Issue 72

N. Naboulsi et alii, Fracture and Structural Integrity, 72 (2025) 247-262; DOI: 10.3221/IGF-ESIS.72.18

Influence of different notches on tensile characteristics of PLA-CB Fig. 11 shows the tensile curves obtained for 3D-printed SENT specimens of PLA-CB with different notch geometries (single U, single V, double U, double V and a central hole) to study the influence of stress concentration on the mechanical behavior of the material. The curves of simple U- and V-notched specimens show that simple U- and V- notches, producing unidirectional weak points, present slightly distinctive behaviors: the U-shaped notches, thanks to their rounded configuration, distribute stresses more efficiently, leading to increased stress rupture and significant deformation prior to failure. On the other hand, V-shaped notches, thanks to their sharp angles, concentrate stresses more intensively, reducing strength and leading to slightly more brittle fracture than the U-shaped notch. This impact is amplified by double notches (U or V), which create two zones of stress concentration, making the material more susceptible to early failure, especially in the case of V-notches. Finally, the samples with the center hole, showing a radial distribution of stresses around the hole, indicates a limitation of fracture that is directly related to the size of the hole, which is 4mm in diameter compared to its width of 20mm. This configuration resulted in progressive fracture, which is generally more significant than single and double U- and V-notches form. In addition, comparing notched specimens to virgin one under tensile testing reveals a clear shift in the material's behavior from ductile to brittle. The notched specimens fractured much faster than the unnotched one and showed almost no significant deformation, with the plastic zone almost disappeared. Consequently, geometries in 3D printed elements have a very important impact on the mechanical strength of the material. The values for maximum - strain just before break related to each notch geometry are shown in Tab. 3.

Figure 11: The effect of Different Notches on the stress-strain curves of conductive PLA printed samples.

Specimen with center hole

Type of Notch

Single U-Notch

Single V-Notch

Double U-Notch Double V-Notch

16.6985 16.6209 3.1392

15.356 13.748 3.0833

11.4682

14.3515 9.9814 2.6059

Maximal stress (MPa) Breaking strength (MPa) Elongation at Break (%)

19.3358 19.3358 3.5693

6.546

2.5835

Table 3 : Effects of notches on the mechanical characteristics of PLA-CB.

Weibull Distribution Figs. 12 and 13 show the tendencies in tensile strength and breaking strain for different specimens tested under the effects of crosshead speed and under the effects of notches. The shape and scale parameters of Weibull's distribution function have

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