Determinação das constantes elásticas da madeira considerando sua ortotropia

Abstract

Corroborating with the current and important the studies on the tropical wood, this research aimed to present a constitutive law of the material of seven species of tropical wood, by Matrix of Constants Elastic, both at ambient and at high temperatures, performing non-destructive tests. As the wood is an orthotropic material, three modules of elasticity, three module of transverse deformation and six Poisson ratio. The constants were determined by two methods: ultrasonic wave propagation and stress wave, to the results destructive tests, were carried following the NBR 7190/97. Tests specimens were made, with the fiber direction in six directions: three mains, radial, tangential and longitudinal; and three intermediates, longitudinal-radial, longitudinal-tangential e radial-tangential. A portable displacement meter was also developed, decharacterizing the destructive aspect from the method, besides the time and funds saving. The species were used are Hymenolobium petraeum, Dinizia excelsa, Bertholletia excelsa, Apuleia leiocarpa, Astronium lecointei, Caryocar villosum e Peltogyne discolor with densities ranging from 650 to 1150kg/m³. The use of two nondestructive methods allowed to define which one is the most efficient to determine the elasticity constants at ambient temperature. Nevertheless, to explain some peculiarities, it was necessary to perform tests to determine the wood grain and microfibrillar angle. The elastics constant determination at high temperature through the nondestructive test were performed only with stress waves. To explain the constants behavior at a high temperature it was performed the wood thermogravimetric analyses. The results allowed to conclude: a) the compression test using the portable displacement meter was capable of determining the values of the longitudinal elasticity modules (E), the transversal elasticity modules (G) and also the Poisson ratio; b) with the ultrasonic waves propagation method it was possible to determine all the elastic constant, however, it was observed a lack of studies about the Poisson rates for neotropical woods; c) the stress waves method helped to determine the E (values of the longitudinal elasticity) and of G (values of transversal elasticity). To determine those constants on high temperature, the stress wave method only did with precision the E (values of the longitudinal elasticity). The database created from this study can be expanded with new studies and made available to interested parties, reflecting the authors desire