PSI - Issue 64

Valentina Tomei et al. / Procedia Structural Integrity 64 (2024) 901–907 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

904

4

Table 1. Dimensions of the dog-bone samples.

b 1 (mm)

b 2 (mm)

h 1 (mm)

h 2 (mm)

t (mm)

r (mm)

Number of samples

H_dog-bone H_Ag_dog-bone V_dog-bone H_Fh_dog-bone H_Fd_dog-bone H_Fh(s)_dog-bone

105 105 105

80 80 80

20 20 20 25 25 25

10 10 10

4 4 4 5 5 5

20 20 20 25 25 25

5 5 5 3 3 2

187.5 187.5 187.5

100 100 100

12.5 12.5 12.5

3. Experimental Results 3.1. Effect of the printing path

The results for dog-bone specimens printed in different directions, namely H_dog-bone and V_dog-bone samples, are depicted in Figure 3 a in terms of normal stress-strain curves. The plots clearly illustrate the influence of the printing direction on both the strength and stiffness of the samples. Specifically, the V_dog-bone samples exhibited higher strength and pre-peak stiffness compared to the H_dog-bone samples. However, the post-peak behavior of the V_dog bone specimens showed a significantly lower ultimate strain (indicating low ductility) and significant softening. These observed differences emphasize the dependence of mechanical properties on the printing process. Figure 3 b presents pictures of the samples at the conclusion of the tests: they showed fractures perpendicular to the length of the elements in the inner part of the sample, for both Horizontal and Vertical cases. H_dog-bone

0 10 20 30 40 50

normal stress  [MPa]

V_dog-bone

0

0.025 0.05 0.075 0.1

strain  [-]

H_dog-bone

V_dog-bone

(a) (b) Figure 3. (a) normal stress-strain curves for H_dog-bone samples and V_dog-bone samples; (b) failure of for H_dog-bone samples and V_dog bone samples 3.2. Effect of the Accelerated Aging Test After the Accelerated Aging Test, noticeable changes in the original shape of the samples were observed (Figure 4b). Specifically, they exhibited a significant curvature perpendicular to their thickness, probably due to temperature variations induced cycles of thermal expansion. Furthermore, the implementation of the Accelerated Aging process affected the tensile response of the tested samples. Figure 4a compares the tensile behavior of the H_Ag_dog-bone samples with that of the H_dog-bone samples (the latter printed using the same process but not subjected to Accelerated Aging). It is evident that the Accelerated Aging process resulted in an increase in both stiffness and strength during the pre-peak stage. Conversely, the post peak behavior exhibited a reduction in ultimate strain and gradual strength degradation (softening), particularly noticeable in four of the tested samples.