PSI - Issue 56

Cristina Vălean et al. / Procedia Structural Integrity 56 (2024) 97– 104 Author name / Structural Integrity Procedia 00 (2023) 000 – 000

100

4

2. Results and discussions 3.1 Tensile results

Figure 2 shows tensile stress-strain and energy-strain curves of 3D-printed samples. It is observed that the investigated samples fracture both at different levels of stresses and strains (Figure 2a). The curves do not show a settlement zone, the linear-elastic zone starting from the beginning of the stress-strain curves. However, the slope of stress-strain curves differs significantly with the material type, with the exception of PLA and PLA+CF samples where almost overlapping slopes are obtained. The most brittle behavior is presented by the PLA+CF samples, and the most ductile by the non-reinforced PLA samples. The other two categories of samples are found between the two behaviors, the first (PLA+GF) showing a quasi-brittle tendency to fracture, and the second (PLA+BP) a slightly ductile one. The PLA samples are the only ones that show a yield zone after reaching the maximum stress, the other samples fracture brittle immediately after the maximum point. Figure 2b shows major differences between the types of material tested in terms of the capacity of the samples to absorb energy until fracture. It can be seen that the samples show different variations of the energy with the strain, especially in the amplitude of the curves. The only similarity is found between the PLA and PLA+CF samples, which show more than half an overlap of the curves. However, the maximum level of fracture energy is in favor of PLA samples. Like the stress-strain curves, the samples from PLA+GF and PLA+BP show a lower energy-strain curve behavior than the other two materials (PLA and PLA+CF).

Fig. 2. Tensile stress-strain (a) and energy-strain (b) curves of printed samples

From both Figure 2a and Figure 3a, it can be easily seen that the PLA samples have the best strength properties. These are followed in order by the PLA+CF, PLA+GF and PLA+BP samples. The percentage difference between the first two materials (PLA and PLA+CF) is 21.6%, and between the extremes (PLA and PLA+BP) is 72.8%. The closest results are found between the PLA+GF and PLA+CF samples, obtaining differences of only 14.7%. Stress at break is slightly lower than tensile strength, the only exceptions being registered in the case of PLA and PLA+BP samples where differences of around 9%, respectively 25% are obtained. The other two materials show differences between the two strength properties (tensile strength and stress at break) of 3.3% (PLA+GF) and 1.6% (PLA+CF).