Relationship between Thermal Diffusivity and Mechanical Properties of Wood

Abstract

This paper describes an experimental study of the relationships between thermal diffusivity and mechanical characteristics including Brinell hardness, microhardness, and Young’s modulus of common pine (Pinus sylvestris L.), pedunculate oak (Quercus robur L.), and small-leaf lime (Tilia cordata Mill.) wood. A dependence of Brinell hardness and thermal diffusivity tensor components upon humidity for common pine wood is found. The results of the measurement of Brinell hardness, microhardness, Young’s modulus, and main components of thermal diffusivity tensor for three perpendicular cuts are found to be correlated. It is shown that the mechanical properties correlate better with the ratio of longitude to transversal thermal diffusivity coefficients than with the respective individual absolute values. The mechanical characteristics with the highest correlation with the abovementioned ratio are found to be the ratio of Young’s moduli in longitude and transversal directions. Our technique allows a comparative express assessment of wood mechanical properties by means of a contactless non-destructive measurement of its thermal properties using dynamic thermal imaging instead of laborious and material-consuming destructive mechanical tests.

Multiscale Mechanical Performance of Wood: From Nano- to Macro-Scale across Structure Hierarchy and Size Effects

“…Evidently, this weak correlation between nano- and macro-properties is due to the difference in cell wall thickness, the relative share of late wood, and the number of large tracheides and other wood structure elements which reduce wood macroscopic strength. To close the gap between nano- and macro- scale mechanical properties, the nanoindentation tests were carried out at loads ranging from 5 to 500 mN and reported in the set of papers [ 116 , 117 , 118 , 119 ], unlike the 0.1–1 mN range usually used in studying cell walls. It extended the deformed region over the whole cell or several cells up to 50–150 μm, as opposed to precise targeting at the cell wall.…”

“…Typical E eff and H eff radial dependencies measured at cross-sections of common pine ( Pinus sylvestris L.), which represent coniferous trees, are shown at Figure 10 , and pedunculate oak ( Quercus robur L.), which represent hardwood trees, are shown at Figure 11 [ 116 , 117 ]. As could be seen, both species manifest pronounced periodicity of local mechanical properties.…”

“…The dependence of thermal diffusivity tensor a ij on Brinelle hardness HB in common pine ( Pinus sylvestris L.), pedunculate oak ( Quercus robur L.), and small-leaf lime ( Tilia cordata Mill. ) wood at various humidity levels was studied in [ 116 , 165 , 166 ].…”

“… Micromechanical properties of pedunculate oak annual growth rings measured at P max = 500 mN [ 116 ]. ( a ) Spatial dependencies of H eff and E eff over radial distance r for six successive rings.…”

“…HB—Brinell hardness (12.7 mm sphere diameter, 1 mm indentation depth), a 1 , a n —thermal diffusivity coefficients along and across the fibers. HB W /HB W 10 is HB W values on radial (A) and tangential (B) faces, as shown in Figure 2 , normalized to HB W at humidity W = 10% (HB W 10 ) [ 116 ].…”