Proceedings e report - Firenze University Press

WOOD SCIENCE FOR CONSERVATION OF CULTURAL HERITAGE
comparison of loading and unloading curves permitted us to validate that measurements took place in
the linear elasticity domain. The infradensity of each sample after drying at 103°C was also
determined.
From the experimental displacement / force curves, the Young's modulus was calculated using the
following equation:
2
l ( L − l)
E = (where α is the slope of the displacement/ force curve)
32 E I . α
F
2 mm (R)
5 mm (T)
laser
l
35 mm (L)
Fig. 1 Experimental configuration for the 4-point bending tests.
2.2. Tensile tests along the radial and tangential directions
Experimental device
Tensile tests were performed with a manual tensile system, whose micrometer screw allows precise
increments. In these tests, the stress value, σ, is measured with a load cell, assuming the section to be
uniform and the strain value, ε, is obtained directly on the sample without contact using image
correlation. For this purpose, the optical microscope is set in reflexion mode and the sample surface
has to be carefully polished [7]. In the specific case of the tangential direction, because of their small
size, the samples have been glued to plastic jaws to facilitate their attachment to the bending device.
Particular attention was paid to the alignment of the jaws and the wood sample before they were
placed on the experimental apparatus. In the case of radial measurement, the sample size was
sufficient for direct fixing to the bending device. During the test, the apparatus itself was attached to
the stage of an optical microscope with two screws. This allows the position of the image to be
carefully chosen and this zone of interest to be tracked during the test (Fig. 2).
Fig. 2 : a) Our custom tensile device placed on the stage of the optical microscope and b) example of image
obtained in reflexion mode.
31
Wood sample
Δh