## 4 Validation I: Simulation of Open-Hole Tension Tests with Optimal GA Solution
### Mesh-Size Sensitivity  
The FE mesh size of the CT geometry used for the calibration of damage input parameters in previous section is 1 mm \(\times\) 1 mm. The investigation of different mesh sizes requires the application of [PERSON]'s crack band scaling approach outlined in Equation (4) where the characteristic length \(l^{*}\) is adjusted based on a given fracture energy \(G^{f}\) and ply strength \(X\). With the optimal damage input parameters shown in Table 2, the ply strength values \(X_{1}=E_{1}\epsilon_{1}^{i}=82.6\) MPa and \(X_{2}=E_{2}\epsilon_{2}^{i}=14.8\) MPa can be calculated. Similarly, the fracture energy can be considered as the area of each stress-strain curve (see Figure 1), therefore \(G_{1}^{f}=0.5X_{1}\epsilon_{1}^{s}=3.5\) kJ/m\({}^{2}\) and \(G_{2}^{f}=0.5X_{2}\epsilon_{2}^{s}=0.6\) kJ/m\({}^{2}\). With the aim to dissipate the same amount of energy for a given strength, regardless of the underlying FE mesh size, Equation (4) suggests scaling the damage saturation strains along the grain direction \(\epsilon_{1}^{s}\) and perpendicular to it \(\epsilon_{2}^{s}\) with respect to the characteristic length \(l^{*}\). Here, three different mesh sizes are compared in OHT test samples with hole diameter of 8 mm. Table 3 lists these mesh sizes with the adjusted damage saturation strains.  
The quantitative and qualitative simulation results using different mesh sizes are shown in Table 4 and Figure 7, respectively. OHT testing of composites typically yields linear mechanical behaviour up to brittle failure [32; 33]. Therefore, only strength data are calculated by considering the maximum measured force and the cross-section of the OHT test sample. Note that the net cross-section (without accounting for the open hole) is used to calculate the OHT strength. Table 4 shows that there are only minor changes to the open-hole strength with maximum differences of less than 1%, implying that mesh convergence has been achieved. It can be concluded that the coarse mesh (1 mm \(\times\) 1 mm)  
Figure 6: Comparison of crack length measurements at approximate displacement of 1.5 mm in compact tension tests between experimental observations [6] and simulation using optimal input parameters shown in Table 2.  
is sufficiently fine to simulate progressive damage of the wood veneer laminates. This is consistent with previous findings on carbon fibre-reinforced laminates [34] where such a coarse mesh achieved mesh-insensitive damage simulations. The qualitative comparison of the damage patterns in Figure 7 further shows that the mesh size does not alter the damage path. The three simulations with different mesh sizes predict a similar damage path that is aligned in a perpendicular direction to the tensile loading. The observed damage refers to the \(0^{\circ}\) plies of the \([90/45/0/-45]_{s}\) beech veneer laminates as indicated by the white in the bottom right corner of each contour plot. The obvious qualitative difference between the simulation results is the damage height since damage localises in one row of elements in typical CDM approaches [34]. This highlights the need for [PERSON]'s crack band scaling in Equation (4) and the adjustment of the damage saturation strains shown in Table 3 so that an equal amount of energy is dissipated regardless of the underlying mesh size.