Three-dimensional orthotropic nonlinear transient moisture simulation for wood: analysis on the effect of scanning curve
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Three‑dimensional orthotropic nonlinear transient moisture simulation for wood: analysis on the effect of scanning curves and nonlinearity Sara Florisson1 · Johan Vessby1 · Winston Mmari1 · Sigurdur Ormarsson1 Received: 16 December 2019 / Published online: 14 August 2020 © The Author(s) 2020
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 30 × 15 × 640 mm3 . 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.
* Sara Florisson [email protected] Johan Vessby [email protected] Winston Mmari [email protected] Sigurdur Ormarsson [email protected] 1
Linnaeus university Faculty of Technology, Växjö, Sweden
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Wood Science and Technology (2020) 54:1197–1222
Introduction 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 therefore cannot result in valid material level properties (Morlier 1994; Muszyński 2006). However, 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). Here, the definition of calibration is the iterative process of adjusting material properties and comparing the model to experimental data until good agreement is found. There are no standard test methods available to study the long-term behaviour of timber beams. Therefore, much divers
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