TW294783B - A conical transducer for measuring the elastic wave displacement parallel to the tangent direction of specimen surface and the method of measuring - Google Patents

Abstract

The present invention relates to a new conical transducer which can measure the displacement parallel to the tangent direction ofspecimen surface and the method of measuring. This transducer provides a tool for elastic wave related research and can be usedas a sensor in the field of nondestructive testing of materials.In making the transducer, a conical piezoelectric ceramics is welded at the center of one end of a cylindrical brass. The direction of transducer polarization should be along the measured displacement direction. The results of analyzing and processing the recorded signal can be utilized to locate flaws or evaluatematerial properties.

Description

294783 A7 B7 Printed by the Consumer Cooperative of the Central Central Bureau of Economics of the Ministry of Economic Affairs 5. Description of the invention (this issue, is it? A kind of elastic displacement lateral displacement signal sensor and complex sensing method, which is pressed by a conical transverse effect The use of electrical materials creates a measurable position parallel to the surface of the specimen, which is parallel to the Lai signal. After analysis, the results can be used to evaluate the internal defects of the sample and = if theory It is extremely valuable in the field of non-destructive testing technology in academic research or industry. The experimental measurement of the main skin has always been focused on longitudinal waves or cutting with the surface of the test body. The displacement signal measurement of the spring universal direction is vertical, but for elasticity The measurement of the wave shift signal is limited to the measurement of the ultrasonic probe based on the shear wave. 1. In the non-destructive detection technology based on the elastic wave theory, the (Ultrasound) detection method is already known. $ Send, sound wave 'and introduce it into the item, and then receive the echo signal from the second wave probe with the original super i. After measuring the time delay of the ultrasonic wave, you can judge the wave speed or internal defect of the item. Acoustic Emission Method) is another Non-destructive detection technology based on the elastic wave theory. When a crack occurs inside an object, the form of the generated wave propagates out, and the characteristics of the sound emission method are installed in the object, watch, and wave sensor to measure and test the body The displacement signal perpendicular to the tangent direction of the surface is intended to record the number of arrivals of the green wave signal to control the internal growth u ride a $ 整 ㈣ 性 异 _ #Axis faces displacement signal two! Ϋ can provide more Or it is different from the longitudinal displacement signal. In the measurement of transmission and ff. Ultrasonic detection method is to generate an elastic slope by ultrasonic probe, also = K probe I receive elastic wave ', so it will not cause waves due to the probe factor. The sound wave probe has its shortcomings. The sound sensor and the sensor are shown in Figure 1, but the signal source to be measured is the elastic wave signal. If you want to make the received signal as much as possible ^ none It is necessary to overcome the following shortcomings of this sensor first, including. Miscellaneous, including piezoelectric block ②, covering (backin_ 'panel (wear plate) Q), and shell ④, etc. have Qin Zi's resonance frequency. When this probe is connected (Please read the notes on the back before filling out this page). . --s Ministry of Economic Affairs, Central Bureau of Precision Industry, Beigong Consumer Cooperation Du Printing Co., Ltd. Λ7 __________B7 V. Description of the Invention (Part 1) When receiving the fluctuation signal, in addition to the reaction of the piezoelectric block itself, the vibration of the cover, panel and shell are all Interference with the piezoelectric block's reaction 2. The covered volume '(the area is only the same as the piezoelectric block, and the length is also short), cannot fully absorb and consume the wave energy transmitted by the piezoelectric block, and reflect the residual wave energy back To the piezoelectric block itself 3. The contact area between the sensor and the test body is large, and it cannot be regarded as a receiver. The response of the sensor is actually the combined effect of the interference of the signal at each point covered by its area. To improve the shortcomings of the above-mentioned acoustic sensor, the following measures can be taken. First, in order to achieve a sensor that is more similar to a point of contact, a piezoelectric material with a smaller wearing area must be used. The structure should be simple to reduce the interference of each component when it is subjected to vibration. In addition, the volume of the coating material behind should be large, and there is enough space to allow the elastic wave energy transmitted by the piezoelectric block to propagate and attenuate within it. Although the wave displacement sensor developed by the National Bureau of Standards has the above advantages, but because it uses piezoelectric materials with capacitance or longitudinal effect as the sensing element, it is only limited to the amount of the displacement signal that is perpendicular to the surface of the sample. Test (Journal: Th〇masM Pr〇cter,

Jr "An Improved Piezoelectric Acoustic Emission Transducer,"

Journal of Acoustic Society America 71 (5), pp. 1163-1168 1982). To measure the displacement signal parallel to the tangent direction of the surface of the sample, a piezoelectric material with transverse effect is needed. This enters the present invention: the present invention is to manufacture an elastic wave sensor to measure the lateral displacement signal parallel to the tangent direction of the surface of the specimen. As shown in Fig. 2 °, in the present invention, the sensor uses a transverse effect piezoelectric material (strain is perpendicular to the direction of electric field change) in order to measure the displacement signal parallel to the tangent direction of the surface of the specimen. The shape is a conical shape @, and its size is: the diameter of the tip @ can be 1.0-1.5mm ’to the fullest 2.5mm, the diameter of the base @ can be 4.〇, _ 6.0mm. The conical design is to improve the frequency response range of the sensor, and to approximate a point wave source, the diameter of the tip should not be too large, too small ^ the method of bearing the weight of the cylindrical copper block. Another increase in thickness can increase the amplitude of the reflected signal, but it will decrease and the frequency response will be reduced. The reclaimed ⑧ adopts a cylindrical copper block, the dimensions are: height ⑨ 25mm, diameter ④ 37mm. When making disaster sensing, fix the conical piezoelectric material on the center of one end of the cylindrical steel block. The method of welding can be welding or pasting with conductive adhesive. When fixing, the center of the base of the conical piezoelectric block and the center of the steel block It is coaxial, and the vibration direction of the piezoelectric block needs to be marked to facilitate the measurement of the polarization direction of the sensor and the displacement direction to be measured. The two ends of the block are plated with gold or silver, which is conducive to the piezoelectric block on the paper size · m: standard (CNS),., 4_secret f: 丨 丨) 0), the competition, ----- --- --------- installed ------ ordered ------ r line (please read the Vi matters on the back before filling this page)

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FT 5. Description of the invention (3) The change of the internal electric field is converted into a collision signal output at both ends a. Before measuring ^, first place the sensor as shown in Figure 3, the sensor 1 owes one to live in the cylindrical copper The ring-layer insulation layer between the block and the metal box prevents the earth-circular right copper block from contacting the metal box. A small hole in the bottom of the metal box allows the piezoelectric block of the sensor to protrude, and then seal the piezoelectric block with an aluminum foil. The aluminum foil is attached to the metal box and contacts the tip of the piezoelectric block, so it can be shaped. ^ Shielding strictly prevents electrical transmission interference u When the sensor is installed in the metal box, the polarization direction of the heart state needs to be marked on the metal box, and the sensor is connected to the BNC connector on the metal box with a wire ® 3 Installation-Ordering • The experimental setup for measurement is shown in Figure 4. In the figure, @ represents the surface point wave source, but it is not limited to the measurement of the elastic wave signal caused by the surface wave source. The fluctuation signal is also the measurement range. The polarization direction of the sensor needs to be consistent with the direction of displacement measurement 'and the metal box is used as the ground end to reverse the sensor. The signal is connected to the amplifier @ or waveform recorder by BNC wiring ⑯. In the amplified state, the weak signal can be amplified ’, but if the amplitude of the signal itself is sufficient, it is not necessary to use * 5. The waveform recorder represented by @ can be an analog / digital, metamorphic or digital oscilloscope. The sampling rate depends on the frequency of the signal to be received. For higher frequency signals, a recorder with a higher sampling rate is needed. Ministry of the Central Standardization Bureau · _Industry and consumer cooperation (ttv "-The theoretically analytical solution to the wave signal generated by a vertical external force on the surface of the semi-random poor domain has been obtained (Book: Karl F. Graff: "Wave motion in dasdc sohds'pp.343-375, 1975), the green signal of the theoretical signal (Green ftmction) and the wave source force-time relationship is convolution (convolution) to calculate the theoretical signal of the arbitrary wave source, this theory The signal will be used as a sensor performance test. During the test, a steel ball hits the surface of the specimen to generate a vertical downward external force. The force-time relationship of the impact wave source can be approximated by a sin1) function (Journal: Wu, τ · τ , Fang, j _s, Liu, G _γ, and

Kuo, M.-K. “Determination of Elastic Constants of a Concrete

Specimen Using Transient Elastic Waves; 1 Journal of Acoustic Society 〇f America, 98 (4), pp. 2142-2148, 1995). The experimental configuration for measuring the test signal is still as shown in Fig. 4 '. According to the aforementioned sensing method, only at this time, the wave source represented by the arrow is the force generated by the steel ball knocking. The following two different materials are tested for steel and concrete. , The size of the conical transverse effect piezoelectric diaphragm of the sensor used is: the base helmet diameter 4mm two thickness 2.5mm, the tip straight S .. 5min ^ The characteristics of the steel are relatively close to the search Λ -f | f 'M ^ tt ^ i '\ s! Λ ::!) · ： ·) · ： f 294783

V. Description of the invention (+). Spoon of homogeneous material, elastic waves propagate within it, which is not easy to attenuate and disperse. ^ The propagation of frequency waves can be struck with smaller steel balls; concrete materials, because of the complex Containing aggregates and tiny pores, it is easy to hinder the advancement of elastic waves to generate, diffract, and scatter. High-frequency elastic waves easily disappear in concrete and impact with large steel balls can make the wavelength of elastic waves generated = Material ^ the particle size is larger 3 Figure 5 is a comparison of the test signal of the steel block and the theoretical value. The test body is a cylindrical steel block. Its elastic wave velocity is 5922m / s longitudinal wave, 3234m / s transverse wave, 15cm in diameter, 20cm in diameter, and 2cm in diameter is impacted by a steel ball with a diameter of 2cm. The duration is about _ Sense The distance between the detector and the wave source is 7 lm helmet; if the boundary shot does not enter the recorded signal, it can be regarded as = the solid line is the experimental measurement signal, and the dashed line = the second calculation office signal bluff, the two are related Than very close, some of them are a little nasty. Figure 6 is based on the comparison of the coagulation signal and the = signal, with the diameter and sensor distance * 15em. ; Kun Ning 5 "approximately" wave source wave 2750m /, u Ϊ, the wave is also a longitudinal wave 46 ~ 0 melon ^, horizontal line) is very close to the _ solid line) _ on the signal (virtually the above experiment verified this fluctuation XianDuTu ^^. Composite materials can be extremely effective in remembering that the green foundation theory is in metal materials or signal transmission. For future academic research :; 3 positions with parallel cutting directions are a very helpful tool ϋ Nine 'skin movement non-destructive testing work, will --------.-- ^ ------ ir ------- ·. #. (PLEASE ^. ^) Read back' &; Attention? ^ Fill in this page again) Printed by Mongong Consumer Cooperatives, Central Huahua Bureau, Ministry of Economic Affairs ¾

Claims (1)

Description of illustration Ultrasonic probe structure diagram of the invention The structure diagram of the lateral polarization displacement sensor of the invention The structure diagram of the horizontal polarization displacement sensor noise isolation device The schematic diagram of the lateral polarization displacement signal measurement instrument configuration diagram The test signal of the steel block is compared with the theoretical value Signal, the dashed line is the theoretical calculation signal) The experimental signal measured by the concrete specimen is compared with the theoretical signal (the solid line is the measurement signal, and the dashed line is the theoretical calculation signal).