Abstract
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 30times 15times 640, {mathrm{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.
Highlights
Lack of standard test method leads to diversityA popular method to determine the strength and stiffness of wood is the three- or four-point bending test
In the first “Moisture content profiles” section, the numerical model will be used to simulate moisture content (MC)-profiles associated with flow in radial, tangential and longitudinal directions separately
The flow properties found in the first section are used as a starting point for the calibration presented in the third “Calibration of numerical model based on experiment” section
Summary
Lack of standard test method leads to diversity. A popular method to determine the strength and stiffness of wood is the three- or four-point bending test. This method is not the most straightforward, though in bending the beam experiences both tension and compression simultaneously and cannot result in valid material level properties (Morlier 1994; Muszyński 2006). The flexural test is still a common method to experimentally calibrate (numerical) models, especially long-term behaviour when subjected to dynamic changes in climate (Honfi et al 2014; Ma et al 2017; Mohager and Toratti 1993). There are no standard test methods available to study the long-term behaviour of timber beams. In the context of the four-point bending test, this is not always sufficiently exercised
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