PSI - Issue 28

Manuel Sardinha et al. / Procedia Structural Integrity 28 (2020) 358–363 Author name / Structural Integrity Procedia 00 (2019) 000–000

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A dedicated material extrusion apparatus [9] and slicer software [10] were used to manufacture the specimens. The apparatus consists of two independent extrusion modules that allow a parallel and collaborative fabrication of parts (Figure 1). To control it, a dedicated slicer software that avoids collisions between modules is used to generate the G code file. The CAD model is firstly generated in Soliworks® and exported as an STL file. Then, the dedicated software slices the model into layers and in each layer allocates a percentage of the area to be produced by each module. Four different types of specimens were produced, differing in seam dimensions as demonstrated in the scheme of Figure 2. The specimens are labelled considering N (non-existing seam) or S (existing seam), seam overlap dimension (between 0 mm and 20 mm ) and lastly the number of the specimen in a specific batch (from 1 to 5). As an example, S_00_1 is the first of five specimens produced with a seam with 0 overlap, S_20_3 is the third specimen produced with a 20 mm overlap and NS_-_5 is the last specimen of its batch which is produced without a seam. In the non existing seam specimens, only one extrusion module was used. It should be underlined that toolpaths are generated for each layer at a time. On the seam area, the contour of the part is generated with a negative offset of the part’s boundary and then cut by the seam line. The infill is generated for each area with an intersection with a set of equally spaced lines. Therefore, the intersection in each layer is achieved by intersecting contours over contours and infill over infill, like it was with a single extruder.

Fig. 2. Scheme of the seam area, different colors representing different extrusion modules. a) First layer and all other uneven number layers. b) Second layer and all other even number layers.

During manufacturing, each layer alternates between Figure 2a and 2b. All specimens are produced with a raster angle of 45/-45, a layer height of 0.2 mm , a nozzle with 0.4 mm diameter, at a 205ºC extrusion temperature and a heated bed at 40ºC. 2.3. Tensile tests Figure 3 displays two drawing views of the specimens. Sections A, B and C mark the areas where experimental measurements were taken, using a caliper. In Table 1 these measurements are shown with each section having a measurement in both y and z axis (ex: Ay and Az respectively), the samples were also weighted in a Baxtran HZ scale.