PSI - Issue 28

Mohamed Ali Bouaziz et al. / Procedia Structural Integrity 28 (2020) 1039–1046 M.A. BOUAZIZ et al/ Structural Integrity Procedia 00 (2019) 000–000

1041

3

2. Experimental tests  SENT specimens were 3D printed with the dimensions shown in Figure 1(a). The notch was also made by AM. The notch dimension meets ASTM E1820 (2011) standard recommendations, namely, specimen width and initial crack length. The specimens were printed by adding molten layers of 17-4PH filament using a Markforged 3D-printer. The material of the process is a resin based filament loaded with the metal powder. The printer unwinds the material spool, heats it up to the resin melting temperature via an extrusion head, and then deposits it as successive layers according to the 3D CAD file. The samples were printed as a solid part, in a flat [+/-45°] orientation and four wall contours (Figure 1(b)). Two post-sintered layer heights were investigated (i.e., 125 µm and 50 µm). The printed green parts were debinded and sintered in a two-step oven process.

(a)

(b)

Fig. 1. Sample geometry and raster orientations. (a) µ-SENT sample dimensions (mm). (b) +/- 45 ° deposition.

In order to ease surface functionalization, the specimen was mechanically polished. The thickness was reduced from 4 mm to 1.6 mm. White speckles with micrometric dimensions were deposited using an airbrush (average diameter equal to 20 µm, Figure 2). The experimental setup consisted of a numerical Keyence VHX-1000 microscope for the surface observation, a tensile micromachine and a triggering system (Table 1). The later allowed images to be recorded at specific rates when the specimen was continuously loaded and each image to be related to the corresponding applied load. Table 1. Experimental setup Microscope Keyence VHX‐1000 Definition 54 Megapixel 3CCD Lens VH‐Z100R (100× to 1000×) Wide‐range zoom lens Image acquisition rate 1 fps Pattering technique airbrush Pattern feature size 10 pixels Load cell 5 kN Cross‐head displacement rate 1.5 µm / s Field of view 3.05 × 2.28 mm² Image scale 2.1 µm / pixel Two specimens were tested with the same experimental conditions. The specimen failure suddenly appeared at relatively low load levels (i.e., 167 N for the 50 µm sample, and 2980 N for the 125 µm specimen). Another difference