Issue 48

C. E. Cruz Gonzalez et alii, Frattura ed Integrità Strutturale, 48 (2019) 530-544; DOI: 10.3221/IGF-ESIS.48.51 537 mm overlapping. The S-N curves for bonding with MM55420 for both 12.7 and 50 mm overlapping are also shown in Fig. 7. As usual, the higher overlapping increases the cyclic maximum load achieved at 10 6 cycles. The maximum fatigue loading for DC80 adhesive at 10 6 cycles is 1.75 kN for overlapping 12.7 mm and 4.8 kN for overlapping 50 mm. For Betamate 120 adhesive maximum fatigue loading at 10 6 cycles is 1.8 kN for 12.7 and of overlapping and 6 kN for 50 mm of overlapping. Finally, for MP55420 the maximum fatigue loading at 10 6 cycles is 1.3 kN for an overlapping of 12.7 mm and 2.9 kN for 50 mm of overlapping. In general terms for an overlapping of 12.7 mm the fatigue behavior is better when the joint is adhered with Betamate 120 but slightly higher than DC 80. When the joint is adhered with an overlapping of 50 mm, Betamate exhibits the best dynamic behavior. Fatigue results were obtained by using 15 specimens per overlapping and per adhesive. The data were statistically treated to get fatigue models such as Whöler or Basquin by using regressions. Tab. 3 shows the coefficients for such models for each adhesive. Overlap (mm) Load (N) Strain×10 -6 % of Maximum Load Overlap (mm) Load (N) Strain×10 -6 % of Maximum Load 12.7 DC-80 500 320 8.36 50.0 DC-80 1000 120 5.58 1000 579 16.72 3000 340 16.75 2000 1000 33.44 6000 1000 33.50 3000 1280 50.17 9000 2108 50.25 4000 1780 66.89 12000 2380 67.00 5000 2160 83.61 16000 2590 89.33 Betamate 120 500 588 8.71 Betamate 120 1000 588 4.77 1000 780 17.41 4000 1000 19.07 2000 1250 34.83 8000 1480 38.13 3000 1377 52.24 12000 2000 57.20 4000 1800 69.65 16000 2800 76.26 5000 2345 87.06 19000 3380 90.56 MP55420 500 200 11.71 MP5542 0 500 320 5.41 1000 540 23.42 1000 654 10.81 2000 800 46.85 2000 1000 21.62 3000 1050 70.27 6000 1680 64.86 4000 1280 93.70 8000 1560 86.49 Table 2: Strain gauge measurements results at different load for the three adhesives with 12.7 and 50.0 mm overlap length. On the other hand, it is important to compare the maximum load achieved under dynamic loading versus quasi-static loading. For DC-80 the load resisted in fatigue (10 6 cycles) represents 27 % of the maximum static loading for both 12.7 and 50 mm overlapping. For Betamate 120 the maximum loading resisting fatigue is 28 % of the maximum static loading reached. Finally, for MP55420, exhibiting the worst static and dynamic maximum load resistance, the fatigue load achieved is 25% of the maximum static strength for 12.7 mm and 31% for 50 mm overlapping. According to the results, of course a bigger overlapping is better, but Betamate 120 exhibits the best behavior when solicited statically and dynamically too. Post fracture analysis The visual inspection results are depicted in Figs. 8a), 8b) and 8c). The DC-80 adhesive test specimen revealed cohesive- adhesive failure where 60 % of the adhesive remained on the aluminum side (see Fig. 8a). On the contrary, Betamate 120