Concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient

Abstract

The invention discloses a concrete damage detection method based on a hysteresis nonlinear ultrasonic coefficient, and belongs to the technical field of civil engineering. The method comprises the following steps: S1, manufacturing a test piece for concrete damage detection and assembling a detection system; s2, performing nonlinear ultrasonic detection on the test piece by using the detection system to obtain an ultrasonic signal; s3, performing time domain analysis on the ultrasonic signal to obtain a time domain graph, and performing time domain conversion to obtain a frequency domain graph; s4, judging whether the ultrasonic signal is valid or not and whether the frequency domain graph is clear or not; if yes, entering the next step, otherwise, returning to S2; s5, acquiring a fundamental frequency wave amplitude, a second harmonic amplitude and a third harmonic amplitude of the ultrasonic signal from the frequency domain graph; s6, substituting the fundamental frequency wave amplitude, the second harmonic amplitude and the third harmonic amplitude into a hysteresis nonlinear coefficient expression to obtain a hysteresis nonlinear coefficient; and S7, analyzing a final detection result according to the nonlinear coefficient. According to the invention, the effect and precision of nonlinear ultrasonic detection of concrete damage can be effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of civil engineering, and in particular relates to a concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient. Background Art

[0002] Concrete is a widely used material in civil engineering and water conservancy projects. Its quality control is crucial to ensure the safety and durability of engineering structures. Nonlinear ultrasonic testing is a nondestructive testing technology. Compared with traditional ultrasonic testing methods that can only detect macroscopic cracks, nonlinear ultrasonic methods can detect early microcracks in concrete, and therefore have received widespread attention in recent years.

[0003] At present, the principle of nonlinear ultrasonic testing is to use the interaction mechanism between ultrasonic waves and crack damage of the tested material, and then use the derived nonlinear coefficient to qualitatively evaluate the damage of the tested concrete. Models include hysteresis model, contact surface model and dual stiffness model.

[0004] However, the nonlinear ultrasonic methods proposed so far have almost never considered the characteristics of concrete materials themselves, discussed the nonlinear characteristics of ultrasonic waves propagating in concrete materials, and accordingly, have not proposed damage indicators (nonlinear coefficients) to evaluate damage. At the same time, the proposed methods have fluctuations in detecting concrete damage and characterizing trends, which affects the detection accuracy.

[0005] Therefore, in order to improve the effect and accuracy of nonlinear ultrasonic detection of concrete damage, it is necessary to develop a method for detecting concrete damage based on the nonlinear coefficient of the nonclassical nonlinear hysteresis stress-strain relationship of concrete materials. Summary of the invention

[0006] The present invention aims to solve one of the technical problems in the above-mentioned related art at least to a certain extent.

[0007] To this end, the purpose of the present invention is to provide a concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient, which can effectively improve the effect and accuracy of nonlinear ultrasonic detection of concrete damage.

[0008] In order to solve the above-mentioned technical problems, the present invention is achieved as follows:

[0009] An embodiment of the present invention provides a concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient, the method comprising:

[0010] S1. Prepare specimens for concrete damage detection and assemble the detection system;

[0011] S2, performing nonlinear ultrasonic testing on the test piece using the detection system to obtain an ultrasonic signal;

[0012] S3, performing time domain analysis on the ultrasonic signal to obtain a time domain graph, and then obtaining a frequency domain graph by time domain conversion;

[0013] S4, judging whether the detected ultrasonic signal is valid and whether the frequency domain graph is clear; if the ultrasonic signal is valid and the frequency domain graph is clear, proceed to the next step, otherwise return to S2;

[0014] S5, obtaining the fundamental frequency wave amplitude A0, the second harmonic amplitude A2 and the third harmonic amplitude A3 of the ultrasonic signal from the frequency domain diagram;

[0015] S6, substituting the fundamental frequency wave amplitude A0, the second harmonic amplitude A2 and the third harmonic amplitude A3 into the hysteresis nonlinear coefficient expression to obtain the hysteresis nonlinear coefficients δ1 and δ2;

[0016] S7. Analyze the final detection result according to the nonlinear coefficient.

[0017] In addition, the concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient according to the present invention may also have the following additional technical features:

[0018] In some of the embodiments, the nonlinear coefficient expression is an expression obtained by solving the wave equation in concrete taking into account the longitudinal propagation factor of the sound wave in the concrete specimen, the elastic hysteresis stress-strain relationship of the concrete material and the boundary conditions.

[0019] In some embodiments, the nonlinear coefficient expression is an expression obtained by solving the wave equation in concrete taking into account external force terms, attenuation terms and nonlinear terms, and satisfies boundary conditions.

[0020] In some of the embodiments, the boundary condition is: one end of the concrete test block is set as the excitation wave input end, and the other end is a free end and is set as a signal receiving end.

[0021] In some of the embodiments, the idea of ​​the perturbation method is used to solve the homogeneous equation of the wave equation in concrete, the equation with the second harmonic component, and the equation with the third harmonic component respectively;

[0022] The displacement amplitudes of the fundamental wave and the second harmonic type are obtained by Fourier transform respectively;

[0023] The solution of the third harmonic equation is recorded as a general vibration form and substituted into the third harmonic wave equation to obtain the displacement amplitude of the third harmonic type;

[0024] The relationship between the hysteresis nonlinear parameters δ1 and δ2 is obtained according to the displacement amplitudes of the fundamental wave, the second harmonic and the third harmonic types, thereby obtaining the expressions of the hysteresis nonlinear coefficients δ1 and δ2.

[0025] In some embodiments, the expressions of the hysteresis nonlinear coefficients δ1 and δ2 are respectively:

[0026]

[0027] Where A0, A2 and A3 are the amplitudes of the fundamental wave, second harmonic and third harmonic respectively.

[0028] In some of the embodiments, the steps of making a test piece for concrete damage detection include making a test piece with prefabricated cracks and a test piece without prefabricated cracks;

[0029] Making a test block with prefabricated cracks: inserting a customized steel sheet during concrete pouring, and pulling out the customized steel sheet during the period from initial setting to final setting of the concrete to form prefabricated cracks in the concrete;

[0030] There are several test blocks with prefabricated cracks, each of which has a prefabricated crack of different lengths.

[0031] In some of the embodiments, the length of the prefabricated crack is 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 6 cm or 7 cm.

[0032] In some embodiments, the detection system in step S1 includes a signal generator, an amplifier, an oscilloscope, a transmitting transducer, and a receiving transducer;

[0033] The signal generator, the amplifier, and the transmitting transducer are connected in sequence, and the transmitting transducer is in contact with one end of the test piece;

[0034] One end of the receiving transducer is in contact with and connected to the other end of the test piece, and the other end of the receiving transducer is connected to the oscilloscope.

[0035] In some embodiments, the frequency of the signal emitted by the signal generator during the detection process is the resonant frequency of the signal generator, 40 kHz.

[0036] Compared with the prior art, the present invention has at least the following beneficial effects:

[0037] In the embodiment of the present invention, the concrete damage detection method based on the hysteresis nonlinear ultrasonic coefficient is provided, which takes into account the characteristics of the concrete material itself and the nonlinear characteristics of ultrasonic wave propagation in the concrete material medium, and can effectively improve the effect and accuracy of nonlinear ultrasonic detection of concrete damage.

[0038] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of theoretical derivation of a concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient disclosed in one embodiment of the present invention;

[0040] Figure 2 The overall flow chart of a concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient disclosed in one embodiment of the present invention;

[0041] FIG3 is a diagram of a nonlinear ultrasonic system for concrete damage detection disclosed in an embodiment of the present invention, wherein (a) is a physical diagram of the detection system, and (b) is a schematic diagram of the detection system;

[0042] Figure 4 A diagram of a concrete specimen with prefabricated cracks of different lengths disclosed in one embodiment of the present invention;

[0043] Figure 5 A time domain diagram of a nonlinear ultrasonic signal conversion disclosed in one embodiment of the present invention;

[0044] Figure 6 A frequency domain diagram of a nonlinear ultrasonic signal conversion disclosed in one embodiment of the present invention;

[0045] Figure 7 This is a trend diagram of the hysteresis nonlinear coefficients δ1 and δ2 varying with the length of concrete crack according to an embodiment of the present invention. DETAILED DESCRIPTION

[0046] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] The embodiments of the present invention are described in detail below through specific embodiments and application scenarios in conjunction with the accompanying drawings.

[0048] The present invention proposes a method for detecting concrete damage by substituting the hysteresis nonlinear hysteresis stress-strain relationship into the wave equation to derive the nonlinear ultrasonic coefficient. For the specific derivation process, please refer to Figure 1 shown.

[0049] Let's start with the basic wave equation. Since the Poisson's ratio of concrete is generally around 0.2, the vibration caused by longitudinal wave propagation is much greater than the vibration caused by transverse wave propagation. Therefore, ignoring the transverse wave propagation vibration, the acoustic wave equation when longitudinal wave propagates under the action of external force is:

[0050] ρU tt =σ x (ε) (1)

[0051] Among them, U is the vibration displacement of the concrete medium particle, and ρ is the density of concrete.

[0052] Concrete material properties have an inelastic hysteresis stress-strain relationship as follows:

[0053]

[0054] Where ε0 is the strain amplitude, δ1 and δ2 are hysteresis nonlinear parameters. Substituting (2) into (1), the wave equation with the hysteresis stress-strain relationship of concrete is obtained as follows:

[0055] U tt -c 2 U xx +μU ttt =c 2 F(U) (3)

[0056]

[0057] Where U is the vibration displacement of the concrete medium particle. c is the longitudinal wave velocity. μU ttt is the introduced linear viscosity term.

[0058] In the actual detection process, the boundary condition can be regarded as the concrete test block inputting the excitation wave at one end and receiving the signal at the other end, which is a free end. Therefore, the boundary condition of the equation can be written as follows:

[0059]

[0060] To facilitate subsequent derivation and calculation, the U(x, t) variable is replaced by V(x, t). The variable replacement here is done for the convenience of calculation. After replacement, it is shown as follows:

[0061] V(x,t)=U(x,t)-A0cosωt(1+sink n x) (6)

[0062] Among them, k n =2πf n / c is the wave number of the resonant frequency of the concrete medium in the nth mode. From the above formula, it can be seen that A0, A2 and A3 have the same properties as V0, V2 and V3.

[0063] After the replacement, the corresponding boundary conditions become as follows:

[0064] V(0,t)=V x (L,t)=0 (7)

[0065] Substituting the substitution term (6) into equation (3), we obtain the following equation:

[0066]

[0067] The right side of the equation has external force terms, attenuation terms, and nonlinear terms. Using the idea of ​​the perturbation method, the homogeneous equation, the equation with the second harmonic component, and the equation with the third harmonic component are solved respectively. First, when the three terms on the right side of the equation are very small compared to the original fluctuation amplitude, they are ignored as 0. At this time, the solution of equation (8) can be written as follows:

[0068] V (1) =V0cos[(ω n +δ)t+ψ]sin(k n x)+W(x,t) (9)

[0069] Where V0 and ψ are the amplitude and phase at the external force frequency ω. W(x,t) is a small quantity and is considered to be omitted. ω n =2πf n , Δω=ω-ω n <<ω n Substituting equation (9) into equation (8) yields the following equation:

[0070]

[0071] It has been verified that the above equation satisfies the boundary condition (7). (1) ) to perform Fourier transform as follows:

[0072] According to V (1) =V0cos[(ω n +Δω)t+ψ]sin(k n x), let Θ = (ω n +Δω)t+ψ, then V (1) =V0cosΘsin(k n x), and the derivative of this formula is as follows:

[0073]

[0074] Further,

[0075]

[0076] There are four cases where Θ belongs to, namely as well as The nonlinear term F(V 1 ) The Fourier transform results, the cos part and the sin part are:

[0077]

[0078] in,

[0079] The right side of formula (10) item, term and 2ω n ΔωV0cosΘsink n The x items are Fourier transformed respectively, and the Fourier transform sum on the right side of equation (10) is set to 0, then the equations for amplitude and phase are as follows:

[0080]

[0081] Solving the above system of equations, we get the following results:

[0082]

[0083] Among them, Δω N is the nonlinear frequency shift, specifically, Δω N =-2(n-1 / 2)a1V0ω n / (3L), μ N is the nonlinear loss factor, μ N =4(n-1 / 2)b1V0 / (3Lω n ).

[0084] Transforming the above formula into the following formula:

[0085]

[0086] From the above formula, we can see that It can be regarded as a function of V0.

[0087] Using the idea of ​​perturbation method, for the generation of higher harmonics, we first consider the generation of second harmonic type, and the corresponding wave equation is as follows:

[0088]

[0089] in,

[0090] The second harmonic solution is written as, V (2) =V2(x)sin(2Θ+φ). Similar to the analysis and derivation process of the fundamental wave, the amplitude and phase equations of the second harmonic type are as follows. Since Δω is a small quantity, it is assumed to be 0.

[0091]

[0092] Let μ2 = 0, remove Items, and the simplified result is obtained.

[0093]

[0094] Combined with the boundary conditions, solving the above equations, we get the following results:

[0095]

[0096] At the receiving signal end, that is, the free end, the condition is satisfied sin2k n L = 0 and cos2k n L = -1, then the solution of the equation corresponding to the second harmonic type can be written as:

[0097]

[0098] Next, consider the generation of the third harmonic type, and the corresponding wave equation is as follows:

[0099]

[0100] in,

[0101] Unlike the second harmonic type, the frequency of the third harmonic type is close to the resonant frequency, so the solution of its corresponding equation can be written in the general vibration form, V 3 (x,t)=V3(x)sin3k n xsin(3Θ+χ). Substituting this formula into equation (22), the displacement amplitude of the third harmonic type is obtained as:

[0102]

[0103] Among them, V0, V2 and V3 are the displacement amplitudes of the fundamental wave, the second harmonic and the third harmonic respectively.

[0104] Combining equations (15), (21) and (23), the relationship between the hysteresis nonlinear parameters δ1 and δ2 is as follows:

[0105]

[0106] Since the actual measurement reflects the relative change trend of damage indicators such as nonlinear coefficients with the change of damage, it is a qualitative discussion, referring to the simplified method of the derivation process of the traditional nonlinear coefficient expression, such as simplifying the wave number and propagation distance. In the difference formula (24), the wave number k is omitted n , propagation distance L, and determine the numerical terms, assuming δ1>δ2, and obtain the simplified difference formula (26).

[0107] Under the same measurement conditions, ω n The term is treated as a constant, so the numerator term in equation (25) The term has the same form as equation (16), so both can be regarded as functions of V0. In addition, by Δω N =-2(n-1 / 2)a1V0ω n / (3L) and μ N =4(n-1 / 2)b1V0 / (3Lω n ) we can see that Δω N and μ N Both terms contain the V0 factor, which is taken out and simplified with the denominator. The remaining terms are similar to the difference formula (24). Since they are all determined terms in the measurement process, they are omitted. Finally, the simplified sum formula (25) is obtained to obtain the simplified sum formula (27).

[0108]

[0109] Analyze the above equations: (1) The simplified difference equation and simplified sum equation above are consistent with the expression of the nonlinear coefficient defined by the classical nonlinear ultrasonic testing method: The forms are similar, and it can be seen that there is no deviation in the derivation direction. (2) Looking back at the derivation process, the hysteresis stress-strain relationship in the concrete material properties belongs to the category of non-classical nonlinear theory. The results obtained can be more suitable for nonlinear ultrasonic damage detection of rock-like materials such as concrete. (3) The expression of the hysteresis nonlinear coefficient obtained has a similar form to the traditional expression and looks simple and intuitive. This is in line with the application of Occam's razor principle in the field of physics. (4) The formula is jointly discussed by two nonlinear coefficients, and then in the actual detection process, the qualitative relationship between the two nonlinear coefficients and the damage change is jointly discussed. Compared with the single nonlinear coefficient discussion of the damage change, this is more robust and can reduce the systematic error generated when a single coefficient is discussed.

[0110] In order to facilitate the calculation of indicators such as the damage coefficient in the actual measurement process, the equation composed of the simplified new nonlinear coefficient expression is solved and the following results are obtained:

[0111]

[0112] In the actual detection process, the overall flow chart of nonlinear ultrasonic detection of concrete damage using the hysteresis nonlinear coefficient expression is as follows: Figure 2 As shown, the specific steps are as follows:

[0113] Step 1: Assemble the components of the nonlinear ultrasonic detection system, including the signal generator DG1022U, the amplifier ATA-2042, the oscilloscope TBS1072B, the transmitting and receiving transducers. The assembled detection system is shown in Figure 3, where Figure (a) is a physical picture and Figure (b) is a schematic diagram. During the detection process, the signal frequency emitted by the signal generator is set to 40kHz.

[0114] Step 2: According to the "Ordinary Concrete Mix Design Code" (JGJ 55-2011), the concrete water-cement ratio is designed to be 0.5, and the corresponding mix ratio is cement 350kg / m 3 , crushed stone 1256kg / m 3 , sand 618kg / m 3 , water 175kg / m 3 By inserting a custom steel sheet during concrete pouring and pulling it out during the initial to final setting of the concrete, prefabricated cracks are formed in the concrete. The prefabricated cracks are cracks of different lengths, ranging from 1cm, 2cm, 3cm, 4cm, 5cm, 6cm, 7cm, plus a concrete specimen without prefabricated cracks, with a length of 0cm. The specific specimen group is as follows Figure 4 shown.

[0115] Step 3: Analyze the nonlinear ultrasonic detection signal obtained by the oscilloscope using mathematical software such as MATLAB to obtain a time domain diagram, such as Figure 5 shown.

[0116] Step 4: Convert the nonlinear ultrasonic signal into a frequency domain graph through time-frequency conversion, such as Figure 6 In the frequency domain diagram, read the amplitude A0, the second harmonic amplitude A2, and the third harmonic amplitude A3 corresponding to the fundamental frequency, and substitute them into the derived nonlinear coefficient expression, as shown below, to calculate the hysteresis nonlinear coefficients δ1 and δ2.

[0117]

[0118] Step 5: Draw the trend graph of the hysteresis nonlinear coefficients δ1 and δ2 with the length of the concrete crack, as shown in Figure 7 .from Figure 7 It can be seen that the nonlinear coefficients δ1 and δ2 increase with the increase of concrete crack length, which is consistent with the characteristic that the nonlinear coefficient represents the degree of concrete damage.

[0119] Parts of the present invention that are not described in detail are well known to those skilled in the art.

[0120] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation modes, which are merely illustrative rather than restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are within the protection of the present invention.

Claims

1. A concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient, characterized in that: The method comprises: S1. Prepare specimens for concrete damage detection and assemble the detection system; S2, performing nonlinear ultrasonic testing on the test piece using the detection system to obtain an ultrasonic signal; S3, performing time domain analysis on the ultrasonic signal to obtain a time domain graph, and then obtaining a frequency domain graph by time domain conversion; S4, judging whether the detected ultrasonic signal is valid and whether the frequency domain graph is clear; if the ultrasonic signal is valid and the frequency domain graph is clear, proceed to the next step, otherwise return to S2; S5, obtaining the fundamental frequency wave amplitude A0, the second harmonic amplitude A2 and the third harmonic amplitude A3 of the ultrasonic signal from the frequency domain diagram; S6, substituting the fundamental frequency wave amplitude A0, the second harmonic amplitude A2 and the third harmonic amplitude A3 into the hysteresis nonlinear coefficient expression to obtain the hysteresis nonlinear coefficients δ1 and δ2; S7. Analyze the final detection result according to the nonlinear coefficient.

2. The concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient according to claim 1 is characterized in that: The nonlinear coefficient expression is an expression obtained by solving the wave equation in concrete taking into account the longitudinal propagation factor of the sound wave in the concrete specimen, the inelastic hysteresis stress-strain relationship of the concrete material and the boundary conditions.

3. The concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient according to claim 1 is characterized in that: The nonlinear coefficient expression is an expression obtained by solving the wave equation in concrete taking into account the external force term, the attenuation term and the nonlinear term, and satisfies the boundary conditions.

4. The concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient according to any one of claims 2-3 is characterized in that: The boundary condition is: one end of the concrete test block is set as the excitation wave input end, and the other end is a free end and is set as a signal receiving end.

5. The concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient according to any one of claims 2-3 is characterized in that: By using the idea of ​​perturbation method, the homogeneous equation of wave equation in concrete, the equation with second harmonic component and the equation with third harmonic component are solved respectively. The displacement amplitudes of the fundamental wave and the second harmonic type are obtained by Fourier transform respectively; The solution of the third harmonic equation is recorded as a general vibration form and substituted into the third harmonic wave equation to obtain the displacement amplitude of the third harmonic type; The relationship between the hysteresis nonlinear parameters δ1 and δ2 is obtained according to the displacement amplitudes of the fundamental wave, the second harmonic and the third harmonic types, thereby obtaining the expressions of the hysteresis nonlinear coefficients δ1 and δ2.

6. The concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient according to claim 5 is characterized in that: The expressions of hysteresis nonlinear coefficients δ1 and δ2 are: Where A0, A2 and A3 are the amplitudes of the fundamental wave, second harmonic and third harmonic respectively.

7. The concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient according to claim 1 is characterized in that: The preparation of specimens for concrete damage detection includes the preparation of specimens with prefabricated cracks and specimens without prefabricated cracks; Making a test block with prefabricated cracks: inserting a customized steel sheet during concrete pouring, and pulling out the customized steel sheet during the period from initial setting to final setting of the concrete to form prefabricated cracks in the concrete; There are several test blocks with prefabricated cracks, each of which has a prefabricated crack of different lengths.

8. The concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient according to claim 7 is characterized in that: The length of the prefabricated crack is 1 cm, 2 cm, 3 cm, 4 cm, 5 cm, 6 cm or 7 cm.

9. The concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient according to claim 1, characterized in that: The detection system in step S1 includes a signal generator, an amplifier, an oscilloscope, a transmitting transducer and a receiving transducer; The signal generator, the amplifier, and the transmitting transducer are connected in sequence, and the transmitting transducer is in contact with one end of the test piece; One end of the receiving transducer is in contact with and connected to the other end of the test piece, and the other end of the receiving transducer is connected to the oscilloscope.

10. The concrete damage detection method based on hysteresis nonlinear ultrasonic coefficient according to claim 9, characterized in that: The frequency of the signal emitted by the signal generator during the detection process is the resonant frequency of the generator, 40 kHz.

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