ABSTRACT This research aimed to evaluate the effect of the number of fatigue cycles (NC, 0 – reference, 450, 4500, 45000, and 90000) for frequencies (Fr) of oscillation equal to 0.5 and 1.0 Hz on the modulus of elasticity (Em) and operating stress (σm) in the static bending of Pinus caribaea wood. Em and σm were determined taking into account three specimens (SPEC) manufactured for reference condition and another three for each of the four NC levels and each Fr level, resulting in 27 SPEC. Sixty experimental determinations were obtained, being the approximate total time of sample exposure to fatigue of 350 hours. The same specimens used to determine Em and σm for the reference condition were also used (via non-destructive tests) to obtain these properties for all fatigue cycles. The frequency and number of cycles significantly influenced both investigated properties. Reductions in Em and σm values were observed after 45000 cycles. The progressive increase in the number of fatigue cycles caused more marked reductions in mechanical properties when compared to the increase in the frequency of oscillation.

ABSTRACT Wood has been used for several purposes such as in civil and rural construction. Knowing wood mechanical behavior under short-term loading is essential for safer structural designs. However, wood toughness is a mechanical property little investigated for this purpose. Thus, this study aimed to evaluate, using exponential and polynomial regression models (linear, quadratic, and cubic), the possibility of estimating toughness as a function of apparent density, compression parallel to grain strength, and modulus of rupture in static bending. Thirty-six Brazilian tropical wood species from south of Roraima, Mato Grosso do Sul, and north and northeast of Mato Grosso were tested. Our results showed the significance and representativeness of all investigated fits, among which a cubic polynomial function is the most indicated for wood toughness estimates.

ABSTRACT According to the ABNT NBR 7190: 1997 standard, tensile strength of wood samples shall be defined as the ratio between the ultimate strength from a stress test and the specimen cross-sectional area (350 mm2). However, due to the complex wood anatomy and experimental difficulties, the fractured surface in tested samples are not perpendicular to the loading direction; therefore, such fractured surface becomes larger than the sample cross section, overestimating tensile strength by this method. Using an alternative approach, we aimed to determine the approximate fracture surface of wood specimens subjected to tensile test. For this purpose, we used the least square method to estimate tensile strength of four hardwood species, which were equally divided into strength classes. Then, we determined the relationship between the cross-sectional areas of intact and fractured specimens. The results showed that the approximate area of a fractured surface was 2.14 higher than that of an intact sample. As a result, tensile strength estimates were 47% lower than those currently estimated, which is unfavorable for the safety of construction structures.

ABSTRACT: Wood is a material that for years has been used by man for a variety of purposes, particularly in rural and civil constructions and furniture industry. The possibility of shortages of some wood species, the characterization of other unfamiliar species is an alternative source for use in civil and rural construction. This study aimed to determine, with the aid of Brazilian standard NBR 7190, physical and mechanical properties of Castelo (Calycophyllum multiflorum) wood specie. Twelve determinations were obtained by property, totaling 204 experimental values. In the characterization of wood, regression models were used to estimate the values of timber strength and stiffness as a function of apparent density, being density the physical property more simple to be obtained. The results of mechanical properties showed consistent with the performance of other species used in construction, which highlights the potential use of the Castelo wood in structural design. Regression models, apparent density was considered significant in the estimation of only 4 among the 14 properties for wood strength and stiffness.

ABSTRACT In Brazil, the characterization of wood is carried out in accordance with the premises established by ABNT NBR 7190standard; however, the determination of wood properties requires the use of equipment, which hinders the wood characterization for the construction professional. To circumvent this problem, the properties of wood strength and stiffness can be estimated through regression models using the apparent density as estimator, being the density a physical property of easy determination. This study aimed to determine 4 physical and 13 mechanical properties of “Angico Branco” wood (Anadenanthera colubrina), and with the aid of regression models based on analysis of variance, estimate the strength and stiffness properties as a function of apparent density. Twelve samples were produced for each test, resulting in a total of 204 experimental determinations. The results of mechanical properties showed consistent performance with other wood species studied, demonstrating their potential use in various applications. From the regression models, only the longitudinal modulus of elasticity in parallel compression to the grain showed a significant result, and the best were obtained with the linear model, which provided determination coefficient (R2) equal to 56.32%.

ABSTRACT This study aims to manufacture and apply polymer-cementitious blends based on a combination of epoxy polymer and Ordinary Portland Cement (OPC) for timber beam repair. The material was used to repair timber beams of “Maçaranduba” (Manilkara sp.) and “Cedro doce” (Cedrella spp) wood species. A full factorial design was conducted to investigate the effect of cement particle content (0wt%, 30wt%, 40wt% and 50wt %), type of cement (ASTM-II and ASTM-III), and pigment addition (0wt% and 0.2wt%) on the physical and mechanical properties of the blend. The cement content factor affected all properties investigated. The highest elastic modulus was achieved by the blends produced with 50wt% of cement and 0.2wt% of pigment inclusion. This condition was used to repair the timber beams evaluated under four-point bending test. The insertion of the blends in timber beams achieved superior load levels to the unreinforced woods in both species, inferior load levels to the reference condition (without defects) in “Cedro doce”, and superior to the reference condition in “Maçaranduba”. These results were justified by the low density of “Cedro doce”, providing a better blend-wood interface adhesion.

RESUMO Este trabalho objetivou avaliar o desempenho mecânico do emprego de materiais compósitos laminados (fibras de vidro; carbono; sisal; piaçava) em matriz epóxi, como reforço em painéis de partículas de madeira Pinus sp. com resina poliuretana bicomponente, derivada de óleo de mamona. Foram investigados, com o uso do ensaio de flexão estática a três pontos, o módulo de elasticidade (MOE) e o módulo de ruptura (MOR). Os compósitos laminados foram fabricados com camada única, reforçando à tração os corpos de prova obtidos dos painéis. Os resultados do MOE e do MOR dos materiais desenvolvidos sem a inclusão dos reforços superaram os limites contidos nos documentos normativos ABNT NBR 14810-2:2002 e A208.1:199, comprovando a viabilidade dos materiais elaborados. Em todos os casos investigados, a inclusão dos reforços conduziu a valores superiores, tanto para o MOE quanto para o MOR, apresentando os compósitos em fibras de vidro os melhores resultados.

ABSTRACT This study aimed to evaluate the mechanical performance of laminated composite materials (fiberglass, carbon, sisal, palm fiber) in epoxy matrix as reinforcement in wood particleboards of Pinus sp. with bicomponent polyurethane resin from castor oil. Modulus of elasticity (MOE) and modulus of rupture (MOR) were investigated using a three-point bending test. Single-layered laminated plates were used to reinforce traction of specimens obtained from boards. MOE and MOR of materials developed without reinforcements exceeded limits in ABNT standards both NBR 12810-2:2002 and A208.1:199, proving therefore their feasibility. In all investigated cases, inclusion of reinforcements led to higher values for both MOE and MOR. Composites in fiberglass presented the best results.

Este trabalho objetiva apresentar uma metodologia alternativa de cálculo fundamentada no Método dos Mínimos Quadrados para a determinação do módulo de elasticidade na flexão, em vigas de madeira de dimensões estruturais. As equações desenvolvidas requerem o conhecimento de três ou cinco pontos medidos em deslocamentos ao longo da peça, permitindo maior confiabilidade sobre a variável resposta, utilizando-se do ensaio de flexão estática a três pontos e de forma não destrutiva, decorrente da imposição das medidas de pequenos deslocamentos L/300 e L/200, sendo a maior delas estipulada pela norma Brasileira NBR 7190:1997. As madeiras testadas foram Angico, Cumaru, Garapa e Jatobá. Além da obtenção dos módulos de elasticidade pela metodologia alternativa proposta, estes foram também obtidos do emprego da norma Brasileira NBR 7190:1997, adaptada para a condição de ensaio não destrutivo (pequenos deslocamentos) e para peças de dimensões estruturais. Os resultados dos módulos de elasticidade das quatro espécies de madeira, segundo ambas as abordagens de cálculo utilizadas, mostraram-se equivalentes, implicando na boa aproximação fornecida pela metodologia de cálculo adaptada da norma Brasileira.

This study aims to present an alternative calculation methodology based on the Least Squares Method for determining the modulus of elasticity in bending wooden beams of structural dimensions. The equations developed require knowledge of three or five points measured in displacements along the piece, allowing greater reliability on the response variable, using the statistical bending test at three points and non-destructively, resulting from imposition of measures from small displacements L/300 and L/200, the largest being stipulated by the Brazilian norm NBR 7190:1997. The woods tested were Angico, Cumaru, Garapa and Jatoba. Besides obtaining the modulus of elasticity through the alternative methodology proposed, these were also obtained employing the Brazilian norm NBR 7190:1997, adapted to the condition of non-destructive testing (small displacements) and for pieces of structural dimensions. The results of the modulus of elasticity of the four species of wood according to both calculation approaches used proved to be equivalent, implying the good approximation provided by the methodology of calculation adapted from the Brazilian norm.