Određivanje dinamičkog modula elastičnosti drvenih konzola

Due to considerable influence of shear deflection and rotary motion, the modulus of elasticity is hardly obtainable in fixed-free flexurally-excited (cantilever) beams. For isotropic materials, Timoshenko has proposed a set of curves to correct the fixed-free modal frequencies as the radius of gyration and free length; however, its performance for wood was not sufficiently conclusive. In this study, rectangular beams of pine wood were tested in a fixed-free condition, altering the free length to height ratios in a proper extent and comparing them to their reference free-free data in terms of natural frequency and dynamic modulus of elasticity shifts. The equality of two pairs of fixed-free versus free-free data, for both frequency and dynamic modulus, was significantly confirmed. The correlation coefficient between experimental and calculated fixed-free frequencies was high enough, and however the correlation coefficient of the modulus of elasticity was rather low.Zbog utjecaja otklona smicanjem i rotacijskog pomaka vrlo je teško odrediti modul elastičnosti konzolnih greda opterećenih na savijanje. Za izotropne materijale Timošenko je predložio skup korekcijskih krivulja za modalne frekvencije konzolnih uzoraka u ovisnosti o radijusu otklona i duljini slobodnog kraka. Međutim, njihova preciznost za drvo nije bila zadovoljavajuća. U prikazanom istraživanju analizirana su svojstva konzolnih greda od borovine pri promjeni omjera slobodne duljine i visine grede u odgovarajućoj mjeri i u usporedbi s prirodnom frekvencijom i dinamičkim modulom elastičnosti slobodne grede. Rezultati istraživanja pokazali su da ne postoji statistički značajna razlika u frekvenciji i dinamičkome modulu elastičnosti između ispitivanih uzoraka u svojstvu slobodnih greda i onih koji služe kao konzole. Koeficijent korelacije između eksperimentalne i proračunske frekvencije za konzole bio je vrlo visok, iako je za isti primjer konzole koeficijent korelacije za dinamički modul elastičnosti bio vrlo malen

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

ORIENTATION AND POSITION EFFECTS OF A LOCAL HETEROGENEITY ON FLEXURAL VIBRATION FREQUENCIES IN WOODEN BEAMS

Studying the influence of defect on the dynamic behavior of wood in order\ud to detect the local heterogeneities is of great importance in non-destructive testing of\ud wood. The natural heterogeneities in wood are oriented in a volume. However, onedimensional\ud models are still used in dynamic characterization of wooden beams. The\ud aim of this study was to experimentally investigate the effects of the orientation and\ud position of an artificial defect on the flexural vibration frequencies. Different batches of\ud Fagus orientalis specimens were drilled in the radial direction at five positions along the\ud specimen. Dynamic tests in free flexural vibration were performed on the specimens\ud before and after drilling both in the longitudinal-radial (LR) and longitudinal-tangential (LT)\ud bending plan. The behavior in free flexural vibration was found to be different depending\ud on the position and orientation of heterogeneity. When the drilling axis lies in the bending\ud plane (LR), the weakening of frequency was maximal at the location of an antinode of\ud vibration. On the contrary, the frequency offset was maximal in the place of a vibration\ud node when the drilling axis was orthogonal to the bending plane (LT)

Dynamic Modulus of Wood Containing Water-Resistant Glue Finger Joint after Severe Steaming

The effect of steaming treatment on the dynamic modulus of oak wood (Quercus castaneifolia, C. A. Mey.; Fagaceae) containing a water resistant glue-finger joint was investigated. Sample joints were made with two different types of waterproof adhesives, polyurethane (PU) and epoxy, and the samples were tested by a free flexural vibration method according to flexural and longitudinal free vibration modes. Compared with the epoxy joints, the PU finger-joints retained elastic moduli closer to their initial values. In all three vibration tests, finger-jointed oak wood specimens with either glue retained their moduli of elasticity, after the steaming treatments. In the case of longitudinal-tangential (LT) vibration, some increases were observed for the evaluated elastic moduli. After steaming, the obtained dynamic values decreased. For epoxy-bonded specimens, the correlation coefficient in terms of the elastic modulus before and after steaming were weak. There were some acceptable PU-bonded specimens, but there was a considerable decrease after steaming

Quality Assessment of Scarf Joints Considering the Acoustic Parameters: A Nondestructive Approach

The present research studied the acoustic properties of 40 oak timber samples (Quercus castaneifolia): the acoustic coefficient (K) and acoustic conversion efficiency (ACE) in free vibration mode, using the free-free bar method with different planes of vibration, i.e., tangential (LT) and radial (LR). These acoustic parameters were considered for both primary virgin wooden beams and modified beams carrying a single scarf joint in four different bonding angles (60°, 65°, 70°, and 75°), individually glued with two different adhesives (isocyanate and polyvinyl acetate). Comparing the acoustic properties of primary solid beams with scarf jointed beams of oak wood in LT and LR planes, the steeper joint angles of 70° and 75° did not result in any serious changes with polyvinyl acetate adhesive. Scarf-jointed beams with smaller joint angles (60° and 65°) had significant effect on the acoustic properties relative to larger angles. Thus, beams having larger joint angles and beams glued using polyvinyl acetate may have enhanced acoustic properties

Color Graphics and Task Complexity in Multivariate Decision Making

The duty of an accountant is more than measurement, classification and simple summarizing of data of financial reports which is used by others and the main purpose of accounting reports is to force an effect on behaviors in term of useful applications. Subjects such as improvement in relationships increase the human body's accuracy in judgments and information processing. Simplification of financial decision making is considered by lots of accountant investigators. This made some studies for modification of information from financial   data. The current research was done considering the fact that "Use of graphical color symbols as a tool for data show, is very effective and familiar" and tested the effects of valuable color charts. Studies showed that all of factors of sexuality, individual characteristics and their psychology, difficulty and kind of decision making are entered in effectiveness of colors. So the current research is pay attention to the effects of uses of color" charts to show the data and accounting information in conditions of difficult problems against simple ones and also tries the carefulness of decisions for ladies against gentlemen. This tends to reach to the main target which is preparation of the information with higher degrees of quality in term of subject, decision environment and decision makers' characteristics. Decision making in current  research  was  in  type  of  prediction  of continuity in the works of companies using test samples  of  gathered information  and  financial  ratios  i n  t he shape of column charts. Results of this research showed that the decision faults is reduced when color charts of financial information of the companies is used for difficult information processing and also made a better accuracy in predictions. Meanwhile, in comparison of the gentlemen, ladies did their judgments better with lower faults when color charts were used

Evaluation of Dynamic Modulus of Elasticity of Medium Density Fiberboard Panel from Longitudinal Vibration Tests on Specimens

It is preferred to perform conformity assessment of wood-based panels on the whole panel without cutting it down to smaller pieces. The modulus of elasticity, a mechanical property of wood, was determined by longitudinal vibration testing with the full-size panel, and the results were compared with results of tests of prismatic beams. The Brancheriau’s correction coefficient was used to compensate for errors from cross-sectional dimension variations and errors from Poisson’s ratio. Longitudinal excitation of the panels along the length was shown to be successful in evaluating the modulus of elasticity. However, strong correlations obtained from plate and beam comparisons along the width of the panels are promising

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.

Investigation and prediction on Fluting Paper Supply &Demand in Iran

Total and per capita consumption of fluting paper was calculated using data and information from production, import and export for last decades. Then based on the fact that consumption of paper and paper products is a function of both per capita consumption and population of any country, regression analysis was used to predict per capita consumption for the period of 1994-2003, total consumption for the period of 2006-2011 as well as the year 2021. Finally based on the calculated consumption of different papers and considering the present and future capacities for paper production, the shortage of paper was derived. Results showed that the fluting paper consumption for the year 2021, will reach 290000 tons which causes 200,000 tons of shortage per year. This shortage will require that almost 70% consumption need to be fulfilled by import