## 2 Materials and Methods
### Methodology for the Analysis of Variance (ANOVA) and Experimental Design
The resulting compressive modes of failure due to these tests can be classified into three primary failure categories that are each split into subcategories. The main categories are flexural buckling, kinking, and shear failures. The first and most common type is flexural buckling failure, which involves three distinct sub-modes: lateral buckling (runs 4, 5, 6, 9, 16, 17, 18); interlaminar delamination causes buckling (runs 19, 20, 21, 22), interfacial debonding and buckling (runs 7, 8, 25, 26, 27); and buckling associated with twisting around the longitudinal axis (runs 11, 13, 24). The kinking failure is the second one, either with a single (run 10) or double (runs 1, 2, 3, 14, 15) kink, and the third failure mode is shearing failure with sliding (runs 12, 23). The factors in the 3D printing process are related to each distinct failure mode. The infill density (ID), in conjunction with the printing orientation angle (ORA), are the primary factors that influence the failure mechanism of the samples. Changes in the values of these factors affect the failure mechanism in the samples, as explained below. The samples (runs  
Figure 5: Specim failure during compression testing. 1 to 9) show the flexural failure of buckling or kinking mode at a printing angle of 0\({}^{\circ}\), demonstrating maximal compressive strength, which even grows in proportion to the infill density (ID), in contrast to other printing angle values. The combination of ORA and RDA control settings that results in specimens with 45-degree-inclined layers causes shear failure because, in the case of low nozzle temperature (runs 11, 12), insufficient interlayer bonding causes sliding at the 45-degree shear plane. For specimens with a 90\({}^{\circ}\) printing angle, flexural buckling failure is observed, either with interlaminar delamination (samples 19, 20, and 21) for a 0\({}^{\circ}\) RDA or with debonding at the interfaces of adjacent layers for a 90\({}^{\circ}\) RDA. As a result, the RDA contributes by altering the primary failure mechanism, which causes secondary failure modes. For a 45\({}^{\circ}\) RDA, for instance, the specimen experiences a twist-type shearing failure concerning the longitudinal axis. Additionally, a specimen that experiences laminar failure is typically strengthened by a 45\({}^{\circ}\) RDA angle because it prevents layer separation brought on by significant interlaminar pressures operating at the boundary of two adjacent layers. Finally, the experimental findings exposed a straightforward correlation between the infill density and the 3D-printed samples' highest compressive resistance. The highest compressive load that the specimen can withstand during the compression test is known as the ultimate compressive strength. This indicates that the distortion caused by the maximum compression load signifies the beginning of the material rupture. No matter the particular failure mode that might take place, the sample's infill density maintains its consistent compressive strength [19]. The process for examining the failure of the 3D-printed PA6 samples brought on by compressive force is demonstrated in Figure 3. The specific failure mechanism in question in this case is buckling. The examined sample is precisely positioned, with its longitudinal axis aligned with the plunger's center line and its ends parallel to the compression plates between them. The compression load is then applied by moving the plunger axially at the 1.3 mm/min standard testing speed. After being subjected to compressive stress, the specimen gradually buckles and is deformed into the C-shape because of the specimen contact friction, the square shape of the specimen end surface, and the support conditions that result. According to the 3D printed structure, buckling failure occurs when the elastic critical compressive load is exceeded. The buckling happens on the plane where the sample has the lower second moment of area value. The samples were exposed to compressive loading until they entirely failed.