## 5 Technical Results
### Mechanical Testing Results  
Table 2 demonstrates the characteristics of each of the designs tested, with Figure 7 illustrating the load applied by the tensile testing machine across the full test duration. The peak load, displacement, stiffness, and energy absorption were physically tested post-production, as seen in Figure 4. The 'Difference' shows the gap between the peak load  
Figure 6: Renders of the outcomes selected by each group. and the predicted load. The differences between the predicted and peak loads and the displacements at fracture are further illustrated in Figures 8 and 9, respectively. There is a 471 N standard deviation across the peak loads for all the designs. The spread is around a mean of 838 N. This demonstrates again the span of outcome performances, showing that different approaches to the GD process achieve wildly different results. Peak load correlates to the predicted load with a coefficient of 0.81. This suggests that despite the unpredictability of AM, the chosen design has a significant impact on structure performance. Design H has the highest energy absorption of 12663.29 Nmm, 700% more than that of Design C, which is 1809.41 Nmm. The population of designs has an energy absorption standard deviation of 3971 Nmm around a mean of 6032 Nmm. This spread demonstrates the compounding variation produced by GD and AM. The energy absorption and peak loads of the design correlate with a coefficient of 0.93, showing that the better performing designs did so across the board rather than the designs, each with their own strengths. All the designs were made from the same amount of PLA, but through suboptimal generation and weaknesses introduced in the AM process, some of the components failed significantly sooner. The load-displacement curves of each of the different designs are presented in Figure 7. The data from mechanical testing show that Designs A*, C, and E had a near-linear development in displacement as the load increased. Linear component stiffness enables simulations to correspond well to physical testing when not using nonlinear solvers. In Designs B and I, the development in displacement increased more at higher loads, similar to that observed in tensile testing of PLA specimens. In Designs B, F, G, and H, the stiffness increased at higher loads. A comparison of simulation results and peak load is presented in Figure 8. There is a massive 592% drop in the peak load between the strongest (Design H) and weakest (Design I) designs. Generally, the predicted load is 40-60% of the peak load, except for Design E. Design E fractured early at the bolt interface, a region not evaluated by the simulation. The spread of predicted loads demonstrates the variation in GD design performance. The simulations assumed constant material properties throughout the design, meaning all performance variation is due to geometry. The further spread of peak loads indicates the effect of compounding AM variation on GD outcome variation. Statistical analysis confirms that the peak loads are significantly greater than the predicted loads (one-tailed \(t\)-test, \(p<0.005\)). This severe underestimation is likely due to the lack of consideration for the anisotropy in AM parts. The simulations operated under the assumption that the UTS of the PLA was 39 MPa, and therefore, they were unable to realize the strengths of the parts for two reasons. Firstly, the stru  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Design**} & **Predicted** & **Peak Load** & **Difference** & **Displacement** & **Displacement at** & **Stiffness** & **Energy Absorption** \\  & **Load (N)** & **(N)** & **(N)** & **(mm)** & **250 N (mm)** & **(N/mm)** & **(N-mm)** \\ \hline A* & 400 & 1055.23 & 655.23 & 19.43 & 3.46 & 64.23 & 11,075.33 \\ \hline B & 593 & 960.43 & 367.43 & 11.3  
parallel plane to the print bed likely have a UTS nearer 69 MPa. Secondly, some regions of a cantilever beam are in compression, providing the struts with a higher yield stress.