# Prediction of Mechanical Performance of Acetylated MDF at Different Humid Conditions
## 3 Results and Discussion
### Finite Element Analysis  
Magnitudes of reaction forces and the deflections under these reactions forces in the z-axis direction, as well as values of maximal principal stress for T1, T2 procedures and experimental values, are presented in Table 6. Reaction forces are equal to half of maximal loading force.  
Finally, it is necessary to add that the values for the T2 model show the maximal values at the time point when the jump in the damage dissipation energy occurs (Figure 7): thus, in this particular case, at the time increment 0.4623 of 1 with index number 30. At this time, the increment of the crack growth is initiated and the crack propagates [28], i.e., we are at beginning of a fracture mechanism.  
The crack occurrence is visualized in Figure 8 using the PHILSM function, i.e., a singled distance function that describes the crack surface [28].  
When we compare results obtained from the two computational models using different simulations techniques T1 (quasi-static stress/displacement) and T2 (extended finite element) with the experimental values, we see percental errors of 8.6% and 14.3%. As expected, these percent errors are relatively high. This demonstrates that the used computational methods do not provide reliable results, and thus, can be considered to have a low fidelity. Despite this fact, these techniques are today used as the main techniques in standard design procedures because they are highly efficient [29; 31]. To be sure, the errors can be minimized by optimizing the input parameters that imitate the real nature of the studied MDF material; however, that requires more necessary testing, like, for example, creep testing and fracture testing, to obtain those data. This means spending more time to set up experiments, more wasted material for creating samples, as well as time to collect and analyze data sets.  
\begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Procedure**} & **Displacement** & **Reaction Force** & **Maximal Principal Stress** \\  & **[mm]** & **[N]** & **[MPa]** \\ \hline T1-quasi- static stress & 8.3 & 599 & 30.98 \\ /displacement & & & \\ \hline T2-extended finite & 8.9 & 641 & 35.60 \\ element method & 7.6 & 563 & 35.89 \\ \hline \end{tabular}
\end{table}
Table 6: Magnitudes of displacements, reaction forces, and maximal principal stress for first approach (T1) and second approach (T2) finite element (FE) procedure, and experimental values.  
Figure 6: Estimated and predicted values of MOEstat and MORstat for Medite Tricoya® MDF samples conditioned at three different climatic conditions.  
A better solution here is to use the help of micromechanical modelling approaches to specify material behaviour on a constituent level that is summarized in [32; 54; 55], and that will provide more reliable results compared with experimental ones and reduce the need for new sets of tests. More precisely, the employment of concurrent material and structural design applying multiscale models comes in since viscoelastic creep damage models and rheological behavior of MDF material are considered [56]. Here, we mean the time-dependent mechanical repose of MDF on a constant load considering the influence material's density as well as fiber orientation, and the existence of voids and interfaces in the material microstructure. More importantly, the macroscale computational techniques used in this work do not take into consideration the very significant dependence of mechanical properties on the moisture and temperature. This, as demonstrated in this work, should be included in the computations to precisely predict mechanical material characteristics such as strength, toughness and elasticity as well as to predict the damage mechanism of the panel product.