PSI - Issue 39

Mario Álvarez-Blanco et al. / Procedia Structural Integrity 39 (2022) 379–386 Author name / Structural Integrity Procedia 00 (2021) 000–000

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The extensometer and DIC technique were applied for the uniaxial tensile test at 1 mm/min to obtain the mechanical properties of PLA more accurately. The test setup before and after the plasticity neck formation are shown in Fig. 6 (a) and (b), respectively. Note that the extensometer is removed once this neck appeared. The DIC’s region of interest is represented as a red oval in Fig. 6, out the plasticity neck. This technique tracks the deformation of this zone during whole test (surface previously speckled with black dots to allow DIC processing).

Fig. 7. Stress-strain relationships obtained by clip extensometer and DIC.

The stress-strain curve of this uniaxial test is represented in Fig. 7. It can be noted that the extensometer and DIC results correlate, validating this practice. The evolution of the strain field analysed by the DIC technique in the region of interest allows to represent the elastic recovery of the material outside the plasticity neck when the force decreases (see Figs. 6 and 7). The post-processing of these results determined the mechanical properties of PLA shown in Table 3.

Table 3. Mechanical properties of PLA. Property

Value

Unit GPa

Apparent Young’s modulus

3.66 0.38 53.0

Poisson’s ratio Tensile strength

-

MPa

3.2. Three-point bending test Once the mechanical characterization of PLA has been done, the three-point bending tests were carried out to analyse the fracture of the prismatic samples. Firstly, the results of the samples with no shell and the orientation where the crack propagates across the plane XY will be presented. The test velocity was the same for all of these tests, 1 mm/min. Force-displacement curves of each tested specimen with different infill densities are represented in Fig. 8. In addition, pictures before and after the bending are shown below these graphics.