Issue 48

C. E. Cruz Gonzalez et alii, Frattura ed Integrità Strutturale, 48 (2019) 530-544; DOI: 10.3221/IGF-ESIS.48.51 543 Baneas’ work for the CFRP (Carbon Fiber Reinforced Polymer) 50.0 mm length overlap joint yield a displacement of 6.0 mm. However, with the same overlap length, both geometrically and stiffness balanced joints yielded a displacement of 5.0 mm. The same trend was noted for the 12.5 mm length overlap. In that sense and considering that the adherents exhibited linear elastic behavior, SLS specimens started their failure at the steel side by global yielding (12.7 mm overlap length) and since they had a similar failure mode, their displacement was similar, not so their strength since it would depend on the adhesive mechanical properties. However, a slightly difference was noted for long overlaps as 50 mm, it may be produced by a difference in the failure mode like the fatigue ( Betamate 120 and MP55420 adhesives) and brittle fracture for DC80 adhesive joints, because in the case of ductile adhesives like MP55420 and Betamate 120, the joint would fail with global yielding. Therefore, the best adhesive joint in terms of dynamic fatigue behavior was the single-lap shear specimens with Betamate 120 adhesive for overlap length of 50 mm under 70 % of applied maximum load, which exhibited fracture containing nearly flat surfaces containing well resolved striations at the highest fatigue loading (6 kN) at 10 6 cycles. It is important to note that fatigue in adhesive joints was present and not only quasi-static fracture can be expected, but cyclic damage can occur if dynamic loads were applied. Fracture surface of specimens failed in fatigue showed characteristics such as striations, river patterns in the crack propagation direction and particle displacements linked to a dynamic load response, confirming the probability to experience a fracture below the maximum static strength as reported [3, 4]. The fatigue behavior observed in these adhesive joints was consistent and the scatter was moderate. The fracture surfaces showed differences, however all the adhesives studied experience fatigue damage micro-features that must be considered in addition to the mechanical characteristics when used in industrial designs. C ONCLUSIONS he fatigue strength and fracture behavior for a dual phase steel-AA6061-T6 bonded joints with three different adhesives (DC-80, Betamate 120 and MP55420) was analyzed. Previously, single lap shear tests were carried out to determine maximum shear loads, for 50 mm overlap length results that were 2 to 3.5 times higher in comparison to the 12.7 mm overlap length specimens. The results for the strain measurement revealed that the higher strain-stress were developed in the 6061-T6 aluminum alloy adherend and in all cases they were lower than the adherends yield strength. Fatigue testing were carried out on five specimen sets at 30, 50 and 70 % of the maximum shear load, 0.1 of reversibility load ratio (R) and 30 Hz of frequency. After testing, Basquin and Wholer graphs were built for each adhesive at 12.7 and 50.0 mm of overlap length. The results suggested that at higher overlapping, the cyclic maximum load increased. Additionally, for 12.7 and 50.0 mm of overlapping, the maximum fatigue loading at 10 6 cycles for Betamate 120 adhesive was 1.8 and 6 kN respectively; followed by the DC80 adhesive with 1.75 and 4.8 kN; finally the MP55420 adhesive reached 1.3 and 2.9 kN. The post-fracture analysis revealed that MP55420 and Betamate 120 adhesives had a cohesive failure, while the DC-80 showed cohesive-adhesive fracture. Additionally, the scanning electron microscopy study on the spew fillet exhibited resolved striations and a network of small micro-dimples for the Betamate 120 and MP55420 adhesives. On the contrary, DC-80 adhesive showed notable facet fragile failure that was confirmed by the shape of stress-strain plot with straight line from the origin until fracture. R EFERENCES [1] Cruz Gonzalez, C., Gonzalez-Garcia, P., Santillan-Gutierrez, S., Taha-Tijerina, J. and R. Romero-Llerenas, (2017). Scanning electron microscopy, atomic force microscopy and optical profilometry applied to adhesive bonding technologies, Microscopy and imaging science: practical approaches to applied research and education, Badajoz, Mendes-Vilas. Formatex Research Center, pp. 464-473. [2] E. M. Petrie (2007). Handbook of Adhesives and Sealants., Chicago, Mc Graw-Hill,. [3] Jeandrau, J.-P., Peyrac, C., Lefebvre, F., Renard, J., Gantchenko, V., Patamaprohm, B. and Guinault, C. (2015). Fatigue behaviour of adhesive joints, 6th Fatigue Design conference, Fatigue Design 2015, Senlis , France. [4] Abdel Wahab, M., (2012). Fatigue in Adhesively Bonded Joints: A Review, International Scholarly Research Network, 12, pp. 1-25. T