Identifikacija neispravnih spojeva u gredama uz pomoć torzijskih vibracija

The determination of the shear dynamic modulus in wood product panels is of greater importance than its determination in wood beams. Yet with regards to the effect of defects on the obtained values of shear modulus, this factor is used to detect the defects and the degree of the defects. In this study, the effect of gluing defects in two joint shapes (scarf (45°) and finger joints (10 mm length and 3 mm pitch) were evaluated non-destructively using the torsional vibration method. Rectangular wood specimens with dimensions of 20 mm × 40 mm × 360 mm (R × T × L) were prepared from clear eastern beech. The joints were located at similar positions in the middle of the beams. The results showed that creating a healthy joint did not significantly change the values obtained for the shear modulus in either of the joint shapes. However, reducing the adhesion level in both types of joints caused a significant reduction in the shear modulus values. The results show that the changes in the dynamic shear modulus values in both joint types, as a result of changes in the glue coverage rating (fully, medium and low-glued joints) allows the detection of the defects as well as the degree of the defects.Određivanje dinamičkog modula smicanja u drvnim pločama važnije je od određivanja tog modula u drvenim gredama. Ipak, s obzirom na utjecaj grešaka na vrijednosti modula smicanja, određivanje tog faktora važno je za otkrivanje grešaka i njihova stupnja na drvnim proizvodima. U ovom je istraživanju metodom torzijskih vibracija nedestruktivno procijenjen utjecaj grešaka lijepljenja u dva oblika spoja: kosim sljubom (45°) i klinastim zupcima (duljine 10 mm i koraka 3 mm). Uzorci drva dimenzija 20 mm × 40 mm × 360 mm (R × T × L) izrađeni su od čiste bukovine, a spojevi su izvedeni na približno istim mjestima na sredini greda. Rezultati su pokazali da izrada zdravog spoja nije bitno promijenila vrijednosti modula smicanja ni za jedan od primijenjenih tipova spoja. Međutim, smanjenje razine adhezije u obje vrste spojeva uzrokovalo je znatno smanjenje vrijednosti modula smicanja. Rezultati pokazuju da promjene vrijednosti dinamičkog modula smicanja u oba tipa spoja kao rezultat promjene stupnja pokrivenosti ljepilom (potpuna, srednja i slaba pokrivenost) omogućuju otkrivanje grešaka lijepljenja, kao i stupnja grešaka drvnih spojeva

Detection of defects in joints using the variations in dynamic shear modulus and Correlation Coefficient factor in Beech Wood

In this study, detect of damage in scarf joint and finger joint using the variations in dynamic shear modulus values and Correlation Coefficient factor of the beech wood specimens was investigated. Numbers of 42 Samples were selected according to ISO 3129 international standard. The Scarf and finger joints created with three different glue coverage rates in samples and then flexural vibration tests in free-free beam were performed. The results showed that defects changed the dynamic shear modulus values in both joints, however it is not possible to realize the amount of defects from these variations. Whereas, the changes in Correlation Coefficient factor were useful to detect the amount of defects in both joints

Dynamic Methods to Evaluate the Shear Modulus of Wood

There are different dynamic or static test methodologies for evaluating the shear and torsional moduli of wood. A preferred method is nondestructive, accurate, and standard. However, dynamic methods using conventional devices previously suggested for determining the orthotropic shear moduli of wood are neither accurate nor standard. Thus, a reliable method for evaluating the torsional modulus of wood through a torsional vibration test exists; however, it is not a standard test method at all. In this study, a standard methodology for refractory materials, ASTM C1548, was fitted to wood to meet the qualifications suggested in measuring the torsional vibration of an orthotropic material. A methodology based on Timoshenko’s advanced theory of free flexural vibration for orthotropic shear moduli was also defined to be compared to these reliable, standard procedures of torsional modulus evaluation. A promising conclusion was derived using improved computer-based instrumentation

Investigation of relationship between dynamic modulus of elasticity and static bending ‎properties in ‎particleboard plates

In this study the relationship between dynamic modulus of elasticity from longitudinal ‎vibration ‎method with static modulus of elasticity and bending strength in two directions: the ‎Parallel ‎machine direction and machine direction have been investigated. For this purpose 4 ‎plates of ‎particleboard with dimensions 124× 90 ×1.6 cm (length× width× thickness) were ‎selected and free ‎longitudinal vibration test in PMD and MD were performed on each plates. ‎After that the primary ‎plates were cut to four plates with dimensions 62× 44 ×1.6 cm (length× ‎width× thickness) and ‎longitudinal vibration test in PMD and MD were performed on each ‎plates again. Finally each plates ‎were cut to the beams with dimensions 36× 1.6 ×1.6 cm and ‎longitudinal vibration test and and ‎static bending test were performed on them. The results show ‎that good correlation between ‎dynamic modulus of elasticity from longitudinal vibration test ‎and static modulus of elasticity and ‎bending strength (result of beams extracted from each ‎plates) in both size of plates in two size ‎‎(124× 90 ×1.6 and 62× 44 ×1.6 cm) and beams ‎extracted from each plates in two directions (PMD ‎and MD). In addition there was good ‎correlation between dynamic modulus of elasticity of ‎longitudinal vibration from two size plates ‎‎(124× 90 ×1.6 and 62× 44 ×1.6 cm). When the samples ‎smaller than primary plates, the ‎dynamic modulus of elasticity values were increased, that it due to ‎the diffusion of waves in ‎samples with larger dimensions. In general, according to results of this ‎research it can be ‎concluded that by applying the appropriate correction factors, longitudinal ‎vibration method an ‎efficiency method for calculation of dynamic and static modulus of elasticity ‎and estimate of ‎the modulus of rupture in plates in full sized.

Nondestructive Evaluation of Effects of Moisture Content and ‎Temperature ‎on the ‎Elastic Properties of Beech Wood ‎Using Flexural Vibration Test

In this study, 10 samples of beech wood, without apparent defect, with dimensions of 360 × ‎‎16 × 16 ‎cm (length × radial × tangential) were selected, and after being exposed to variable ‎temperature (60, ‎‎80, 100, 120, 140, 160, and 180°C) and moisture content conditions ‎‎(moisture content in conditions ‎of: saturated with water (EMC=35±5%), equilibrium moisture content ‎exposed to air (EMC=19±5%), ‎and conditioning moisture content in a climatic chamber (EMC=12±2%), they underwent free ‎flexural ‎vibration test in two longitudinal-tangential and longitudinal-radial planes‎‏,‏‎ and some ‎of the physical, ‎mechanical, and acoustical properties in both planes‎ were investigated. The ‎results showed that the ‎correlation coefficient of the first three modes of flexural vibration in ‎both planes under ‎climatic ‎chamber had a similar situation, but when the samples were in the ‎water-saturated condition, they ‎showed an adverse behavior in each plane. The effect of ‎increasing the temperature above 100°C ‎caused stresses resulting from shrinkage leading to ‎the development of micro-cracks and reduction in ‎the modulus of elasticity of cell walls and ‎ultimately reduction in wave propagation ability of wood, ‎thus increase in the damping ‎vibration values in both longitudinal-tangential and longitudinal-radial ‎planes of the samples. ‎Also, the concurrent changes in modulus of elasticity and damping vibration in ‎both vibration ‎planes are a desirable indicator for monitoring the process from the primary logging ‎process ‎stages to processes such as wood drying and heat treatment.

Nondestructive evaluation of dynamic properties in beach wood using free vibration method on free- free bar

In this study effect of different NDT methods on dynamic properties in beech wood (flexural vibration and longitudinal vibration method) were evaluated .29 clear samples with nominal dimension of 2×4×36 cm selected and bending vibration in free-free beams and longitudinal vibration tests was performed on them. Results shows strong correlation between dynamic Young's modulus and acoustic coefficient measured with both Longitudinal vibration and flexural vibration method. Measuring damping factor values was significantly higher in flexural vibration compared to longitudinal vibration method, While the acoustic converting efficiency values from flexural vibration was smaller than values of this factor in longitudinal vibration method .There was good correlation between dynamic shear modulus of elasticity from flexural vibrations and dynamic modulus of elasticity in both methods, that it provides possibility of estimate the shear modulus of elasticity values according to dynamic Young's modulus of elasticity values from longitudinal vibration test.The results also indicated was a good correlation between the phase velocity in first to third modes from the bending vibration. In addition there was good correlation between sound velocity from longitudinal vibration and the phase velocity in first to third modes from the bending vibration

Nedestruktivne metode na bazi vibracija za provjeru učinkovitosti sušenja drva

The capability of application of flexural vibration test in nondestructive evaluation of wood drying was studied. Poplar timbers were conventionally kiln dried under three different drying schedules down to the final moisture content of 12 ±2 %. Dynamic Modulus of Elasticity, damping (internal friction), acoustic coefficient, and acoustic converting efficiency of each sample were evaluated using free flexural vibration test of both-ends free bars before and after the drying, while dynamic responses in each individual step were also monitored. Results revealed that emerging of some defects in the dried timber caused signifi cant changes through the studied parameters of samples by different extents. Cracks were amongst the most prevalent defects influencing the studied factors. The desired schedule, which caused the least abundance of defects in the dried timber, was then identified using this technique. It can be stated that the existing destructive and traditional methods could be replaced by the free vibration method to evaluate the final drying quality accurately.U radu se ispituje mogućnost primjene vibracijskog testa savijanja pri nedestruktivnoj procjeni kvalitete sušenja drva. Drvo topole sušeno je u konvencionalnoj sušionici pri tri različita režima sušenja do konačnog sadržaja vode 12 ± 2 %. Dinamički modul elastičnosti, prigušivanje (unutarnje trenje), akustični koeficijent i učinkovitost akustične konverzije svakog uzorka ocijenjeni su uz pomoć vibracijskog testa slobodnog savijanja poluge, slobodne na oba kraja, prije i nakon sušenja, dok je dinamički odgovor praćen u svakom pojedinom koraku. Rezultati su pokazali da je postojanje nekih grešaka osušenog drva prouzročila znatne promjene istraživanih svojstava uzoraka u različitim omjerima. U najčešće greške osušenog drva koje utječu na ispitivana svojstva ubrajaju se pukotine. U radu je identificiran poželjni režim sušenja koji je prouzročio najmanje grešaka osušenog drva. Na temelju rezultata provedenih istraživanja može se zaključiti da je postojeće destruktivne i tradicionalne metode za procjenu kvalitete sušenja moguće zamijeniti metodom slobodnih vibracija, kojom se postiže dobra procjena konačne kvalitete sušenja

Vibration Based NDT Methods to Verify Wood Drying Efficiency

The capability of application of flexural vibration test in nondestructive evaluation of wood drying was studied. Poplar timbers were conventionally kiln dried under three different drying schedules down to the final moisture content of 12 ±2 %. Dynamic Modulus of Elasticity, damping (internal friction), acoustic coefficient, and acoustic converting efficiency of each sample were evaluated using free flexural vibration test of both-ends free bars before and after the drying, while dynamic responses in each individual step were also monitored. Results revealed that emerging of some defects in the dried timber caused signifi cant changes through the studied parameters of samples by different extents. Cracks were amongst the most prevalent defects influencing the studied factors. The desired schedule, which caused the least abundance of defects in the dried timber, was then identified using this technique. It can be stated that the existing destructive and traditional methods could be replaced by the free vibration method to evaluate the final drying quality accurately.U radu se ispituje mogućnost primjene vibracijskog testa savijanja pri nedestruktivnoj procjeni kvalitete sušenja drva. Drvo topole sušeno je u konvencionalnoj sušionici pri tri različita režima sušenja do konačnog sadržaja vode 12 ± 2 %. Dinamički modul elastičnosti, prigušivanje (unutarnje trenje), akustični koeficijent i učinkovitost akustične konverzije svakog uzorka ocijenjeni su uz pomoć vibracijskog testa slobodnog savijanja poluge, slobodne na oba kraja, prije i nakon sušenja, dok je dinamički odgovor praćen u svakom pojedinom koraku. Rezultati su pokazali da je postojanje nekih grešaka osušenog drva prouzročila znatne promjene istraživanih svojstava uzoraka u različitim omjerima. U najčešće greške osušenog drva koje utječu na ispitivana svojstva ubrajaju se pukotine. U radu je identificiran poželjni režim sušenja koji je prouzročio najmanje grešaka osušenog drva. Na temelju rezultata provedenih istraživanja može se zaključiti da je postojeće destruktivne i tradicionalne metode za procjenu kvalitete sušenja moguće zamijeniti metodom slobodnih vibracija, kojom se postiže dobra procjena konačne kvalitete sušenja

Development of Tomographic Technology (Case Study: Trees from Karaj City)

Reaching to the technology of acoustical Tomography and imaging, this project was ordered for facilitating the work for green space researchers and managers in urban standing trees. Comparing the sensors and micro-second timers with those of a certified European device in radial to tangential and longitudinal directions showed a good agreement for the Iranian made device. So, a new horizon was opened for the researchers of this approach supported by the local scientific knowledge and technology. Holding this technology, the selected trees concerning the collar defect symptoms were firstly inspected visually, then the visual accuracy was monitored by sonic tomography. Some trees were extremely defected internally, while the visual inspection showed their intactness (9 from 23). Meanwhile some trees holding visually defect signs were proved to be intact after carrying the tomography images (up to 10 from 53). It is concluded that the visual tree defect inspection is not satisfactory for saving or omitting the individual and these kinds of decision makings must be supported by the methods showing the hidden discontinuities