Ultrasonic detection method and system for axial force of cable clamp screw considering uneven distribution of temperature and stress

Abstract

The present invention discloses an ultrasonic detection method and system for the axial force of a cable clamp screw considering the uneven distribution of temperature and stress, including: obtaining the wave velocity of an ultrasonic longitudinal wave in the cable clamp screw under a zero stress state based on the length data of the cable clamp screw before being stressed; obtaining the temperature coefficient through linear fitting, and then obtaining the propagation time of the ultrasonic longitudinal wave on the deformation of the cable clamp screw and the round-trip transit time of the ultrasonic longitudinal wave in the screw; constructing a fitness function based on the round-trip transit time of the ultrasonic longitudinal wave in the screw and a particle swarm detection algorithm; updating the particle velocity and position in the particle swarm based on the particle swarm detection algorithm, and when a preset threshold condition is reached, the particle swarm detection algorithm outputs the global optimal position of all particles, and obtains the axial screw force of the cable clamp screw. The present invention obtains the relationship between the round-trip transit time of the ultrasonic longitudinal wave in the screw and the stress state by adopting a microelement modeling method, and searches in combination with a particle swarm optimization algorithm, thereby effectively improving the measurement accuracy.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic nondestructive testing, and relates to an ultrasonic detection method and system for the axial force of a cable clamp screw considering non-uniform distributions of temperature and stress. Background Art

[0002] The cable clamp is an important structural component connecting the main cable of a suspension bridge and the hanger. During long-term service, affected by factors such as material creep, alternating loads, and environmental temperature, the axial force of the cable clamp screw will decay, resulting in a decrease in frictional resistance, causing problems such as cable clamp slippage, hanger inclination, reduced main cable sealing performance, and redistribution of the structural system forces.

[0003] Currently, the traditional method for measuring the axial force of a cable clamp screw is the "pull-out method", where the screw is tensioned by a jack until the nut loosens. At this time, the tension of the jack is equal to the axial force of the screw. This method has a small operation difficulty but a low detection accuracy. In addition, the detection of the screw axial force also includes the torque method, the resistance strain gauge method, the pressure ring method, the ultrasonic detection method, etc. The torque method generally controls the pre-tightening force of the screw through a torque wrench. This method is simple and efficient but not applicable to the detection of large-sized cable clamp screws. The resistance strain gauge method pastes strain gauges on the screw to measure the surface strain value of the screw. According to Hooke's law, the axial force of the screw is calculated using the relationship between stress and strain. This method has a high detection accuracy, but the installation of the strain gauges is difficult and the durability is not high. The pressure ring method places a pressure ring at the stress-bearing part of the screw and directly monitors the axial force through the pressure ring. The measurement is highly targeted. Although this method can achieve long-term monitoring of the axial force, it is not applicable to large-scale rapid detection.

[0004] Due to its non-destructive, efficient, and high-precision characteristics, the ultrasonic detection method has become an effective method for detecting the cable clamp screw force of a suspension bridge in recent years. Existing ultrasonic detections generally assume that the stress in the stress-bearing part of the screw is uniformly distributed. However, under the action of the clamped part and the nut, the axial stress of the screw is inevitably non-uniformly distributed, especially the stress attenuation at the end of the nut is the most obvious. Such an estimation of the effective clamping length of the screw will inevitably cause an error in the axial force measurement. There is an urgent need for a model that conforms to the actual stress situation of the screw and a measurement method that can accurately measure the effective clamping length of the screw. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem that in the prior art, ultrasonic detections generally assume that the stress in the stress-bearing part of the screw is uniformly distributed, which does not conform to the actual situation and leads to inevitable errors in axial force measurement. The present invention provides an ultrasonic detection method and system for the axial force of a cable clamp screw considering non-uniform distributions of temperature and stress.

[0006] To achieve the above purpose, the present invention adopts the following technical solutions:

[0007] An ultrasonic detection method for the axial force of the clamp screw considering the uneven distribution of temperature and stress, including:

[0008] Collect the length data of the clamp screw before and after loading, and construct a two-dimensional simplified model of the clamp screw under load;

[0009] Based on the length data of the clamp screw before loading and the two-dimensional simplified model of the load, obtain the wave velocity of the ultrasonic longitudinal wave in the clamp screw under zero stress and standard calibration temperature conditions;

[0010] Conduct ultrasonic longitudinal wave velocity measurement tests on the screw at different temperatures and record them to obtain the arrival times of the screw at different temperatures under zero stress state, and obtain the temperature coefficient through linear fitting;

[0011] Based on the deformation amount, temperature coefficient of the clamp screw after loading, and the wave velocity of the ultrasonic longitudinal wave in the clamp screw, and considering the ambient temperature, compensate for the temperature effect to obtain the propagation time of the ultrasonic longitudinal wave on the deformation amount of the clamp screw, and then obtain the round-trip transit time of the ultrasonic longitudinal wave in the screw;

[0012] Based on the round-trip transit time of the ultrasonic longitudinal wave in the screw and the particle swarm detection algorithm, construct a fitness function;

[0013] Based on the particle swarm detection algorithm, update the particle velocity and position in the particle swarm, and then continuously optimize the fitness function value of the particle, update the individual optimal value and optimal position of each particle, and update the global optimal value and optimal position of all particles;

[0014] When the preset threshold condition is reached, the particle swarm detection algorithm outputs the global optimal position of all particles and obtains the axial force of the clamp screw shaft.

[0015] A further improvement of the present invention lies in:

[0016] Further, to obtain the wave velocity of the ultrasonic longitudinal wave in the clamp screw under zero stress state, specifically: based on the acoustoelastic theory, the relationship between the wave velocity of the ultrasonic longitudinal wave propagating along the stress direction in a homogeneous isotropic material and the stress is:

[0017]

[0018] Among them, ρ 0 is the density of the material; V L is the longitudinal wave velocity; λ, μ are second-order elastic constants; m, l are third-order elastic constants; σ is the stress value in the material;

[0019] Among them, at the standard calibration temperature T 0 the wave velocity of the ultrasonic longitudinal wave under zero stress state is:

[0020]

[0021] Substituting Equation (2) into Equation (1) gives, at the standard calibration temperature T 0 the relationship between the longitudinal wave velocity and stress as follows:

[0022]

[0023] where A L is the acoustoelastic coefficient of the ultrasonic longitudinal wave; A L is negative, that is, the longitudinal wave velocity decreases with the increase of stress;

[0024] The temperature coefficient obtained by linear fitting is specifically:

[0025] α = Δt / ΔT

[0026] where ΔT = T - T0; T is any temperature; Δt is the time difference of the ultrasonic longitudinal wave velocity passing through the clamp screw at different temperatures.

[0027] Furthermore, at the standard calibration temperature T 0 the deformation of the clamp screw after being stressed is specifically: both ends of the clamp screw are threaded, and nuts are fixedly arranged on the threads at both ends of the clamp screw; the nut arranged at the other end of the clamp screw deforms under the action of an external force; the length of the stressed area of the clamp screw becomes L σ , and the length of the non-stressed part remains L 0 ; the original length of the stressed part is the effective clamping length L e , and its length is between the outer distance and the inner distance of the two nuts; the original length L i of the screw is expressed as:

[0028] L i = L e + L 0 (4)

[0029] At the zero-stress state and any temperature T, the wave velocity is corrected specifically as follows:

[0030]

[0031] where t(T 0 ) is the arrival time at the calibration temperature;

[0032] Assuming that the stress on each cross-section of the stressed part is the same, and the stress distribution curve along the axis is σ(x); using the infinitesimal element method to intercept an infinitesimal segment dx, then at any temperature T, the length of the screw after being stressed is [[1 + E -1 σ(x)](1 + γΔT)dx, and at this time, the length L σ,T of the stressed part of the screw is expressed as:

[0033]

[0034] Among them, E is the Young's modulus of the material, and γ is the linear expansion coefficient.

[0035] Furthermore, obtain the propagation time of the longitudinal ultrasonic wave on the deformation of the cable clamp screw, specifically:

[0036]

[0037] Among them, the propagation time of the longitudinal ultrasonic wave on the micro-segment is the length of the micro-segment divided by the longitudinal wave velocity;

[0038] The acquisition of the round-trip transit time of the longitudinal ultrasonic wave in the screw is specifically:

[0039]

[0040] Combining formula (6) and formula (8) gives:

[0041]

[0042] Among them, ε is a point in the integration interval [0, L e , and σ(ε) represents the average axial stress in the stress interval.

[0043] Furthermore, based on the round-trip transit time of the longitudinal ultrasonic wave in the screw and the particle swarm detection algorithm, construct a fitness function, specifically: The particle swarm detection algorithm is applicable to solving single-objective optimization problems. Combining formula (9), establish a fitness function:

[0044]

[0045] Among them, the fitness function f is the optimization objective of the particle swarm algorithm. Through the iteration of the particle swarm algorithm, continuously search for the minimum value of the fitness function to obtain the optimal solution of the variable.

[0046] Furthermore, based on the particle swarm detection algorithm, update the particle velocity and position in the particle swarm, specifically:

[0047] Step 1: Initialize the particle swarm parameters, including the number of particles P, learning factors c 1 、c 2 、the maximum number of iterations T and the position search range; use the elastic modulus, acoustoelastic coefficient and longitudinal wave velocity of the cable clamp screw as input values;

[0048] Step 2: Randomly generate the initial positions and velocities of each particle. The position is a two-dimensional matrix containing the effective clamping length L e and the average axial stress σ(ε);

[0049] Step 3: Calculate the fitness function value of the particles, save the individual optimal value and optimal position of each particle, and save the global optimal value and optimal position of all particles;

[0050] Step 4: Update the velocity and position of each particle;

[0051] Step 5: Recalculate the fitness function value of the particles, update the individual optimal value and optimal position of each particle, and update the global optimal value and optimal position of all particles;

[0052] Step 6: Repeat the above steps until the maximum number of iterations is reached or the loop end condition is satisfied, then exit the loop, and output the global optimal position, that is, the effective clamping length L e and the optimal values of the average axial stress σ(ε), so as to obtain the bolt force of the stay cable clip screw shaft.

[0053] Furthermore, to update the velocity and position of each particle, specifically: the velocity and position update formulas of the particle swarm algorithm are respectively:

[0054]

[0055] X i (t) = V i (t) + X i (t - 1) (12)

[0056] where V i (t) = [V i1 (t), … V iN (t)] T and X i (t) = [X i1 (t), … X iN (t)] T respectively represent the N-dimensional velocity and position matrices of the i-th particle at the t-th iteration, i = 1 … P, P is the number of particles, t = 1 … T, T is the maximum number of iterations; X i pbest is the individual optimal value of the i-th particle during the iteration process, X gbest is the global optimal value searched by all particles; w(t) represents the inertia weight, which reflects the influence of the previous iteration velocity on the current velocity; the larger w(t) is, the stronger the global search ability of the particle, and it can avoid falling into the local optimal solution; c 1 , c 2 are the individual learning factor and the social learning factor, which reflect the inheritance and learning of the particle for the individual optimal value and the local optimal value during the iteration process; r 1 and r 2 are random numbers between 0 and 1.

[0057] Further, the cable clamp screw shaft screw force is obtained as follows: multiplying the optimal value of the measured average axial stress σ(ε) by the screw cross-sectional area to obtain the cable clamp screw shaft screw force; the cross-sectional area of the screw is obtained by measuring the cross-section of the screw.

[0058] An ultrasonic detection system for the cable clamp screw shaft force considering the uneven distribution of temperature and stress, comprising:

[0059] An acquisition module, which acquires the length data of the cable clamp screw before and after being stressed, and constructs a two-dimensional simplified model of the cable clamp screw under stress;

[0060] A first acquisition module, which, based on the length data of the cable clamp screw before being stressed and the two-dimensional simplified model of the cable clamp screw under stress, acquires the wave velocity of the ultrasonic longitudinal wave in the cable clamp screw in the zero-stress and standard calibration temperature state;

[0061] A fitting module, which measures and records the wave velocity of the ultrasonic longitudinal wave of the screw at different temperatures, obtains the arrival time of the screw at different temperatures in the zero-stress state, and obtains the temperature coefficient through linear fitting;

[0062] A second acquisition module, which, based on the deformation amount of the cable clamp screw after being stressed, the temperature coefficient, and the wave velocity of the ultrasonic longitudinal wave in the cable clamp screw, and considering the ambient temperature, compensates for the temperature effect, obtains the propagation time of the ultrasonic longitudinal wave on the deformation amount of the cable clamp screw, and further obtains the round-trip transit time of the ultrasonic longitudinal wave in the screw;

[0063] A construction module, which constructs a fitness function based on the round-trip transit time of the ultrasonic longitudinal wave in the screw and the particle swarm detection algorithm;

[0064] An update module, which, based on the particle swarm detection algorithm, updates the particle velocity and position in the particle swarm, and further continuously optimizes the fitness function value of the particle, updates the individual optimal value and optimal position of each particle, and updates the global optimal value and optimal position of all particles;

[0065] A third acquisition module, which, when the preset threshold condition is reached, the particle swarm detection algorithm outputs the global optimal position of all particles, and obtains the cable clamp screw shaft screw force.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] The present invention obtains the wave velocity of longitudinal ultrasonic waves in the cable clamp screw under zero stress state through the length data of the cable clamp screw before stress application; obtains the temperature coefficient through linear fitting, and further obtains the propagation time of longitudinal ultrasonic waves on the deformation of the cable clamp screw and the round-trip transit time of longitudinal ultrasonic waves in the screw; constructs a fitness function based on the round-trip transit time of longitudinal ultrasonic waves in the screw and the particle swarm detection algorithm; updates the particle velocity and position in the particle swarm based on the particle swarm detection algorithm. When the preset threshold condition is reached, the particle swarm detection algorithm outputs the global optimal position of all particles and obtains the axial screw force of the cable clamp screw. By adopting the micro-element modeling method, the present invention obtains the relationship between the round-trip transit time of longitudinal ultrasonic waves in the screw and the stress state, and combines the particle swarm optimization algorithm for search, which can effectively improve the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0069] Figure 1 is a schematic flow chart of the ultrasonic detection method for the axial force of the cable clamp screw considering the uneven distribution of temperature and stress according to the present invention;

[0070] Figure 2 is a schematic diagram of the cable clamp screw in an unloaded state;

[0071] Figure 3 is a schematic diagram of the cable clamp screw in a loaded state;

[0072] Figure 4 is a schematic flow chart of the screw force detection based on the particle swarm algorithm;

[0073] Figure 5 is a schematic structural diagram of the ultrasonic detection system for the axial force of the cable clamp screw considering the uneven distribution of temperature and stress according to the present invention;

[0074] Figure 6 is a schematic diagram of the acoustoelastic coefficient test device;

[0075] Figure 7 is a schematic diagram of the Young's modulus fitting curve;

[0076] Figure 8 is a schematic diagram of the relationship between the longitudinal wave emission and the echo signal;

[0077] Figure 9 is a schematic diagram of the autocorrelation calculation result of the two echo signals after denoising;

[0078] Figure 10 Schematic diagram for fitting acoustoelastic coefficients Specific implementation manners

[0079] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. The components of the embodiments of the present invention usually described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0080] Therefore, 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 merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0081] It should be noted that: like reference numerals and letters denote like items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0082] In the description of the embodiments of the present invention, it should be noted that if terms such as "upper", "lower", "horizontal", "inner", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the inventive product is usually placed during use, it is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation to the present invention. In addition, terms such as "first", "second", etc. are only used for distinguishing descriptions and cannot be construed as indicating or implying relative importance.

[0083] In addition, if the term "horizontal" appears, it does not mean that the component is required to be absolutely horizontal, but it can be slightly inclined. For example, "horizontal" only means that its direction is more horizontal relative to "vertical", and does not mean that the structure must be completely horizontal, but it can be slightly inclined.

[0084] In the description of the embodiments of the present invention, it should also be noted that unless otherwise clearly specified and limited, if terms such as "set", "installed", "connected", "connected" are understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0085] The present invention will be further described in detail below in conjunction with the accompanying drawings:

[0086] See Figure 1 , the present invention discloses an ultrasonic detection method for the axial force of the cable clamp screw considering the uneven distribution of temperature and stress, including:

[0087] S101: Collect the length data of the cable clamp screw before and after being stressed, and construct a two-dimensional simplified model of the stressed cable clamp screw;

[0088] S102: Based on the length data of the cable clamp screw before being stressed and the two-dimensional simplified model of the stress, obtain the wave velocity of the ultrasonic longitudinal wave in the cable clamp screw under the state of zero stress and standard calibration temperature;

[0089] Based on the acoustoelastic theory, the relationship between the wave velocity of the ultrasonic longitudinal wave propagating along the stress direction in a homogeneous isotropic material and the stress is:

[0090]

[0091] where ρ 0 is the density of the material; V L is the longitudinal wave velocity; λ, μ are second-order elastic constants; m, l are third-order elastic constants; σ is the stress value in the material;

[0092] where, under the standard calibration temperature T 0 , the wave velocity of the ultrasonic longitudinal wave in the zero stress state is:

[0093]

[0094] Substitute formula (2) into formula (1) to obtain the relational formula between the longitudinal wave velocity and the stress under the standard calibration temperature T 0 as:

[0095]

[0096] where A L is the acoustoelastic coefficient of the ultrasonic longitudinal wave; A L is negative, that is, the longitudinal wave velocity decreases with the increase of stress.

[0097] S103: Conduct ultrasonic longitudinal wave velocity measurement tests on the screw at different temperatures and record, obtain the arrival time of the screw at different temperatures in the zero stress state, and obtain the temperature coefficient through linear fitting;

[0098] The temperature coefficient obtained through linear fitting is specifically:

[0099] α = Δt / ΔT

[0100] where, ΔT = T - T0; T is any temperature; Δt is the time difference for the ultrasonic longitudinal wave velocity to pass through the clamp screw at different temperatures.

[0101] S104. Compensate for the temperature effect based on the deformation amount, temperature coefficient of the clamp screw after being stressed, and the wave velocity of the ultrasonic longitudinal wave in the clamp screw, and consider the ambient temperature to obtain the propagation time of the ultrasonic longitudinal wave on the deformation amount of the clamp screw, and further obtain the round-trip transit time of the ultrasonic longitudinal wave in the screw.

[0102] See Figure 2 and Figure 3 , at the standard calibration temperature T 0 , the deformation amount of the clamp screw after being stressed is specifically: both ends of the clamp screw are threaded, and nuts are fixedly arranged on the threads at both ends of the clamp screw; the nut arranged at the other end of the clamp screw deforms under the action of an external force; d is the outer diameter of the screw, and L n is the distance between the inner sides of the nuts. The length of the screw will change after being stressed, and the length of the stressed area of the clamp screw becomes L σ , and the length of the non-stressed part remains L 0 ; the original length of the stressed part is the effective clamping length L e , and its length is between the distance between the outer sides of the two nuts and the distance between the inner sides; the original length L i of the screw is expressed as:

[0103] L i = L e + L 0 (4)

[0104] At the zero-stress state and any temperature T, correct the wave velocity, specifically:

[0105]

[0106] where, t(T 0 ) is the arrival time at the calibration temperature

[0107] Assume that the stress is the same on each cross-section of the stressed part, and the stress distribution curve along the axial direction is σ(x); use the infinitesimal element method to intercept a micro-segment dx, then at any temperature T, the length of the screw after being stressed is [[1 + E -1 σ(x)](1 + γΔT)dx. At this time, the length L σ,T of the stressed part of the screw is expressed as:

[0108]

[0109] where, E is the Young's modulus of the material, and γ is the linear expansion coefficient.

[0110] Obtain the propagation time of the ultrasonic longitudinal wave on the deformation of the clamp screw, specifically:

[0111]

[0112] Among them, the propagation time of the ultrasonic longitudinal wave on the micro-segment is the length of the micro-segment divided by the longitudinal wave velocity;

[0113] The obtaining of the round-trip transit time of the ultrasonic longitudinal wave in the screw is specifically:

[0114]

[0115] Combining formula (6) and formula (8), we can get:

[0116]

[0117] Among them, ε is a point within the integration interval [0, L e , and σ(ε) represents the average axial stress in the stress interval.

[0118] S105: Based on the round-trip transit time of the ultrasonic longitudinal wave in the screw and the particle swarm detection algorithm, construct a fitness function;

[0119] The particle swarm detection algorithm is applicable to solving single-objective optimization problems. Combining formula (8), establish a fitness function:

[0120]

[0121] Among them, the fitness function f is the optimization objective of the particle swarm algorithm. Through the iteration of the particle swarm algorithm, continuously search for the minimum value of the fitness function to obtain the optimal solution of the variable.

[0122] S106: Based on the particle swarm detection algorithm, update the velocity and position of the particles in the particle swarm, and then continuously optimize the fitness function value of the particles, update the individual optimal value and optimal position of each particle, and update the global optimal value and optimal position of all particles;

[0123] See Figure 4 , based on the particle swarm detection algorithm, update the velocity and position of the particles in the particle swarm, specifically:

[0124] Step 1: Initialize the particle swarm parameters, including the number of particles P, learning factors c 1 , c 2 , the maximum number of iterations T and the position search range; take the elastic modulus, acoustoelastic coefficient and longitudinal wave velocity of the clamp screw as input values;

[0125] Step 2: Randomly generate the initial position and velocity of each particle. The position is the effective clamping length L eTwo-dimensional matrix of the sum average axial stress σ(ε);

[0126] Step 3: Calculate the fitness function value of the particles, save the individual optimal value and optimal position of each particle, and save the global optimal value and optimal position of all particles;

[0127] Step 4: Update the velocity and position of each particle;

[0128] Step 5: Recalculate the fitness function value of the particles, update the individual optimal value and optimal position of each particle, and update the global optimal value and optimal position of all particles;

[0129] Step 6: Repeat the above steps until the maximum number of iterations is reached or the loop end condition is satisfied, then exit the loop, and output the global optimal position, that is, the effective clamping length L e and the optimal value of the average axial stress σ(ε), so as to obtain the screw force of the clamp screw shaft.

[0130] S107: When the preset threshold condition is reached, the particle swarm detection algorithm outputs the global optimal position of all particles and obtains the screw force of the clamp screw shaft.

[0131] Update the velocity and position of each particle. Specifically, the velocity and position update formulas of the particle swarm algorithm are respectively:

[0132]

[0133] X i (t) = V i (t) + X i (t - 1) (12)

[0134] where V i (t) = [V i1 (t), … V iN (t)] T and X i (t) = [X i1 (t), … X iN (t)] T respectively represent the N-dimensional velocity and position matrices of the i-th particle in the t-th iteration, i = 1 … P, P is the number of particles, t = 1 … T, T is the maximum number of iterations; X i pbest is the individual optimal value of the i-th particle in the iterative process, and X gbest is the global optimal value searched by all particles; w(t) represents the inertia weight, which reflects the influence of the previous iteration velocity on the current velocity; the larger w(t) is, the stronger the global search ability of the particle is, and it can avoid falling into the local optimal solution; c 1 、c 2are the individual learning factor and the social learning factor, which reflect the inheritance and learning of the particle for the individual optimal value and the local optimal value in the iterative process; r 1 and r 2 are random numbers between 0 and 1.

[0135] Obtain the screw force of the clamp screw shaft. Specifically: Multiply the optimal value of the measured average axial stress σ(ε) by the cross-sectional area of the screw to obtain the screw force of the clamp screw shaft; The cross-sectional area of the screw is obtained by measuring the cross-section of the screw.

[0136] See Figure 5 , the present invention discloses an ultrasonic detection system for the axial force of a clamp screw shaft considering non-uniform temperature and stress distributions, including:

[0137] Acquisition module, the acquisition module acquires the length data of the clamp screw before and after being stressed, and constructs a two-dimensional simplified model of the stressed clamp screw;

[0138] First acquisition module, the first acquisition module is based on the length data of the clamp screw before being stressed and the two-dimensional simplified model of the stressed state, and acquires the wave velocity of the ultrasonic longitudinal wave in the clamp screw under the state of zero stress and standard calibration temperature;

[0139] Fitting module, the fitting module measures and records the wave velocity of the ultrasonic longitudinal wave of the screw at different temperatures, obtains the arrival time of the screw at different temperatures under the zero stress state, and obtains the temperature coefficient through linear fitting;

[0140] Second acquisition module, the second acquisition module is based on the deformation amount of the clamp screw after being stressed, the temperature coefficient, and the wave velocity of the ultrasonic longitudinal wave in the clamp screw, and compensates for the temperature effect considering the ambient temperature, obtains the propagation time of the ultrasonic longitudinal wave on the deformation amount of the clamp screw, and further obtains the round-trip transit time of the ultrasonic longitudinal wave in the screw;

[0141] Construction module, the construction module constructs a fitness function based on the round-trip transit time of the ultrasonic longitudinal wave in the screw and the particle swarm detection algorithm;

[0142] Update module, the update module updates the particle velocity and position in the particle swarm based on the particle swarm detection algorithm, and then continuously optimizes the fitness function value of the particle, updates the individual optimal value and the optimal position of each particle, and updates the global optimal value and the optimal position of all particles;

[0143] Third acquisition module, when the preset threshold condition is reached, the particle swarm detection algorithm outputs the global optimal position of all particles, and obtains the screw force of the clamp screw shaft.

[0144] Embodiment:

[0145] The present invention discloses an ultrasonic detection method for the axial force of the cable clamp screw considering the uneven distribution of temperature and stress, including: first measuring the Young's modulus of the screw, as well as the longitudinal wave velocity and acoustoelastic coefficient in the stress-free state, then obtaining the propagation time of the ultrasonic longitudinal wave on the deformation of the cable clamp screw, and further obtaining the round-trip transit time of the ultrasonic longitudinal wave in the screw, and constructing a fitness function; based on the particle swarm detection algorithm, updating the velocity and position of the particles in the particle swarm, and further continuously optimizing the fitness function value of the particles, updating the individual optimal value and optimal position of each particle, and updating the global optimal value and optimal position of all particles; when the preset threshold condition is reached, the particle swarm detection algorithm outputs the global optimal position of all particles, and obtains the axial force of the cable clamp screw shaft.

[0146] First, select two screws of the same batch as test specimens. One is used as a calibration piece to measure the Young's modulus of the screw, the longitudinal wave velocity and acoustoelastic coefficient in the stress-free state; the other is used as a test piece to measure the axial force using the parameters of the calibration piece to verify the correctness of the ultrasonic detection method. The parameters of the test specimens are shown in Table 1. The high-strength nut material is 35CrMo, which meets the type dimensions and technical condition requirements of GB / T 1229-2006 "High-strength large hexagon nuts for steel structures".

[0147] Table 1 Screw parameters

[0148] Specimen Material Original length / mm Outer diameter / mm Tensile strength / MPa Calibration piece 40CrNiMoA 450 34.4 ≥980 Test piece 40CrNiMoA 409.62 34.4 ≥980

[0149] Measure the screw parameters. The Young's modulus of the calibration piece is measured by the static method. Use a WAW-1000-G universal testing machine to apply axial tension to the test specimen, and use a contact electronic extensometer with a gauge length of 250 mm to measure its deformation. Fit the stress-strain curve of the test specimen to obtain the Young's modulus. First, apply an initial test force of 50 kN to the test specimen to eliminate the deviations caused by gaps, specimen arcs, original chucks, etc., and then load it to 150 kN at a speed of 1 (kN·s -1 ) until it reaches 150 kN. Repeat the test three times.

[0150] To determine the acoustoelastic coefficient of the calibration piece, it is necessary to stretch the test specimen and collect the longitudinal wave echo signal. See Figure 6, the upper and lower ends are auxiliary loading devices, which ensure the installation space of the longitudinal wave probe and can avoid the bending stress in the bolts. The end face of the screw rod is polished smooth and wiped clean with alcohol, and ultrasonic longitudinal wave coupling agent is evenly applied on the end face to improve the coupling effect between the longitudinal wave probe and the specimen. A longitudinal wave probe with a center frequency of 2.25 MHz is used, and the longitudinal wave probe is installed on the end face of the screw rod of the calibration piece, and the longitudinal wave echo signal is transmitted and received by using the CTS 8077PR of Shantou Ultrasonic. An ultrasonic signal acquisition system is developed based on the LabVIEW program. The distance Ln between the inner sides of the nuts at both ends of the specimen and the effective clamping length Le are changed, and the longitudinal wave echo signals under different axial forces are measured. The test scheme is shown in Table 2, and a total of 3 groups of tests are carried out.

[0151] To avoid the influence of residual stress, the longitudinal wave velocity of the calibration piece in the stress-free state should be measured in advance before loading. The test device is the same as Figure 6 that, and the longitudinal wave echo signal of the screw rod without axial force is measured. The signal is collected three times to reduce errors.

[0152] Table 2 Test scheme for acoustic elasticity coefficient measurement

[0153]

[0154] The Young's modulus is fitted. The test data of the Young's modulus measured in three groups are processed, and the stress-strain values of the screw rod are linearly fitted. The results are as Figure 7 shown. The linear relationship between stress and strain in the three groups of tests is significant (in the first group of tests, it was not loaded to 150 kN and some data were missing). The slope of the fitted straight line is the value of the Young's modulus. The average value of the three groups of tests is taken, and the Young's modulus of the screw rod is obtained as 206.19 GPa.

[0155] Calculate the stress-free state wave velocity and acoustic elasticity coefficient of the ultrasonic longitudinal wave; the emission and echo signals of the ultrasonic longitudinal wave are as Figure 8 shown. The first and second echo signals are intercepted. The echo signals are highly similar. The acoustic time difference between the two echoes is calculated by using the autocorrelation algorithm, that is, the transit time of the longitudinal wave traveling back and forth in the screw rod. This method can avoid the pulse delay caused by the propagation of the longitudinal wave in the cable and the acoustic coupling layer. Wavelet denoising is used to reduce the influence of noise and improve the calculation accuracy of the acoustic time difference. The autocorrelation calculation results of the two echo signals after denoising in this test are as Figure 9 shown.

[0156] The formula for calculating the stress-free state wave velocity of the ultrasonic longitudinal wave is:

[0157]

[0158] where, t L0is the transit time in the stress-free state of the longitudinal wave. The measurement results of the wave velocities of the three groups of longitudinal waves in the stress-free state are shown in Table 3, and the average wave velocity is 5893.3 (m·s -1 ).

[0159] Table 3 Measurement Results of Longitudinal Wave Velocities in the Stress-Free State

[0160]

[0161] As can be seen from Equation (3), the change in the ultrasonic longitudinal wave velocity affected by stress is very small and can be approximated as a first-order infinitesimal:

[0162] V L0 ≈V L (14)

[0163] Taking the differential of both sides of Equation (3) and combining with Equation (14), we can obtain:

[0164]

[0165] Substituting V L =2L i / t L into Equation (15), we can obtain:

[0166]

[0167] It can be seen from this that there is an approximate linear relationship between stress and the longitudinal wave transit time, and the acoustoelastic coefficient can be obtained through fitting. The fitting results of the three groups of loading tests of the calibration specimens are as Figure 10 shown. Since the third group of data deviates greatly from the test results of the first two groups, the third group of results is discarded, and the average value of the test acoustoelastic coefficient is -3.092×10 -11 .

[0168] To verify the correctness of the proposed method, the same tensile test as that of the calibration specimen was carried out on the test specimen, and the longitudinal wave echo signal was collected. The test scheme is shown in Table 4. By changing the screw clamping length, the echo signals under different axial forces were collected.

[0169] Table 4 Tensile Test Scheme of the Test Specimen

[0170]

[0171] Using the autocorrelation algorithm to calculate the longitudinal wave transit time t L , substituting t L and the measured screw parameters in Table 1 into Equation (9), setting the search ranges of the effective clamping length L e and the average axial stress σ(ε), and obtaining the effective clamping length L e by iteratively searching for the minimum value of the fitness functionand the optimal value of the average axial stress σ(ε), and then calculate the measured axial force of the screw. The inner distance of the nuts in the first group of tests is 264.78 mm, and the search range of the effective clamping length is [260, 280] mm; the inner distance of the nuts in the second group is 293.36 mm, and the range is [290, 310] mm. The search range of the average axial stress is [0, 360] MPa. Multiply the measured average axial stress by the cross-sectional area of the screw to convert it into axial force. Since the search results of the particle swarm algorithm are random, search 5 times for each axial force state and take the average value. The measurement results are shown in Tables 5 and 6.

[0172] Table 5 Measurement Results of Axial Force by Ultrasonic Wave in the First Group

[0173]

[0174] Table 6 Measurement Results of Axial Force by Ultrasonic Wave in the Second Group

[0175]

[0176] It can be seen from Tables 5 and 6 that there is a positive correlation between the axial force and the acoustic time. The larger the acoustic time, the greater the corresponding axial force. The average measured values of the effective clamping lengths of the screws in the two groups of tests are 268.48 mm and 299.22 mm respectively. The measured values of the effective clamping length penetrate into the inner side of the nut, meeting the definition of the screw clamping length. According to the "Technical Specification for Maintenance of Highway Cable Structure System Bridges" (JTGT 5122—2021) in China, it is stipulated that "the axial force of the cable clamp screw should be kept not less than 70% of its installation design value". The results show that at 70% of the maximum test stress, the relative error is less than 7.22%, and the measurement results have little fluctuation, verifying the robustness of the ultrasonic detection method. The effective clamping lengths measured by the ultrasonic detection method are 3.7 mm and 5.9 mm greater than the inner distance of the nut respectively, and the penetration length is about 7% of the nut thickness, which is in line with the actual stress situation of the screw. If the empirical formula is used for estimation, it is the length of the inner distance of the nut plus the outer diameter of the screw, exceeding the inner distance of the screw by 34.4 mm, which does not match the actual stress length of the screw. Therefore, the effective clamping length of the large-diameter screw cannot be estimated by the empirical formula, which will cause a large error.

[0177] When the axial force is small, the absolute error and relative error of the axial force measured by ultrasonic testing are large. For example, when the theoretical axial force is 40 kN, the absolute error is 29.83 kN and the relative error is as high as 74.58%. The large measurement error when the axial force is small may be caused by the measurement error of the transit time. When the tensile force is small, the axial stress of the bolt is small, the axial elongation is small, and the change in wave velocity is not obvious, resulting in an insignificant change in the transit time of the longitudinal wave. Therefore, the measurement error of the transit time is large when the tensile force is small. For example, the transit times measured at 100 kN and 80 kN in Tables 5 and 6 are both 0.13926 μs, but theoretically, the transit time at 100 kN should be larger. Therefore, errors are introduced when substituting the transit time into the particle swarm algorithm for solution. As the actual axial force increases, the absolute error and relative error gradually decrease. The absolute error and relative error at 300 kN are reduced to 13.05 kN and 4.35%, respectively. Therefore, the present invention is applicable to the measurement of high stresses of the cable clip screws of suspension bridges.

[0178] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, various modifications and variations can be made to the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An ultrasonic detection method for the axial force of a cable clamp screw considering the uneven distribution of temperature and stress, characterized in that: include: Collect the length data of the cable clamp screw before and after being stressed, and construct a simplified two-dimensional stress model of the cable clamp screw; Based on the length data of the cable clamp screw before being stressed and the simplified two-dimensional stress model, the wave velocity of the ultrasonic longitudinal wave in the cable clamp screw under zero stress and standard calibration temperature is obtained; The ultrasonic longitudinal wave velocity test of the screw was carried out at different temperatures and recorded to obtain the arrival time of the screw at different temperatures in the zero stress state, and the temperature coefficient was obtained by linear fitting; Based on the deformation of the cable clamp screw after being stressed, the temperature coefficient and the wave velocity of the ultrasonic longitudinal wave in the cable clamp screw, and considering the ambient temperature, the temperature effect is compensated, the propagation time of the ultrasonic longitudinal wave on the deformation of the cable clamp screw is obtained, and then the round-trip transit time of the ultrasonic longitudinal wave in the screw is obtained; Based on the round-trip transit time of ultrasonic longitudinal waves in the screw and the particle swarm detection algorithm, a fitness function is constructed; Based on the particle swarm detection algorithm, the particle speed and position in the particle swarm are updated, and then the fitness function value of the particles is continuously optimized, the individual optimal value and optimal position of each particle are updated, and the global optimal value and optimal position of all particles are updated; When the preset threshold condition is reached, the particle swarm detection algorithm outputs the global optimal position of all particles and obtains the screw force of the cable clamp screw shaft; The wave velocity of the ultrasonic longitudinal wave in the cable clamp screw under the zero stress state is obtained as follows: Based on the acoustic elasticity theory, the relationship between the wave velocity of the ultrasonic longitudinal wave propagating along the stress direction in a uniform isotropic material and the stress is: Where ρ0 is the density of the material; V L is the longitudinal wave velocity; λ and μ are the second-order elastic constants; m and l are the third-order elastic constants; σ is the stress value in the material; Among them, at the standard calibration temperature T0, the wave velocity of ultrasonic longitudinal wave in zero stress state is: Substituting formula (2) into formula (1), we can obtain the relationship between longitudinal wave velocity and stress at the standard calibration temperature T0: Among them, A L A is the acoustic elastic coefficient of ultrasonic longitudinal wave; L It is a negative value, that is, the longitudinal wave velocity decreases with the increase of stress; The temperature coefficient is obtained by linear fitting, specifically: α=Δt / ΔT Wherein, ΔT=T-T0; T is any temperature; Δt is the time difference of ultrasonic longitudinal wave velocity passing through the cable clamp screw at different temperatures; At the standard calibration temperature T0, the deformation amount of the cable clamp screw after being subjected to force is specifically as follows: both ends of the cable clamp screw are threads, and nuts are fixedly arranged on the threads at both ends of the cable clamp screw; the nut arranged at the other end of the cable clamp screw is deformed under the action of external force; the length of the force-bearing area of ​​the cable clamp screw becomes L σ , the length of the unstressed part is still L0; the original length of the stressed part is the effective clamping length L e , its length is between the outer distance and inner distance of the nuts at both ends; the original length of the screw L i It is expressed as: L i =L e +L0 (4) Under zero stress state and at any temperature T, the wave velocity is corrected as follows: Where, t(T0) is the arrival time at the calibration temperature; Assuming that the stress on each section of the force-bearing part is the same, the stress distribution curve along the axial direction is σ(x); using the infinitesimal method to intercept the micro-segment dx, the length of the micro-segment after the screw is subjected to force at any temperature T is [[1+E -1 σ(x)](1+γΔT)dx, at this time, the length of the force-bearing part of the screw is L σ,T It is expressed as: Where E is the Young's modulus of the material, and γ is the linear expansion coefficient; The acquisition of the propagation time of the ultrasonic longitudinal wave on the deformation of the cable clamp screw is specifically as follows: Among them, the propagation time of ultrasonic longitudinal wave on the micro segment is the length of the micro segment divided by the longitudinal wave velocity; The method of obtaining the round trip transit time of the ultrasonic longitudinal wave in the screw is specifically as follows: Combining formula (6) and formula (8), we can get: Among them, ε is the integration interval [0,L e ], σ(ε) represents the average axial stress in the stress interval; The fitness function is constructed based on the round-trip transit time of the ultrasonic longitudinal wave in the screw and the particle swarm detection algorithm. Specifically, the particle swarm detection algorithm is suitable for solving single-objective optimization problems. Combined with formula (9), the fitness function is established: Among them, the fitness function f is the optimization target of the particle swarm algorithm. Through the iteration of the particle swarm algorithm, the minimum value of the fitness function is continuously searched to obtain the optimal solution of the variable; The particle swarm detection algorithm is based on which the particle speed and position in the particle swarm are updated, specifically: Step 1: Initialize the particle swarm parameters, including the number of particles P, learning factors c1, c2, maximum number of iterations T, and position search range; take the elastic modulus, acoustic elastic coefficient, and longitudinal wave velocity of the cable clamp screw as input values; Step 2: Randomly generate the initial position and velocity of each particle. The position includes the effective clamping length L. e and the two-dimensional matrix of the mean axial stress σ(ε); Step 3: Calculate the fitness function value of the particle, save the individual optimal value and optimal position of each particle, and save the global optimal value and optimal position of all particles; Step 4: Update the velocity and position of each particle; Step 5: Recalculate the fitness function value of the particle, update the individual optimal value and optimal position of each particle, and update the global optimal value and optimal position of all particles; Step 6: Repeat the above steps until the maximum number of iterations is reached or the loop end condition is met, then exit the loop and output the global optimal position, i.e., the effective clamping length L. e and the optimal value of the average axial stress σ(ε), thereby obtaining the screw force of the cable clamp screw shaft; The updating of the speed and position of each particle is specifically as follows: The speed and position updating formulas of the particle swarm algorithm are: X i (t)=V i (t)+X i (t-1) (12) Among them, V i (t)=[V i1 (t),…V iN (t)] T and X i (t) = [X i1 (t),…X iN (t)] T They represent the N-dimensional velocity and position matrices of particle i for t iterations, i = 1…P, P is the number of particles, t = 1…T, T is the maximum number of iterations; X i pbest is the individual optimal value of particle i in the iteration process, X gbest is the global optimal value searched by all particles; w(t) represents the inertia weight, which reflects the influence of the previous iteration speed on the current speed; the larger w(t) is, the stronger the global search ability of the particle is, and it can avoid falling into the local optimal solution; c1 and c2 are individual learning factors and social learning factors, which reflect the inheritance and learning of the individual optimal value and local optimal value of the particle in the iteration process; r1 and r2 are random numbers between 0 and 1.

2. The method for ultrasonically detecting the axial force of a cable clamp screw considering the uneven distribution of temperature and stress according to claim 1, characterized in that: The method of obtaining the screw force of the cable clamp screw shaft is specifically as follows: the optimal value of the measured average axial stress σ(ε) is multiplied by the cross-sectional area of ​​the screw to obtain the screw force of the cable clamp screw shaft; the cross-sectional area of ​​the screw is obtained by measuring the cross section of the screw.

3. The ultrasonic detection system for the axial force of the cable clamp screw considering the uneven distribution of temperature and stress is characterized by: The detection method according to claim 1 or 2, comprising: A collection module, wherein the collection module collects length data of the cable clamp screw before and after being subjected to force, and constructs a simplified two-dimensional force model of the cable clamp screw; A first acquisition module, which acquires the wave velocity of the ultrasonic longitudinal wave in the cable clamp screw under zero stress and standard calibration temperature state based on the length data of the cable clamp screw before being subjected to force and the simplified two-dimensional force model; A fitting module, wherein the fitting module performs ultrasonic longitudinal wave velocity measurement tests on the screw at different temperatures and records the results, obtains the arrival time of the screw at different temperatures in a zero stress state, and obtains the temperature coefficient by linear fitting; A second acquisition module, which is based on the deformation of the cable clamp screw after being stressed, the temperature coefficient and the wave velocity of the ultrasonic longitudinal wave in the cable clamp screw, and takes into account the ambient temperature to compensate for the temperature effect, and obtains the propagation time of the ultrasonic longitudinal wave on the deformation of the cable clamp screw, and then obtains the round-trip transit time of the ultrasonic longitudinal wave in the screw; A construction module, wherein the construction module constructs a fitness function based on the round-trip transit time of ultrasonic longitudinal waves in the screw and a particle swarm detection algorithm; An update module, which updates the speed and position of particles in the particle swarm based on a particle swarm detection algorithm, thereby continuously optimizing the fitness function value of the particles, updating the individual optimal value and optimal position of each particle, and updating the global optimal value and optimal position of all particles; The third acquisition module, when the preset threshold condition is reached, the particle swarm detection algorithm outputs the global optimal position of all particles and obtains the screw force of the cable clamp screw shaft.

Images