RU2830704C1 - Method for determining physical and mechanical properties of wood of growing trees - Google Patents

Abstract

FIELD: forestry; timber industry.

SUBSTANCE: invention can be used for rapid non-destructive determination of physical and mechanical properties of wood of growing trees, assessment of changes in properties along the radius and height of the trunk, as well as selection of rational technologies of wood processing. Method includes measuring the height of the tree, the diameter of the trunk, the acoustic characteristics of the wood, for example, the speed of ultrasound along the diameter and height of the trunk, and measurement of profile of resistance of wood to drilling. On the diagram of change of resistance of wood to drilling from drilling depth, points of beginning and completion of drilling of xylem are fixed. Profile of resistance of wood to drilling is corrected by exclusion of data corresponding to friction of shank of thin drill bit, value of which is determined by linear equation passing through points with coordinates: X₁—beginning of xylem drilling plus 10 millimeters, Y₁=0 and X₂—end of xylem drilling, Y₂—value of drill shank friction at its exit from the tree trunk. Drill shank friction to point X₁, Y₁ is equal to zero, and after point X₂, Y₂ the value of drill shank friction at its exit from the tree trunk.

EFFECT: invention provides higher accuracy and efficiency of determining physical and mechanical properties of wood by radius and height of the trunk of a growing tree.

3 cl, 1 dwg

Description

The invention relates to forestry and the forest industry and can be used for the rapid non-destructive determination of the physical and mechanical properties of wood of growing trees, the assessment of changes in properties by the radius and height of the trunk, and the selection of rational technologies for wood processing.

A method of comparative testing of wood is known, in which samples are taken (made) from sawn timber, timber or growing trees in the form of cores. Additionally, samples of standard sizes are made from the object of study, for example, 20×20×30 mm ³ . The essence of the method lies in determining the transition coefficient between the speed of ultrasound passage through the core and the strength characteristics obtained in laboratory conditions on standard samples [1].

The disadvantage of this method is the use of standard samples for laboratory research, which removes this method from the group of non-destructive methods for assessing the physical and mechanical properties of wood of growing trees. At the same time, the use of this method does not allow assessing the change in the physical and mechanical properties of wood within the annual layer.

A method and devices for indirectly determining the physical and mechanical properties of wood based on the method of measuring drilling resistance are also known [2]. The method is based on the use of a mobile unit for drilling wood with thin drill bits. During the measurements, the energy and/or speed parameters of the drilling process, which are associated with the physical and mechanical properties of wood, are recorded. The method makes it possible to determine the variation in the properties of wood within the annual layer and is widely used to assess the properties and internal state of wood in growing trees. The disadvantages of this method include a decrease in the accuracy of predicting the physical and mechanical properties of wood with an increase in the drilling depth due to an increase in the friction of the shank of the thin drill bit against the chips and the walls of the hole, which is often recorded when assessing the properties of wood in growing trees. The existing method for adjusting the profile of wood resistance to drilling, presented in work [3], which makes it possible to partially exclude the friction component of the thin drill bit from the general profile of wood resistance to drilling, was developed for samples of solid wood, without taking into account the specifics of determining the properties of wood in growing trees. The transformation of the drilling resistance profile into a profile of the physical and mechanical properties of wood requires the use of models of the relationship between these parameters, which can be obtained on the basis of drilling and subsequent physical and mechanical testing of standard wood samples [4], which is an additional disadvantage, also removing this method from the list of non-destructive methods for assessing the properties of wood.

The technical result is an increase in the accuracy and efficiency of determining the physical and mechanical properties of wood along the radius and height of the trunk of a growing tree, as well as within the annual layer, based on a method for measuring drilling resistance with the removal of a core from a growing tree.

The technical result is achieved by adjusting the wood resistance profile to drilling by eliminating the values corresponding to the friction of a thin drill bit against the chips and the hole walls, while in the areas of drilling the bark and phloem of the tree (bast), as well as the initial section of drilling the xylem (wood), equal to 10 millimeters, the friction value of the drill shank is equated to zero. A cylindrical core is taken from a growing tree with an increment borer in the radial direction at a distance of 5 or more millimeters from the place of penetration or exit of the thin drill bit from the tree trunk. After appropriate preparation, the core is divided into parts without chips. The physical and mechanical properties of each part of the core are determined: moisture, density, acoustic characteristics and mechanical properties. The values of physical and mechanical properties are compared with the average values of the sections of the corrected drilling resistance profile corresponding to the drill's passage through the annual xylem layers (and/or their sections) located on the core parts. Regression models of the relationship between the physical and mechanical properties of wood in the core parts and the values of wood drilling resistance are determined for one or several model trees and can be used to transform the data obtained on other trees of the cenopopulation.

Determination of the physical and mechanical properties of wood in a growing tree includes selection of a model tree (trees), measurement of the tree height, trunk diameter, acoustic characteristics of wood, for example, the speed of ultrasound transmission along the diameter and height of the trunk and measurement of the profile of resistance to drilling of wood with subsequent removal of a cylindrical core with an increment borer in the radial direction at a distance of 5 or more millimeters from the point of penetration or exit of a thin drill bit from the tree trunk. The profile of resistance to drilling of wood, as well as the preceding measurements of the height, diameter and acoustic characteristics of wood, for a growing tree can be obtained an unlimited number of times at any height relative to the neck of the tree in the radial and tangential directions relative to the direction of the fibers and in any direction relative to the cardinal directions.

The drilling resistance profile, which is the dependence of the numerical energy-force and/or speed data of the drilling process on the penetration depth of a thin drill bit, for growing trees can be divided into four main sections: the initial section (No. 1), which is the section of drilling through the bark and adjacent phloem, the main section (No. 2), which is the section of drilling through the xylem, the subsequent section (No. 3), which is also the section of drilling through the bark and xylem, but from the opposite side of the tree, and the section (No. 4) of maximum friction of the shank of the thin drill bit when its cutting part exits the tree (Fig. 1). When drilling through the bark and phloem in the first and third sections, according to the drilling resistance profile shown in Fig. 1, the friction of the shank of the thin drill bit can be equated to zero. The basis for accepting this hypothesis is the low density and strength, as well as the high porosity of these tissues of a growing tree compared to xylem. The design of the cutting part of a thin drill bit, which has a larger diameter compared to the diameter of its tail, allows us to attribute the frictional forces along the cutting part to the total cutting forces during drilling. The friction of the shank of a thin drill bit against the chips and the walls of the hole, taking into account the average length of the cutting part of the drill of 10 millimeters, is proposed to be taken into account from a drilling depth of 10 millimeters from the point of starting to drill xylem (the point of starting to drill section 2 in Fig. 1).

Taking into account the above, a new, refined method for adjusting the profile of wood resistance to drilling for growing trees is proposed (Fig. 1). On the graph of the profile of resistance to drilling, where the Y axis is the resistance to drilling, the X axis is the drilling depth, the points of the beginning and end of drilling of the tree xylem are marked (section 2). Then the profile is adjusted by excluding the data corresponding to the friction of the shank of a thin drill bit, the value of which is determined from the graph of a linear equation passing through the points with the coordinates: X ₁ - the beginning of drilling of the xylem plus 10 millimeters, Y ₁ = 0 and X ₂ - the end of drilling of the xylem, Y ₂ - the value of friction of the drill shank when it exits the tree trunk (maximum friction of the shank). The friction of the drill shank before the point (X ₁ , Y ₁ ) is equal to zero, and after the point (X ₂ , Y ₂ ) to the value of friction of the drill shank when it exits the tree trunk. An example of adjusting the profile of change in drilling resistance is shown in Fig. 1. In the case of no friction of the drill shank when exiting the tree trunk, it is not necessary to adjust the profile of drilling resistance.

Next, the bark and phloem are separated from the extracted core(s) in laboratory conditions, and the core is divided into parts without chips. Each part of the core may consist of one or more annual rings and/or sections of annual rings. For each part of the core, the physical and mechanical properties such as moisture content, density, acoustic properties, such as ultrasound velocity, and strength, such as compression or shear strength along the fibers, are determined. The values of the physical and mechanical properties of the core parts are compared with the average values of the sections of the corrected drilling resistance profile corresponding to drilling of the same annual rings (or parts thereof) of which the core part consists. Based on the values of the average values of wood drilling resistance and the physical and mechanical properties of the cores and/or parts thereof, regression models of the relationship between these parameters are determined, using which the obtained profiles of wood drilling resistance can be transformed into profiles of changes in physical and mechanical properties. Regression models can be obtained for one or more model trees and subsequently used to transform drilling resistance profiles into profiles of changes in physical and mechanical properties for other trees in the cenopopulation.

This method allows, with high accuracy and without significant impact on the viability of trees, to determine the change in the physical and mechanical properties of wood along the radius and height of the trunk, as well as within the annual layers of wood of a growing tree.

The study was supported by the Russian Science Foundation grant No. 23-16-00220, https://rscf.ru/project/23-16-00220/.

Used analogues and prototypes:

1. Method for comparative testing of wood: patent 2522862 Russian Federation: G01N 33/46 / Kolesnikova A.A., Fedorova A.A., Mazurkin P.M. - No. 2012133089/15; declared 01.08.2012; published 20.07.2014.

2. Gao S., Wang X., Wiemann M.C., Brashaw B.K., Ross R.J., Wang L. (2017) A critical analysis of methods for rapid and nondestructive determination of wood density in standing trees. Annals of Forest Science, DOI:doi.org/10.1007/s13595-017-0623-4.

3. Sharapov E., Wang X., Smirnova E. (2017) Drill bit friction and its effect on resistance drilling measurements in logs. In: Proceedings of the 20th International Nondestructive Testing and Evaluation of Wood Symposium, 12-15 September 2017, USDA Forest Service, Forest Products Laboratory, Madison, WI, pp. 405-415,

4. Sharapov E., Brischke C., Militz H., Smirnova E. (2019) Prediction of modulus of elasticity in static bending and density of wood at different moisture contents and feed rates by drilling resistance measurements. European Journal of Wood and Wood Products 77(5):833-842, DOI:doi.org/10.1007/s00107-019-01439-2.

Fig. 1 Graph of change in wood resistance to drilling and friction of thin drill bit shank along tree diameter with drilling sections: 1 - bark and phloem (bast) when drill enters tree, 2 - drilling xylem (wood), 3 - phloem and bark when drill exits tree, 4 - maximum friction of thin drill bit shank against shavings and hole walls when drill exits tree. Determination of sections of wood resistance profile to drilling (average values of resistance profile sections) with core parts. Point (X ₁₊₁₀ , Y ₁ =0) - start of friction and point (X ₂ , Y ₂ ) - end of friction of thin drill bit shank against shavings and hole walls.

Claims (3)

1. A method for determining the physical and mechanical properties of wood of growing trees, including measuring the height of the tree, the diameter of the trunk, the acoustic characteristics of the wood, for example the speed of ultrasound transmission along the diameter and height of the trunk, and measuring the profile of the resistance of the wood to drilling, characterized in that on the graph of the change in wood resistance to drilling from the drilling depth, the points of the beginning and end of xylem drilling are recorded, the profile of wood resistance to drilling is corrected by excluding the data corresponding to the friction of the shank of a thin drill bit, the value of which is determined by a linear equation passing through points with coordinates: X₁– the beginning of xylem drilling plus 10 millimeters, Y₁=0 and X₂– end of xylem drilling, Y₂– the amount of friction of the drill shank when it exits the tree trunk, while the friction of the drill shank to point X₁, Y₁is equal to zero, and after point X₂, Y₂the amount of friction of the drill shank as it exits the tree trunk. 2. The method according to item 1, characterized in that the core is taken at a distance of 5 or more millimeters from the point of penetration or exit of a thin drill bit from a tree trunk, the bark and phloem are separated from the core, the core is divided into parts without chips, followed by determination of the moisture content, density, acoustic characteristics and mechanical properties of the parts of the core, and the models of the relationship of these physical and mechanical properties of the parts of the core with the drilling resistance are determined by comparing the average values of the sections of the drilling resistance profile corresponding to the passage of the drill through annual layers and/or their parts located on the parts of the core, followed by determination of regression models of the relationship of the physical and mechanical properties of the parts of the core with the drilling resistance of the wood. 3. The method according to paragraph 1, characterized in that the model of the relationship between the resistance of wood to drilling with thin drill bits and the moisture content, density, acoustic characteristics and mechanical properties of the core wood is determined for one or several model trees and is subsequently used to transform data obtained on other trees of the cenopopulation.