Three-dimensional orthotropic nonlinear transient moisture simulation for wood: analysis on the effect of scanning curves and nonlinearity

This paper introduces, with the development of user-subroutines in the finite-element software Abaqus FEA®, a new practical analysis tool to simulate transient nonlinear moisture transport in wood. The tool is used to revisit the calibration of moisture simulations prior to the simulation of mechanical behaviour in bending subjected to climate change. Often, this calibration does not receive sufficient attention, since the properties and mechanical behaviour are strongly moisture dependent. The calibration of the moisture transport simulation is made with the average volumetric mass data experimentally obtained on a paired specimen of Norway spruce (Picea abies) with the dimensions $$30\times 15\times 640\, {\mathrm{mm}}^{3}$$ 30 × 15 × 640 mm 3 . The data, from a 90-day period, were measured under a constant temperature of 60 °C and systematic relative humidity cycles between 40 and 80%. A practical method based on analytical expressions was used to incorporate hysteresis and scanning behaviour at the boundary surface. The simulation tool makes the single-Fickian model and Neumann boundary condition readily available and the simulations more flexible to different uses. It also allows for a smoother description of inhomogeneity of material. The analysis from the calibration showed that scanning curves associated with hysteresis cannot be neglected in the simulation. The nonlinearity of the analysis indicated that a coherent set of moisture dependent diffusion and surface emission coefficient is necessary for the correct description of moisture gradients and mass transport.

An Empirical Approach for Modeling Hysteresis Behavior of Pyroclastic Soils

For modeling physical and mechanical phenomena that occur in unsaturated soils, it is very important to identify the correct relationship between suction and water content. This relationship defines the soil water retention curve (SWRC). Its shape depends on numerous factors, including grain size composition, particles’ thickening state and, above all, the hydraulic and stress soil history. In particular, the SWRC in wetting phase differs from SWRC in drying phase, showing a hysteretic behavior. Hysteresis domain is defined by the main drying and wetting curves; when moving from one phase to another, relationship between suction and water content defines secondary curves within them. In this paper, a laboratory experiment was carried out to determine main wetting and drying curves of a pyroclastic ash sample from southern Italy. In same site of the sample collection, a monitoring station was installed that measured the suction and water content values. The experimental curves were compared with the data recorded on the site. In this paper, moreover, an empirical procedure is proposed to model secondary curves (or scanning curves) within the hysteresis domain. The scanning curves obtained with this method were compared with data collected by the in-situ monitoring network, revealing the ability to describe a situation realistically with a good adaptation. With this procedure, it is therefore possible to minimize errors since it covers a hysteretic behavior.

Water sorption hysteresis in wood: I review and experimental patterns – geometric characteristics of scanning curves

The origin of sorption hysteresis in the wood-water system is still under debate. In nanoporous-fluid systems, in general, hysteresis is explained as the manifestation of metastable states in a single pore-fluid system and that is further complicated by the pore connectivity. Cell walls are considered as micro-mesoporous materials and capillary condensation in the entire hygroscopic region is proposed as an alternative sorption mechanism. In the present work, the woods of Douglas-fir, aspen and western red cedar were in focus and the pore connectivity has been investigated by observing five experimentally generated hysteresis patterns comprised by up to 4th scanning curves at 25 and 40°C. Special attention was given to the congruency property from one pattern as it is known from the literature that deviation from this property can reveal the extent of pore connectivity. Consistent patterns were found for the species-temperature combinations. Further, the high extent of congruency property indicated the dominance of independent cell wall pores.