Proceedings e report - Firenze University Press

4. Results
Young's modulus (10^4 Mpa)
4
3.5
3
2.5
2
1.5
ELASTIC PROPERTIES OF MINUTE SAMPLES OF WOOD ALONG THE THREE MATERIAL DIRECTIONS
34
transverse plane
Fig. 6 : Sampling in radial and tangential directions.
(a)
1
0.4 0.45 0.5 0.55 0.6
Density(g/cm3)
T1
T2
T3
T4
T5
N1
N2
N3
N4
O1
O2
Young's modulus (MPa)
1800
1600
1400
1200
1000
800
600
400
200
(b)
tangential
direction
radial direction
0
0.4 0.45 0.5 0.55 0.6
Density (g/cm3)
Fig. 8: Young's modulus of tension (T), normal (N) and opposite (O) wood in the longitudinal (a), radial and
tangential (b) directions in relation with their density.
Table 1 : Specific modulus of tension (T), opposite (O) and normal (N) poplar wood in radial (R), tangential (T)
and longitudinal (L) directions.
E (c) R ET EL Density E' (a) R E'T E'L
T 1 143 416 34 300 0.55 2 078 756 62 364
SD (b) 111 60 1 400 0.02
O 1 170 478 15 500 0.47 2 489 1 017 32 979
SD 269 109 2 000 0.05
N 1 484 573 18 200 0.43 3 451 1 333 42 326
SD 75 65 2 600 0.04
(a) E’: Specific modulus (Mpa.kg -1 .m 3 )
(b) SD: Standard deviation
(c) E: Young’s modulus (MPa)
Density (g/cm 3 )
In the longitudinal direction, the variability of Young's modulus in the differences samples of each
type of wood (tension, normal and opposite wood) is low compared to the transversal direction.
Particularly, in the case of opposite wood, the standard deviation of the Young's modulus is rather
high; the Young's modulus is variable despite the proximity of all samples to the same annual ring.
This could be due to the fact that, as ring widths are very narrow in opposite wood, the sample can
easily involve adjacent annual rings. For normal wood and tension wood, quite good values of
standard deviation have to be noticed.
In the longitudinal direction, the difference between tension wood and the group of normal and
opposite wood is huge, E=35000MPa for tension wood and E=17000MPa for opposite and normal
wood. On the contrary, the results in the transversal direction present low differences of Young’s
E_rt
E_ro
E_rn
E_tt
E_to
E_tn