CN105784848A - Piezoelectric sensor based on in-plane shearing - Google Patents

Abstract

The invention discloses a piezoelectric sensor based on in-plane shearing, and belongs to the field of ultrasonic nondestructive testing.A polycrystal material PZT is cut in a specific direction, and then polarized in the thickness direction, an electrode is additionally arranged in the thickness direction, and a d312-type piezoelectric plate is formed.In the cartesian coordinate system, polycrystals of the polycrystal material PZT grow in the z direction, and are cut along the plane (011) and finally polarized in the [011] direction.Lamb waves and SH waves which are transmitted in a specific direction are excited in a structure such as a plate or a tube at the same time.

Description

A kind of piezoelectric transducer based on inplane shear

Technical field

The present invention is a kind of piezoelectric transducer based on inplane shear, belongs to field of ultrasonic nondestructive detection, can motivate the Lamb wave along specific direction propagation and SH ripple in the structure such as plate or pipe simultaneously.

Background technology

Sheet metal and tubing, as a kind of basic industrial raw materials, are widely used in the fields such as Aero-Space, building, machinery.But inevitably there is crackle in metal current sheet material, be layered, the defect such as is mingled with in process of production, is necessary so utilizing Dynamic Non-Destruction Measurement that it is carried out quality testing.Supersonic guide-wave technology is a kind of emerging Non-Destructive Testing new technique, compare traditional detection method, it has that detection range is big, efficiency is high, decay the advantage such as little, all quite sensitive for structural surface defects and internal flaw, therefore supersonic guide-wave technology is widely used in Nondestructive Evaluation and the health monitoring of multiclass engineering structure.Supersonic guide-wave technology is a kind of emerging Dynamic Non-Destruction Measurement, it has that detection range is big, efficiency is high, decay the advantage such as little, sensitivity for structural surface defects and internal flaw is all significantly high, it may be achieved the isostructural effective detection of plate, pipeline, bar, gets more and more people's extensive concerning in recent years.Based on guided wave propagation characteristic in the structure, select suitable sensed-mode and frequency range is fairly heavy wants.Due to supersonic guide-wave lowest-order horizontal shear mode SH₀Non-Dispersion in communication process, can be used for distance detection so that plate or tubular construction Non-Destructive Testing are had some superiority by this mode.

At present, the mode of conventional excitation supersonic guide-wave mainly has two kinds, a kind of piezoelectric transducer (PZT) being based on material piezoelectric effect, generally only encourage a kind of mode guided wave, and Conventional piezoelectric sensor is difficult to motivate SH mode guided wave.Another way is based on the Electromagnetic Acoustic Transducer (ElectromagneticAcousticTransducer, EMAT) of electromagnetic coupling effect.EMAT has two kinds of working mechanisms, Lorentz force and magnetostrictive effect, and its structure is changeable, designability strong, by changing coil configuration and bias magnetic field direction, it is possible to motivate different modalities guided wave.1979, R.B.Thompson etc. utilized inflection coil to produce horizontal shear mode SH in ferrimagnet based on magnetostriction mechanism₀.Nineteen ninety, R.B.Thompson etc. adopts the EMAT that periodic permanent magnet ferrum (PeriodicPermanentMagnet, PPM) is constituted to motivate horizontal shear mode SH in aluminium sheet₀.Being made from multiple components relative to EMAT, the present invention proposes a kind of new d₃₁₂Type piezoelectric transducer, can produce the horizontal shear wave propagated along specific direction and the Lamb wave propagated along other directions in thin plate or light wall pipe.Can be used for the detection of all directions defect.

Summary of the invention

It is contemplated that design a kind of piezoelectric transducer based on inplane shear, can can produce the SH ripple propagated along specific direction and the Lamb wave propagated along other directions in thin plate or light wall pipe, utilize this novel sensor to be capable of plate or tubular construction on a large scale, high efficiency monitoring structural health conditions and Non-Destructive Testing.

To achieve these goals, the present invention adopts the following technical scheme that.

A kind of piezoelectric transducer, it is characterised in that by cutting polycrystalline material PZT along specific direction, then polarizing at thickness direction, thickness direction adds electrode, forms a kind of d₃₁₂Type piezoelectric transducer.

Under cartesian coordinate system, polycrystalline material PZT polycrystal grows along z direction, cuts along plane (011), finally can polarize on [011] direction.

Its piezoelectric constant coefficient matrix is given below:

$d_{ijk}=\left[\begin{array}{cccccc}0& 0& 0& d_{123}& d_{113}& d_{112}\\ 0& 0& 0& d_{223}& d_{213}& 0\\ d_{311}& d_{322}& d_{333}& 0& 0& d_{312}\end{array}\right]$

Work as d₁₂₃、d₂₁₃、d₃₁₂It is called d during equal to 0₃₁Type piezoelectric patches, and work as d₁₂₃、d₂₁₃、d₃₁₂D then it is called when being all not equal to 0₃₁₂Type piezoelectric patches.Present invention piezoelectric patches after above-mentioned cutting, embodies d₃₁The performance of type piezoelectric patches and d₃₁₂Type piezoelectric patches performance, but main with d₃₁₂Type piezoelectric patches performance is main.d₃₁Type piezoelectric patches can motivate Lamb wave in thin plate and (include A₀And S₀Mode), and due to piezoelectric coefficient d₃₁₂Impact, it also can produce shearing deformation, so it can produce Lamb wave and horizontal shear wave simultaneously.

Described piezoelectric transducer is plus after the electric field of z direction (being perpendicular to plane of crystal), when only considering d₃₁₂Time, namely linear piezoelectric equation is simplified as following form:

${\mathrm{\τ}}_{12}=\frac{E}{1+v}({\mathrm{\γ}}_{12}-d_{312}{E}_3)$

$D_3=d_{312}{\mathrm{\τ}}_{12}+{\mathrm{\γ}}_3^T{E}_3$

Wherein γ₁₂And τ₁₂Respectively strain and stress tensor, E₃And D₃Respectively electric field and dielectric displacement component, other are the parameter that this area is conventional.

For a d not having extra electric field and applied stress freely₃₁₂Type piezoelectric patches, along z direction, after the making alive of piezoelectric patches two ends, its face planted agent becomes:

${\mathrm{\γ}}_{12}=d_{312}{E}_3=\frac{d_{312}}{t}V$

Wherein t is the thickness of piezoelectric patches, and V is institute's making alive.Piezoelectric patches is eventually caused to produce various deformation, including the main inplane shear deformation γ being perpendicular to polarised direction_xyAnd γ_yx(being one group of orthogonal shearing deformation along four edges of wafer), also has telescopic shape change and the telescopic shape change along its length of through-thickness simultaneously.

Described piezoelectric transducer is plus the electric field along z direction (being perpendicular to plane of crystal), after mechanical-electric coupling, thin plate can produce the horizontal shear wave (SH ripple) along specific direction propagation and Lamb wave, and not only can produce the C-SH ripple along the propagation of pipeline circumference and C-Lamb ripple in the duct, also can produce the longitudinal wave guide along pipeline Propagation.

Described sensor can simultaneously the C-SH ripple of excitation circumference in the duct and circumference C-Lamb ripple and axially SH ripple, and these three kinds of wavelength-divisions are not based on axial displacement, radial displacement and circumferentially displaced, the defect of different directions distribution in pipeline can be detected simultaneously, as circumferential wave guide is mainly used to detect axial flaw, and longitudinal wave guide is mainly used to detect circumferential defect.

The size of described sensor can be adjusted according to the external diameter of actually detected pipeline, all can motivate circumference C-SH ripple and C-Lamb ripple in the pipeline of various outer diameter.

Described piezoelectric transducer volume ratio is more small, can be permanently affixed at surface or the inside of detected test specimen and the d of its generation₃₁₂Coefficient is compared to the d of conventional piezoelectric wafer₃₁Coefficient is much larger, more can motivate the horizontal shear wave that amplitude is bigger, for the detection of defect.

Accompanying drawing explanation

Fig. 1 is d₃₁₂Piezoelectric chip cut direction schematic diagram；

Fig. 2 is d under new coordinate system₃₁₂Piezoelectric chip deformation schematic diagram；

Fig. 3 is the group velocity dispersion curve of 1mm thickness aluminium sheet；

Fig. 4 is the phase velocities dispersion curve of 1mm thickness aluminium sheet；

Fig. 5 be in 1mm thickness aluminium sheet supersonic guide-wave excite schematic diagram；

Fig. 6 is the time-domain signal figure in aluminium sheet；

Fig. 7 be in 1mm thickness aluminum pipe supersonic guide-wave excite schematic diagram；

Fig. 8 is the time-domain signal figure in aluminum pipe；

Detailed description of the invention

Below in conjunction with drawings and Examples, the invention will be further described.Based on piezoelectric effect, devise a kind of novel piezoelectric sensor, utilize this sensor to motivate supersonic guide-wave on aluminium sheet or aluminum pipe.

Embodiment 1

Have selected aluminium sheet thick for 1mm as test specimen, the piezoelectric chip material adopted is that PZT is when cutting this material along particular orientation (such as Fig. 1), i.e. YZW-45 ° of cutting, represent that thickness direction is parallel to Y-axis, longer axis parallel is in Z axis, and it is rotated in a clockwise direction 45 ° around width, i.e. first letter representative thickness direction, second letter represents length direction, 3rd letter represents rotor shaft direction, and-45 representatives are rotated in a clockwise direction 45 °, obtain square wafer, now relative to original crystal, this wafer is many d₃₁₂This piezoelectric constant, then added electric field when polarizing in the thickness direction thereof, namely can produce detrusion in face, obtain the shearing force being parallel to each other a pair, and deformation is as shown in phantom in Figure 2.But it also can produce stretching and the compressive deformation of thickness and length direction.Therefore it can produce horizontal shear wave and Lamb wave simultaneously.

Adopt PZFlex simulation software, according to the Phase and group velocities dispersion curve of 1mm aluminium sheet in Fig. 3 and Fig. 4, when being 160kHz when selecting mid frequency, excite schematic diagram as shown in Figure 5, with X-axis positive axis for 0 °, it is counterclockwise positive direction, piezoelectric chip length, width and height respectively 4mm is set, 4mm, 0.5mm.Pumping signal is the sine wave of 5 cycle Hanning window modulation.Extract from piezoelectric patches 60mm, angle respectively 0 °, 45 °, the displacement signal at 90 ° of three place, wherein 0 ° is its Y-direction displacement, and 45 ° is its X, Y-direction displacement resultant displacement on its direction of propagation vertical, 90 ° is its X-direction displacement, as shown in Figure 6, by dispersion curve Fig. 3 it can be seen that low order horizontal shear wave SH under this frequency₀Corresponding group velocity speed is about 3130m/s, by time flight method ToF (TimeofFlight), Fig. 6 calculates first direct wave bag velocity of wave and is about 3000m/s, substantially conform to SH₀Corresponding group velocity, so this piezoelectric chip can produce low order horizontal shear wave SH along 0 °, 90 ° directions₀, on 45 ° of directions then can not, be consistent with theory.

In like manner, also can excitation ultrasound guided wave in aluminum pipe, outer diameter tube is 64mm, wall thickness 1mm, as it is shown in fig. 7, circumferential direction arranges reception point from piezoelectric patches quadrant girth position, obtain its axial displacement as shown in Figure 8, by time flight method ToF (TimeofFlight), calculating first direct wave bag velocity of wave is 2940m/s, substantially conforms to SH₀Corresponding group velocity, it was demonstrated that can inspire circumference SH₀Mode.

Claims (7)

1. the piezoelectric transducer based on inplane shear, it is characterised in that by cutting polycrystalline material PZT along specific direction, then polarizing at thickness direction, thickness direction adds electrode, forms a kind of d₃₁₂Type piezoelectric patches.

2. according to a kind of piezoelectric transducer of claim 1, it is characterised in that under cartesian coordinate system, polycrystalline material PZT polycrystal grows along z direction, cuts along plane (011), finally polarizes on [011] direction.

3. according to a kind of piezoelectric transducer of claim 1, it is characterised in that the piezoelectric constant coefficient matrix of piezoelectric patches:

$d_{ijk}=\left[\begin{array}{cccccc}0& 0& 0& d_{123}& d_{113}& d_{112}\\ 0& 0& 0& d_{223}& d_{213}& 0\\ d_{311}& d_{322}& d_{333}& 0& 0& d_{312}\end{array}\right]$

Work as d₁₂₃、d₂₁₃、d₃₁₂It is called d during equal to 0₃₁Type piezoelectric patches, and work as d₁₂₃、d₂₁₃、d₃₁₂D then it is called when being all not equal to 0₃₁₂Type piezoelectric patches；Piezoelectric transducer embodies d₃₁The performance of type piezoelectric patches and d₃₁₂Type piezoelectric patches performance, d₃₁Type piezoelectric patches can motivate Lamb wave in thin plate, and due to piezoelectric coefficient d₃₁₂Impact, it also can produce shearing deformation, can produce Lamb wave and horizontal shear wave simultaneously.

4. according to a kind of piezoelectric transducer of claim 3, it is characterised in that piezoelectric transducer embodies d₃₁The performance of type piezoelectric patches and d₃₁₂Type piezoelectric patches performance, mainly with d₃₁₂Type piezoelectric patches performance is main.

5. according to a kind of piezoelectric transducer of claim 1, it is characterized in that, piezoelectric transducer is plus the electric field being namely perpendicular to plane of crystal along z direction, after mechanical-electric coupling, thin plate can produce the horizontal shear wave along specific direction propagation and Lamb wave, and the C-SH ripple along the propagation of pipeline circumference and C-Lamb ripple can be produced in the duct, and the longitudinal wave guide along pipeline Propagation.

6. according to a kind of piezoelectric transducer of claim 1, it is characterized in that, piezoelectric transducer can simultaneously the C-SH ripple of excitation circumference in the duct and circumference C-Lamb ripple and axially SH ripple, and these three kinds of wavelength-divisions are not based on axial displacement, radial displacement and circumferentially displaced, it is possible to the defect of different directions distribution in pipeline is detected simultaneously.

7., according to a kind of piezoelectric transducer of claim 1, it is characterised in that piezoelectric transducer size is adjusted according to the external diameter of actually detected pipeline, the pipeline of various outer diameter all can motivate circumference C-SH ripple and C-Lamb ripple.