PSI - Issue 24

Michele Perrella et al. / Procedia Structural Integrity 24 (2019) 601–611 Author name / Structural Integrity Procedia 00 (2019) 000–000

603

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2. Materials and methods Tensile static and creep tests were performed on specimens made of a commercial epoxy resin (Sikadur 30 by Sika). Flat dogbone samples were prepared according to the ASTM D638 standard. The dimensions of the specimens are reported in Table. 1.

Table 1. Dimensions of dogbone specimens with rectangular cross section. Thickness [mm] Gage width [mm] Gage length [mm] Overall length [mm]

Radius of fillet [mm]

Width of grip section [mm]

5

15

70

160

12.5

35

A modular molding system was used for realizing the specimens (Fig. 1). Metallic components of the mold were adequately lubricated using a PTFE silicone based release spray. Tensile (PT) and creep (PC) specimens were cured at 30° C for 72 hours. Excess resin was removed by means of fine grit sandpaper. Cured samples were measured by a digital micrometer in order to evaluate their effective volume and theoretical mass. Thus, comparing the measured mass with the theoretical one, an evaluation of the air voids percentage was performed for each specimen (Table 2).

Table 2. Air voids evaluation in samples. Specimen

Theoretical mass [g]

Measured mass [g]

Voids [%]

PT1 PT2 PT3 PT4 PT5 PC1 PC2 PC3 PC4 PC5 PC6 PC7 PC8

28.59 28.36 28.48 28.69 28.71 28.39 28.29 28.80 28.63 28.84 28.53 28.68 28.74

27.39 27.56 27.91 27.62 27.75 27.51 26.40 27.09 28.03 27.57 27.78 27.96 28.07

4.20 2.82 2.00 3.73 3.34 3.10 6.68 5.94 2.10 4.40 2.63 2.51 2.33

The percentage of air voids in the laboratory specimens is between 2.0 and about 7.0%. This voids percentage seemed to have no effect on the average materiel properties measurements. Tensile tests were performed under displacement control, imposing a rate of 0.5 mm/min, by means of an MTS Insight 30 testing machine, equipped with an axial extensometer and a vision system. Strains were evaluated both by extensometer and DIC technique. The resulting mechanical properties of epoxy resin Sikadur 30 are reported in Table 3.

Table 3. Average mechanical properties of epoxy resin Sikadur 30. Tensile strength [MPa] Young Modulus [GPa] Poisson’s ratio [-] 28.84 10.95 0.27