PSI - Issue 25

F.J.C.F.B. Loureiro et al. / Procedia Structural Integrity 25 (2020) 63–70 Loureiro et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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tensile tests permitted to obtain the Young’s modulus ( E ), tensile yield stress (  y ), tensile strength (  f ) and tensile failure strain (  f ) of each adhesive. Shear characterization of the adhesives relied on performing TAST experiments, giving the shear modulus ( G ), shear yield stress (  y ), shear strength (  f ) and shear failure strain (  f ) of each adhesive. The DCB test was selected to obtain J IC and the ENF test was used for J IIC . The mechanical properties and curing conditions of the Araldite ® 2015 is summarized in Table 1.

Table 1 – Properties of the adhesive Araldite ® 2015 (Campilho et al. 2011, Campilho et al. 2013).

Property

2015

Young’s modulus, E [GPa]

1.85±0.21

Poisson’s ratio, 

0.33 a

12.63±0.61 21.63±1.61 4.77±0.15 14.6±1.3 17.9±1.8 43.9±3.4 0.43±0.02 4.70±0.34 0.70

Tensile yield stress,  y [MPa] Tensile failure strength,  f [MPa] Tensile failure strain,  f [%] Shear modulus, G [GPa] Shear yield stress,  y [MPa] Shear failure strength,  f [MPa] Shear failure strain,  f [%]

J IC [N/mm] J IIC [N/mm]

a manufacturer’s data

2.2. SLB geometry, fabrication and testing For the mixed- mode analysis undertaken in this work, the selected specimen’s geometry for the testing was the SLB (Fig. 1). The SLB specimens were manufactured according to the following dimensions: mid-length between supports L =100 mm, initial crack length a 0 ≈60 mm, width B =25 mm, h =3 mm and t A =1 mm.

Fig. 1. Geometry and dimensions of the SLB specimens.

Seven specimens were manufactured, from 3 composite plates. Each plate was constructed from 0.125 mm thick pre preg roll layers, stacked until h =3 mm was reached. Subsequently, the composite plates were cured in a hot-plates press with the thermal cycle recommended by the manufacturer. Next, the adherends were cut into specimens and surface prepared through abrasive techniques, and cleaned with acetone. Spacers were manufactured to guarantee the t A design value of 1 mm. Moreover, the front spacers were also responsible to create the pre-crack. These spacers were assembled from a blade with 0.10 mm thickness in-between two dummy sheets. Bonding was accomplished in a dedicated bonding platform, which contained precisely the adherends locations. After curing the adhesive at room temperature for one week, the adhesive excess was removed manually and then a grindstone was used to shape the adhesive in the edges of the test specimen. The total specimens’ thickness was measured at this stage with a digital micrometre and, by subtracting the individual h values measured before bonding for each adherend, it was found that 1.03≤ t A ≤1.11 mm. Before initiating the experimental tests, the final preparation was to glue a paper scale into the specimens, to record a propagation during the course of the test. For the experimental testing program, an electro mechanic testing machine Shimadzu AG-X 100 (Shimadzu, Kyoto, Japan) with a loading cell of 100 kN was used.