Comparison of Two Methods to Determine the Bending Modulus of Elasticity of Wood (original) (raw)
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Influence of the Wood Specimen Position on Calculus of the Bending Modulus of Elasticity
International Journal of Materials Engineering, 2013
For the anisotropy presented by wood, the established positions of the specimens in the bending test can significantly alter the properties of strength and stiffness. This study aimed to evaluate, with the aid of the Brazilian standard ABNT NBR 7190:1997, the influence of the wood specimens position to determine the bending modulus of elasticity. The wood species used in the trials (three point static bending) were Corymbia citriodora and Pinus elliottii, and used six specimens per species. Each piece gave rise to four experiments, performed with a non-destructive form, differentiated only by the position of the specimen in the bending test(sides: A-lowest; B; C; D-higher value), providing four values of elastic modulus per specimens. The experiments were considered non-destructive for the largest displacement value in trials does not exceed the measure L/200 (L-usable length of the specimen), ensuring physical and geometriclinearity fo r the woods tested, as established by the Brazilian standard. The results of analyses of variance showed statistical equivalency between the modulus of elasticity of both wood species, resulting in independence of the specimen position to determine the bending stiffness. Ho wever, by the orthotropic behaviour of wood, the results obtainedcannot be extrapolated to other woods of the same or different species, thereby justifying the change of the specimenposition in the bending test, allowing evaluate the equivalence or not between the modulus of elasticity.
This study compares variability in the longitudinal Modulus of Elasticity (MOE) values, measured by three different methods, for eight tropical wood species covering a wide range of densities, a property that has been little described in the literature for some of the species studied. The modulus of elasticity in wood species is one of the main mechanical properties measured to characterize wood materials. However, this property is seldom described for the tropical wood species studied here, and the method used is often variable. The aim is to answer the following questions. In the methods used, what are the main variability factors which influence modulus measurement? Is the modulus different with regard to the solicitation direction (radial or tangential)? Which relationship exists between modulus and density for these species? The samples were subjected to the four-point bending test, then to the free vibration test and to the forced-vibration test (which allows tests on small sa...
Evaluation of Longitudinal Modulus of Elasticity in Wood Species for Structural Application
Advanced Materials Research, 2014
This research aimed to investigate possible differences in values of longitudinal modulus of elasticity (E) for wood species usually employed for structural purposes, as Castanheira (Bertholletia excelsa), Cambará (Erisma uncinatum), Cumaru (Dipteryx odorata), Jatobá (Hymenaea stilbocarpa), Garapa (Apuleia leiocarpa) and Peroba Rosa (Aspidosperma polyneuron).
BioResources
In Brazil, standard ABNT NBR 7190 (1997) prescribes the determination of strength (fM) and modulus of elasticity (EM) in static bending from specimens measuring 5 cm × 5 cm × 115 cm. Thus, the relationship between the test span (L) and the specimen height (h) greater than or equal to 21 (L/h ≥ 21) is respected, ensuring that the effect of shear in the calculation of displacements is negligible (Euler Bernoulli Theory). Considering the expressive number of tree species cataloged in the Brazilian Amazon Forest, any procedure that aims to facilitate the realization of experimental tests is highly desirable because it provides the knowledge of unusual species. These wood species may potentially replace woods that have been traditionally used and historically exploited. Using five hardwood species, this research aimed to verify, while maintaining constant L/h ≥ 21 ratios, the influence of specimens dimensions in the determination of fM and EM. For all species studied, the statistical ana...
Anisotropy Influence in Obtaining Stiffness Property in Bending of Brazilian Wood Species
International Journal of Materials Engineering, 2014
The design of timber structures, and other materials, must follow the procedures and methods of calculation of normative standards. Some normative documents in the design of timber structures adopt quite simple arithmetical relationships to relate wood properties in order to make it simple and quick evaluation of the behavior of structural elements, as is the specific case of Brazilian standard ABNT NBR 7190:1997, establishing a single relation for the shear (G) and the longitudinal (E) modulus of elasticity [E=G/20], which implies taking statistical equivalence to the values of the elastic moduli in the longitudinal-radial (G LR ) and longitudinal-tangential (G LT ) directions, which are important properties in relation to the requirements of structural projects. In this context, this study aimed to investigate, with the aid of four and three points static bending tests performed on the of dicotyledonous wood species grown in Brazil, the determination of the values of E LR , E LT , G LR and G LT to confirm the possibility of its equivalence (E LR and E LT , G LR and G LT ), and for establishing correlations among them. The results of the hypothesis testing between the shear and longitudinal modulus of elasticity exhibited equivalent by species and simultaneously for all species, and the results of the linear regression model showed not possible to estimate the shear modulus of elasticity with knowledge of the longitudinal modulus of elasticity, and the optimal coefficient found by least squares method to the relation between the modulus of elasticity was equal to 35 (E=G/35), suggesting the need for an adjustment of the coefficient for this scale more safe wooden structures.
For structural use, the properties of large size specimens are preferred to those of small clear specimens because of unavoidable defects such as knots and shakes found in wood. The objective of this study was to assess the bending strength, modulus of elasticity properties and failure behaviour of ten Lesser-used Species (LUS) by use of structural size dimensions (50mm x 120 mm x 2000 mm). The ten species were Albizia ferruginea, (Gulland Perr) Beuth., Sterculia rhinopetala,(K. Schum), Blighia sapida,(Koenig), Canarium schweinfurthii (Engl.), Petersianthus macrocarpus, (P. Beauv.) Liben, Sterculia oblonga, (Mast.) Cola gigantea, (A.Chev.) Celtis zenkeri, (Engl.) Antiaris toxicaria (Lesch.) and Amphimas pterocarpoides (Harms.). The moisture contents of the 10 timber species used ranged from 16.1% (Antiaris toxicaria) to 51.0% (Albizia ferruginea). It was observed during loading under flexure that the elastic stiffness and rate of increase in the strength capacity of the beams did not change after three cycles of loading and unloading. All the beams failed in a form of tension rupture. The breaks were usually splintering tension failure or brittle (brashness) tension failure or a combination of the two modes of failure. Sterculia rhinopetala exhibited the highest bending strength with a 5 th percentile bending strength of 56.8 /mm 2 and a mean local modulus of elasticity of 15,973 /mm 2 . Sterculia oblonga was also found to be the 2 nd best in terms of material properties with a 5 th percentile bending strength of 52.1 /mm 2 and a mean local modulus of elasticity of 16,408 /mm 2 . Celtis zenkeri which had the highest mean local modulus of elasticity, however, had the 6 th best 5 th percentile bending strength of 39.9 /mm 2 . A good linear correlation (69.6-91.3%) was established between mechanical strength properties for average density, average bending strength, average local modulus of elasticity and average global modulus of elasticity.
BioResources, 2020
Accurate estimation of average modulus of elasticity in compression parallel to the grain (Ec0) is of paramount importance for rational sizing of timber structures, given the use of this property in the estimation of stability of compressed parts (ultimate limit state, ULS) and in calculation of excessive strains (serviceability limit state, SLS). In Brazil, if values cannot be experimentally determined, ABNT NBR 7190 (1997) allows for estimation of Ec0 through relations to average modulus of elasticity both in tension parallel to the grain (Et0) (Ec0 = Et0) and in bending (EM) (Ec0 = EM/0.90). This research aimed to access the efficiency of these relations by testing 30 tropical wood species. The analysis of variance results showed that Ec0 and Et0 were statistically equal. However, Ec0 and EM/0.90 were not statistically equal, and the method of least squares resulted in a coefficient of 0.98, which was 8.89% higher than the one suggested by ABNT NBR 7190 (1997) and close to 1, thu...
International Journal of Materials Engineering, 2017
Toughness is the mechanical property that determines the wood strength when a force acts in a short time interval. Its value is determined in the bending impact test. Timber has to resist to impact forces in several applications, nevertheless this property is not widely studied to tropical wood species from Brazil. This study aimed to correlate the toughness and the impact strength of wood with the modulus of elasticity and the strength in the compression parallel to grain test. Therefore ten tropical species, from different strength classes, grown in Brazil were tested according to the Brazilian Standard Code ABNT NBR 7190:1997. The studied species were: Cedro (Cedrella sp.), Cambará Rosa (Erisma uncinatum Warm), Cedrorana (Cedrelinga cateniformis), Catanudo (Calophyllum sp.), Cupiúba (Goupia glabra), Angelim Saia (Parkia spp.), Tatajuba (Bagassa guianensis Aubl.), Guaiçara (Luetzelburgia sp.), Cumaru (Dipteryx odorata) and Angelim Vermelho (Dinizia excelsa Ducke). It was developed a relation between the studied properties through regression models, evaluated according to the variance analysis (ANOVA). The results of the statistical analysis revealed led to the conclusion that there is no correlation between the proposed properties for the analyzed species.
Shear and longitudinal modulus of elasticity in wood: relations based on static bending tests
Acta Scientiarum. Technology, 2017
Improve quality of timber structures design is an aim that must be systematically sought by engineers in this area. An important topic that can contribute directly to be achieved in this subject is the more consistent knowledge related to structural properties of wood. Know values of longitudinal modulus of elasticity (E) and shear modulus (G) is essential for proper evaluation of plate structures performance, as example. It has been usual to adopt statistical equivalence for E and G values in plans longitudinal-radial and longitudinal-tangential, although experimental confirmation of this hypothesis is required. In this context, the aim of this work is to determine values of E LR , E LT , G LR and G LT , based on static bending tests, to five dicotyledonous species. Results showed statistical equivalence between the elastic properties in both plans, and the relation E = 35G was obtained for the five wood species here considered.
Verification of Test Conditions to Determine the Compression Modulus of Elasticity of Wood
International Journal of Agriculture and Forestry, 2013
The obtaining the modulus of elasticity in compression of the wood with the use of dial gauges, fixed on opposite faces of the specimens, may lead to deformation values and consequently to different elastic modulus as a function of the faces chosen for its attachment, being the timber an anisotropic material. This study aimed to evaluate the influence of two distinct positions for setting the dial gauges (A and B) in wood specimens tested in compression, using the assumptions of the test methods and calculation of the Brazilian standard ABNT NBR 7190: 1997. The woods evaluated in trials were the Pinus elliottii and Corymbia citriodora, being used seven specimens per species. A specimen was taken to the rupture, obtained the values of the ma ximu m stress and strain (references) needed to obtain the elastic moduli of the six remaining specimens per species, certain non-destructively (two tests per piece). The results of analysis of variance revealed the equivalence between modules elasticity in compression parallel to the grain for both wood species investigated, resulting not significantly arrangement of dial gaugesto determine the properties of stiffness. However, the anisotropy of wood, these results cannot be extrapolated to other woods of the same or d ifferent species, justifying the setting of dial gauges in two different positions, allo wing for judging whether or not the equivalence between the modulus of elasticity.