement of the pulling head;

[0080] Analog output channel A01: Connects to an electro-proportional pressure valve and is used to output a control voltage signal to adjust the cylinder loading force;

[0081] Digital output channels D01 and D02: connected to the solenoid directional valve, used to drive the switching of the cylinder's direction of motion.

[0082] The signal acquisition controller communicates with the host computer, and the host computer's built-in testing software can perform the following functions:

[0083] Test procedure parameter settings, such as loading speed, maximum tensile force, and holding time;

[0084] Start / stop loading control;

[0085] Real-time graphical display of the force-displacement curve;

[0086] It automatically saves test data and calculates mechanical properties such as bond strength.

[0087] This system achieves high response speed and control precision through pneumatic loading. The closed-loop feedback control loop consisting of sensor-controller-actuator ensures stable force and reliable data during the pulling process, making it suitable for various asphalt bonding performance testing needs in the laboratory and on-site.

[0088] Control methods:

[0089] To further improve the loading accuracy and control stability of the asphalt material pull-out test system, this embodiment constructs a closed-loop control strategy and system implementation architecture based on model predictive control theory, which can dynamically adjust the loading force and suppress the influence of disturbances.

[0090] The system includes a pneumatic loading structure, a sensor feedback unit, a signal acquisition controller, and a host computer control module. The signal acquisition controller is used to acquire analog signals from the force sensor and displacement sensor in real time, and input these signals as system state variables into the MPC algorithm to achieve predictive optimization control.

[0091] (1) System Modeling

[0092] The signal acquisition controller first performs discretized state-space modeling of the loading system. Based on the dynamic response of the actuator cylinder under different control inputs (such as voltage or air supply ratio), the following state-space model is established:

[0093] x(k+1)=Ax(k)+Bu(k),y(k)=Cx(k)

[0094] Wherein, the state variable x(k) represents the loading state of the system (such as loading force F(k) and loading speed F'(K)), the control input u(k) represents the input control quantity of the electro-proportional pressure valve, the output quantity y(k) is the current tension value of the system, and the system matrices A, B, and C can be obtained through experimental identification or least squares modeling.

[0095] In this invention, the state vector is selected in the following form:

[0096]

[0097] (2) Rolling Forecasting Mechanism

[0098] Within each control cycle, starting from the current state x(k), the system output at N future time points is predicted using the model.

[0099] The prediction recursion is as follows:

[0100]

[0101] The entire predicted output vector is:

[0102]

[0103] Where N is the prediction step size and M is the control step size, and M≤N.

[0104] (3) Cost function construction

[0105] The control objective is to make the predicted output trajectory as close as possible to the target trajectory y. ref This also suppresses drastic changes in the control variables. The cost function is constructed as follows:

[0106]

[0107] in

[0108] y ref (k+i): Expected loading trajectory;

[0109] Δu(k+i)=u(k+j)-u(k+j-1): control increment;

[0110] λ: Controller smoothing weight factor, used to prevent control jumps.

[0111] This optimization problem is transformed into a standard quadratic optimization problem (QP) in the form of:

[0112]

[0113] (4) Constraint Design

[0114] To ensure the physical feasibility and system security of the loading process, the following constraints are introduced:

[0115] Loading range limitations:

[0116] Control input restrictions: u min ≤u(k+i)≤u max

[0117] Control increment limit: |Δu(k+i)|≤Δu max

[0118] The above inequality constraints are uniformly written into matrix form to construct G and h, and the open-source solver qpOASES is called to achieve fast solution.

[0119] (5) Online optimization solution and execution

[0120] Within each sampling period, the following optimization process is executed:

[0121] 1) Obtain the current system state x(k);

[0122] 2) Constructing the prediction model and inequality constraints;

[0123] 3) Construct the cost function and generate the QP problem;

[0124] 4) Use the solver to obtain the optimal control sequence U * ;

[0125] 5) Only execute the first control variable u of the optimal sequence. * (k) is used to drive the electro-proportional pressure valve;

[0126] 6) Repeat the above steps in the next cycle.

[0127] (6) State update and disturbance rejection mechanism

[0128] After each control cycle, the controller updates its state based on the actual load value y(k) fed back by the tension sensor.

[0129] If some states of the system are unmeasurable, a Kalman filter can be introduced for estimation.

[0130] If persistent bias exists, a perturbation observer can be used to correct the model error.

[0131] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A pull-out device for testing the bond strength of asphalt materials, characterized in that... The device includes a base, a vertically mounted column on the base, and a horizontally mounted beam on the column. A tension sensor is installed at the free end of the beam to detect the tension signal generated during the pull-out process of the bonded specimen under test. A pneumatic push rod is installed below the tension sensor and is capable of axial linear movement to provide controllable tension. A displacement sensor is installed on one side of the pneumatic push rod to test its displacement. A pull-out head is connected to the end of the pneumatic push rod and is used to connect with the surface of the bonded specimen under test to achieve interface separation during the loading process of the pneumatic push rod.

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