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CN-122017020-A - Nondestructive testing method for elastic modulus of wood

CN122017020ACN 122017020 ACN122017020 ACN 122017020ACN-122017020-A

Abstract

The invention discloses a nondestructive testing method for wood elastic modulus, which relates to the technical field of wood detection and comprises the steps of S1, preparing a beam-shaped wood test piece to be tested, S2, respectively adhering two piezoelectric ceramic sheets on two sides of the beam-shaped wood test piece, S3, installing strip-shaped foam in the center area of the lower side of the beam-shaped wood test piece to enable the beam-shaped wood test piece to be in a longitudinal free constraint state, S4, respectively connecting positive and negative leads of piezoelectric ceramics coupled on the wood test piece to two binding posts of an impedance meter, S5, setting the frequency range and amplitude of alternating current excitation voltage in the impedance meter, synchronously shrinking or synchronously elongating the two piezoelectric ceramic sheets, and conducting longitudinal vibration mode excitation on the beam-shaped wood test piece, S6, extracting the main peak-peak value frequency of a piezoelectric admittance real part response curve as the first-order longitudinal vibration mode frequency of the beam-shaped wood test piece, calculating the elastic modulus of the wood test piece, and realizing the longitudinal vibration mode excitation through the piezoelectric ceramic sheets, thereby meeting the requirement of the longitudinal vibration mode excitation of a small-size test piece.

Inventors

  • LI SHAOCHENG
  • ZHANG ZHAO
  • XU ZHAOJUN

Assignees

  • 南京林业大学

Dates

Publication Date
20260512
Application Date
20260210

Claims (7)

  1. 1. The nondestructive testing method for the elastic modulus of the wood is characterized by comprising the following steps of: S1, preparing a beam type wood test piece to be tested; s2, respectively adhering two piezoelectric ceramic sheets to two sides of a beam-type wood test piece; s3, installing strip-shaped foam 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, positive and negative wires of two pieces of piezoelectric ceramics on the beam type wood test piece are respectively connected to two binding posts of an impedance instrument, one end of the impedance instrument is provided with an upper computer, and the impedance instrument is connected with the upper computer through a communication cable; S5, setting the frequency range and amplitude of alternating current excitation voltage in the impedance meter through the upper computer, and synchronously contracting or synchronously extending the two piezoelectric ceramic sheets to excite the longitudinal vibration mode of the beam-type wood test piece; and S6, extracting the main peak-to-peak frequency of the piezoelectric admittance real part response curve as the first-order longitudinal modal frequency of the beam-type wood test piece, and calculating the elastic modulus E of the wood test piece.
  2. 2. The nondestructive testing method of elastic modulus of wood according to claim 1, wherein in the step S2, the piezoelectric ceramic sheet material is PZT-5H material, the piezoelectric ceramic sheet is rectangular, the aspect ratio of the piezoelectric ceramic sheet is greater than or equal to 2, the length-thickness 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 0.2mm, the piezoelectric ceramic sheet is of a flanging structure, the negative electrode of the piezoelectric ceramic sheet extends to the positive electrode surface, the two piezoelectric ceramic sheets are respectively stuck on symmetrical positions of the upper surface and the lower surface of the beam-type wood test piece, the length direction of the piezoelectric ceramic sheet is consistent with the length direction of the beam-type wood test piece, the polarization direction of the piezoelectric ceramic sheet is the thickness direction of the piezoelectric ceramic sheet, and the polarization directions of the two piezoelectric ceramic sheets stuck on the beam-type wood test piece are opposite.
  3. 3. A nondestructive testing method for elastic modulus of wood according to claim 1, wherein in step S2, the longitudinal vibration equation of the longitudinal vibration mode excitation is as follows: ;(1); In the above formula, E is the longitudinal elastic modulus of the beam-type wood test piece, u (x, t) is longitudinal vibration displacement, x is longitudinal coordinates, t is time, and ρ is the density of the beam-type wood test piece.
  4. 4. The nondestructive testing method of elastic modulus of wood according to claim 1, wherein in step S5, the upper computer controls the impedance meter to apply sweep alternating current excitation voltage to the piezoelectric ceramic sheet, the amplitude of the alternating current excitation voltage is set to be 1V or 2V, the sweep frequency range is set to be 2000-18000 Hz, the sweep interval is set to be 4Hz, the first main peak-to-peak frequency is determined through a piezoelectric admittance real part response curve obtained through large-scale sweep, the sweep range only comprising the first main peak-to-peak frequency is reset, the sweep interval is set to be 1Hz, the admittance response is rebunched and collected, and the main peak-to-peak frequency f of the piezoelectric admittance real part response curve is extracted.
  5. 5. A nondestructive testing method of elastic modulus of wood according to claim 4, wherein in step S5, the beam-type wood test piece is equivalent to the material of mass m, damping c and rigidity k, wherein the mechanical impedance of the piezoelectric ceramic sheet is far smaller than that of the beam-type wood test piece, and a piezoelectric admittance model is constructed : ;(2); In the above, C is the capacitance of the piezoelectric ceramic sheet, Wherein l, b and t are the length, width and thickness of the piezoelectric ceramic sheet respectively, J is an imaginary unit, K 31 is an electromechanical coupling coefficient, where, , Respectively piezoelectric constant, compliance coefficient and dielectric constant of the piezoelectric ceramic sheet, And The mechanical impedance of the piezoelectric ceramic sheet and the beam type wood test piece are respectively.
  6. 6. A nondestructive testing method for elastic modulus of wood according to claim 5 wherein in step S5, the real part R (Y) of the piezoelectric admittance is: ;(3); At the frequency of And when the excitation frequency is the first-order longitudinal vibration mode frequency f of the beam-type wood test piece, obtaining the main peak-to-peak frequency f of the piezoelectric admittance real part response curve.
  7. 7. The nondestructive testing method of wood elastic modulus according to claim 6, wherein in step S6, the longitudinal elastic modulus of the wood specimen is calculated by extracting the principal peak frequency f of the real part response curve of admittance: ;(4); In the above formula, E is the longitudinal elastic modulus of the beam-shaped wood test piece, ρ is the density of the beam-shaped wood test piece, L is the length of the beam-shaped wood test piece, and f is the first-order longitudinal vibration modal frequency of the beam-shaped wood test piece.

Description

Nondestructive testing method for elastic modulus of wood Technical Field The invention belongs to the technical field of wood detection, and particularly relates to a nondestructive detection method for elastic modulus of wood. Background The wood has natural environment-friendly characteristics, is widely applied to household industries such as wood structure buildings, furniture manufacturing and the like, mechanical property detection is needed before the wood is used, elastic modulus is one of important indexes for measuring the mechanical property of the wood, three nondestructive detection methods, namely a transverse vibration method, an ultrasonic method and a longitudinal vibration method, are developed at present, the length-thickness ratio requirement of the traditional transverse vibration method on a wood test piece is required to be more than 50, the ultrasonic method predicts the elastic modulus according to the propagation speed of ultrasonic waves in the wood test piece, a detection system is relatively complex, the longitudinal vibration method is mainly excited at one end of a beam-type wood test piece by adopting a stress hammer to generate excitation load along the length direction of the test piece, a vibration response signal is received at the other end of the beam-type wood test piece by an acceleration or sound pressure sensor, and the modal response signal is subjected to Fourier transformation to obtain the first-order longitudinal vibration frequency of the test piece, so that the elastic modulus of the test piece is determined. In the traditional longitudinal vibration method, the stress hammer excitation frequency range is limited, and the method is only suitable for longitudinal vibration mode excitation of a longer test piece, in addition, the traditional longitudinal vibration method needs to carry out Fourier transformation on vibration response signals to obtain first-order longitudinal vibration mode frequency of the beam-type wood test piece, so that the required wood test piece is excessive in material and low in elastic modulus measurement efficiency. Disclosure of Invention The invention aims to overcome the defects in the prior art, and the nondestructive testing method for the elastic modulus of the wood provided by the invention has the advantages that the test piece materials are saved, and the measuring efficiency and the effect of the elastic modulus of the test piece in a longitudinal vibration method are improved. In order to solve the technical problems, the invention adopts the following technical scheme that the nondestructive testing method for the elastic modulus of the wood comprises the following steps: S1, preparing a beam type wood test piece to be tested, wherein the cross section of the selected beam type wood test piece is square, the length-thickness ratio of the test piece is 10-15, and the preferred dimensions are 200mm multiplied by 20mm, 220mm multiplied by 20mm or 240mm multiplied by 20mm; s2, respectively adhering two piezoelectric ceramic sheets to two sides of a beam-type wood test piece; s3, installing strip-shaped foam 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 welding wires on the positive electrode and the negative electrode of the piezoelectric ceramics, respectively twisting the two positive electrodes and the two negative electrode wires of the two piezoelectric ceramics together, and then respectively connecting the positive electrode wires and the negative electrode wires of the two piezoelectric ceramics on the beam-type wood test piece to two binding posts of an impedance instrument, wherein one end of the impedance instrument is provided with an upper computer, and the impedance instrument is connected with the upper computer through a communication cable; S5, setting the frequency range and amplitude of alternating current excitation voltage in the impedance meter through the upper computer, and synchronously contracting or synchronously extending the two piezoelectric ceramic sheets to excite the longitudinal vibration mode of the beam-type wood test piece; And S6, extracting the main peak-to-peak frequency of the piezoelectric admittance real part response curve as the first-order longitudinal vibration modal frequency of the beam-type wood test piece, and calculating the elastic modulus E of the wood test piece. Further, in step S2, the piezoelectric ceramic sheet material is PZT-5H material, the shape of the piezoelectric ceramic sheet is a rectangular sheet, the aspect ratio of the piezoelectric ceramic sheet is equal to or greater than 2, the length-thickness ratio of the piezoelectric ceramic sheet is equal to or greater than 10, the thickness of the piezoelectric ceramic sheet is equal to or less than 0.2mm, the piezoelectric ceramic sheet is in a flange structure, the negative electrode o