RESUMOO Pinus radiata (Pinus Radiata D. Don), uma espécie de crescimento rápido no Chile, tem uma resistência mecânica inferior ao de outras coníferas utilizadas como madeira estrutural, mesmo bem abaixo de algumas madeiras chilenas com altas qualidades estruturais. O objetivo desta pesquisa foi estudar o efeito de um tratamento termohigromecânico do tipo fluência sobre as propriedades nanomecânicas do pinheiro radiata. Os exemplares do tipo I foram adaptados de acordo com a ASTM D638-14, de plantações de rápido crescimento na região de Bío-Bío, Chile. O tratamento termo-higromecânico foi realizado sob condições controladas de carga, umidade e temperatura. Oito tratamentos com dois níveis de carga (por 30 minutos), duas condições de temperatura e dois tempos pós-tratamento foram estabelecidos para a avaliação das propriedades

Quasistatic nanoindentation is a proven tool that provides information on the micromechanical behavior of wood cell walls. However, quasistatic tests cannot probe the time-dependent mechanical behavior shown by wood. Nanoindentation dynamic mechanical analysis (nanoDMA) can mesaure the viscoelastic properties of wood cell walls. This research aimed to study the quasistatic and viscoelastic properties of individual radiata pine wood (Pinus radiata D. Don) cell wall layers. To minimize variability and retrieve both properties at the same locations, a load function composed of a multiload-quasistatic function followed by dynamic reference frequency segments was developed. Nanoindentations were then performed on the S2 layer and compound corner middle lamella (CCML) of unembedded latewood cells. Because the S2 layer is anisotropic, both transverse and longitudinal-tangential wood planes were studied. In the transverse plane, the average results of the quasistatic elastic moduli (Es) for the S2 layer and CCML were 15.7 GPa and 4.6 GPa, respectively. In the longitudinal-tangential plane, the E_s was 3.9 GPa. In the transverse section, the hardness (H) of the S2 layer and CCML were 331 MPa and 277 MPa, respectively, and in the longitudinal-tangential section H was 244 MPa. To acquire the viscoelastic properties, measurements were made over more than three decades of frequency. An increase of the storage modulus (E'), and a reduction of the loss modulus (E'') and loss factor (tan⁡ δ ) as frequency increased were found in both wood orientations. The quasi-static and dynamic indentations equivalent at 0.1 Hz showed similar values for Es and E’. This study contributes to our knowledge of wood cell wall micromechanical properties.

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This study aimed to evaluate the effect of water immersion on the release of growth stresses in 17-year-old Eucalyptus nitens logs. A total of 18 of 90 trees evaluated in the field were selected. The average diameter at the height breast of all the trees was 37 cm. The first section of the tree, from the stump to 2.44 m, was used. Three stress levels (low, medium, and high) were established. Six logs were studied for each level, which was divided into two groups: three for control and three for water immersion. Peripheral longitudinal strains on standing trees, freshly felling, and after the immersion process were determined by an extensometer. The deflection of the sawn timber and log-end splitting before and after air-drying were evaluated. In addition, the distribution of growth stresses was determined. The results showed that deflection, the log-end splitting index, and stress distribution were reduced in the three levels. The water immersion method allowed a reduction of growth stresses in Eucalyptus nitens logs.