CN113109440A - Concrete material parameter evaluation method based on piezoelectric vibration mechanism and stress wave - Google Patents

Concrete material parameter evaluation method based on piezoelectric vibration mechanism and stress wave Download PDF

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CN113109440A
CN113109440A CN202110476918.3A CN202110476918A CN113109440A CN 113109440 A CN113109440 A CN 113109440A CN 202110476918 A CN202110476918 A CN 202110476918A CN 113109440 A CN113109440 A CN 113109440A
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乔丕忠
余海帆
陆林军
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Shanghai Jiaotong University Design And Research Institute Co ltd
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Abstract

The invention provides a concrete material parameter evaluation method based on a piezoelectric vibration mechanism and stress waves, aiming at providing a concrete dynamic elastic modulus and Poisson's ratio measurement scheme based on a piezoelectric sensor electromechanical conversion mechanism and a Rayleigh wave and body wave propagation mechanism, which comprises the proposal of a sensor arrangement scheme based on a piezoelectric exciter receiver vibration mechanism; optimizing the center frequency, the waveform and the size of the sensor of the excitation signal; the application of a physical model between dynamic characteristic parameters of different types of stress waves and propagation medium material parameters in signal processing. Compared with the prior art, the invention has the advantages that: the method does not depend on the traditional mathematical statistics signal processing technology any more, and has stronger universality; a clear dynamic physical model is used as a support, so that the engineering application reliability is high; the sensor placement scheme is researched based on the piezoelectric vibration mechanism theory, so that the signal-to-noise ratio can be effectively improved; the signal frequency response range is wide, the detection area is large, and the measurement scheme is economical and efficient.

Description

Concrete material parameter evaluation method based on piezoelectric vibration mechanism and stress wave
Technical Field
The invention relates to the field of concrete nondestructive testing, in particular to a concrete material parameter evaluation method based on a piezoelectric vibration mechanism and stress waves.
Background
Concrete is a widely used structural material in the capital construction projects such as buildings, bridges, tunnels, dams and the like. However, unreasonable maintenance conditions and severe service environment usually cause the degradation of concrete production materials and the accumulation of structural damage, which affect the structural safety and service life and cause accidents. Therefore, the establishment of a set of real-time and reliable concrete nondestructive testing system has urgent engineering requirements. The elastic modulus and the Poisson ratio are important evaluation parameters of the mechanical behavior and the service performance of the concrete structure, and domestic and foreign scholars propose a series of dynamic evaluation systems and measurement methods.
The existing concrete material parameter measuring methods can be generally divided into two main categories: destructive testing and non-destructive testing. The compression test is a destructive testing technology commonly used in engineering, but for a complex concrete structure, the method needs to prefabricate a large number of standard cube samples, and the samples can generate great difference with the performance of the actual structure due to different environments after the concrete structure is in service for many years; and it is generally undesirable in engineering to extract samples from the original structure for destructive testing. Another type of non-destructive testing method mainly comprises: acoustic Emission (AE), electromechanical Impedance (EMI), and Wave Propagation (WP). However, the test and engineering application cases based on the AE and EMI methods usually focus on establishing performance evaluation factors and damage factors based on mathematical statistics, and due to the lack of support of a physical model, the discreteness of test results is usually large, and the rule search of the test results is difficult. Therefore, the concrete material performance evaluation method based on the fluctuation method with clear physical significance is established, the problems that signal processing depends on statistics and a model is difficult to adapt to different working conditions in the concrete material performance evaluation process are solved, and the concrete material performance evaluation method has important academic significance and engineering value.
The wave velocity of a stress wave propagating in the concrete is related to the elastic modulus and the Poisson ratio to evaluate the material performance of the concrete by the wave motion method, and the exciting tool of the stress wave mainly comprises a force hammer and PZT. The hammering method is relatively susceptible to interference from environmental noise and requires a high skill and proficiency on the part of the operator. And PZT has better application prospect in concrete structure health monitoring because of the advantages of good signal linear relation, low power consumption, real-time monitoring and the like. The existing concrete nondestructive detection technology based on PZT usually ignores the influence of a sensor vibration mechanism and a stress wave propagation mechanism on a detection result, the stress wave propagation mechanism plays a crucial role in establishing the quantitative relation between information such as a stress wave amplitude and physical defects and damages of an object to be detected, and is also a key parameter for researching the attenuation of the stress wave, the selection of a target signal type usually depends on the information such as the stress wave amplitude, but no specific general solution or suggestion exists for selecting the target signal suitable for general conditions until now; on the other hand, the type of action of stress waves and the arrangement scheme of the sensors, which are closely related to the vibration mechanism of the sensors, are also important factors influencing the difficulty of signal processing and the detection effect, and the research on the aspect is not yet mature.
Therefore, a systematic concrete material parameter measuring method based on built-in and surface-bonded PZT is necessary, and the vibration mechanism and the stress wave propagation mechanism of the sensor are clear.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a concrete material parameter evaluation method based on a piezoelectric vibration mechanism and a stress wave, and provides a concrete dynamic elastic modulus and Poisson's ratio measurement scheme based on a piezoelectric sensor electromechanical conversion mechanism and a Rayleigh wave and body wave propagation mechanism.
In order to achieve the above object, the present invention provides a concrete material parameter evaluation method based on a piezoelectric vibration mechanism and rayleigh waves, comprising the steps of:
s1: determining an arrangement scheme of a piezoelectric sensor according to the vibration mechanism research of a piezoelectric actuator and a piezoelectric receiver, wherein the piezoelectric sensor comprises the piezoelectric actuator and the piezoelectric receiver; if the longitudinal wave is selected as the target signal, the placing angle of the piezoelectric exciter is 0 degree or 90 degrees, and the placing angle of the piezoelectric receiver is 0 degree; if the shear wave is selected as the target signal, the placing angle of the piezoelectric receiver is consistent with that of the piezoelectric exciter and is 0 degree or 90 degrees;
s2: designing an excitation signal according to the aggregate particle size of the concrete to be detected, and optimizing an excitation center frequency, a waveform and a sensor size selection scheme;
s3: the piezoelectric exciter generates mechanical vibration, the piezoelectric receiver captures Rayleigh wave and longitudinal wave signals, the Rayleigh wave and longitudinal wave signals are converted into electric signals, and the electric signals are recorded and processed by the collector and the algorithm program;
s4: calculating to obtain the dynamic elasticity modulus E and the Poisson ratio v of the concrete based on a physical model between the dynamic characteristic parameter of the stress wave and the material parameter of the concrete to be detected, wherein the physical model between the dynamic characteristic parameter of the stress wave and the material parameter of the concrete to be detected comprises a calculation formula:
Figure BDA0003047364260000031
Figure BDA0003047364260000032
wherein, cL、cS、cRThe propagation velocities of longitudinal waves, shear waves and Rayleigh waves in the concrete to be measured are respectively, and rho is the density of the concrete to be measured.
Preferably, the step S1 is preceded by the step of:
introducing the influence of the stress wave interface transmission effect between the concrete to be tested and the piezoelectric actuator on the signal to noise ratio into the optimization of the sensor arrangement scheme, wherein the calculation formula of the stress wave interface transmission ratio is as follows:
Figure BDA0003047364260000033
wherein A isTAnd I is transmitted and incident waves, respectivelyThe amplitude of the amplitude is,
Figure BDA0003047364260000034
and
Figure BDA0003047364260000035
the propagation speeds, rho, of longitudinal waves in the piezoelectric actuator and the concrete to be tested respectively1And ρ2The densities of the piezoelectric actuator and the concrete to be measured are respectively.
Preferably, in the step S1:
when the PZT receiver is used as the piezoelectric receiver, a voltage response to an external load or deformation in a thickness direction is more significant than that in a length or width direction, and the thickness direction of the piezoelectric receiver should be perpendicular to the vibration direction of the target signal particles.
Preferably, the piezoelectric sensor is divided into a built-in piezoelectric sensor and a surface-stuck piezoelectric sensor according to a fixing mode on the concrete to be measured; the built-in piezoelectric sensor comprises a built-in PZT sensor; the surface-mount piezoelectric sensor includes a surface-mount PZT sensor.
Preferably, the built-in PZT sensor comprises 1 piezoelectric actuator and 1 piezoelectric receiver, and the distance between the piezoelectric actuator and the piezoelectric receiver is set to be 2-5 times of the wavelength of the target signal; adopt including i surface-pasted PZT sensor's surface-pasted formula PZT sensor array, surface-pasted formula PZT sensor is followed the central point axial of the concrete surface that awaits measuring is pasted fixedly, and i is the natural number that is greater than 1, piezoelectric actuator and first surface-pasted formula PZT sensor piezoelectric receiver's interval is each at least 2 times of surface-pasted formula PZT sensor distance between the piezoelectric receiver.
Preferably, the built-in PZT sensor is sequentially packaged, cured and maintained through a waterproof insulating glue layer and a concrete protective layer and then is built in a to-be-detected area in the to-be-detected concrete; the surface-bonded PZT sensor is bonded on the surface of the concrete to be detected through an adhesive prepared from epoxy resin and a curing agent according to a ratio of 2: 1.
Preferably, in the step S2:
the excitation signal is a sine pulse signal subjected to Hanning window function windowing, the excitation center frequency is 40-100 kHz, the number of wave crests of the waveform is 5-7, and the length-thickness ratio of the size of the sensor is 10-20.
Preferably, the step of S3 further comprises the steps of:
carrying out Fourier transform on the preset excitation signal to obtain a frequency domain signal;
setting the frequency corresponding to the 1 st sidelobe on the two sides of the main lobe of the frequency domain signal as the band-pass filtering frequency of a filter, and filtering noise in the stress wave signal;
and acquiring the stress wave signals for filtering the environmental noise by using an oscilloscope, and automatically identifying the time when different stress waves reach each PZT receiver by using a program algorithm so as to calculate the wave velocity of the stress waves.
Preferably, the automatically identifying, by a programmed algorithm, the time at which the different stress waves reach each of the PZT receivers comprises the steps of:
performing Hilbert-Huang transformation on the stress wave signal to obtain an envelope curve of a wave packet;
taking the time corresponding to the maximum amplitude point of the envelope curve of the 1 st arrival wave packet of the PZT receiver of the built-in PZT sensor as the arrival time of the longitudinal wave through a program;
using a program to take the maximum amplitude point corresponding to the envelope curve of the 2 nd arrival wave packet of the PZT receiver of the built-in PZT sensor as the arrival time of the shear wave;
and taking the time corresponding to the maximum amplitude point of the envelope curve of the 2 nd arrival wave packet of the PZT receiver of the surface-mounted PZT sensor as the Rayleigh arrival time by a program.
Due to the adoption of the technical scheme, the invention has the following beneficial effects:
the piezoelectric sensor arrangement scheme provided by the embodiment of the invention is based on the research of a piezoelectric vibration mechanism theory, the influence of the transmission effect of the sensor and the interface of the structure to be detected and the vibration mechanism of the exciter receiver on the detection result is fully considered, and the signal-to-noise ratio and the detection precision can be effectively improved by the optimization scheme.
The material parameter acquisition method disclosed by the embodiment of the invention does not depend on traditional mathematical statistics signal processing technologies such as fitting and fuzzy logic, takes a clear dynamic physical model as a support, directly combines three types of stress waves through physical relations to simultaneously acquire the Poisson's ratio and the elastic modulus of the concrete, has stronger universality, and has the advantages of wide signal frequency response range, large detection area, economic and efficient measurement scheme, simple operation process and wide engineering application prospect.
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FIG. 1 is a schematic view of an application scenario of a concrete material parameter evaluation method based on a piezoelectric vibration mechanism and stress waves according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of a PZT sensor vibration mechanism and an arrangement optimization scheme of a concrete material parameter evaluation method based on a piezoelectric vibration mechanism and stress waves according to an embodiment of the invention;
fig. 3 is a flow chart of a concrete material parameter evaluation method based on a piezoelectric vibration mechanism and stress waves according to an embodiment of the invention.
Detailed Description
The following description of the preferred embodiments of the present invention will be provided in conjunction with the accompanying drawings, which are set forth in detail below to provide a better understanding of the function and features of the invention.
Referring to fig. 1, a concrete material parameter evaluation method based on piezoelectric vibration mechanism and stress wave according to an embodiment of the present invention is applied to a nondestructive testing system as shown in fig. 1, where the system includes a signal generator 1, an amplifier 2, a filter 3, an oscilloscope 4, a concrete structure 5 to be tested, a PZT actuator 6 with built-in and surface-mounted structures, and a PZT receiver array 7 with built-in and surface-mounted structures; the signal generator 1, the amplifier 2 and the PZT actuator 6 are connected in sequence; the PZT receiver array 7, the filter 3, and the oscilloscope 4 are connected in sequence.
Referring to fig. 2, a PZT sensor arrangement optimization scheme for a concrete material parameter evaluation method based on a piezoelectric vibration mechanism and stress waves according to an embodiment of the present invention is based on a study on a piezoelectric effect of an exciter and a receiver, a vibration mechanism, and different types of stress wave action mechanisms, and in order to maximize a target signal and improve a signal-to-noise ratio and an effective signal identification accuracy, 4 cases of PZT receivers which are placed perpendicular to each other and take longitudinal waves and shear waves as target signals are respectively considered, and a PZT sensor arrangement optimization scheme is summarized from a theoretical angle of a constitutive equation and a result of numerical simulation verification.
Referring to fig. 1 to 3, for convenience of understanding, the following explains an embodiment of the present invention by taking an embodiment of the present invention applied to the monitoring system as an example, and a method for evaluating concrete material parameters based on a piezoelectric vibration mechanism and a stress wave according to an embodiment of the present invention includes the steps of:
s1: determining an arrangement scheme of a piezoelectric sensor according to the vibration mechanism research of a piezoelectric actuator and a piezoelectric receiver, wherein the piezoelectric sensor comprises the piezoelectric actuator and the piezoelectric receiver; if the longitudinal wave is selected as the target signal, the placing angle of the piezoelectric exciter is 0 degree or 90 degrees, and the placing angle of the piezoelectric receiver is 0 degree; if the shear wave is selected as a target signal, the placing angle of the receiver is consistent with that of the exciter, namely, the placing angle is 0 degree or 90 degrees;
preferably, S1 is preceded by the step of:
the influence of stress wave interface transmission effect between the concrete to be tested and the piezoelectric actuator on the signal to noise ratio is introduced into the optimization of the sensor arrangement scheme, and the calculation formula of the stress wave interface transmission ratio is as follows:
Figure BDA0003047364260000061
wherein A isTAnd I is the amplitude of the transmitted and incident waves respectively,
Figure BDA0003047364260000062
and
Figure BDA0003047364260000063
longitudinal waves in the piezoelectric actuator and the concrete to be tested respectivelyPropagation velocity of p1And ρ2The densities of the piezoelectric actuator and the concrete to be measured are respectively.
In the step S1:
when the PZT receiver is used as the piezoelectric receiver, a voltage response to an external load or deformation in the thickness direction is more significant than in the length or width direction, and the thickness direction of the piezoelectric receiver should be perpendicular to the vibration direction of the target signal particles.
Preferably, the built-in PZT sensor is sequentially packaged, cured and maintained through a waterproof insulating glue layer and a concrete protective layer and then is built in a to-be-detected area in the to-be-detected concrete; the surface-adhered PZT sensor is adhered to the surface of the concrete to be measured by an adhesive prepared from epoxy resin and a curing agent according to the ratio of 2: 1.
S2: designing an excitation signal according to the aggregate particle size of the concrete to be detected, and optimizing an excitation center frequency, a waveform and a sensor size selection scheme;
illustratively, a preset excitation signal is sent to PZT actuators inside and on the surface of the concrete to be tested, and the excitation signal is a sine pulse signal after a Hanning window function is added.
In some embodiments, the concrete aggregate has a particle size of 16mm, the wavelength range of the stress wave is larger than the particle size to weaken the scattering effect of the aggregate interface, preferably, the excitation center frequency is 40 kHz-100 kHz, the wave crest number of the wave form is 5-7, and the length-thickness ratio of the sensor size is 10-20.
S3: the piezoelectric exciter generates mechanical vibration, the piezoelectric receiver captures Rayleigh wave and longitudinal wave signals, the Rayleigh wave and longitudinal wave signals are converted into electric signals, and the electric signals are recorded and processed by the collector and the algorithm program;
illustratively, signal generator 1 is of the type Tektronix AFG-3152C; the model of the signal amplifier 2 is Agitek ATA-2032, and the model of the filter 3 is Krohn-Hite 3944; the oscilloscope 4 is model Tektronix MDO-3054.
Preferably, the piezoelectric sensor is divided into a built-in piezoelectric sensor and a surface-stuck piezoelectric sensor according to a fixing mode on the concrete to be measured; the built-in piezoelectric sensor comprises a built-in PZT sensor; the surface-mount piezoelectric sensor includes a surface-mount PZT sensor.
In order to improve the accuracy of the wave velocity of the stress wave and further improve the measurement precision, the built-in PZT sensor comprises 1 piezoelectric exciter and 1 piezoelectric receiver, and the distance between the piezoelectric exciter and the piezoelectric receiver is set to be 2-5 times of the wavelength of a target signal; the method comprises the steps that a surface-pasted PZT sensor array comprising i surface-pasted PZT sensors is adopted, the surface-pasted PZT sensors are pasted and fixed along the axial direction of the central point of the surface of the concrete to be measured, i is a natural number larger than 1, and the distance between a piezoelectric actuator and a piezoelectric receiver of a first surface-pasted PZT sensor is at least 2 times that between the piezoelectric receivers of the surface-pasted PZT sensors.
Preferably, the filtering of the noise signal in the received signal comprises the steps of:
carrying out Fourier transform on a preset excitation signal to obtain a frequency domain signal;
setting the frequency corresponding to the 1 st sidelobe at two sides of the main lobe of the frequency domain signal as the band-pass filtering frequency of a filter 3, and filtering noise in the stress wave signal;
illustratively, the bandpass filtering frequencies corresponding to different excitation signals used in the embodiment of the present invention are shown in table 1:
TABLE 1 selection table of band-pass filtering frequency (kHz)
Figure BDA0003047364260000081
And acquiring stress wave signals for filtering environmental noise by using the oscilloscope 4, and automatically identifying the time when different stress waves reach each PZT receiver by using a program algorithm so as to calculate the wave velocity of the stress waves.
S4: the method comprises the following steps of calculating to obtain the dynamic elasticity modulus E and the Poisson ratio v of the concrete based on a physical model between the dynamic characteristic parameter of the stress wave and the material parameter of the concrete to be detected, wherein the physical model between the dynamic characteristic parameter of the stress wave and the material parameter of the concrete to be detected comprises a calculation formula:
Figure BDA0003047364260000082
Figure BDA0003047364260000083
wherein, cL、cS、cRThe propagation velocities of the longitudinal wave, the shear wave and the Rayleigh wave in the concrete to be measured are respectively, and rho is the density of the concrete to be measured.
Preferably, the step of automatically identifying by a programmed algorithm the time at which the different stress waves reach the respective PZT receiver comprises the steps of:
performing Hilbert-Huang transformation on the stress wave signal to obtain an envelope curve of the wave packet;
taking the time corresponding to the maximum amplitude point of the envelope curve of the 1 st arrival wave packet of the PZT receiver of the built-in PZT sensor as the arrival time of the longitudinal wave through a program;
using a program to take the time corresponding to the maximum amplitude point of the envelope curve of the 2 nd arrival wave packet of the PZT receiver of the built-in PZT sensor as the arrival time of the shear wave;
and (3) taking the corresponding time of the maximum amplitude point of the envelope curve of the 2 nd arrival wave packet of the PZT receiver of the surface-mounted PZT sensor as the Rayleigh arrival time by a program.
In order to compare and verify the effectiveness of the embodiment of the invention, a cube standard compressive strength test is carried out in the embodiment of the invention, and the elastic modulus of the concrete is calculated to be 30.4 GPa. According to the embodiment of the invention, under different working conditions, the concrete elastic modulus (WMoE) measured based on the fluctuation method of the surface-bonded PZT is respectively shown in the following tables 2, 2 and 4:
TABLE 2 WMoE TABLE FOR VARYING CENTRE FREQUENCY OF EXCITATION
Figure BDA0003047364260000091
The waveform is 5 peak wave, and the PZT sensor size is 10X 1 mm.
TABLE 3 WMoE TABLE UNDER DIFFERENT EXCITATION WAVEFORMS
Figure BDA0003047364260000092
The center frequency of the excitation was 40kHz and the PZT sensor size was 10X 1 mm.
TABLE 4 WMoE METER UNDER PZT SENSORS WITH DIFFERENT SIZES
Figure BDA0003047364260000093
The excitation center frequency is 40kHz, and the waveform is 5 peak waves.
As can be seen from the data in tables 2, 3 and 4, the excitation center frequency is selected to be 40-100 kHz, the excitation waveform is selected to be 5-7 peak waves, the width-to-thickness ratio of the PZT sensor is selected to be 10-20 (thickness is 1mm), and the measurement accuracy of the elastic modulus of the concrete based on the surface-bonded PZT fluctuation method is high and is within 10%.
Compared with the prior art, the invention has the following beneficial effects and advantages:
the piezoelectric sensor arrangement scheme provided by the embodiment of the invention is based on the research of a piezoelectric vibration mechanism theory, the influence of the transmission effect of the sensor and the interface of the structure to be detected and the vibration mechanism of the exciter receiver on the detection result is fully considered, and the signal-to-noise ratio and the detection precision can be effectively improved by the optimization scheme.
The material parameter acquisition method disclosed by the embodiment of the invention does not depend on traditional mathematical statistics signal processing technologies such as fitting and fuzzy logic, takes a clear dynamic physical model as a support, directly combines three types of stress waves through physical relations to simultaneously acquire the Poisson's ratio and the elastic modulus of the concrete, has stronger universality, and has the advantages of wide signal frequency response range, large detection area, economic and efficient measurement scheme, simple operation process and wide engineering application prospect.
While the present invention has been described in detail and with reference to the embodiments thereof as illustrated in the accompanying drawings, it will be apparent to one skilled in the art that various changes and modifications can be made therein. Therefore, certain details of the embodiments are not to be interpreted as limiting, and the scope of the invention is to be determined by the appended claims.

Claims (9)

1. A concrete material parameter evaluation method based on a piezoelectric vibration mechanism and stress waves comprises the following steps:
s1: determining an arrangement scheme of a piezoelectric sensor according to the vibration mechanism research of a piezoelectric actuator and a piezoelectric receiver, wherein the piezoelectric sensor comprises the piezoelectric actuator and the piezoelectric receiver; if the longitudinal wave is selected as the target signal, the placing angle of the piezoelectric exciter is 0 degree or 90 degrees, and the placing angle of the piezoelectric receiver is 0 degree; if the shear wave is selected as the target signal, the placing angle of the piezoelectric receiver is consistent with that of the piezoelectric exciter and is 0 degree or 90 degrees;
s2: designing an excitation signal according to the aggregate particle size of the concrete to be detected, and optimizing an excitation center frequency, a waveform and a sensor size selection scheme;
s3: the piezoelectric exciter generates mechanical vibration, the piezoelectric receiver captures Rayleigh wave and longitudinal wave signals, the Rayleigh wave and longitudinal wave signals are converted into electric signals, and the electric signals are recorded and processed by the collector and the algorithm program;
s4: calculating to obtain the dynamic elasticity modulus E and the Poisson ratio v of the concrete based on a physical model between the dynamic characteristic parameter of the stress wave and the material parameter of the concrete to be detected, wherein the physical model between the dynamic characteristic parameter of the stress wave and the material parameter of the concrete to be detected comprises a calculation formula:
Figure FDA0003047364250000011
Figure FDA0003047364250000012
wherein, cL、cS、cRRespectively the propagation velocities of longitudinal waves, shear waves and Rayleigh waves in the concrete to be measured, and rho is the density of the concrete to be measuredAnd (4) degree.
2. The method for evaluating parameters of concrete materials based on piezoelectric vibration mechanism and stress wave according to claim 1, wherein said S1 is preceded by the steps of:
introducing the influence of the stress wave interface transmission effect between the concrete to be tested and the piezoelectric actuator on the signal to noise ratio into the optimization of the sensor arrangement scheme, wherein the calculation formula of the stress wave interface transmission ratio is as follows:
Figure FDA0003047364250000021
wherein A isTAnd I is the amplitude of the transmitted and incident waves respectively,
Figure FDA0003047364250000022
and
Figure FDA0003047364250000023
the propagation velocities, rho, of longitudinal waves in the piezoelectric actuator and the concrete to be tested respectively1And ρ2The densities of the piezoelectric actuator and the concrete to be measured are respectively.
3. The method for evaluating parameters of concrete materials based on piezoelectric vibration mechanism and stress wave according to claim 1, wherein in the step of S1:
when the PZT receiver is used as the piezoelectric receiver, a voltage response to an external load or deformation in a thickness direction is more significant than that in a length or width direction, and the thickness direction of the piezoelectric receiver should be perpendicular to the vibration direction of the target signal particles.
4. The method for evaluating concrete material parameters based on piezoelectric vibration mechanism and stress wave according to claim 3, wherein said piezoelectric sensor is divided into a built-in piezoelectric sensor and a surface-mounted piezoelectric sensor according to the fixing manner on the concrete to be measured; the built-in piezoelectric sensor comprises a built-in PZT sensor; the surface-mount piezoelectric sensor includes a surface-mount PZT sensor.
5. The method for evaluating the parameters of the concrete material based on the piezoelectric vibration mechanism and the stress wave according to claim 4, characterized in that the built-in PZT sensor comprises 1 piezoelectric exciter and 1 piezoelectric receiver, and the distance between the piezoelectric exciter and the piezoelectric receiver is set to be 2-5 times of the wavelength of the target signal; adopt including i surface-pasted PZT sensor's surface-pasted formula PZT sensor array, surface-pasted formula PZT sensor is followed the central point axial of the concrete surface that awaits measuring is pasted fixedly, and i is the natural number that is greater than 1, piezoelectric actuator and first surface-pasted formula PZT sensor piezoelectric receiver's interval is each at least 2 times of surface-pasted formula PZT sensor distance between the piezoelectric receiver.
6. The method for evaluating the parameters of the concrete material based on the piezoelectric vibration mechanism and the stress wave according to claim 4, wherein the built-in PZT sensor is sequentially packaged, cured and maintained by a waterproof insulating glue layer and a concrete protective layer and then is built in a to-be-measured area in the to-be-measured concrete; the surface-bonded PZT sensor is bonded on the surface of the concrete to be detected through an adhesive prepared from epoxy resin and a curing agent according to a ratio of 2: 1.
7. The method for evaluating parameters of concrete materials based on piezoelectric vibration mechanism and stress wave according to claim 6, wherein in said step of S2:
the excitation signal is a sine pulse signal subjected to Hanning window function windowing, the excitation center frequency is 40-100 kHz, the number of wave crests of the waveform is 5-7, and the length-thickness ratio of the size of the sensor is 10-20.
8. The method for evaluating parameters of concrete materials based on piezoelectric vibration mechanism and stress wave according to claim 7, wherein said step of S3 further comprises the steps of:
carrying out Fourier transform on the preset excitation signal to obtain a frequency domain signal;
setting the frequency corresponding to the 1 st sidelobe on the two sides of the main lobe of the frequency domain signal as the band-pass filtering frequency of a filter, and filtering noise in the stress wave signal;
and acquiring the stress wave signals for filtering the environmental noise by using an oscilloscope, and automatically identifying the time when different stress waves reach each PZT receiver by using a program algorithm so as to calculate the wave velocity of the stress waves.
9. The method of claim 8, wherein the step of automatically identifying by a programmed algorithm the time at which different stress waves reach each PZT receiver comprises the steps of:
performing Hilbert-Huang transformation on the stress wave signal to obtain an envelope curve of a wave packet;
taking the time corresponding to the maximum amplitude point of the envelope curve of the 1 st arrival wave packet of the PZT receiver of the built-in PZT sensor as the arrival time of the longitudinal wave through a program;
using a program to take the maximum amplitude point corresponding to the envelope curve of the 2 nd arrival wave packet of the PZT receiver of the built-in PZT sensor as the arrival time of the shear wave;
and taking the time corresponding to the maximum amplitude point of the envelope curve of the 2 nd arrival wave packet of the PZT receiver of the surface-mounted PZT sensor as the Rayleigh arrival time by a program.
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