RESUMO -O conhecimento do comportamento da madeira mediante ações de curta duração contribui para um projeto estrutural mais seguro, entretanto não sendo a tenacidade parte integrante das propriedades mecânicas comumente investigadas na caracterização deste material. Este trabalho objetivou avaliar, com o uso de modelos de regressões polinomial linear, quadrática e cúbica, a possibilidade da estimativa da tenacidade com o conhecimento da densidade aparente de seis espécies de madeira (Angico, Eucalipto, Jatobá, Paricá, Pinus e Teca). Os resultados dos modelos de regressão evidenciaram a significância e representatividade de todos os ajustes investigados, consistindo o polinomial cúbico o mais eficiente na estimativa da tenacidade da madeira.Palavras-chave: Tenacidade; Modelos de regressão; Densidade aparente.
WOODEN TOUGHNESS AS FUNCTION OF THE APPARENT DENSITYABSTRACT -The knowledge on the behavior of wood in situations of short load contributes to the development of a safer structural design. However, toughness is not part of the mechanical properties commonly investigated in the characterization of this material. Therefore, the present study aimed to evaluate, the possibility to estimate the toughness with the knowledge of the apparent density of 6 Brazilian tropical wooden species (Angico, Eucalyptus, Jatobá, Paricá, Pine and Teak), by using linear, quadratic and cubic polynomial regression models. The results highlighted the significance and representation of all adjustments investigated, and the cubic polynomial was the most efficient for estimating the wood toughness.
Wood is a material widely used in various sectors of construction, such as in structures and building components. The volume of wood extracted from tropical forests has reached a considerable amount, and this wood is marketed with popular names without prior characterization. Wood density is an easy property to measure, and its use as an estimator of other properties is very common in this sector. This study investigated the possibility of the estimation of important quantities in dimensional stability of Brazilian tropical woods by using the density at 12% moisture content, anhydrous density, and basic density. Testing the ability to estimate radial, axial, tangential, and volumetric shrinkage, anisotropy coefficient, coefficient of volumetric rate of volumetric shrinkage, as well as the rate of volumetric swelling using the densities above, with linear, exponential, geometric, and logarithmic models, the best determination coefficient was: R 2 = 19.58%. The results were, in summary, that the variable density was not a good estimator of the dimensional stability of the wood.
This paper discusses the potential use of sugarcane bagasse in two different fiber lengths (5 mm and 8 mm) of the same density as a raw material for the production of particleboards, using castor oil-based two-component polyurethane adhesive. The quality of the product that can be manufactured industrially was evaluated based on density, thickness swell (TS), absorption (WA), modulus of elasticity (MOE), modulus of rupture (MOR) in static bending and internal bond (IB), according to the Brazilian NBR 14.810:2006 standard. The results revealed a significant difference between the particleboards made with 5-mm-long fibers and those made with 8-mm-long fibers. An analysis by scanning electron microscopy (SEM) indicates that the interparticle spaces are filled with castor oil-based two-component polyurethane adhesive, contributing to improve the physicomechanical properties of the particleboards. A durability assessment based on accelerated aging tests shows that waterproofed particleboards can be used in moist environments.
Tests simulating exposure to severe weather conditions have been relevant in seeking new applications for particleboard. This study aimed to produce particleboards with residues of CCB (chromium-copper-boron oxides) impregnated Pinus sp. and castor oil-based polyurethane resin, and to evaluate their performance before and after artificial accelerated aging. Panels were produced with different particle mass, resin content and pressing time, resulting eight treatments. Particles moisture and size distribution were determined, beyond panel physical and mechanical properties, according to NBR14810-3: 2006. After characterization, treatments B and G (small adhesive consumption and better mechanical performance, respectively) were chosen to artificial aging tests. Statistical results analysis showed best performances were achieved for waterproof aged samples, of both B and G treatments. As example, in treatment B, MOR and MOE values were 23 MPa and 2,297 MPa, samples before exposure; 26 MPa and 3,185 MPa, 32 MPa and 3,982 MPa for samples after exposure (non-sealed and sealed), respectively.
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