RU2523033C2 - Device for sample fixation during dendro-acoustic tests for early determination of resonance parameters of standing wood - Google Patents

Abstract

FIELD: test equipment.

SUBSTANCE: invention refers to timber industry and is intended for early determination of resonance parameters of standing wood. Sample is fixated with 1.0 Nm torque through general-purpose rubber band of 50-60 conditional units hardness, applied in contact area of cam lock, with 1.0-2.0 mm process clearance 1.0 between band ends.

EFFECT: fast and precise determination of resonance parameters in timber.

4 dwg, 2 tbl, 1 ex

Description

The invention relates to the field of early detection of the resonant properties of standing wood for its further target cultivation in order to obtain high-quality timber, for the manufacture of the main sound-emitting part of musical instruments - decks.

The concept of “resonant wood” is complex and is characterized by the acoustic sound emission constant K, first formulated by Acad. N.N. Andreev as a derivative of the dynamic Young's modulus Е _din and material density ρ in the following ratio:

$$K=\sqrt{\frac{E_{d\mathrm{and}n}}{\rho 3}}\left(\mathrm{one}\right)$$

The threshold value for the category of resonant wood is K≥12 m ⁴ / kg · s.

Determination of wood density ρ is carried out by generally accepted methods according to GOST 16483.1 “Wood. The method of determining the density "and does not present great technical difficulties.

A more complex process is the determination of the indicator E _din , although there are several ways to do this, and the main one is “Wood. Established in accordance with GOST 16483.31 Resonance method for determining the moduli of elasticity and shear and decrement of vibrations. "

The essence of the method lies in the excitation of a sample with free ends of longitudinal vibrations of the fundamental harmonic and bending vibrations of the second overtone. The elastic modulus (E _W ) of samples with humidity W at the time of testing is determined by the frequencies of the resonant vibrations with an accuracy of 25 MPa according to the formula

where b, h, l - respectively, the width, height and length of the sample, m (cm);

m is the mass of the sample without plates, kg;

f _CR - the resonant frequency of longitudinal vibrations of the fundamental harmonic of the sample, Hz;

β - correction for the mass of the attached plates, equal to the ratio of the mass of the sample with the plates to the mass of the sample without plates and calculated with an error of not more than 0.5 · 10 ^-2 .

The disadvantage of this method is that it is based on the excitation and analysis of longitudinal vibrations, which will require mandatory felling of the tree, the selection of material and the production of standard samples in the form of racks with dimensions of 20 × 20 × 300 mm according to GOST 16483.21. Therefore, the method, in addition to the high complexity, complexity and low productivity, in principle, cannot be applicable for non-destructive diagnostics of the acoustic quality of standing wood.

The known method of sound resonance, more specifically the frequency-amplitude method, which is the most convenient and accurate for determining E _din on small wood samples (H. Lindstrom, P. Harris, R. Nakada. Methods for measuring the stiffness of young trees (Lindstrom, H .; Harris , P .; Nakada, R. 2002: Methods for measuring stiffness of young trees. Holz als Roh-und Werkstoff 60: 165-167).

The method is based on the identification of the natural (resonant) frequency of the sample, f, and the determination of E _din taking into account its length, thickness (radius), and also the density of the material.

For the practical implementation of the sound resonance method, there are special technical means - acoustic analyzers, which allow you to create an electromagnetic field using a loudspeaker (either ordinary or piezoceramic), corresponding to the weight (i.e. density) and the cross-sectional area of the sample, while detecting and fixing the resulting vibration inside the sample. The spectral characteristics of the sample are determined directly from the resonance modes.

The disadvantage of this method is that it is also based on the excitation and analysis of longitudinal vibrations with respect to the wood fibers, and for acoustic analysis it is necessary to produce cylindrical samples by sawing them from the stem of the tree at the internodes, which makes it impossible to diagnose the undergrowth while maintaining its viability.

The main disadvantage: this method allows you to identify only one indicator of wood, the dynamic modulus of elasticity, and the resonance properties are not determined at all.

The prototype is a method for early diagnosis of the resonance properties of standing wood, mainly undergrowth, by determining the dendroacoustic properties of the test sample in the form of a stalk 50-65 mm long taken from the undergrowth on the south side from the middle of the side branches, excluding the last three-year growths; the resonance method determines the natural vibration frequency of the selected cuttings, and using a personal computer with a full-duplex sound card in automatic mode, a frequency-amplitude histogram is obtained with its further identification with the previously obtained reference histogram taking into account the density and actual thickness of the handle; according to the results of identification with a given degree of probability of not less than 0.95, the resonance properties of the undergrowth are determined (Patent No. 2439561, authors: Fedyukov V.I., Saldaeva E.Yu., Vasenev A.L. “Method for early diagnosis of the resonant properties of standing wood”).

The disadvantage of this method is that with the existing method of cantilever type of fastening with three clamping cams, the test wood sample from young shoots with a soft cloth, moreover, not always rounded, is clamped unevenly on its circumferential surface and, most importantly, due to the lack of the clamp of the load on the clamping device when it is twisted, it is almost impossible to establish the necessary clamping force at which the stability of the frequency-amplitude indicators would be achieved, therefore, in repeated measurements x even of the same sample there is a large variation in the values (Table 1).

Tab. one The oscillation frequency of the same sample during repeated tests without a load clamp, Hz one 2 3 four 5 6 7 8 9 10 117 117 116 108 117 117 108 117 117 108

The technical result is an increase in measurement accuracy for early diagnosis of the resonant properties of standing wood.

The technical result is achieved by the fact that the method of fixing the sample during dendroacoustic tests for early detection of the resonant properties of standing wood, which consists in the fact that the sample is fixed in a fixing device with a tightening force of 1.0 Nm through a tape of general purpose rubber with a hardness in the range of 50-60 conventional units, laid in the contact zone of the jaws of the clamp, with a technical gap between the ends of the tape of 1.0-2.0 mm.

An example of fixing the sample is illustrated by drawings.

Figure 1 shows a General view of the installation, figure 2 shows the console for fixing the sample, figure 3 shows a cross section of the console, figure 4 shows the image of a tape made of rubber

On one end of the test sample (1) in the form of a handle 50-65 mm long, a layer of tape (2) is made of general-purpose rubber with a hardness within 50-60 conventional units according to GOST 263-75; in order to avoid the formation of an "accordion" when clamping the tape, its length l is selected so that a technical gap Δ (3) between the ends of the tape of 1.0-2.0 mm remains, and the gap itself is set between the clamping cams (4), while the minimum the clearance value is set when measuring cuttings with a small diameter in the range of 4.0 mm, and the maximum - with d equal to 4.0-8.0 mm; to determine the length of the tape use the following working formula:

The thickness of the tape is in the range of 1.0-1.5 mm, its width corresponds to the depth of the console socket, where the handle is vertically inserted and squeezed uniformly around its circumference with the help of a fixing device and, guided by the readings of the torque wrench, strictly on a certain amount of tightening force, equal to 1.0 Nm.

Since the rubber retainer partially absorbs vibrations and, accordingly, reduces the natural frequency of the sample, stable measurement results obtained by the fixing device are multiplied by a correction factor of 1.08 and the true value of the vibration frequency of the tested wood sample is obtained (Table 2).

Tab. 2 The oscillation frequency of the same sample during repeated tests with a fixation device, Hz one 2 3 four 5 6 7 8 9 10 Frequency measured with lock 108 108 108 108 108 108 108 108 108 108 Frequency, taking into account the correction factor 117 117 117 117 117 117 117 117 117 117

Claims (1)

The method of fixing the sample during dendroacoustic tests for early detection of the resonance properties of standing wood, which consists in the fact that the sample is fixed in a fixing device with a tightening force of 1.0 Nm through a general-purpose rubber tape with hardness in the range of 50-60 conventional units, laid in the zone contacts of the jaws of the clamp, with a technical gap between the ends of the tape of 1.0-2.0 mm

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