CN113188940B - Wood strain measurement method and device based on growth wheel dimension - Google Patents
Wood strain measurement method and device based on growth wheel dimension Download PDFInfo
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Abstract
The invention relates to a wood strain measurement method based on growth wheel dimension, which comprises the following steps: s1: oven dried samples were prepared. S2: and (3) putting the oven-dried sample into a dynamic moisture adsorption analyzer, and continuously recording the weight change of the wood sample at fixed time intervals until the moisture content equilibrium state is reached. S3: and keeping the same time interval, and continuously photographing the wood sample by adopting a video white light microscope until the moisture content equilibrium state is reached. S4: and analyzing and processing the image to obtain the moisture content, the radial and chordal wet expansion rate of the wood sample at each time. S5: and (4) after the moisture content of the wood sample reaches the equilibrium state, reducing the relative humidity, and repeating the steps S2-S3. S6: and (5) analyzing the image in the step (S5) to obtain the water content and the radial chord direction shrinkage rate of the wood sample at each time. The invention combines the dynamic moisture adsorption analyzer with the video white light microscope, and can synchronously obtain the moisture content of the wood sample and the corresponding strain quantity of the dry shrinkage and the wet expansion under any state in real time.
Description
Technical Field
The invention belongs to the technical field of wood measurement, and particularly relates to a wood strain measurement method and device based on growth wheel dimensions.
Background
The phenomenon of wood shrinking its size due to drying is called dry shrinkage, and the phenomenon of increasing its size due to moisture absorption is called wet swelling. The phenomena of dry shrinkage and wet swelling occur under the condition that the moisture content of the wood is less than the fiber saturation point, and when the moisture content of the wood is above the fiber saturation point, the size and the volume of the wood hardly change.
The phenomena of dry shrinkage and wet swelling have a great influence on the utilization of wood: drying shrinkage can cause dimensional shrinkage of the wood product resulting in gaps, warping, and cracking. The swelling not only can increase the size of the wooden products, cause floor uplift and door and window failure, but also can reduce the mechanical property of the wood.
The dry shrinkage/wet expansion of the wood comprises axial dry shrinkage/wet expansion and transverse dry shrinkage/wet expansion, the axial dry shrinkage/wet expansion is along the direction perpendicular to the trunk of the wood, the dry shrinkage/wet expansion value is small, and the utilization of the wood is not greatly influenced. Transverse dry shrinkage/wet expansion includes radial dry shrinkage/wet expansion and chordwise dry shrinkage/wet expansion. The radial dry shrinkage/wet expansion is larger in value along the diameter direction on the cross section of the wood, and the chord dry shrinkage/wet expansion is larger in value along the tangential direction of the growth wheel and is not negligible.
In the wood growing wheel, the radial and chordal shrinkage or wet expansion of the wood is influenced by the structural difference, the balance water content difference and the connection mode between the early wood and the late wood. Therefore, the drying shrinkage/swelling experiments are carried out on the scale of the growth wheel, and the wood samples of the early wood, the late wood and the growth wheel are taken as research objects. In the prior art, a method for measuring the dry shrinkage/wet expansion strain on the scale of a growing wheel of wood comprises the following steps:
weighing the wood samples with different moisture content equilibrium states, calculating to obtain the moisture content of the wood samples, shooting the wood samples with different moisture content equilibrium states, obtaining images, analyzing, and obtaining the dry shrinkage/wet expansion strain capacity of the wood samples. The disadvantages of this method are: only the water content and the dry shrinkage/wet expansion strain of the sample in the water content equilibrium state can be measured, and the water content and the dry shrinkage/wet expansion strain of the sample in the water absorption and desorption processes cannot be measured.
Therefore, there is a need for a method for measuring the moisture content and the amount of dry shrinkage and wet expansion strain of a sample in a moisture content equilibrium state, and for measuring the moisture content and the amount of dry shrinkage and wet expansion strain of a sample during moisture absorption and desorption.
Disclosure of Invention
Technical problem to be solved
In order to solve the problem that the water content and the shrinkage/swelling strain quantity of a sample in the moisture absorption/desorption process cannot be measured in the prior art, the invention provides a wood strain measurement method based on the growth wheel scale. In addition, the invention also provides a device for measuring the wood strain quantity, which is used for the measuring method.
(II) technical scheme
In order to achieve the purpose, the invention adopts the main technical scheme that:
a wood strain measurement method based on growth wheel dimension comprises the following steps:
s1: preparing oven-dried samples of wood;
s2: putting the oven-dried sample obtained in the step S1 into a dynamic moisture adsorption analyzer with constant temperature and certain relative humidity, keeping a fixed time interval, and continuously recording the weight change of the wood sample until the wood sample reaches a moisture content equilibrium state;
s3: keeping the same time interval as the step S2, and continuously photographing the wood sample by adopting a video white light microscope until the wood sample reaches a moisture content equilibrium state;
s4: analyzing and processing the image obtained in the step S2 to obtain the water content, the radial wet expansion rate and the chord direction wet expansion rate of the wood sample at each time;
s5: in the step S3, after the moisture content of the wood sample reaches the equilibrium state, reducing the relative humidity in the dynamic moisture adsorption analyzer, and then repeating the steps S2-S3;
s6: and analyzing and processing the image obtained in the step S5 to obtain the water content, the radial dry shrinkage and the chord dry shrinkage of the wood sample at each time.
In the above-described measurement method, it is preferable that, in step S2, the temperature in the dynamic moisture adsorption analyzer is 20 to 25 ℃ and the relative humidity is 0 to 98%.
In the measurement method described above, preferably, the interval between the recording of the quality change in step S2 and the capturing of the image in step S3 is 1min;
in step S3, the video white light microscope is adjusted so that the pixels of the photographed picture are 1280 × 960.
In the above measurement method, preferably, before the step S4, the image obtained in the step S3 is subjected to noise reduction processing, where the noise reduction processing of the image specifically includes: the brightness, contrast, exposure, RGB curves and tone scale of the picture are adjusted to enhance the details of the measurement area.
In the above measurement method, preferably, in step S1, the determining the mark point of the image corresponding to the oven dry sample specifically includes:
importing the noise-reduced image into AutoCAD software, finding out 4 cell corners on the wheel boundary line of the wood sample growth wheel, and then amplifying the image of the wood sample until a pixel block is visible;
and (3) in the cell corner, making 4 marking points at the positions where the pixel blocks have obvious color boundaries, connecting the 4 marking points one by one along the radial direction and the chord direction to obtain 4 straight lines, and measuring the lengths of the 4 straight lines to obtain the lengths of the straight lines.
In the above measurement method, preferably, in step S4, the determining the mark point of the image of the wood sample in the swelling process specifically includes:
importing the noise-reduced image into AutoCAD software, finding out 4 cell corners on the wheel boundary line of the wood sample growth wheel, and then amplifying the image of the wood sample until a pixel block is visible;
in the cell corner, 4 marking points are made at the positions where the color boundary characteristics of the pixel blocks appear are the same as those of the pixel blocks in the process of determining the absolute dry sample marking points, the 4 marking points are connected one by one along the radial direction and the chord direction to obtain 4 straight lines, and the length of the 4 straight lines is measured to obtain the length of the straight lines;
the calculation formula of the wet swelling rate of the wood sample at any time is as follows:
in the formula:
ε RH the unit is the radial/chordal wet expansion rate of the sample in any relative humidity environment;
l RH the radial/chordal dimension of the sample at any time in a certain relative humidity environment is expressed in the unit of mu m;
l 0 is the radial or chordal dimension of the oven dry sample in μm.
In the above measurement method, preferably, in step S6, the determining the mark point of the image of the wood sample during the drying process specifically includes:
importing the noise-reduced image into AutoCAD software, finding out 4 cell corners on the wheel boundary line of a wood sample growth wheel, and then amplifying the image of the wood sample until a pixel block is visible;
in the cell corner, 4 marking points are made at the positions where the color boundary characteristics of the pixel blocks appear are the same as those of the pixel blocks in the process of determining the absolute dry sample marking points, the 4 marking points are connected one by one along the radial direction and the chord direction to obtain 4 straight lines, and the length of the 4 straight lines is measured to obtain the length of the straight lines;
in step S6, the calculation formula of the dry shrinkage is:
in the formula:
ε RH the unit is the dry shrinkage rate of the sample in the radial direction/chord direction in any relative humidity environment;
l RH the unit is the radial/chord-wise size of the sample at any time in a certain relative humidity environment, and the unit is mum;
l 0 is the radial or chordal dimension of the oven dry sample in μm.
In the above measurement method, preferably, in step S4 and step S6, at any time, the water content of the wood sample is calculated by the following formula:
MC RH the water content of the sample in any relative humidity environment is shown in unit;
M RH the mass of the sample in mg in any relative humidity environment;
M 0 is the mass of the oven dried sample in mg.
The invention also provides a device for measuring the wood strain quantity, which comprises a dynamic moisture adsorption analyzer and a video white light microscope;
the dynamic moisture adsorption analyzer comprises an ultramicro electronic antenna and a gas flow controller;
the video white light microscope is positioned below the ultramicro electronic balance and is electrically connected with the dynamic moisture adsorption analyzer.
(III) advantageous effects
The invention has the beneficial effects that:
the measurement method combines a dynamic moisture adsorption analyzer with a white light microscope imaging technology, the dynamic moisture adsorption analyzer measures the weight change of the wood sample, the video white light microscope shoots and obtains the image of the wood sample under the same state, and the data of the strain quantity of the dry shrinkage and the wet expansion of the growth wheel scale in the moisture adsorption/desorption process are synchronously obtained in real time by matching with the image processing. The measuring method can be used for carrying out weight and photographing on the wood sample with any water content at any time, and can ensure that the obtained water content, the obtained dry shrinkage rate and the obtained wet expansion rate are all real data of the wood sample in the same state.
The invention provides an image measuring method for a wood drying shrinkage-swelling test with a growth wheel size, which has the advantages of accurate positioning, high accuracy and convenient operation. The measuring method of the invention has the following advantages: (1) the method can measure the dry shrinkage strain capacity and the wet expansion strain capacity of any water content state lower than the fiber saturation point and the one-to-one corresponding data of the dry shrinkage strain capacity and the wet expansion strain capacity and the water content, and can explore the relation between the water content of any wood and the dry shrinkage or wet expansion strain. (2) The measuring mark points of the wood sample can be accurately positioned. (3) The measurement precision of the strain capacity of dry shrinkage and the strain capacity of wet expansion can reach 0.01 mu m.
The measuring method can be used for synchronously measuring the moisture absorption/desorption isotherm and the dry shrinkage/wet expansion rate of the wood in real time, further researching the relation between the moisture content of the wood and the radial and chordal dry shrinkage/wet expansion rates, researching whether the wood has a hysteresis phenomenon and a change rule thereof, and researching the influence factors thereof. The measuring method leads the research of the wood drying shrinkage/wet expansion behavior to mesoscopic view from macro view, and has important scientific value and practical significance for reasonably and efficiently utilizing the wood by deeply knowing the influence of the water content and the mutual action mechanism of the wood drying shrinkage/wet expansion behavior from the scale of a growth wheel.
Drawings
FIG. 1 is a schematic image processing of a wood sample according to the present invention;
FIGS. 2a-2j are graphs showing the relationship between the water content of early Aronia melanocarpa and the radial and chordwise wet expansion ratios at 0% RH, 10% RH, 20% RH, 30% RH, 40% RH, 50% RH, 60% RH, 70% RH, 80% RH, 90% RH, 10 relative humidity stages, respectively;
FIGS. 3a-3j are graphs showing the relationship between the water content of late Aronia melanocarpa and the radial and chordwise wet expansion ratios at 0% RH, 10% RH, 20% RH, 30% RH, 40% RH, 50% RH, 60% RH, 70% RH, 80% RH, 90% RH, respectively, at 10 relative humidity levels;
FIGS. 4a to 4j are graphs showing the relationship between the water content of the growth wheel and the radial and chordal wet expansion ratios at 10 relative humidity levels of 0% RH, 10% RH, 20% RH, 30% RH, 40% RH, 50% RH, 60% RH, 70% RH, 80% RH, 90% RH, respectively;
FIGS. 5a-5j are graphs showing the relationship between the water content of early Aronia melanocarpa and the radial and chordwise dry shrinkage ratios at 10 relative humidity levels of 90% RH, 80% RH, 70% RH, 60% RH, 50% RH, 40% RH, 30% RH, 20% RH, 10% RH, 0% RH, respectively;
FIGS. 6a-6j are graphs showing the relationship between the water content of late Aronia melanocarpa and the radial and chordwise dry shrinkage ratios at 10 relative humidity levels of 90% RH, 80% RH, 70% RH, 60% RH, 50% RH, 40% RH, 30% RH, 20% RH, 10% RH, 0% RH, respectively;
FIGS. 7a to 7j show the relationship between the water content of the growth wheel and the radial and chordal dry shrinkage ratios at 10 relative humidity levels of the 90% RH, 80% RH, 70% RH, 60% RH, 50% RH, 40% RH, 30% RH, 20% RH, 10% RH, 0% RH, respectively.
[ description of reference ]
1: an original image shot by a video white light microscope; 2: reducing the noise of the processed image; 3: amplifying to 4 visible mark points of the pixel block; 4: chordwise dry shrinkage/wet expansion strain; 5: radial dry shrinkage/wet swell strain.
Detailed Description
For a better understanding of the present invention, reference will now be made in detail to the present embodiments of the invention, which are illustrated in the accompanying drawings.
Referring to fig. 1 to 7, the present embodiment provides a method for measuring wood strain based on growth wheel dimensions, including the following steps:
s1: oven dried samples of wood were prepared.
S2: and (3) putting the oven-dried sample obtained in the step (S1) into a dynamic moisture adsorption analyzer with constant temperature and certain relative humidity, keeping a fixed time interval, and continuously recording the weight change of the wood sample until the wood sample reaches a moisture content equilibrium state.
S3: and keeping the same time interval as the step S2, and continuously photographing the wood sample by adopting a video white light microscope until the wood sample reaches a moisture content equilibrium state.
S4: and analyzing and processing the image obtained in the step S2 to obtain the water content, the radial wet expansion rate and the chord direction wet expansion rate of the wood sample at each time.
S5: in step S3, after the moisture content of the wood sample reaches the equilibrium state, the relative humidity in the dynamic moisture adsorption analyzer is reduced, and then the steps S2 to S3 are repeated.
S6: and analyzing and processing the image obtained in the step S5 to obtain the water content, the radial dry shrinkage and the chord dry shrinkage of the wood sample at each time.
According to the measurement method, a dynamic moisture adsorption analyzer is combined with a white light microscope imaging technology, the dynamic moisture adsorption analyzer measures the weight change of the wood sample, the video white light microscope shoots and obtains the image of the wood sample in the same state, and strain data of dry shrinkage and wet expansion of growth wheel scales under any moisture content are obtained in real time and synchronously in cooperation with image processing, so that the obtained moisture content, dry shrinkage and wet expansion are real data of the wood sample in the same state.
Preferably, in step S2, the temperature in the dynamic moisture adsorption analyzer is 20 to 25 ℃, and the relative humidity is 0 to 98%.
Preferably, the interval time of the quality change recording in the step S2 and the interval time of the image shooting in the step S3 are both 1min, and the tester can adjust the weighing and shooting time intervals according to the experiment requirements. In step S3, the video white light microscope is adjusted so that the pixels of the photographed picture are 1280 × 960.
The step S2 specifically includes:
and cleaning the quartz tray special for photographing by using distilled water to ensure that no impurities exist on the quartz tray. Then the quartz tray containing early wood, late wood or growing wheel wood samples is placed in a sample bin of the dynamic moisture adsorption instrument. The weight of the wood sample is 15-50mg, and the transverse section of the wood sample is downward. The tester can adjust the position of the wood sample in the quartz tray according to the shot object.
Preferably, before step S4, the image obtained in step S3 is subjected to noise reduction processing, where the noise reduction processing of the image specifically includes: photoshop is adopted to adjust the brightness, contrast, exposure, RGB curve and color level of the picture so as to enhance the details of the measuring area.
Preferably, in step S1, determining the marking points of the image corresponding to the oven dry sample by using AutoCAD includes:
inputting an attaching command-XRFE, selecting 'attaching A', and importing the image after the noise reduction treatment into AutoCAD. The corners of 4 cells were found on the wheel boundary of the wood sample growth wheel and the image of the wood sample was magnified until blocks of pixels were visible.
And (3) in the cell corner, making 4 marking points at the positions of the pixel blocks with obvious color boundaries, recording the positions of the 4 marking points, and connecting the 4 marking points into a straight LINE along the radial direction and the chord direction by using a command 'LINE'. The length measurements and recordings were made on 4 straight lines by command "DIMALIGNED". By adopting the method for determining the mark points, the measurement precision of the dry shrinkage strain quantity and the wet expansion strain quantity can reach 0.01 mu m.
Preferably, in step S4, the determining the mark points of the image of the wood sample in the swelling process specifically includes:
inputting an attachment command of-XRFE, selecting 'attachment A', and importing the image after noise reduction processing into AutoCAD. The 4 cell corners were found on the wheel boundary of the wood sample growth wheel and the image of the wood sample was magnified until the block of pixels was visible.
And in the cell corner, 4 marking points are made at the positions where the color boundary characteristics of the pixel block appear are the same as those of the pixel block in the process of determining the absolute stem sample marking points, the positions of the 4 marking points are recorded, and the 4 marking points are connected into a straight LINE along the radial direction and the chord direction through a command 'LINE'. The length measurements and recordings were made on 4 straight lines by command "DIMALIGNED".
The calculation formula of the wet swelling rate of the wood sample at any time is as follows:
in the formula:
ε RH the unit is the radial/chord wet expansion rate of the sample in any relative humidity environment;
l RH the radial/chordal dimension of the sample at any time in a certain relative humidity environment is expressed in the unit of mu m;
l 0 is the radial or chordal dimension of the oven dry sample in μm.
Preferably, in step S6, the determining the mark points of the image of the wood sample during the drying process specifically includes:
inputting an attachment command of-XRFE, selecting 'attachment A', and importing the image after noise reduction processing into AutoCAD. The 4 cell corners were found on the wheel boundary of the wood sample growth wheel and the image of the wood sample was magnified until the block of pixels was visible.
And in the cell corner, 4 marking points are made at the positions where the color boundary characteristics of the pixel block appear are the same as those of the pixel block in the process of determining the absolute stem sample marking points, the positions of the 4 marking points are recorded, and the 4 marking points are connected into a straight LINE along the radial direction and the chord direction through a command 'LINE'. The length measurements and recordings were made for 4 straight lines by command "DIMALIGNED".
In step S6, the calculation formula of the dry shrinkage is:
in the formula:
ε RH the dry shrinkage rate of the sample in the radial/chord direction in any relative humidity environment is expressed in percent.
l RH The unit is the radial/chordal dimension of the sample at any time in a certain relative humidity environment, and is μm.
l 0 Is the radial or chordal dimension of the oven dry sample in μm.
Preferably, in step S4 and step S6, at any time, the calculation formula of the water content of the wood sample is:
MC RH the water content of the sample in any relative humidity environment is shown in percentage.
M RH The mass of the sample achieved in any relative humidity environment is in mg.
M 0 Is the mass of the oven dried sample in mg.
Example 1
The embodiment provides a wood strain measurement method based on a growth wheel scale, which is used for researching the relationship between the moisture content and the swelling strain of an Early Wood (EW) of catalpa bungei, and specifically, the measurement method of the embodiment comprises the following steps:
s1: setting the temperature in the dynamic moisture adsorption analyzer to 25 ℃, the temperature is accurate to 0.1 ℃, and the relative humidity is set to 0 percent RH, putting the early wood sample of catalpa bungei into the dynamic moisture adsorption analyzer to obtain an oven-dried sample, and taking an image of the oven-dried sample by using a video white light microscope.
S2: the oven-dried sample obtained in step S1 is subjected to weight measurement and image capturing. And (3) carrying out noise reduction on the image, and then finishing the determination of the mark points of the image of the oven-dried sample by adopting AutoCAD. Specifically, the image after noise reduction processing is introduced into AutoCAD, 4 cell corners are found on the wheel boundary line of the early wood sample growth wheel, and then the image of the early wood sample is enlarged until the pixel block is visible. In each cell corner, 4 marked points are made at the positions where the pixel blocks have obvious color boundaries, the positions of the 4 marked points are recorded, and the 4 marked points are connected into a straight LINE along the radial direction and the chord direction by a command 'LINE'. The length measurements and recordings were made for 4 straight lines by command "DIMALIGNED".
S3: maintaining the temperature within the dynamic moisture adsorption analyzer, adjusting the relative humidity within the dynamic moisture adsorption analyzer to 0-10-RH, 20-RH, 30-RH, 40-RH, 50-RH, 60-RH, 70-RH, 80-RH, 90-RH in the order of 10 relative humidity stages under 0-90-RH, recording the weight of the early wood sample once every 1min, simultaneously capturing the image, subjecting the image to noise reduction and marking point processing, and calculating the water content and the radial direction wet expansion ratio toward the wet expansion ratio at each time according to the correspondence formula.
In this example, nearly 100 measurement points are taken at each humidity stage, a graph is drawn, and linear regression analysis is performed on the moisture content and the radial swell ratio, and the moisture content and the chord swell ratio of the catalpa bungei early wood, respectively, to obtain fig. 2a-2j.
As can be seen from FIGS. 2a-2j, the water content of the early wood of catalpa bungei at 10 relative humidity stages has a linear positive correlation with the radial swelling rate and the chord-direction swelling rate. Wherein the 10 relative humidity stages in the 0, 10, 20% RH, 30% RH, 40% RH, 50% RH, 60% RH, 70% RH, 80% RH, 90% RH, radial determination coefficients are respectively: 0.991, 0.998, 0.994, 0.993, 0.990, 0.987, 0.989, 0.981, 0.987. The chord direction determining coefficients are respectively: 0.996, 0.998, 0.994, 0.993, 0.990, 0.993, 0.992, 0.995.
Example 2
The present example provides a method for measuring wood strain based on growth cycle scale to explore the relationship between the moisture content and the swelling strain capacity of late catalpa (LW), specifically, the method of the present example is the same as example 1 except that the late catalpa is selected as the wood sample.
In this example, nearly 100 measurement points are taken at each humidity stage, a graph is drawn, and linear regression analysis is performed on the water content and the radial swelling rate, and the water content and the chord direction swelling rate of the late catalpa bungei, respectively, to obtain fig. 3a-3j.
3a-3j, under 10 relative humidity stages, the water content of the catalpa bungei late wood has a linear positive correlation with the radial swelling rate and the chord-direction swelling rate. Wherein the 10 relative humidity stages in the 0, 10, 20% RH, 30% RH, 40% RH, 50% RH, 60% RH, 70% RH, 80% RH, 90% RH, radial determination coefficients are respectively: 0.989, 0.998, 0.995, 0.985, 0.991, 0.981, 0.992, 0.995, 0.994 and 0.995. The chord direction determining coefficients are respectively: 0.990, 0.998, 0.997, 0.989, 0.993, 0.984, 0.994, 0.995 and 0.996.
Example 3
The present example provides a method for measuring wood strain based on the dimension of a growth wheel, in order to explore the relationship between the moisture content and the swelling strain of a catalpa bungei growth wheel (ELW), and specifically, the measurement method of the present example is the same as that of example 1, except that the catalpa bungei growth wheel is selected as a wood sample.
In this example, approximately 100 measurement points are taken at each humidity stage, a graph is drawn, and linear regression analysis is performed on the water content and the radial swelling ratio, and the water content and the chord swelling ratio of the catalpa bungei growth wheel, respectively, to obtain fig. 4a to 4j.
As can be seen from FIGS. 4a to 4j, the water content of the catalpa bungei growth wheel has a linear positive correlation with the radial swelling rate and the chord-wise swelling rate at 10 relative humidity stages. Wherein the 10 relative humidity stages in the 0, 10, 20% RH, 30% RH, 40% RH, 50% RH, 60% RH, 70% RH, 80% RH, 90% RH, radial determination coefficients are respectively: 0.981, 0.997, 0.994, 0.987, 0.982, 0.986, 0.984, 0.993, 0.996. The chord direction determination coefficients are respectively: 0.989, 0.998, 0.997, 0.994, 0.990, 0.991, 0.989, 0.993, 0.996.
Example 4
The embodiment provides a wood strain measurement method based on growth wheel dimension, which is used for researching the relationship between the moisture content and the shrinkage strain of a catalpa bungei early wood, and specifically, the measurement method of the embodiment comprises the following steps:
s1: the catalpa bungei sample with the water content of 90% rh obtained in example 1 was placed in a dynamic moisture adsorption analyzer, the temperature in the dynamic moisture adsorption analyzer was kept at 25 ℃, the weight of the catalpa bungei early wood in this state was recorded, and the sample in this state was imaged by a video white light microscope.
S2: the image of the original catalpa bungei sample in the step S1 is subjected to noise reduction processing, and then the determination of the image mark point is completed by adopting AutoCAD. Specifically, the image after noise reduction processing is introduced into AutoCAD, 4 cell corners are found on the wheel boundary line of the early wood sample growth wheel, and then the image of the early wood sample is enlarged until the pixel block is visible. In each cell corner, 4 marked points are made at the positions where the pixel blocks have obvious color boundaries, the positions of the 4 marked points are recorded, and the 4 marked points are connected into a straight LINE along the radial direction and the chord direction by a command 'LINE'. The length measurements and recordings were made on 4 straight lines by command "DIMALIGNED".
S3: maintaining the temperature in the dynamic moisture adsorption analyzer, adjusting the relative humidity in the dynamic moisture adsorption analyzer to 90% RH, 80% RH, 70% RH, 60% RH, 50% RH, 40% RH, 30% RH, 20% RH, 10% RH, 0% RH, recording the weight of the early wood sample every 1min, simultaneously shooting the image, performing noise reduction and mark point processing on the image, and calculating the water content and the radial shrinkage rate toward shrinkage rate at each time according to a chord correspondence formula, according to 10 relative humidity stages under 90-0 RH.
In this embodiment, nearly 100 measurement points are taken at each humidity stage, a graph is drawn, and linear regression analysis is performed on the water content and the radial shrinkage rate, and the water content and the chord shrinkage rate of the catalpa bungei early wood respectively to obtain fig. 5a to 5j.
As can be seen from FIGS. 5a-5j, the water content of the early wood of catalpa bungei at 10 relative humidity stages has a linear positive correlation with the radial shrinkage rate and the chord shrinkage rate. Wherein, at 10 relative humidity stages at 90-RH, 80-RH, 70-RH, 60-RH, 50-RH, 40-RH, 30-RH, 20-RH, 10-RH, 0-RH, the radial determining coefficients are, respectively: 0.994, 0.982, 0.989, 0.973, 0.984, 0.986, 0.988, 0.984, 0.983, 0.996. The chord direction determination coefficients are respectively: 0.996, 0.992, 0.990, 0.988, 0.989, 0.991, 0.993, 0.989, 0.997.
Example 5
The present example provides a method for measuring wood strain based on growth cycle scale to explore the relationship between the moisture content and the dry shrinkage strain of late catalpa bungei, and specifically, the method of measurement in the present example is the same as that in example 4, except that the late catalpa bungei is selected as the wood sample.
In this example, approximately 100 measurement points were taken at each humidity stage, plotted, and linear regression analysis was performed on the moisture content and the radial shrinkage rate, and the moisture content and the chord shrinkage rate of the late catalpa bungei, respectively, to obtain fig. 6a to 6j.
As can be seen from FIGS. 6a to 6j, the water content of the late catalpa bungei at 10 relative humidity stages has a linear positive correlation with the radial shrinkage rate and the chord shrinkage rate. Wherein the 10 relative humidity stages in the 90, 80, 70% RH, 60% RH, 50% RH, 40% RH, 30% RH, 20% RH, 10% RH, 0% RH, the radial determination coefficients are respectively: 0.993, 0.986, 0.988, 0.982, 0.978, 0.992, 0.997. The chord direction determination coefficients are respectively: 0.987, 0.991, 0.989, 0.991, 0.992, 0.989, 0.985, 0.992, 0.995 and 0.997.
Example 6
The present example provides a method for measuring wood strain based on the dimension of a growth wheel, in order to explore the relationship between the moisture content and the shrinkage strain of a catalpa bungei growth wheel, and specifically, the measurement method of the present example is the same as that of example 4, except that the catalpa bungei growth wheel is selected as a wood sample.
In this example, approximately 100 measurement points are taken at each humidity stage, a graph is drawn, and linear regression analysis is performed on the water content and the radial shrinkage rate, and the water content and the chord shrinkage rate of the catalpa bungei growth wheel, respectively, to obtain fig. 7a to 7j.
As can be seen from FIGS. 7a to 7j, the water content of the late catalpa bungei at 10 relative humidity stages has a linear positive correlation with the radial shrinkage rate and the chord shrinkage rate. Wherein the 10 relative humidity stages in the 90, 80, 70% RH, 60% RH, 50% RH, 40% RH, 30% RH, 20% RH, 10% RH, 0% RH, the radial determination coefficients are respectively: 0.982, 0.987, 0.990, 0.993, 0.985, 0.982, 0.977, 0.973, 0.991, 0.998. The chord direction determination coefficients are respectively: 0.992, 0.984, 0.991, 0.994, 0.979, 0.988, 0.985, 0.979, 0.993, 0.999.
In the embodiment of the invention, catalpa bungei is taken as a research wood, but the invention is not limited to catalpa bungei, and a person skilled in the art can research the relationship between the water content and the radial and chord shrinkage/wet expansion rates of any wood, research whether the hysteresis phenomenon and the change rule thereof exist, and research the influence factors thereof, thereby reasonably and efficiently utilizing the wood.
The above embodiments are merely illustrative, and not restrictive, of the scope of the invention, and those skilled in the art will be able to make various changes and modifications within the scope of the appended claims without departing from the spirit of the invention.
Claims (8)
1. A wood strain measurement method based on growth wheel dimension is characterized by comprising the following steps:
s1: preparing oven-dried samples of wood; the method for determining the mark points of the image corresponding to the oven dry sample specifically comprises the following steps:
importing the noise-reduced image into AutoCAD software, finding out 4 cell corners on the wheel boundary line of the wood sample growth wheel, and then amplifying the image of the wood sample until a pixel block is visible;
making 4 marking points at the positions of the pixel blocks with obvious color boundaries in the cell corners, connecting the 4 marking points one by one along the radial direction and the chord direction to obtain 4 straight lines, and measuring the lengths of the 4 straight lines to obtain the lengths of the straight lines;
s2: putting the oven-dried sample obtained in the step S1 into a dynamic moisture adsorption analyzer with constant temperature and certain relative humidity, keeping a fixed time interval, and continuously recording the weight change of the wood sample until the wood sample reaches a moisture content equilibrium state;
s3: keeping the same time interval as the step S2, and continuously photographing the wood sample by adopting a video white light microscope until the wood sample reaches a moisture content equilibrium state;
s4: analyzing and processing the image obtained in the step S2 to obtain the water content, the radial wet expansion rate and the chord direction wet expansion rate of the wood sample at each time; the method specifically comprises the following steps:
importing the noise-reduced image into AutoCAD software, finding out 4 cell corners on the wheel boundary line of a wood sample growth wheel, and then amplifying the image of the wood sample until a pixel block is visible;
in the cell corner, 4 marking points are made at the positions where the color boundary characteristics of the pixel blocks appear are the same as those of the pixel blocks in the process of determining the absolute dry sample marking points, the 4 marking points are connected one by one along the radial direction and the chord direction to obtain 4 straight lines, and the length of the 4 straight lines is measured to obtain the length of the straight lines;
s5: in the step S3, after the moisture content of the wood sample reaches the equilibrium state, reducing the relative humidity in the dynamic moisture adsorption analyzer, and then repeating the steps S2-S3;
s6: analyzing the image obtained in the step S5 to obtain the water content, the radial shrinkage rate and the chord shrinkage rate of the wood sample at each time; the method specifically comprises the following steps:
importing the noise-reduced image into AutoCAD software, finding out 4 cell corners on the wheel boundary line of the wood sample growth wheel, and then amplifying the image of the wood sample until a pixel block is visible;
in the cell corner, 4 mark points are made at the positions where the color boundary characteristics of the pixel block appear and the color boundary characteristics of the pixel block in the absolute dry sample mark point determining process are the same, the 4 mark points are connected one by one along the radial direction and the chord direction to obtain 4 straight lines, and the length of the 4 straight lines is measured to obtain the length of the straight lines;
before step S4, the image obtained in step S3 is subjected to noise reduction processing.
2. The method according to claim 1, wherein the temperature in the dynamic moisture adsorption analyzer is 20 to 25 ℃ and the relative humidity is 0 to 98% in step S2.
3. The measurement method according to claim 1, wherein the interval between the quality change recording in step S2 and the image capturing in step S3 is 1min;
in the step S3, the video white light microscope is adjusted so that the pixels of the photographed picture are 1280 × 960.
4. The measurement method according to claim 1, wherein the image denoising process specifically comprises: the brightness, contrast, exposure, RGB curves and tone scale of the picture are adjusted to enhance the details of the measurement area.
5. The measurement method according to claim 1, wherein, in step S4,
the calculation formula of the wet swelling rate of the wood sample at any time is as follows:
in the formula:
ε RH the unit is the radial/chord wet expansion rate of the sample in any relative humidity environment;
l RH the radial/chordal dimension of the sample at any time in a certain relative humidity environment is expressed in the unit of mu m;
l 0 is the radial or chordal dimension of the oven dry sample in μm.
6. The measuring method according to claim 1,
in step S6, the calculation formula of the dry shrinkage is:
in the formula:
ε RH the unit is the dry shrinkage rate of the sample in the radial direction/chord direction in any relative humidity environment;
l RH the radial/chordal dimension of the sample at any time in a certain relative humidity environment is expressed in the unit of mu m;
l 0 is the radial or chordal dimension of the oven dry sample in μm.
7. The method according to claim 1, wherein in step S4 and step S6, the water content of the wood sample at any time is calculated by the following formula:
MC RH the water content of the sample in any relative humidity environment is shown in unit;
M RH the mass of the sample in mg in any relative humidity environment;
M 0 is the mass of the oven dried sample in mg.
8. A device for measuring the amount of wood strain for use in the method of any one of claims 1 to 7, comprising a dynamic moisture adsorption analyzer and a video white light microscope;
the dynamic moisture adsorption analyzer comprises an ultramicro electronic antenna and a gas flow controller;
the video white light microscope is positioned below the ultramicro electronic balance and is electrically connected with the dynamic moisture adsorption analyzer.
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