PSI - Issue 68

Estera Vălean et al. / Procedia Structural Integrity 68 (2025) 955 – 961 Vălean et al./ Structural Integrity Procedia 00 (2025) 000–000

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The impact and flexural tests of the samples were performed according to ISO 179-1 (2023) standard for Charpy tests, and ISO 178 (2019) for flexural.

(a)

(b)

Fig. 1. Geometries of the impact and bending specimens: smooth (a) and with notch (b). Both specimens are 4 mm thick.

The bending tests were done on 5 kN Zwick Roell machine. The tests were conducted at a loading velocity of 2 mm/min, with displacement control, at room temperature. The dynamic tests were performed on the instrumented pendulum, Instron CEAST 9050 equipment, with a 0.9225 kg hammer that impacts the specimens at a velocity of 2.9 m/s. The specimens were tested in an edgewise direction, with a 60 mm span between the anvils. The hammer is released at an angle of 150 degrees. For each type of material and type of specimen, 6 specimens were made. A total number of 24 samples were tested for each type of static and dynamic test.

2. Results 2.1. Static Results - Bending tests

Figure 2 shows the force-displacement and flexural stress - flexural strain curves of 3D-printed samples (PLA and PLA-CF are the results for smooth specimens and PLA/PLA-CF-notch are the results for the samples with notch). All curves highlight a linear elastic zone starting from the beginning of the curves and it is observed that the flexural modulus has a very close value for the two materials (~1766 MPa -PLA/~1679MPa-PLA-CF). The specimens made of PLA show a brittle behaviour, while for those made of PLA-CF the fracture is ductile. Figure 2a shows major differences between the types of material and type of specimens tested. The maximum force is high in the case of smooth specimens, in the case of notched specimens the force value is much lower. Thus for PLA from an average value of 485 N (smooth specimens) the force decreases to approximately 235 N for notched specimens, and for the material reinforced PLA-CF, from 360 N (smooth specimens) the maximum force decreases to 165 N (notched specimens) due to the effect of the notch. The low mechanical flexural strength of PLA-CF samples can be attributed to the specific process parameters employed during the fabrication of these specimens. These parameters may lead to suboptimal adhesion between the filaments and the PLA matrix, as well as between the PLA matrix and the carbon fibers. This was also observed in the previous study in which the effect of carbon fiber reinforcement on tensile and fatigue properties was studied Vălean E. et al. (2023).