# Prediction of Mechanical Performance of Acetylated MDF at Different Humid Conditions
## 1 Introduction
However, values of dynamic bending properties vary depending on the method used and, most importantly, on the moisture content levels of wood panels. Prediction of static bending properties of acetylated MDF using acoustic techniques under different humid conditions is lacking. Considering that acetylated MDF is more hydrophobic than conventional MDF, fewer internal bond failures and associated changes of internal structure should be expected by repeated swelling and shrinkage. That in turn should lead to more stable static bending behavior. Nevertheless, establishing the relationship between acoustic and static bending properties of acetylated MDF at different humid conditions would ensure reliable and safe predictions of their performance for intended end uses. Another available method to predict and analyze material behavior of MDF is creating macro scale finite element (FE) models of MDF board's structure. Following classic design procedures for macroscale modelling, the material characteristics obtained from the experiments presented in this paper were used as input values to define the material, and the geometry and boundary conditions of the experiment set up were imitated in the FE model. Here, two analysis approaches that are implemented in a SIMULIA(tm) Abaqus/CEA (Systemes(r)) were used to imitate a static three-point bending test. The first approach was a standard quasi-static stress/displacement procedure to control the time incrementation, and the approach is named T1 in this work [28]. Additionally, a second and more advanced technique, the extended finite element method (XFEM) [29], was used and is named T2. This technique allows us to model discontinuities as an enriched feature and it is an extension to the conventional finite element method [28]. Both techniques are classified as macroscale techniques that are nowadays typically used while designing structures [30; 31]. The outcome of both analyses are displacements, reaction forces and maximum principal stresses of the studied FE models. These models should be later optimized to achieve higher fidelity, meaning to create more sophisticated models accounting for the environmental loads as well as mechanical loads, for example, multiscale models [32]. Yet, there is not enough systematic information on the dimensional stability and mechanical properties of acetylated MDF panels under different humid conditions. Establishing correlations between elastic properties measured nondestructively with bending strength and stiffness of acetylated MDF would lead to a quick and reliable means of assessment of the safety margins for different applications. Thus, this study was focused on elucidating the dimensional and static bending properties of acetylated MDF and on evaluating possibilities to predict its bending behavior from acoustic data by using standard statistical and multiscale prediction modelling methods. Dry (35% RH), standard (65% RH) and wet (85% RH) climatic conditions were considered to represent different moisture content situations as well as accelerated weathering.