Tenacidade da madeira

Abstract

Wood often exhibits different behavior, depending on the kind of acting forces. GeneraIly, wood can resist greater solicitations if short time intervals are considered. The mechanical property involved in these cases is the touglmess, which values are determined in impact bending tests. Several basic uses of timber depend on the touglmess, property not widely studied to tropical species grown in Brazil. This work, conducted in Wood and Timber Structures Laboratory (LaMEM), Department of Structural Engineering (SET), São Carlos Engineering School (EESC), São Paulo University (USP), aims to: a. determine the relation between touglmess and wood density at 12% of moisture; b. determine the relation between toughness and moisture content (O -30%). In order to reach the first object, experimental results related to thirty six tropical species (density range 0,55 -1,05 g/cm3) were considered, no less than twelve specimens for specie. To reach the second object, essences like Angelim Saia (Vatairea sp), Eucalipto Citriodora (Eucalyptus citriodora), Eucalipto Grandis (Eucalyptus grandis), Pinus Elliottü (Pinus elliottii), were employed, with weIl-sampled and climatized specimens, thirty for specie. AlI tests were conducted using 2cm x 2cm x 30cm specimens, according to the indications of Annex B of the Brazilian Standard to the Design of Timber Structures (NBR 7190/1997). Conclusions are interesting contributions to facilitate the required evaluation to improve wood applications, in cases where touglmess parameters are fundamental. IntroductionA tough piece ofwood is one that sustains large deformation in bending or twisting before rupture. However, strict usage has reserved the term for a particular mechanical property to classify wood under the action of an impact load that causes failure, BODIG & JA YNE (1992). A ductile material that offers the same resistance than a non-ductile material, needs more energy to failure, exhibiting a higher touglmess value, VAN VLACK (1989). Toughness is the work required to break a given specimen onder an impact load, that is, it's the capacity of the material in absorbing energy at plastic zone.Knowledge of physical and mechanical properties of wood makes possible its better use. Since there are difficulties in doing tests to characterize the species, many times wood is applied without knowing its basic properties, resulting in a bad usage and loss. Special importance is regarded on studying behavior of wood, considering need of knowing its performance when it is impacted onder dynamical actions to its appropriate dimensioning of structural elements, furniture and packaging.Touglmess provides precious tools to evaluate the behavior of wood onder dynamical actions. Measurements of toughness are attained from impact bending tests. One of them wiIl be described in details at the following items of this paper.This work, conducted in Wood and Timber Structures Laboratory, Department of Structural Engineering, São Carlos Engineering School, São Paulo University, aims to: a. determin...

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