Issue 48

J.P.S.M.B. Ribeiro et alii, Frattura ed Integrità Strutturale, 48 (2019) 332-347; DOI: 10.3221/IGF-ESIS.48.32 337 existence of cross-section balanced adherends. This occurs if the middle adherend has twice h than the outer adherends [29]. However, this was a testing choice that does not compromise the fracture envelopes’ validation purpose that this work aims to. Six specimens for each condition were tested for the fracture tests, while five specimens were evaluated for the lap geometries. Figure 3: Geometry and dimensions of the single (a) and double-lap joint (b) . Figure 4: Test setup for the SLB specimens. For both CFRP and aluminium adherends, the surface preparation prior to bonding was similar: the bonding surfaces were manually abraded using a fine sandpaper to completely remove the shiny surface or aluminium oxide layer, respectively, followed by cleaning and degreasing with acetone. For all tests, and to promote a reliable and dimensionally accurate bonding, the joined parts were placed in a steel mould during the curing process. To guarantee a correct value of t A , for the DCB, ENF and SLB specimens, calibrated metallic spacers were placed between the superior and inferior adherends’. Before their placement, the spacers were coated with demoulding agent to simplify their extraction after curing. These specimens shared the same pre-crack induction method, which consisted in the placement of spacers, in which the crack-tip spacer had a centred sharp razor blade. Nonetheless, to avoid any blunting effects, in each specimen the crack was manually propagated for a length between 1 and 3 mm, and only after the a 0 measurement took place. In the case of the SLJ and DLJ, t A was achieved using metallic blocks that were placed in the mould. Regardless the joint type, after pouring the adhesive in one of the adherends, the two adherends were joined and pressured until there was contact with the spacers. This process had to be repeated one more time for the DLJ. Then, the curing process initiated. This took place over one week for all joints. After curing, the spacers or blocks were removed, and the excess adhesive was removed using milling techniques. To allow the measurement of a , one side of the DCB, ENF and SLB joints was painted with a brittle white paint and a numbered scale was glued on that side to allow tracking crack propagation. All specimens were tested in an electro-mechanical testing machine Shimadzu AG-X 100 equipped with a 100 kN load cell. The fracture tests were documented by taking pictures with 5 s intervals, using a digital 18 MPixel camera with no zoom and placed at a focal distance of 100 mm. The DCB, SLJ (a) (b)