Issue 48

C. E. Cruz Gonzalez et alii, Frattura ed Integrità Strutturale, 48 (2019) 530-544; DOI: 10.3221/IGF-ESIS.48.51 542 Figure 11: SEM fractographs of fatigue fractured single-lap shear specimens with overlap length of 50 mm containing DC ‒ 80 adhesive at fillet zone: a) quasi-cleavage brittle failure, b) well-defined river patterns on facets, and c) facets at major magnification. Discussion The static tensile tests, for the bulk adhesives revealed that the adhesives ranged to a low strength one to a higher strength one. The MP55420 adhesive had lower strength and higher ductility, its elastic properties suggested that it yield at lower normal loads in comparison to the Betamate 120 and DC-80 adhesives. In addition, MP55420 adhesive could sustain higher strains in contrast to the other two adhesives. However, MP55420 had lower strength in comparison to the other two adhesives. Typically, in lap shear joints there are two components of stress: shear (  ) and normal (  y ) stresses. Since that MP55420 failed first since its lower strength, for that reason the strain in the adherents was lower in comparison to the other adhesives. In balanced joints (same thickness and material), the normal stress occurred because an eccentricity was generated during specimen loading. Additionally, failure predictions for balanced joints were proposed by Karachalios et al [20] suggesting that for the short overlaps, failure was dominated by global yielding in the adhesive layer. If the adhesive is ductile, then this method of prediction could probably be valid for longer overlaps too. However, if the adhesive is brittle, global yielding as a failure criterion would only be applicable for short overlaps. Similar trend was reported by Banea et al [27], for the case of multi-material joints (high strength steel and carbon fiber reinforced plastics-Aluminum). However, Shiu [28] results suggested that for dissimilar adherends, the maximum shear stress occurs at the free end of adhesive region near to the adherend with higher stiffness. A difference in displacements was noted, since that the brittle adhesives seem to sustain a higher displacement in comparison to ductile one. In that sense, Banea et al [27] reported for multi-material joints that geometrical balanced joints (approximately same thickness) promoted higher strength than that of the stiffness balanced joints (thickness of one adherend was approximately twice the other) because large rotation and displacements are promoted. For example, within