Issue 48

C.M.S. Vincente et alii, Frattura ed Integrità Strutturale, 48 (2019) 748-756; DOI: 10.3221/IGF-ESIS.48.68 750 and the mechanical behavior of 3D printed PLA parts (before and after protective coatings application), was not previously systematically investigated. M ATERIALS AND M ETHODS 3D printing and protective coatings Ultimaker 2 ™ machine was used to print all the samples from the same white PLA filament roll. The 3D models were modelled in SolidWorks ® and exported in a stereolithographic (STL) file to the slicing software Cura ® , to generate the g–code file. For the constant printing parameters, the recommended standard profile by Cura ® was adopted. The infill density as set to 60% for all samples. The extrusion was performed with a nozzle diameter of 0.4 mm. The temperature of the platform was set to 60 o C. The printing speed was 40 mm.s –1 for the first layer, external layers (top and bottom) and contours. The printing speed chosen for internal contours and filling layers was 60 and 80 mm.s –1 , respectively. The thickness of the contours is 0.4 mm, while for tops and bottoms is equal to 0.8 mm. The thickness of initial layer as set to 0.3 mm. Two kind of samples (LVL1 and LVL2) were printed with the levels of printing parameters, displayed on Tab. 1. For each sample three repetitions were considered. PARAMETERS Samples Layer thickness (mm) Raster angle ( o ) Extrusion temperature (ºC) LEVELS LVL1 0.1 (0 o /90 o ) 220 LVL2 0.2 (–45 o /45 o ) 200 Table 1 : FDM process parameters and its levels. The tensile tests specimens were printed on the flat direction, with the geometry and dimensions displayed on Fig. 1. Figure 1 : Geometry and dimensions of tensile tests specimens. Water absorption samples consists on coated and uncoated cubes with dimensions of approximately 10 mm, which were fabricated with the printing parameters of Tab. 1. Two different protective coatings were selected: a PU wood sealant (Lakeone™) and an acrylic aqueous varnish (Luxens™). Before the application of protective coatings and water immersion tests, the samples were placed in an oven during 24 hours, in order to ensure that the water content was minimum and equal for all samples. After the application of coatings, the PLA coated samples were dried at room temperature, for complete solvent removal. Tensile tests Tensile tests were performed using a universal testing machine (INSTRON 3369) with a load cell of 50 kN and a strain rate of 2 mm.min –1 . At least three tests were made for each sample manufacturing conditions. Stress-strain curves were obtained for each test from the load vs. displacement curves. The toughness of each specimen was calculated from the integration of the stress–strain curve [29]. A