Development of a technique to determine the 3d elasticity tensor of wood as applied to drying stress modeling
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Universidad del Bío Bío
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The objective of this study was to develop an accurate and simple method for measuring theengineering coeffi cients of the 3D elasticity tensor of wood. A method using a semi-ring extensometer(SRE) and a compression specimen (6-specimen technique) is proposed. The SRE is made of a semi-ringstainless steel blade pin-jointed to two aluminum fi xing plates, and two resistance strain gauges bondedto the top and bottom faces of the blade at mid-span position. Groups of fi ve matched compressionspecimens (20 mm x 20 mm x 60 mm) from black spruce wood (Picea mariana (Mill.) B.S.P.), cut in sixdifferent orientations with respect to load axis (three orthotropic directions and three diagonal directionsat an angle of 45 degrees to the load axis) were used for the calibration of the SRE. A resistance straingauge bonded directly to the wood surface was used as a reference for both the axial and transversemeasurements. The validation of the technique was made with another series of specimens cut in thesame six orientations. The axial strain data of the SRE were then compared to the ones obtained from alinear displacement sensor (LVDT). For the transverse directions, the SRE results in terms of Poisson sratios and shear moduli were compared with corresponding data obtained from the literature. Resultsshowed that the R2 value of the relationship between the Young s moduli determined with the SREand the LVDT varied from 0.88 to 0.97. The SRE technique appeared also reliable to evaluate both thePoisson s ratios and shear moduli as the obtained values were in good agreement with the literaturedata. As compared to bonded strain gauges, the SRE technique is reusable, simpler and cheaper to useand its sensitivity is nearly independent of temperature.
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