**Table 3.** FDM fixed parameters of the research.

**Figure 2.** *Cont.*

**Figure 2.** Geometrical dimensions and internal features of the sample. (**a**) 3D printing of bronze polylactic acid (Br-PLA) samples, (**b**) 3D printed samples, (**c**) 3D printing of polylactic acid (PLA) samples [18], (**d**) dimensions of the tensile test sample according to ISO 527-2.

The build time was measured by a digital timer after the printing of each sample; the maximum failure load was determined by the tensile strength test. The tensile strength tests were carried out with a universal testing machine based on ASTM D638 (ASTM International, Conshohocken. PA, USA). The brittle fracture of the samples (PLA and Br-PLA) on the universal testing machine is represented in Figure 3. Figure 4 also shows extension-force diagrams of samples #2 and #5. The results showed that the behavior of samples under load could be classified as a brittle and tough fracture. Almost 80% of the results in the design matrix had brittle fracture because PLA is relatively brittle under tensile loading. The fracture of brittle samples occurred at the elastic limit, while tough specimens showed the ability to undergo a low degree of plastic deformation before fracture. Therefore, samples with higher maximum failure load and elongation at the break had a tough fracture. However, a sudden brittle fracture is usually observed in samples at the elastic limit and in a lower failure load. Also, in the previous study [18], extruder temperature (230 ◦C), infill percentage (16.86%), and layer thickness (0.23 mm) were selected as controlled parameters by optimum settings for PLA printed parts, and, in this study, the failure load was compared with Br-PLA.

**Figure 3.** (**a**) Brittle fracture of the specimen (sample #12 Br-PLA), (**b**) Brittle fracture of the optimum PLA specimen, (**c**) fracture of #1 to #6 samples.

**Figure 4.** Extension-force diagrams of (**a**) sample #2 and (**b**) sample #4.
