阅读说明：本技术 混凝土材料表面损伤的非线性超声评价装置及方法 (Nonlinear ultrasonic evaluation device and method for concrete material surface damage ) 是由 刘福东 王文强 李良图 于 2020-05-20 设计创作，主要内容包括：本发明公开一种混凝土材料表面损伤的非线性超声评价装置及方法,将混凝土待测试试件放入加载端中,将其两端固定,并在试件的表面设定位置放置超声探头,非线性声学检测设备的高能脉冲信号输出端通过放大后,与超声波换能器进行交互,在表面激起瑞雷波并在试件中传播后由特殊设置的空气耦合换能器接收超声波信号,并经过信号处理得到非线性超声参数,其能够有效反映试件所受损伤。本发明能够实现混凝土材料材料加载过程中损伤的在线监测,而且在测量损伤中无需将试件从加载台上取下,从而可以准确评价外界往复载荷作用下在役构件的力学状况,降低了由于混凝土构件因损伤而产生断裂失效造成的风险,解决了现有设备操作不便,不能在加载过程中进行监测的缺点,具有商业应用推广价值。(The invention discloses a nonlinear ultrasonic evaluation device and method for concrete material surface damage, which comprises the steps of placing a concrete test piece to be tested into a loading end, fixing two ends of the concrete test piece, placing an ultrasonic probe at a set position on the surface of the test piece, enabling a high-energy pulse signal output end of nonlinear acoustic detection equipment to interact with an ultrasonic transducer after being amplified, exciting Rayleigh waves on the surface, transmitting the Rayleigh waves in the test piece, receiving ultrasonic signals by a specially arranged air coupling transducer, and obtaining nonlinear ultrasonic parameters through signal processing, wherein the nonlinear ultrasonic parameters can effectively reflect the damage of the test piece. The invention can realize the online monitoring of the damage of the concrete material in the loading process, and the test piece does not need to be taken down from the loading platform in the damage measurement, thereby accurately evaluating the mechanical condition of the in-service member under the action of the external reciprocating load, reducing the risk caused by the fracture and failure of the concrete member due to the damage, solving the defects that the existing equipment is inconvenient to operate and cannot monitor in the loading process, and having commercial application and popularization values.)

1. A nonlinear ultrasonic evaluation device for concrete material surface damage is characterized in that: the device comprises a signal generator, a signal amplifier, an oscilloscope and a contactor wedge-shaped transducer; the signal generator generates a multi-period sine wave, and the output signal of the signal generator is amplified through signal amplification to obtain a signal with high acoustic energy; then, converting a signal containing high acoustic energy into a longitudinal wave by using a contactor wedge-shaped transducer, and transmitting the converted longitudinal wave into a wedge; the longitudinal wave reaches the surface of the test piece to be tested from the inclined wedge to excite the Rayleigh surface wave in the volume sample and propagates on the surface of the test piece along the sound axis; an ultrasonic probe is placed on the surface of a test piece to be tested, and the other end of the test piece to be tested detects the Rayleigh surface wave diffused into the air through an air coupling transducer with a fixed inclined angle O.

2. The apparatus for nonlinear ultrasonic evaluation of concrete material surface damage according to claim 1, characterized in that: the contactor wedge-shaped transducer adopts a narrow-band piezoelectric contact type ultrasonic transmitting transducer, and is fixed on the wedge; the wedge is made of acrylic acid, and the wedge is a concave bottom surface with the same curvature as that of the concrete cylinder to be detected.

3. The apparatus for nonlinear ultrasonic evaluation of concrete material surface damage according to claim 1, characterized in that: and lubricating oil is adopted between the wedge and the transducer, and between the transducer and a to-be-tested element to realize acoustic coupling.

4. An evaluation method based on the nonlinear ultrasonic evaluation device for concrete material surface damage according to claims 1 to 3, characterized in that: the method comprises the following steps:

(1) test parameters

Calculating the inclination angle O of the air coupling transducer; the angle of inclination O is equal to the angle of the longitudinal wave propagating in the air emanating from the surface of the test piece with respect to the normal to the surface, i.e. the angle of inclination

Wherein, c_airObtaining the wave velocity of the body wave in air for pre-test measurements, c_RThe wave velocity of Rayleigh waves on the thin surface of the test piece is obtained;

(2) excitation and receiving device for arranging surface Rayleigh waves

Firstly, a signal generator generates a multi-period sine wave, and a signal amplifier is used for amplifying an output signal of the signal generator to obtain a signal with high acoustic energy; then, converting the obtained signals into longitudinal waves by using a contactor wedge-shaped transducer, and sequentially transmitting the longitudinal waves into the wedge and the surface of the test piece to be tested so as to excite Rayleigh surface waves in the sample and propagate on the surface of the test piece along the sound axis; detecting the Rayleigh surface wave diffused into the air by using an air coupling transducer with a fixed inclined angle O at the other end of the to-be-tested piece; amplifying the detected signal by a signal amplifier with a preposed broadband, and carrying out averaging digital processing on the signal by using an oscilloscope;

(3) test system stability

The input voltage of a signal generator in the ultrasonic signal generating system is fixed, and under the same other conditions, the distance between a transmitting probe and an ultrasonic signal receiving probe is changed to generate an ultrasonic signalThe ultrasonic signal is received by the air coupling transducer, and the ultrasonic signal leaked from the test piece to be tested into the air is received by the air coupling transducer; carrying out Fourier transformation on a body wave signal received by an air coupling ultrasonic transducer probe to obtain a fundamental frequency amplitude A1 and a frequency multiplication amplitude A2 of the signal wave, obtaining corresponding A1 parameter index and A2 parameter value under different probe distances, and fitting the A1 parameter index and A2 parameter value to obtain A2-A1 parameter²The direct proportional relation is approximate, which shows that the instrument can work normally according to the formulaObtaining accurate nonlinear coefficients B under different conditions through nonlinear ultrasonic testing;

(4) non-linear coefficient measurement of test pieces under different loading cycles

Carrying out cyclic loading or constant load loading on a concrete to-be-tested piece by using an electronic universal tester, and exciting and receiving Rayleigh waves by using a nonlinear ultrasonic testing device at different loading stages while loading; carrying out corresponding signal processing on the received signal, analyzing and obtaining a fundamental frequency amplitude and a frequency multiplication amplitude in the received signal, and calculating to obtain a nonlinear coefficient B until the bearing capacity of the test piece is lost;

in the process, the relative nonlinear coefficient corresponding to the state of the test piece before loading is recorded as B₀Relative nonlinear coefficient B after loading different stresses on the test piece to be tested_xIs divided by B₀Carrying out regularization; obtaining a relation curve graph between a regularization relative nonlinear coefficient and a loading cycle based on fundamental frequency and frequency multiplication;

(5) repeatable operation testing

Changing the distance between the ultrasonic transmitting probe and the air coupling transducer, and completely repeating the steps after the adjustment is completed, namely: fixing a contactor wedge-shaped transducer on a wedge, then processing ultrasonic signals of the same test piece to be tested after different loads by exciting and receiving Rayleigh surface waves with certain strength to obtain nonlinear ultrasonic coefficients, and repeatedly testing to ensure the reliability and accuracy of the test result, thereby finally obtaining the nonlinear coefficients of the test piece with different degrees of surface damage.

5. The evaluation method of the apparatus for nonlinear ultrasonic evaluation of concrete material surface damage according to claim 4, characterized in that: in the step (2), the distance z between the piece to be tested and the midpoint of the excitation area of the air coupling transducer is 3.3-3.5 mm.

Technical Field

The invention relates to a concrete testing technology, in particular to a nonlinear ultrasonic evaluation device and method for concrete material surface damage.

Background

Concrete members widely used in engineering structures cause damage and local microcrack expansion inside materials due to long-term load action and external environment influence (such as weathering, freeze thawing and the like), so that the mechanical properties of the structures are degraded. After the damage is accumulated to a certain degree, the structure can be suddenly brittle-broken, which causes serious engineering accidents. Research shows that the load borne by the structure plays a crucial role in the initiation and propagation of cracks, and in practical engineering, the structure is subjected to cyclic load in most cases, and fatigue brittle failure is easy to occur under the condition. The diagnosis of early mechanical property degradation of the structure is very important for timely carrying out safety early warning and maintenance measures, but the detection technology for early mechanical property degradation is not developed and matured. Therefore, it is crucial to develop a diagnostic tool that can study the characteristics of materials and structures at early stages of mechanical property degradation under load conditions, so that engineers can monitor the initiation and growth of microcracks in-situ during the service life of concrete infrastructure.

The ultrasonic nondestructive detection technology is one of important methods in modern detection technology, and is widely applied to industrial manufacturing, structural damage detection and other aspects. At present, the mature ultrasonic nondestructive detection mainly aims at the initial and final failure stages of the structure or material defects, and the existence and the distribution of the defects such as microcracks in the material are measured by mainly utilizing the time course, attenuation, scattering, impedance and other characteristic information of waves in the material. These linear parameters are often not very sensitive to degradation of the early mechanical properties of the structure. In recent years, many studies show that the degradation of the mechanical properties of materials is closely related to the ultrasonic nonlinear effect. The nonlinear parameter can sensitively reflect the change of the early mechanical behavior of the material. Ultrasonic waves of a single frequency tend to generate higher order harmonics of integer multiples of the frequency in a medium with nonlinear characteristics. By obtaining the acoustic nonlinear coefficients of different damage stages, the change of the microstructure in the material can be understood, so that the early mechanical property degradation of the structure and the material can be effectively detected. Although highly sensitive non-linear acoustic techniques have been investigated for monitoring early damage to concrete (including alkali-silicon reaction induced microstructural changes, carbonization, drying shrinkage and thermal damage, etc.), there is a lack of experimental techniques for applying these non-linear acoustic techniques to characterize concrete damage due to loading, primarily due to the difficulty of adapting the measurement apparatus to the sample under loaded conditions. There are experimental devices that use wedge-shaped transducers for transmission and detection of nonlinear rayleigh surface waves. However, this method is time consuming and complicated to operate and can produce large signal fluctuations due to acoustic differences between the wedge transducer receiving the signal and the surface of the test piece. Therefore, a method capable of applying the nonlinear ultrasonic technology to real-time monitoring of the damage of the concrete sample under the load condition needs to be developed.

Disclosure of Invention

The purpose of the invention is as follows: the invention aims to overcome the defects in the prior art and provides a nonlinear ultrasonic evaluation device and method for concrete material surface damage.

The technical scheme is as follows: the invention relates to a nonlinear ultrasonic evaluation device for concrete material surface damage, which comprises a signal generator, a signal amplifier, an oscilloscope and a contactor wedge-shaped transducer, wherein the oscilloscope is connected with the signal generator; the signal generator generates a multi-period sine wave, and the output signal of the signal generator is amplified through signal amplification to obtain a signal with high acoustic energy; then, converting a signal containing high acoustic energy into a longitudinal wave by using a contactor wedge-shaped transducer, and transmitting the converted longitudinal wave into a wedge; the longitudinal wave reaches the surface of the test piece to be tested from the inclined wedge to excite the Rayleigh surface wave in the volume sample and propagates on the surface of the test piece along the sound axis; an ultrasonic probe is placed on the surface of a test piece to be tested, and the other end of the test piece to be tested detects the Rayleigh surface wave diffused into the air through an air coupling transducer with a fixed inclined angle O.

In order to transmit the acoustic energy to the concrete piece to be tested to the maximum extent, the contactor wedge-shaped transducer adopts a narrow-band piezoelectric contact type ultrasonic transmitting transducer, and is fixed on a wedge; the wedge is made of acrylic acid, and the wedge is a concave bottom surface with the same curvature as that of the concrete cylinder to be detected.

Furthermore, lubricating oil is adopted between the wedge and the transducer, and between the transducer and a to-be-tested element to realize acoustic coupling.

The invention also discloses an evaluation method of the nonlinear ultrasonic evaluation device for the concrete material surface damage, which comprises the following steps:

(1) test parameters

Calculating the inclination angle O of the air coupling transducer; the angle of inclination O is equal to the angle of the longitudinal wave propagating in the air emanating from the surface of the test piece with respect to the normal to the surface, i.e. the angle of inclination

Wherein, c_airObtaining the wave velocity of the body wave in air for pre-test measurements, c_RThe wave velocity of Rayleigh waves on the thin surface of the test piece is obtained;

(2) excitation and receiving device for arranging surface Rayleigh waves

Firstly, a signal generator generates a multi-period sine wave, and a signal amplifier (with high power) is used for amplifying an output signal of the signal generator to obtain a signal with high acoustic energy (so as to ensure that the signal has a good signal-to-noise ratio); then, converting the obtained signals into longitudinal waves by using a contactor wedge-shaped transducer, and sequentially transmitting the longitudinal waves into the wedge and the surface of the test piece to be tested so as to excite Rayleigh surface waves in the sample and propagate on the surface of the test piece along the sound axis; detecting the Rayleigh surface wave diffused into the air by using an air coupling transducer with a fixed inclined angle O at the other end of the to-be-tested piece; amplifying the detected signal by a signal amplifier with a preposed broadband, and carrying out averaging digital processing on the signal by using an oscilloscope;

(3) test system stability

The input voltage of a signal generator in the ultrasonic signal generating system is fixed, and under the same other conditions, the distance between a transmitting probe and an ultrasonic signal receiving probe (namely the distance between a wedge-shaped contact transducer and an air coupling transducer) is changed to generate an ultrasonic signal to driveThe sensor receives an ultrasonic signal leaked from a piece to be tested into the air through the air coupling transducer; carrying out Fourier transformation on a body wave signal received by an air coupling ultrasonic transducer probe to obtain a fundamental frequency amplitude A1 and a frequency multiplication amplitude A2 of the signal wave, obtaining corresponding A1 parameter index and A2 parameter value under different probe distances, and fitting the A1 parameter index and A2 parameter value to obtain A2-A1 parameter²The direct proportional relation is approximate, which shows that the instrument can work normally according to the formulaObtaining accurate nonlinear coefficients B under different conditions through nonlinear ultrasonic testing;

(4) non-linear coefficient measurement of test pieces under different loading cycles

Carrying out cyclic loading or constant load loading on a concrete to-be-tested piece by using an electronic universal tester, and exciting and receiving Rayleigh waves by using a nonlinear ultrasonic testing device at different loading stages while loading; carrying out corresponding signal processing on the received signal, analyzing and obtaining a fundamental frequency amplitude and a frequency multiplication amplitude in the received signal, and calculating to obtain a nonlinear coefficient B until the bearing capacity of the test piece is lost;

in the process, the relative nonlinear coefficient corresponding to the state of the test piece before loading is recorded as B₀Relative nonlinear coefficient B after loading different stresses on the test piece to be tested_xIs divided by B₀Carrying out regularization; obtaining a relation curve graph between a regularization relative nonlinear coefficient and a loading cycle based on fundamental frequency and frequency multiplication;

(5) repeatable operation testing

Changing the distance between the ultrasonic transmitting probe and the air coupling transducer, and completely repeating the steps after the adjustment is completed, namely: fixing a contactor wedge-shaped transducer on a wedge, then processing ultrasonic signals of the same test piece to be tested after different loads by exciting and receiving Rayleigh surface waves with certain strength to obtain nonlinear ultrasonic coefficients, and repeatedly testing to ensure the reliability and accuracy of the test result, thereby finally obtaining the nonlinear coefficients of the test piece with different degrees of surface damage.

In order to reduce the attenuation and diffraction effect of the leakage ultrasonic wave in the air, in the step (2), the distance z between the test piece and the middle point of the excitation area of the air coupling transducer is 3.3 mm-3.5 mm.

Has the advantages that: the invention converts the electric signal into the ultrasonic longitudinal wave through the ultrasonic transmitting transducer, transmits the ultrasonic longitudinal wave into the wedge contacted with the ultrasonic transmitting transducer, excites Rayleigh wave on the surface of the test piece to be tested, simultaneously arranges the air-coupled ultrasonic receiving transducer at the other end of the test piece, improves the signal-to-noise ratio of the received ultrasonic signal by a method of multiple tie, obtains the fundamental frequency and high-frequency amplitude parameters A1 and A2 of the ultrasonic signal by fast Fourier transform, and substitutes the parameters into a formula to obtain the nonlinear coefficients of the test piece with different degrees of damage.

Compared with the prior art, the invention has the following advantages:

(1) the method utilizes a non-contact method to detect Rayleigh waves in the material of the test piece to be detected, avoids loss and change in the process of ultrasonic multi-medium transmission, greatly simplifies the complexity of operation, and makes the measurement result more accurate and simpler.

(2) The invention can realize convenient point-changing measurement on the same to-be-tested part. In the existing detection, the change of the nonlinear coefficient B can be generally detected only by changing the voltage, but the change of the voltage can introduce the nonlinearity of an ultrasonic system and influence the reflection of the nonlinear coefficient on the nonlinearity of the material. The invention can realize the detection of the change of the nonlinear parameter through point-changing measurement, and the change is almost completely caused by the nonlinearity of the material in the ultrasonic propagation process, so that better detection effect can be obtained.

(3) Compared with other nonlinear ultrasonic detection methods, the method has the advantages that the detection devices are reduced, and the method can be directly arranged in the concrete test piece in a loading state, so that the test piece does not need to be detached from the loading device, and the measurement can be carried out while loading, and therefore, the method is particularly suitable for measuring the damage of the concrete test piece caused by the loading process.

(4) Conventional ultrasonic detection means only utilize linear ultrasonic parameters such as sound velocity, scattering dissipation and the like, which are not sensitive to damage under load conditions, while ultrasonic nonlinear parameters prove to be very sensitive to the damage, so that the damage can be effectively evaluated by utilizing a nonlinear ultrasonic method.

Drawings

FIG. 1 is a schematic view of a measuring apparatus according to the present invention;

FIG. 2 is a graph of the ratio of the frequency multiplication amplitude to the square of the fundamental frequency amplitude (nonlinear ultrasound coefficient) at different propagation distances in an implementation;

FIG. 3 is a graph showing the variation of the nonlinear ultrasonic coefficient with the test piece loading period in the example.

Detailed Description

The technical solution of the present invention is described in detail below, but the scope of the present invention is not limited to the embodiments.

As shown in fig. 1, the evaluation method of the nonlinear ultrasonic evaluation device for concrete material surface damage of the present invention comprises the following steps:

(1) test parameters

For best acoustic signals, the tilt angle O (fig. 1) of the air-coupled transducer needs to be calculated, which is equal to the angle of the longitudinal wave propagating in the air from the surface of the test piece relative to the normal to the surface. Measuring and obtaining wave velocity C of body wave in air before test_airWave velocity C of Harley wave on thin surface of test piece_rAccording to the formulaAnd calculating to obtain the inclination angle O of the air coupling transducer.

(2) Excitation and receiving device for arranging surface Rayleigh waves

Firstly, a signal generator generates a multi-period sine wave, and a signal with high acoustic energy is obtained by using an output signal of a signal generator of a high-power amplifier so as to ensure that the signal has a good signal-to-noise ratio. Converting an electric signal into ultrasonic longitudinal waves by using an ultrasonic transmitting transducer with narrow-band pressure electrical contact, transmitting the ultrasonic longitudinal waves into an acrylic wedge in contact with the ultrasonic longitudinal waves, and then reaching the surface of a test piece to excite Rayleigh surface waves in a sample and transmitting the Rayleigh surface waves along a sound axis on the surface of the test piece; the rayleigh surface wave diffused into the air is detected at the other end of the test piece with an air-coupled transducer having a fixed tilt angle O. The detected signal is amplified by a broadband preamplifier, and then an oscilloscope is used for carrying out averaging digital processing on the signal. The whole system is synchronized by a trigger signal from a signal generator.

(3) Test system stability

The input voltage of the ultrasonic signal generating system is fixed, under the same other conditions, the distance between the transmitting probe and the ultrasonic signal receiving probe is changed, an ultrasonic signal is generated to the driving sensor, and the ultrasonic signal leaked from the test piece to the air is received through the air coupling transducer. Carrying out Fourier transform on a body wave signal received by an air coupling ultrasonic transducer probe to obtain a fundamental frequency amplitude A1 and a frequency multiplication amplitude A2 of the signal wave; obtaining corresponding A1 and A2 parameter values under different probe distances, and fitting the parameter values to obtain A2 and A1²The direct proportional relation is approximate, which shows that the instrument can work normally according to the formulaThe nonlinear ultrasonic test can obtain an accurate nonlinear coefficient B as shown in fig. 2 and 3.

(4) Non-linear coefficient measurement of test pieces under different loading cycles

Carrying out cyclic loading or constant load loading on a concrete sample by using an electronic universal tester, and exciting and receiving Rayleigh waves by using a nonlinear ultrasonic testing device at different cyclic loading stages while loading; and carrying out corresponding signal processing on the received signal, analyzing and obtaining a fundamental frequency amplitude and a frequency doubling amplitude in the received signal, and calculating to obtain a nonlinear coefficient B until the bearing capacity of the test piece is lost. The relative nonlinear coefficients based on fundamental and multiplied amplitudes are defined and used as follows:

and calculating the relative nonlinear coefficient of the ultrasonic waves in the test piece according to the formula. Recording a relative nonlinear coefficient corresponding to the state of the test piece before loading as B₀. Relative non-linear system after loading different stresses to test pieceNumber B_xIs divided by B₀And carrying out regularization. And obtaining a relation curve graph between the regularization relative nonlinear coefficient and the loading cycle based on the fundamental frequency and the frequency multiplication.

(5) Repeatable operation testing

Changing the position between the ultrasonic emission probe and the air coupling transducer, adjusting and then completely repeating the step work, namely bonding the Nichoic acid chip-embedded transducer on the organic glass wedge; then adhering the organic glass wedge to the surface of the metal plate-shaped test piece by using a binder so as to excite and receive Rayleigh surface waves with certain strength; and then repeating the work in the step, exciting and receiving Rayleigh wave signals after loading different stresses on the same test piece, and performing repeated test once to ensure the reliability and accuracy of the test result, thereby obtaining the nonlinear coefficients of the test piece with surface damage of different degrees.