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Wood material has a thermo-hygromechanical behaviour because its deformation depends on the combined action of temperature, relative humidity and mechanical load variations. Stresslaminated timber bridge deck show a reduction of stress in the tension bars mainly due to the relaxation and shrinkage of wood, increasing with moisture content and temperature changes within the wood. The aim of this research was to study the rheological behavior of stress-laminated timber bridge deck samples under temperature and relative humidity variations. A total of 16 samples were previously treated with four types of preservative treatments, which were subjected to four cycles of temperature and relative humidity in a climate chamber. Wood samples deformation and stress in the steel bars were measured. The results showed a significant stress reduction in the steel bar during the summer season and a significant increase during the winter season. The results also showed significant differences between the deformations of control samples compared to the preservative treated samples for each cycle. However, for interlaminar stress, differences were significant only in the winter season. Moreover, for both deformation and interlaminar stress, no significant differences between cycles three and four were found. Therefore there is no evidence of thermo-hygromechanical creep or relaxation of wood in the conditions considered in this study. [ABSTRACT FROM AUTHOR]

The aim of this study was to define a representative volume element to characterize the mechanical properties of stress-laminated deck specimens of radiata pine and Eucalyptus nitens. The determination of the representative volume element allowed to identify the smallest representative section of the stress-laminated deck. For this, the nanomechanical properties of the cell walls and middle lamellas were determined by nanoindentations. This study was conducted in two phases. In the first phase, the growth ring representative of the pieces of wood under compression perpendicular to the grain was determined. In the second phase, the board representative of the stress-laminated deck specimens subjected to long-term compression loads and variable environmental conditions was determined. The results obtained in the first phase of the study showed that there was no specific tendency of the nanomechanical properties through growth rings in the cross-section of Pinus radiata and Eucalyptus nitens specimens subjected to compression loads perpendicular to the grain. In the second phase of the study, it was found that long-term compression loads in stress-laminated deck specimens mainly affect the mechanical properties of the cellular structure of exterior and central boards. Finally, the representative volume element in a stress-laminated deck specimen was found in the earlywood of the growth ring farthest to the pith in the cross section of the central board. [ABSTRACT FROM AUTHOR]

In the production of thermal laser radiation detectors, like the thermopiles and the pyroelectric detector, the absorption coefficient of the incident radiation plays an important role in the detector characteristics. The detector surface exposed to the laser radiation possesses a coating that elevates this coefficient and decreases the dependence with the wavelength. In this paper different products in order to improve the absorption radiation in thermal detectors of He-Ne and CO2 lasers of the thermopiles type are evaluated. The studied compounds exposed to the laser radiation are deposited on the metallic laminates. The sensitivity and response time of the detector are presented. [ABSTRACT FROM AUTHOR]