Issue 41

A. A. Ahmed et alii, Frattura ed Integrità Strutturale, 41 (2017) 252-259; DOI: 10.3221/IGF-ESIS.41.34 256 E XPERIMENTAL RESULTS lain and notched specimens were additively manufactured via 3D-printer Ultimaker 2 Extended+ by using as parent material New Verbatim filaments of white PLA with initial diameter of 2.85mm. The values of the adopted manufacturing parameters were as follows: nozzle size=0.4 mm, nozzle temperature=240ºC, build-plate temperature=60ºC, layer height=0.1 mm, shell thickness=0.4 mm, fill density=100%, and print speed=30 mm/s. According to Fig. 2, the flat samples being tested were manufactured horizontally on the build-plate by setting angle θ p equal to 0º, 30º, 45º, 60º, and 90º. In particular, while the extruded filaments were deposited, layer upon layer, always at ±45º to the axis y p of the build-plate, the angle between the longitudinal axis of the specimens and axis y p was varied in the range 0º-90º (see Fig. 2). All samples had thickness, t, equal to 4mm, with the un-notched specimens having net width equal to 15 mm. The sharply U-notched specimens being manufactured had net width, w n , equal to 15.4 mm, gross width, w g , to 24.9 mm, and notch root radius, r n , equal to 0.5 mm. These dimensions returned a value for the net stress concentrator factor, K t , equal to 4.76. The specimens containing the intermediate U-notches had the following average dimensions: w n =15.3 mm, w g =24.9 mm, and r n =1.0 mm (resulting in a K t value equal to 3.51). Finally, the dimensions of the bluntly U-notched specimens were as follows: w n =15.2 mm, w g =25.1 mm, and r n =3.0 mm (K t =2.22). For the notched specimens being investigated the corresponding values for the stress concentration factors were estimated using Peterson’s diagrams [14]. A number of specimens containing crack-like notches were also additively manufactured in order to determine the fracture toughness for t=4 mm. In particular, the relevant dimensions for these specimens were as follows: w n =16.4 mm, w g =24.9 mm, and r n ≈0.01 mm. By setting the displacement rate equal to 2 mm/min, the plain specimens as well as the samples containing both U- notches and crack-like notches were tested under quasi-static tensile loading by using a Shimadzu universal machine. In the un-notched specimens, the local strains were measured during testing via an axial extensometer with gauge length equal to 50 mm. Three different specimens were tested for any geometry/manufacturing configuration that was investigated. (a) (b) (c) Figure 4 : Influence of manufacturing angle θ p on E (a) , σ UTS (b) , and K C (c) . 2000 2500 3000 3500 4000 0 10 20 30 40 50 60 70 80 90 E [MPa] Manufacturing Angle, θ p [  ] +2S D -2S D E=3296 MPa 20 30 40 50 60 0 10 20 30 40 50 60 70 80 90 σ UTS [MPa] Manufacturing Angle, θ p [  ] +2S D -2S D σ UTS =42.5 MPa 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 0 10 20 30 40 50 60 70 80 90 K C [MPa·m 1/2 ] Deposition Angle, θ p [  ] +2S D -2S D K c =3.4 MPa·m 1/2 P