## 2 Material Testing
### Tensile Testing
The resulting stress-strain graphs are shown in Figure 4.  
The ultimate tensile strength \(\sigma_{\text{u,t}}\), tensile elastic modulus \(E_{\text{t}}\), strains at ultimate tensile stress \(\varepsilon_{\text{u,t}}\) and tensile fracture strains \(\varepsilon_{\text{f,t}}\) determined for each specimen are shown in Table 2, while average values for these properties for each layering orientation are shown in Table 3. It can be seen in Figure 5 that the printed PLA material is stiffer and stronger across all orientations than the printed ABS material, while in Figure 6, it can be seen that the ABS material is more ductile. These findings agree with previous test results for 3D-printed PLA and ABS [2; 31; 32; 33; 24; 25; 26; 27; 28; 29; 31] and confirm that, when loaded parallel to the printing toolpath, i.e., in the X and Y orientations, PLA and ABS can outperform conventional structural materials like timber, concrete and brick in terms of the tensile strength (approximately 50 N/mm\({}^{2}\) and 30 N/mm\({}^{2}\) for PLA and ABS, respectively), suggesting useful applications in resisting loads; however, the relatively low stiffness of these printed materials (PLA 2900 N/mm\({}^{2}\); ABS 1700 N/mm\({}^{2}\)) requires careful consideration in terms of allowable deformations and serviceability, but applications in aerospace, automotive and other mechanical contexts, in addition to temporary applications in construction, are envisaged. Figure 2: (**a**) Nominal dimensions of tensile specimens in accordance with EN ISO 527-2 [33]; (**b**) printing orientations of tensile specimens. Figure 3: Tensile specimen positioned in Tinius Olsen HK25 universal testing machine. \begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline
**Specimen** & \(b_{\text{t,1}}\) & \(b_{\text{t,2}}\) & **COV(\(b_{\text{t,1}}\))** & **COV(\(b_{\text{t,2}}\))** & \(E_{\text{t}}\) & \(\sigma_{\text{u,t}}\) & \(\varepsilon_{\text{u,t}}\) & \(\varepsilon_{\text{t,t}}\) \\  & **(mm)** & **(mm)** & **(\%)** & **(\%)** & **(N/mm\({}^{2}\))** & **(N/mm\({}^{2}\))** & **(\%)** & **(\%)** \\ \hline _PLA_ & & & & & & & & \\ T01-PLA-X-1 & 9.92 & 4.20 & 0.94 & 6.03 & 2774 & 40.7 & 1.48 & 1.48 \\ T02-PLA-X-2 & 9.95 & 4.20 & 0.59 & 6.23 & 2795 & 51.5 & 1.88 & 1.88 \\ T03-PLA-X-3 & 9.91 & 4.18 & 1.07 & 5.53 & 2834 & 53.1 & 2.10 & 2.13 \\ T04-PLA-Y-1 & 10.91 & 3.98 & 11.11 & 1.30 & 3089 & 53.4 & 1.93 & 1.93 \\ T05-PLA-Y-2 & 10.87 & 3.98 & 10.62 & 1.17 & 3213 & 50.6 & 1.76 & 1.76 \\ T06-PLA-Y-3 & 10.90 & 3.98 & 11.03 & 1.16 & 3231 & 53.9 & 1.90 & 1.91 \\ T07-PLA-Z-1 & 10.35 & 4.35 & 4.33 & 10.84 & 3069 & 37.6 & 1.33 & 1.33 \\ T08-PLA-Z-2 & 10.38 & 4.40 & 4.62 & 12.15 & 3106 & 46.2 & 1.87 & 1.87 \\ T09-PLA-Z-3 & 10.33 & 4.36 & 4.08 & 11.03 & 2968 & 44.9 & 1.76 & 1.76 \\ _ABS_ & & & & & & & \\ T10-ABS-X-1 & 10.13 & 4.19 & 1.69 & 5.96 & 1692 & 31.1 & 2.38 & 2.90 \\ T11-ABS-X-2 & 9.85 & 4.16 & 1.88 & 4.85 & 1772 & 32.1 & 2.32 & 2.49 \\ T12-ABS-X-3 & 9.86 & 4.17 & 1.76 & 5.23 & 1770 & 31.9 & 2.33 & 2.66 \\ T13-ABS-Y-1 & 10.54 & 3.96 & 6.57 & 1.25 & 1739 & 34.0 & 2.38 & 2.4  
As shown in Figure 5, the results for \(E_{\text{t}}\) for both materials are approximately equal across all printing orientations and thus can be assumed to be isotropic for the purposes of analysis and design. The results for \(\sigma_{\text{u,t}}\) and \(\epsilon_{\text{u,t}}\) shown in Figures 5 and 6 suggest some orthotropy, with the Z specimens being weaker than the X and Y specimens. This effect is particularly noticeable for the ABS specimens and results from the tensile load acting across the interfaces between successive printing layers, which are typically the weakest regions of the printed part.