Nondestructive testing method for elasticity modulus of wood

Abstract

The invention discloses a nondestructive testing method for the elasticity modulus of wood, and relates to the technical field of wood detection, and the nondestructive testing method comprises the following steps: S1, preparing a to-be-tested beam type wood test piece; s2, two piezoelectric ceramic sheets are pasted to the two sides of the beam type wood test piece respectively; s3, strip-shaped foam is installed in the center area of the lower side of the beam-shaped wood test piece, so that the beam-shaped wood test piece is in a longitudinal free constraint state; s4, respectively connecting positive and negative wires of the piezoelectric ceramic coupled on the wood test piece to two binding posts of an impedance instrument; s5, setting the frequency range and amplitude of alternating-current excitation voltage in an impedance instrument, synchronously contracting or synchronously extending the two piezoelectric ceramic sheets, and performing longitudinal vibration modal excitation on the beam-type wood test piece; and S6, extracting the peak value frequency of the main peak of the piezoelectric admittance real part response curve as the first-order longitudinal vibration modal frequency of the beam-type wood test piece, calculating the elastic modulus of the wood test piece, and realizing longitudinal vibration modal excitation through the piezoelectric ceramic sheet to meet the longitudinal vibration modal excitation requirement of the small-size test piece.

Description

Technical Field

[0001] This invention belongs to the field of wood testing technology, specifically a non-destructive testing method for the elastic modulus of wood. Background Technology

[0002] Wood has natural environmental protection properties and is widely used in the home furnishing industry, such as timber structure construction and furniture manufacturing. Before use, wood needs to undergo mechanical property testing. The modulus of elasticity is one of the important indicators for measuring the mechanical properties of wood. Currently, three non-destructive testing methods have been developed: transverse vibration method, ultrasonic method, and longitudinal vibration method. The traditional transverse vibration method requires the length-to-thickness ratio of the wood specimen to be above 50. The ultrasonic method predicts the modulus of elasticity based on the propagation speed of ultrasonic waves in the wood specimen, and the testing system is relatively complex. The longitudinal vibration method usually uses a stress hammer to excite one end of the beam-shaped wood specimen, generating an excitation load along the length of the specimen. At the other end of the beam-shaped wood specimen, an acceleration or sound pressure sensor receives the vibration response signal. By performing a Fourier transform on the response signal, the first-order longitudinal vibration mode frequency of the specimen is obtained, thereby determining the modulus of elasticity of the specimen.

[0003] In the traditional longitudinal vibration method, the excitation frequency range of the stress hammer is limited, and it is only suitable for longitudinal vibration mode excitation of longer specimens. In addition, the existing longitudinal vibration method requires Fourier transform of the vibration response signal to obtain the first-order longitudinal vibration mode frequency of the beam-shaped wood specimen, which results in an excessive amount of wood specimen material required and low efficiency in elastic modulus measurement. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects in the prior art. The invention provides a non-destructive testing method for the elastic modulus of wood, thereby saving specimen materials and improving the measurement efficiency and effect of the elastic modulus of specimens in the longitudinal vibration method.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a non-destructive testing method for the elastic modulus of wood, comprising the following steps:

[0006] S1. Prepare beam-shaped timber specimens to be tested. The cross-section of the selected beam-shaped timber specimens is square, and the length-to-thickness ratio of the specimens is 10 to 15. The preferred dimensions are 200mm×20mm×20mm, 220mm×20mm×20mm or 240mm×20mm×20mm.

[0007] S2. Attach two piezoelectric ceramic sheets to both sides of the beam-shaped wood specimen, respectively;

[0008] S3. Install strip foam in the central area of ​​the lower side of the beam-shaped timber specimen to put the beam-shaped timber specimen in a longitudinally free and constrained state.

[0009] S4. Weld wires to the positive and negative poles of the piezoelectric ceramics respectively, twist the two positive poles and two negative poles of the two piezoelectric ceramics together, and then connect the positive and negative poles of the two piezoelectric ceramics on the beam-shaped wood specimen to the two terminals of the impedance meter respectively. The impedance meter is equipped with a host computer at one end, and the impedance meter is connected to the host computer through a communication cable.

[0010] S5. By setting the frequency range and amplitude of the AC excitation voltage in the impedance instrument through the host computer, the two piezoelectric ceramic sheets shrink or elongate synchronously to excite the longitudinal vibration mode of the beam-shaped wood specimen.

[0011] S6. Extract the peak frequency of the main peak of the piezoelectric admittance real part response curve as the first longitudinal vibration mode frequency of the beam-shaped wood specimen, and calculate the elastic modulus E of the wood specimen.

[0012] Further, in step S2, the piezoelectric ceramic sheet material is PZT-5H material, the piezoelectric ceramic sheet shape is a rectangular sheet, the aspect ratio of the piezoelectric ceramic sheet is greater than or equal to 2, the aspect ratio of the piezoelectric ceramic sheet is greater than or equal to 10, the thickness of the piezoelectric ceramic sheet is less than or equal to 0.2 mm, the piezoelectric ceramic sheet has a flanged structure, extending the negative electrode of the piezoelectric ceramic to the surface of the positive electrode, and two piezoelectric ceramic sheets are respectively pasted on the symmetrical positions of the upper and lower surfaces of the beam-shaped wood specimen, with the length direction of the piezoelectric ceramic sheet consistent with the length direction of the beam-shaped wood specimen, the polarization direction of the piezoelectric ceramic sheet being its thickness direction, and the polarization directions of the two piezoelectric ceramic sheets pasted on the beam-shaped wood specimen being opposite.

[0013] Furthermore, in step S2, the longitudinal vibration equation for the longitudinal vibration modal excitation is as follows:

[0014] (1);

[0015] In the above formula, E is the longitudinal elastic modulus of the beam-shaped timber specimen, u(x, t) is the longitudinal vibration displacement, x is the longitudinal coordinate, t is time, and ρ is the density of the beam-shaped timber specimen.

[0016] Further, in step S5, the host computer controls the impedance meter to apply a swept-frequency AC excitation voltage to the piezoelectric ceramic sheet. The amplitude of the AC excitation voltage is set to 1V or 2V, the swept-frequency range is set to 2000~18000Hz, and the swept-frequency interval is 4Hz. The first main peak frequency is determined by the piezoelectric admittance real part response curve obtained by sweeping the frequency over a wide range. The swept-frequency range containing only the first main peak frequency is reset, the swept-frequency interval is 1Hz, the frequency is swept again, and the admittance response is collected. The main peak frequency f of the piezoelectric admittance real part response curve is extracted.

[0017] Furthermore, in step S5, the beam-shaped timber specimen is equivalent to a material with mass m, damping c, and stiffness k, wherein the mechanical impedance of the piezoelectric ceramic sheet is much smaller than that of the beam-shaped timber specimen, thus constructing a piezoelectric admittance model. :

[0018] (2)

[0019] In the above formula, C is the capacitance of the piezoelectric ceramic sheet. Where l, b, and t are the length, width, and thickness of the piezoelectric ceramic sheet, respectively. Where K is the frequency, j is the imaginary unit, and K is the frequency. 31 Let be the electromechanical coupling coefficient, where , These represent the piezoelectric constant, compliance coefficient, and dielectric constant of the piezoelectric ceramic sheet, respectively. and The mechanical impedances of the piezoelectric ceramic sheet and the beam-shaped wood specimen are respectively. Mechanical resistance of piezoelectric ceramic sheets .

[0020] Further, in step S5, the real part of the piezoelectric admittance R(Y) is:

[0021] (3);

[0022] In frequency When the excitation frequency is the first-order longitudinal vibration mode frequency of the beam-shaped wood specimen, the peak frequency f of the main peak of the piezoelectric admittance real part response curve is obtained.

[0023] Further, in step S6, the longitudinal modulus of elasticity of the wood specimen is calculated by extracting the peak frequency f of the main peak of the admittance real part response curve:

[0024] (4);

[0025] In the above formula, E is the longitudinal modulus of elasticity of the beam-shaped timber specimen, ρ is the density of the beam-shaped timber specimen, L is the length of the beam-shaped timber specimen, and f is the first-order longitudinal vibration mode frequency of the beam-shaped timber specimen.

[0026] Beneficial Effects: This invention discloses a non-destructive testing method for the elastic modulus of wood. Compared with the existing transverse vibration method, this method can achieve higher testing accuracy when the length-to-thickness ratio of the specimen reaches 10. It overcomes the problems of the traditional longitudinal vibration method, which uses a stress hammer with a small excitation frequency range and a complex testing process. This method only requires an impedance meter and does not require the signal transformation of the traditional longitudinal vibration method. It uses a piezoelectric ceramic sheet to achieve longitudinal vibration excitation of the specimen. The excitation frequency is adjustable and the excitation is more stable, meeting the requirements of longitudinal vibration modal excitation for small-sized specimens. The piezoelectric ceramic sheet is both an actuator and a sensor. By extracting the peak frequency of the main peak of the piezoelectric admittance real part response curve as the first-order longitudinal modal frequency of the beam-shaped wood specimen, the elastic modulus E of the wood specimen is calculated. This saves wood specimen material and improves the measurement efficiency and effect of the elastic modulus of wood specimens. Attached Figure Description

[0027] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0028] In the attached diagram:

[0029] Figure 1 This is a flowchart of a non-destructive testing method for the elastic modulus of wood according to the present invention;

[0030] Figure 2 This is a schematic diagram showing the positions of the strip-shaped foam and the beam-shaped wood specimen of the present invention;

[0031] Figure 3 This describes the wiring method between the piezoelectric ceramic sheet and the impedance meter in this invention;

[0032] Figure 4 For the stress analysis of the beam-shaped timber specimen of this invention;

[0033] Figure 5 This is a schematic diagram of the piezoelectric admittance model of the beam-shaped wood specimen of the present invention;

[0034] Figure 6 The piezoelectric admittance real part response curves of nine types of wood specimens according to the present invention;

[0035] Figure 7 The Fourier transform results are shown for the vibration response signals of nine types of wood specimens in this invention.

[0036] The following are the labels in the figure: 1. Beam-shaped timber specimen; 2. Strip foam; 3. Impedance meter; 4. Piezoelectric ceramic sheet; 5. Conductor. Detailed Implementation

[0037] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following text is only used to describe an implementation method of a non-destructive testing method for the elastic modulus of wood of the present invention, and does not strictly limit the scope of protection specifically claimed by the present invention.

[0038] Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0039] Example 1: As Figure 1 As shown, this invention discloses a non-destructive testing method for the elastic modulus of wood, comprising the following steps:

[0040] S1. Prepare the beam-shaped timber specimen 1 to be tested. The cross-section of the selected beam-shaped timber specimen 1 is square, and the length-to-thickness ratio of the specimen is 10 to 15. The preferred size is 200mm×20mm×20mm, 220mm×20mm×20mm or 240mm×20mm×20mm.

[0041] S2. Two piezoelectric ceramic sheets 4 (PZT) are attached to both sides of the beam-shaped wood specimen 1 respectively;

[0042] S3, such as Figure 2 As shown, strip foam 2 is installed in the lower central area of ​​beam-shaped timber specimen 1 to keep beam-shaped timber specimen 1 in a longitudinally free constraint state;

[0043] S4, such as Figure 3 As shown, wires 5 are welded to the positive and negative poles of the piezoelectric ceramics respectively. The two positive poles and two negative poles of the two piezoelectric ceramics are twisted together. Then, the positive and negative poles of the two piezoelectric ceramic sheets 4 on the beam-shaped wood specimen 1 are connected to the two terminals of the impedance meter 3 respectively. One end of the impedance meter 3 is equipped with a host computer. The impedance meter 3 is connected to the host computer through a communication cable.

[0044] S5. By setting the frequency range and amplitude of the AC excitation voltage in the impedance instrument 3 through the host computer, the two piezoelectric ceramic sheets 4 synchronously shrink or elongate to perform longitudinal vibration mode excitation on the beam-shaped wood specimen 1.

[0045] S6. Extract the peak frequency of the main peak of the piezoelectric admittance real part response curve as the first longitudinal vibration mode frequency of beam-shaped wood specimen 1, and calculate the elastic modulus E of the wood specimen.

[0046] In Example 1, as Figure 3As shown, in step S2, the piezoelectric ceramic sheet 4 is made of PZT-5H material, the piezoelectric ceramic sheet 4 is rectangular, the aspect ratio of the piezoelectric ceramic sheet 4 is greater than or equal to 2, the aspect ratio of the piezoelectric ceramic sheet 4 is greater than or equal to 10, the thickness of the piezoelectric ceramic sheet 4 is less than or equal to 0.2 mm, the piezoelectric ceramic sheet 4 has a flanged structure, extending the negative electrode of the piezoelectric ceramic to the surface of the positive electrode, and two piezoelectric ceramic sheets 4 are respectively pasted on the symmetrical positions of the upper and lower surfaces of the beam-shaped wood specimen 1, with the length direction of the piezoelectric ceramic sheet 4 consistent with the length direction of the beam-shaped wood specimen 1, the polarization direction of the piezoelectric ceramic sheet 4 being its thickness direction, and the polarization directions of the two piezoelectric ceramic sheets 4 pasted on the beam-shaped wood specimen 1 being opposite.

[0047] In Example 1, in step S2, the longitudinal vibration equation for the longitudinal vibration modal excitation is as follows:

[0048] (1);

[0049] In the above formula, E is the longitudinal elastic modulus of beam-shaped timber specimen 1, u(x,t) is the longitudinal vibration displacement, x is the longitudinal coordinate, t is time, and ρ is the density of beam-shaped timber specimen 1.

[0050] In Example 1, as Figure 4 As shown, Figure 4 The force diagram of beam-shaped timber specimen 1 shown in Figure a uses a long strip of PZT sheet. Under sinusoidal voltage excitation, the strain and force generated due to the inverse piezoelectric effect are mainly in its length direction, such as... Figure 4 The diagram shown in b illustrates the equivalent force of the beam-shaped timber specimen 1. According to the law of force translation, the equivalent force can excite the longitudinal vibration mode of the beam-shaped timber specimen.

[0051] In Embodiment 1, in step S5, the host computer controls the impedance meter 3 to apply a swept AC excitation voltage to the piezoelectric ceramic sheet 4. The amplitude of the AC excitation voltage is set to 1V or 2V. First, the swept frequency range is set to 2000~18000Hz, and the swept frequency interval is 4Hz. The first main peak frequency is determined by the piezoelectric admittance real part response curve obtained by sweeping the frequency over a wide range. The swept frequency range is then reset to include only the first main peak frequency, and the swept frequency interval is 1Hz. The frequency is swept again and the admittance response is collected. The main peak frequency f of the piezoelectric admittance real part response curve is extracted.

[0052] In Example 1, in step S5, as follows Figure 5 As shown, the beam-shaped timber specimen 1 is equivalent to a material with mass m, damping c, and stiffness k. The mechanical impedance of the piezoelectric ceramic sheet 4 is much smaller than that of the beam-shaped timber specimen 1, and a piezoelectric admittance model is constructed. :

[0053] (2);

[0054] In the above formula, C is the capacitance of the piezoelectric ceramic sheet 4. Where l, b, and t are the length, width, and thickness of the piezoelectric ceramic sheet 4, respectively. Where K is the frequency, j is the imaginary unit, and K is the frequency. 31 Let be the electromechanical coupling coefficient, where , These represent the piezoelectric constant, compliance coefficient, and dielectric constant of the piezoelectric ceramic sheet 4, respectively. and The mechanical impedances of the piezoelectric ceramic sheet 4 and the beam-shaped wood specimen 1 are respectively, where the mechanical impedance of the beam-shaped wood specimen 1 is... Mechanical resistance of piezoelectric ceramic sheet 4 .

[0055] In Example 1, in step S5, the real part of the piezoelectric admittance R(Y) is:

[0056] (3);

[0057] In frequency When the excitation frequency is the first-order longitudinal vibration mode frequency of the beam-shaped wood specimen 1, the main peak frequency f of the piezoelectric admittance real part response curve is obtained.

[0058] In Example 1, in step S6, the longitudinal elastic modulus of the wood specimen is calculated by extracting the peak frequency f of the main peak of the admittance real part response curve.

[0059] (4);

[0060] In the above formula, E is the longitudinal elastic modulus of beam-shaped timber specimen 1, ρ is the density of beam-shaped timber specimen 1, L is the length of beam-shaped timber specimen 1, and f is the first-order longitudinal vibration mode frequency of beam-shaped timber specimen 1.

[0061] Example 2: To verify the effectiveness of the non-destructive testing method for the elastic modulus of wood of the present invention, nine types of wood, namely elm, larch, radiata pine, walnut, mahogany, red oak, beech, rubberwood, and Scots pine, were tested. The longitudinal vibration method of the nine types of wood specimens was used to dynamically test them by means of traditional stress hammer vibration modal excitation and sound pressure sensor response signal reception.

[0062] In Example 2, test specimens of nine types of wood, namely elm, larch, radiata pine, walnut, mahogany, red oak, beech, rubberwood, and Scots pine, were prepared. The specimen size was 240mm×20mm×20mm.

[0063] In Example 2, two piezoelectric ceramic sheets 4, each measuring 20mm × 10mm × 0.2mm and made of PZT-5H, with their polarization direction along their thickness, were glued to the upper and lower surfaces of the specimen using 502 glue. The geometric center of the PZT-5H sheet was to be aligned with the geometric center of the specimen surface as much as possible, and the length direction of the PZT-5H sheet was to be aligned with the length direction of the specimen.

[0064] In Example 2, wires 5 are welded to the positive and negative electrodes of the PZT-5H sheet, and the two positive and two negative wires 5 of the two piezoelectric ceramics are twisted together.

[0065] In Example 2, the wood specimen was placed on the strip foam support 2, and the foam only supported the middle local surface area of ​​the specimen, so that the specimen was in a longitudinally free and constrained state.

[0066] In Example 2, the positive and negative wires 5 of the piezoelectric ceramic attached to the wood specimen are connected to the two terminals of the impedance meter 3, and the communication cable connection between the impedance meter 3 and the host computer is completed.

[0067] In Example 2, the AC excitation voltage scanning frequency range in the impedance meter 3 was set to 8200Hz~12200Hz, with a sweep frequency interval of 1Hz. The impedance meter 3 was controlled to run and the real part of the admittance response curve was extracted. The piezoelectric admittance real part response curves of nine types of wood specimens are shown below. Figure 6 As shown, where Figure 6 a represents the curve of the real part of the admittance of elm wood at different frequencies. Figure 6 b represents the real part of the admittance of larch at different frequencies. Figure 6 c represents the curve of the real part of the admittance at different frequencies. Figure 6 d represents the curve of the real part of the admittance of walnut wood at different frequencies. Figure 6 e represents the real part admittance curve of mahogany at different frequencies. Figure 6 f represents the curve of the real part of the admittance of red oak at different frequencies. Figure 6 g represents the curve of the real part of the admittance of the beech fiber at different frequencies. Figure 6 h represents the curve of the real part of the admittance of rubberwood at different frequencies. Figure 6 i represents the real part admittance variation curve of Pinus sylvestris at different frequencies, and the main peak frequency of the real part admittance response curve of nine types of wood was obtained.

[0068] In Example 2, based on the peak-to-peak frequency of the main peak of the piezoelectric admittance real part response curve, the elastic modulus of nine types of wood specimens was calculated according to the effectiveness of the non-destructive testing method for the elastic modulus of wood provided by this invention. The existing longitudinal vibration method based on stress hammer vibration modal excitation and acoustic pressure sensor response signal reception was then used to dynamically test the nine types of wood specimens. The Fourier transform results of the vibration response signals of the nine types of wood are as follows: Figure 7 As shown, where Figure 7 'a' represents the Fourier transform result of the vibration response signal of elm, larch, and radiata pine wood specimens. Figure 7 b represents the Fourier transform results of the vibration response signals of walnut, mahogany, and red oak wood specimens. Figure 7 c represents the Fourier transform results of the vibration response signals of beech, rubberwood, and pine wood specimens, from... Figure 7 It can be seen from the results that the Fourier transform of the vibration response signal of beam-shaped timber specimen 1 in this experiment has obvious interference peaks, indicating that the stability of the first-order longitudinal vibration mode excitation using a stress hammer is insufficient. The elastic modulus of nine types of timber specimens was calculated using two different methods, and the test results are shown in the table below:

[0069] Timber Category <![CDATA[Density (kg / m 3 )]]> f(Hz) (Method of the present invention) f(Hz) (existing longitudinal vibration method) E (MPa) (Method of this invention) E (MPa) (existing longitudinal vibration method) relative error Elm wood 638 9831 9838 14207 14227 0.14% larch 623 10998 11024 17362 17444 0.47% Radiata pine 492 11595 11600 15240 15253 0.10% Walnut wood 602 9149 9153 11610 11620 0.10% mahogany 456 9766 9777 10020 10043 0.23% Red Oak 743 10974 10983 20616 20650 0.16% Beech 644 9663 9677 13855 13895 0.29% rubberwood 748 9819 9823 16616 16629 0.10% Pinus sylvestris 448 10985 11000 12455 12490 0.28%

[0070] As can be seen from the test results in the table above, the relative error of the elastic modulus E test result of the non-destructive testing method for wood elastic modulus provided by the present invention is less than 0.5% compared with the traditional longitudinal vibration method. This indicates that the non-destructive testing method for wood elastic modulus provided by the present invention has the same testing accuracy as the existing longitudinal vibration method. However, the excitation frequency range of the method of the present invention can be set independently, and it can be used to test beam-shaped wood specimens with smaller dimensions.

[0071] The above description only describes the present invention and its embodiments. This description is not restrictive. Those skilled in the art will realize that the embodiments described herein are to help readers understand the principles of the present invention and should be understood as not limiting the scope of protection of the present invention to such specific statements and embodiments. Those skilled in the art can make various other specific modifications and combinations without departing from the essence of the present invention based on the technical teachings disclosed in the present invention, and these modifications and combinations are still within the scope of protection of the present invention.

Claims

1. A non-destructive testing method for the elastic modulus of wood, characterized in that, Includes the following steps: S1. Prepare beam-shaped timber specimens to be tested; S2. Attach two piezoelectric ceramic sheets to both sides of the beam-shaped wood specimen, respectively; S3. Install strip foam in the central area of ​​the lower side of the beam-shaped timber specimen to put the beam-shaped timber specimen in a longitudinally free and constrained state. S4. Connect the positive and negative leads of the two piezoelectric ceramics on the beam-shaped wood specimen to the two terminals of the impedance meter, respectively. The impedance meter is equipped with a host computer at one end, and the impedance meter and the host computer are connected through a communication cable. S5. By setting the frequency range and amplitude of the AC excitation voltage in the impedance instrument through the host computer, the two piezoelectric ceramic sheets shrink or elongate synchronously to excite the longitudinal vibration mode of the beam-shaped wood specimen. S6. Extract the peak frequency of the main peak of the piezoelectric admittance real part response curve as the first longitudinal modal frequency of the beam-shaped wood specimen, and calculate the elastic modulus E of the wood specimen.

2. The non-destructive testing method for the elastic modulus of wood according to claim 1, characterized in that: In step S2, the piezoelectric ceramic sheet material is PZT-5H material, the piezoelectric ceramic sheet shape is a rectangular sheet, the aspect ratio of the piezoelectric ceramic sheet is greater than or equal to 2, the aspect ratio of the piezoelectric ceramic sheet is greater than or equal to 10, the thickness of the piezoelectric ceramic sheet is less than or equal to 0.2 mm, the piezoelectric ceramic sheet has a flanged structure, extending the negative electrode of the piezoelectric ceramic to the surface of the positive electrode, and two piezoelectric ceramic sheets are respectively pasted on the symmetrical positions of the upper and lower surfaces of the beam-shaped wood specimen, with the length direction of the piezoelectric ceramic sheet consistent with the length direction of the beam-shaped wood specimen, and the polarization direction of the piezoelectric ceramic sheet being its thickness direction. The polarization directions of the two piezoelectric ceramic sheets pasted on the beam-shaped wood specimen are opposite.

3. The non-destructive testing method for the elastic modulus of wood according to claim 1, characterized in that: In step S2, the longitudinal vibration equation for the longitudinal vibration modal excitation is as follows: ；（1）； In the above formula, E is the longitudinal elastic modulus of the beam-shaped timber specimen, u(x, t) is the longitudinal vibration displacement, x is the longitudinal coordinate, t is time, and ρ is the density of the beam-shaped timber specimen.

4. The non-destructive testing method for the elastic modulus of wood according to claim 1, characterized in that: In step S5, the host computer controls the impedance meter to apply a swept AC excitation voltage to the piezoelectric ceramic sheet. The amplitude of the AC excitation voltage is set to 1V or 2V, the swept frequency range is set to 2000~18000Hz, and the swept frequency interval is 4Hz. The first main peak frequency is determined by the piezoelectric admittance real part response curve obtained by sweeping the frequency over a wide range. The swept frequency range is reset to include only the first main peak frequency, the swept frequency interval is 1Hz, the frequency is swept again and the admittance response is collected, and the main peak frequency f of the piezoelectric admittance real part response curve is extracted.

5. The non-destructive testing method for the elastic modulus of wood according to claim 4, characterized in that: In step S5, the beam-shaped timber specimen is equivalent to a material with mass m, damping c, and stiffness k, where the mechanical impedance of the piezoelectric ceramic sheet is much smaller than that of the beam-shaped timber specimen, thus constructing a piezoelectric admittance model. : ；(2)； In the above formula, C is the capacitance of the piezoelectric ceramic sheet. Where l, b, and t are the length, width, and thickness of the piezoelectric ceramic sheet, respectively. Where K is the frequency, j is the imaginary unit, and K is the frequency. 31 Let be the electromechanical coupling coefficient, where , These represent the piezoelectric constant, compliance coefficient, and dielectric constant of the piezoelectric ceramic sheet, respectively. and The mechanical impedances are those of a piezoelectric ceramic sheet and a beam-shaped wood specimen, respectively.

6. The non-destructive testing method for the elastic modulus of wood according to claim 5, characterized in that: In step S5, the real part of the piezoelectric admittance R(Y) is: ；(3)； In frequency When the excitation frequency is the first-order longitudinal vibration mode frequency f of the beam-shaped wood specimen, the main peak frequency f of the piezoelectric admittance real part response curve is obtained.

7. The non-destructive testing method for the elastic modulus of wood according to claim 6, characterized in that: In step S6, the longitudinal modulus of elasticity of the wood specimen is calculated by extracting the peak frequency f of the main peak of the admittance real part response curve. ；(4)； In the above formula, E is the longitudinal modulus of elasticity of the beam-shaped timber specimen, ρ is the density of the beam-shaped timber specimen, L is the length of the beam-shaped timber specimen, and f is the first-order longitudinal vibration mode frequency of the beam-shaped timber specimen.

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