Determinação do módulo de elasticidade da madeira em função da inclinação das fibras utilizando tomógrafo acústico

Abstract

RESUMOOs objetivos deste trabalho são determinar, a partir de ensaios não destrutivos, o módulo de elasticidade em função da inclinação das fibras da madeira através de um tomógrafo acústico, comparar e discutir a aplicação de seis critérios de falha adaptados para ensaios não destrutivos e modificar as equações para determinar os critérios de falha mais adequados para o ensaio não destrutivo proposto. Para isto foram ensaiados 6 corpos de prova de 150x15x4 cm de 6 espécies de madeira. Utilizou-se um tomógrafo acústico com oito transdutores. Estes sensores são fixados e excitados mecanicamente com um martelo. Cada vez que um sensor é excitado os outros captam o tempo que a onda mecânica tardou em chegar, logo é determinada a velocidade e calculado o módulo de elasticidade. A inclinação das fibras é determinada a partir dos ângulos formados por cada transdutor em relação a direção destas. Os resultados experimentais foram comparados com seis teorias de critérios de ruptura mecânica. Conclui-se que é possível utilizar o tomógrafo acústico para determinar o mó-dulo de elasticidade inclinado ás fibras, com apenas um ensaio experimental. Todos os seis modelos matemá-ticos avaliados não apresentam significância estatística em seu formato original. Com as modificações feitas nos modelos os que apresentaram significância foram apenas os modelos: hiperbólica, Karlsen e Hankinson, portanto eles são os mais indicados para estimar os valores do módulo de elasticidade dinâmico em função da inclinação das fibras.Palavras-chave: madeira; módulo de elasticidade; ensaios não destrutivos; tomógrafo acústico. ABSTRACTThe objectives of this work are to determine, from non-destructive tests, the modulus of elasticity as a function of the inclination of the wood fibers through an acoustic tomograph, to compare and discuss the application of six fault criteria adapted for non destructive tests and to modify the formulas for to determine the most suitable failure criteria for the proposed non-destructive test. To determine the most suitable failure criteria for the proposed non-destructive test. For this, 6 specimens of 150x15x4 cm of 6 species of wood were tested. An acoustic tomograph with eight transducers was used. These sensors are fixed and mechanically excited with a hammer. Each time a sensor is excited the others capture the time the mechanical wave took to arrive, then the speed is determined and the modulus of elasticity is calculated. The inclination of the fibers is determined from the angles formed by each transducer in relation to the direction thereof. The experimental results were compared with six theories of mechanical rupture criteria. It is concluded that it is possible to use the acoustic tomograph to determine the modulus of elasticity inclined to the fibers, with only one experimental test. All six mathematical models evaluated do not present statistical significance in their original format. With the modifications made in the models those that presented significance were only the models:

Wave Propagation Technology in Non-destructive assays for Wood Qualifying in Tropical Amazon

“…Few studies have been performed to determine the MOEd of a specimen by pulse tomography; most researchers use voltage wave emission or transverse vibration. However, Carrasco et al (2017), who used the acoustic tomograph, concluded that it could be helpful for determining the modulus of elasticity in the fibres by only one experimental test. This work confirms the need to agree on a standard classification for the dynamic method; it is needed because too little is known about these tests of live trees in the Amazon and the values obtained.…”

Oleoresin prospection in Copaifera sp. trees by using impulse tomography

“…Other studies validated the use of tomography to determine the physical properties of wood, such as resistographic amplitude (Rollo et al, 2013), moisture content (Putri et al, 2017); Latorraca et al, 2011), and mechanical properties (Young and shear modulus) (Gonçalves et al, 2014;Gonçalves et al, 2011;Sedik et al, 2010), elasticity modulus (Carrasco et al, 2017), knots interference, juvenile wood, and reaction wood (Palma et al, 2018). Also, research was carried out to determine the pith´s location (Perlin et al, 2018) and address aspects related to wood anisotropy (Perlin et al, 2019;Arciniegas et al, 2014).…”

“…Impulse tomography is based on the propagation of mechanical stress waves generated from hammer shocks (Mendes and Silva Filho, 2019;Carrasco et al, 2017;Castro et al, 2011). The emission and capture of signals, which result in time and distance information, with which propagation speed is calculated, is done by sensors attached to the trunk by metal nails (Heidelberg, 2011).…”

Estimation of Modulus of Elasticity in Static Bending of Wood in Structural Dimensions as a Function of Longitudinal Vibration and Density

“…In order to use wood in construction, it is necessary to determine its physical and mechanical properties [21,22] according to specific Standard Codes, such as Brazilian [23] and European [24]. However, when it is impossible to produce specimens [25] or pieces present structural dimensions [26], nondestructive tests are performed by different techniques, including transverse vibration [27,28], acoustic tomography [29] and ultrasound [30]. In addition, it is also possible to estimate wood properties as a function of other known properties using regression models [31][32][33][34].…”