## 3 Materials and Methods
### Instruments and Methods  
For the application of MSLA 3D printing technology, the Elegoo Mars 5 Ultra printer (Elegoo, Shenzhen, China) is available, with the parameters shown in Table 2. The printer is also a readily available, general-purpose, residential printer that is often used in industrial applications. Masked stereolithography apparatus (MSLA) printing is a \"bottom-lit\" form of vat photopolymerization (where liquid resin is stored in a vat form and then solidified layer by layer using light to build a 3D model), where a light source of UV LEDs is \"masked\" by a large LCD panel. The panel's pixels act as gate-openers: where a pixel is off, it allows light to pass through; where it is on, it blocks it. In this way, the entire layer pattern generated by the slicer is bound in the resin in a single flash, rather than point by point, as in classical laser SLA. MSLA printing technology is characterized by the fact that the finished printed product remains resinous due to the immersion method, which necessitates its removal from the surface. Therefore, at the end of the 3D printing process, the printed test pieces must be washed with isopropyl alcohol. Another technological property is that the finished product only reaches its final strength when it is cured by UV light after printing. A general characteristic of resins is that they reach their final mechanical properties when exposed to UV light. Resin manufacturers do not specify an exact curing time because it depends largely on the size, shape, and transparency of the product. Generally speaking, a curing time of 10-15 min is sufficient for test specimens prepared in the experiments. For this purpose, the Elegoo Mercury V3.0 Wash and Cure apparatus (Shenzhen Elegoo Technology Co., Ltd., Shenzhen, China) was used, the main parameters of which are given in Table 3.  
The test specimens were prepared as described above and subjected to mechanical loading. Most literature uses the traditional tensile test or the Charpy impact test. The present research is a more complex application, but it better demonstrates the real stresses that occur in practice. It was inspired by the traditional 3-point bending test and the Erichsen cupping test standard (ISO 20482:2013) [74]. The Erichsen test is designed for sheet materials and essentially creates biaxial loading, whereas the 3-point bending test creates bending loading. The stresses acting on some products in real-life conditions are also \begin{table}
\begin{tabular}{c c} \hline \hline
**Specifications** & **Elegoo Mars 5 Ultra** \\ \hline Printing technology & MSLA \\ Build volume & 153.36 \(\times\) 77.76 \(\times\) 165 mm\({}^{3}\) \\ Light source & COB Light Source (wavelength 405 nm) \\ Printing speed & max. 150 mm/h \\ LCD screen size & 7-inch 9K Mono LCD \\ Layer thickness & 0.01–0.2 mm \\ XY resolution & 18 \(\times\) 18 \(\mu\)m (8520 \(\times\) 4320) \\ Z-axis accuracy & 0.02 mm \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of the MSLA printer used. \begin{table}
\begin{tabular}{c c} \hline \hline
**Specifications** & **Elegoo Mercury V3.0 Wash and Cure** \\ \hline Max. washing volume & 214 mm \(\times\) 135 mm \(\times\) 180 mm (with build plate) \\  & 230 mm \(\times\) 135 mm \(\times\) 260 mm (without build plate) \\ Max. curing size & \(\diameter\)250 mm \(\times\) 290 mm (H) \\ Time setting & 0–30 min \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Parameters of the Wash and Cure machine used for post-processing. rather complex; therefore, the [PERSON] test apparatus has been modified to accommodate the test data. The equipment was modified with a 3D-printed adapter (Figure 1), and the forming stamp remained the standard 20 mm diameter spherical end tool. This creates biaxial-like stress on the surface due to the spherical tool, which can be interpreted as even more bending stress for small displacements. For simplicity, this test is referred to in this article as the bending test.