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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The sliding of the equivalent specimen in the fixtures seats is evident (see Figure 12 b): the problem is common to the standard specimens, albeit to a lesser extent. In the case of fixtures for the equivalent specimen, however, it is possible to estimate a corrective factor that makes it possible to obtain gage length deformation starting from crosshead displacement. The geometry of the specimen shoulders remains constant and it is believed that the strain deviation can vary according to the stiffness of the material and/or the coefficient of friction between specimen and fixture. The same activity is more difficult to achieve with the traditional fixtures because the fixture-specimen interaction is difficult to model due to its strong dependence on the clamping force, which is not always the same for different materials. A numerical model to accurately analyze the specimen-fixture interaction and the sensitivity study to the variation of parameters such as elastic modulus of the tested material, friction coefficient between specimen and fixture seat, tolerance in the seat, is under development and will be object of future works.

Appendix A. Experimental results

Table 8. Mechanical properties obtained during experimental campaigns: (a) ABS at 90° orientation, (b) FDM printed PLA at 0° orientation, (c) PVC* at 0° orientation, (d) PVC* at 90° orientation ABS 90° PLA 0°

F m

R m

E

A S %

s M

F m

R m

E

A S %

s M

ASTM D638

ASTM D638

[N]

[MPa] [MPa] [mm/mm] [mm]

[N]

[MPa] [MPa] [mm/mm] [mm]

Average value Standard dev.

1143.42 28.64 1778.96

1.94

2.02 0.03

Average value Standard dev.

1957.61 49.63 2743.71

2.18

2.48 0.05

11.73

0.29

6.45

0.0002

32.57

0.83

54.58

0.0287

F m

R m

E

A m %

s m

F m

R m

E

A m %

s m

Equivalent

Equivalent

[N]

[MPa] [MPa] [mm/mm] [mm]

[N]

[MPa] [MPa] [mm/mm] [mm]

Average value Standard dev.

1162.93 28.52 1818.34

1.92

3.68 0.07

Average value Standard dev.

1832.23 49.62 2971.07

2.04

4.92 0.33

8.90

0.22

28.16

0.0003

48.63

1.32

22.05

0.0013

% Variation

1.7%

0.4%

2.2%

0.9%

82.5%

% Variation

6.4%

0.0%

8.3%

6.8%

99.0%

(a)

(b)

PVC 0°

PVC 90°

F m

R m

E

A S %

s M

F m

R m

E

A S %

s M

ASTM D638

ASTM D638

[N]

[MPa] [MPa] [mm/mm] [mm]

[N]

[MPa] [MPa] [mm/mm] [mm]

Average value Standard dev.

2001.42 52.51 2689.54

2.55

2.73 0.05

Average value Standard dev.

1561.02 40.79 2411.69

1.96

2.09 0.05

10.83

0.28

16.35

0.0006

65.09

1.70

71.62

0.0006

F m

R m

E

A m %

s m

F m

R m

E

A m %

s m

Equivalent

Equivalent

[N]

[MPa] [MPa] [mm/mm] [mm]

[N]

[MPa] [MPa] [mm/mm] [mm]

Average value Standard dev.

1992.65 51.82 2712.22

2.53

3.43 0.01

Average value Standard dev.

1601.00 42.64 2560.21

1.95

2.75 0.03

8.19

0.21

26.73

0.0005

3.17

0.08

19.59

0.0009

% Variation

0.4%

1.3%

0.8%

0.9%

25.8%

% Variation

2.6%

4.5%

6.2%

0.7%

32.0%

(c)

(d)