PSI - Issue 12

Lorenzo Bergonzi et al. / Procedia Structural Integrity 12 (2018) 392–403 Lorenzo Bergonzi / Structural Integrity Procedia 00 (2018) 000 – 000

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Figure 11. Equivalent specimen mounted by mean of adapters on MTS machine.

Table 6. Specimens used in first (a) and second (b) test campaigns.

N° spec.

Material

Angle Geometry

N° spec. Material Angle Geometry

5 5 3 3

PVC PVC PVC PVC

0°

ASTM ASTM

ABS ABS ABS ABS

0°

ASTM ASTM

5 5 5 5 5 5

90°

90°

0°

Equivalent Equivalent

0°

Equivalent Equivalent

90°

90°

PLA-FDM PLA-FDM

0° 0°

ASTM

Equivalent

(a)

(b)

4.1. Results and discussion

Experimental results confirm what has been determined by mean of FEM models: the mechanical characteristics obtained using the standard and equivalent specimen can be considered compatible with each other. As an example, in Table 7 results obtained with ABS test and 0° orientation are reported for both geometries. In Appendix A. are reported the results of each campaign. From the data it is possible to note how results dispersion is similar for the two geometries, slightly lower for the equivalent specimen. Comparing the results of the two types of specimen, we note a good agreement, except in the case of crosshead displacement. As already inferred from the FEM models used to evaluate fixture seating (see paragraph 3.1), specimen sliding affects the results: in particular, to obtain the same stress state in the equivalent specimen, a greater crosshead displacement is necessary. From averaged stress-strain curves obtained with 0° ABS orientation, for both types of specimens, it is possible to see in Figure 12 (a) how the curves that refer to gage length deformation show the same behavior: for each averaging point standard deviation has been reported as well. However, let's consider the whole length of specimen free to deform (L0): in the ASTM case it corresponds to the entire portion of the specimen outside the grips, while in the case of the equivalent specimen L0 has been established to correspond to the initial distance between the holes centers present in the specimen heads. Obtaining the strain from