# Mechanical and Tribological Performance of Carbon Fiber-Reinforced PETG for FFF Applications
## 2 Materials and Methods
### Methods  
An XY Core kinematic 3D printer, Two Trees model Sapphire Plus (TwoTrees Technology, Shenzhen, China) with a generic brass nozzle of 0.4 mm diameter, was used for specimen fabrication. The specimen geometry was determined based on ASTM D638 [20] for the \"bone-type\" specimens and ASTM D695 [21] for the cylindrical specimens tested under compression. During this entire process, measures were taken to ensure the reproducibility and consistency of the specimens used in the tensile and compression tests. For this purpose, all the material and all the specimens were stored and kept under controlled temperature and humidity conditions. The sketches of both specimens are shown in Figure 2.  
For the tensile and compression tests, the equipment used is the same: Shimadzu AG-X 50 kN with a 50 kN maximum load cell without extensometer (Shimadzu Corporation, Kyoto, Japan), with specific tools used to perform each test. Regarding the fabrication parameters, the layer thickness determines the vertical resolution of the printed model and the infill influences the mechanical strength of the printed model [28]. Moreover, the manufacturing temperature affects the viscosity of the  
Figure 1: Experimental Methodology flowchart. Figure 2: “Bone-type” test specimen (**a**), and cylindrical test specimen (**b**). material and its adhesion to the printing bed, and can also affect the crystallinity of the material, influencing the strength and durability of the printed part [29]. Therefore, layer thickness and temperature have been selected as the process parameters. The rest of the parameters are considered to be constant, including the printing speed, which has been set to 60 mm/s as it has been estimated to be optimal in previous studies [12]. Based on previous experimental studies, a set of parameters have been considered as optimal conditions for the development of the specimens used in this research. The parameters used are shown in Table 1. Three specimens were fabricated with each parameter variation. The mechanical tests were conducted using a Shimadzu AG-X 50 kN testing machine, under the control of Trapezium X 2.71 software (Shimadzu Corporation, Kyoto, Japan). The testing machine has a sensitivity of 0.01 N and a speed range spanning from 0.001 to 500 mm/min. For the case of the bone-type specimens, with a characteristic length of 135 mm, the test was carried out at a constant tensile speed of 5 mm/min. Regarding the compression tests, the cylindrical specimens of 12.7 mm diameter were initially subjected to loads at a constant compression speed of 1.3 mm/min, increasing to 5 mm/min when the elastic limit of the material was achieved, ending the test when 10 mm of deformation was reached. Before carrying out the tests, a geometric characterization of the specimens was carried out in order to analyze possible deviations and study their possible influence on the obtained results. Likewise, a characterization by microscopy techniques was carried out before and after the tests in order to analyze the typical manufacturing defects, as well as the type of fracture that appears. The study of visual defects was carried out by SOM microscopy and focus variable microscopy technology using a Leica S9i (Leica Camera, Wetzlar, Germany) and a Bruker/Alicona Infinite Focus G5+ systems (Bruker/Alicona, Raaba, Austria), Figure 3, also used for the evaluation of Ra and Rz roughness parameters. To evaluate the CF reinforcement effects on the friction and wear behavior, Pin-on-Disc (PoD) tests, following ASTM G99-17 Standard, have been carried out, using a MT/60/NI Microtest Tribometer (Microtest S.A., Madrid, Spain), Figure 4, and setting a 15 N load