In this paper, considering different parameters and various patch materials, the effect of disbond on the efficiency and durability of a composite patch repair is investigated in mode I and mixed-mode. One of the most important aspects of the composite patch repair is the bond strength. Repair patch disbond may occur at the patch edges or the crack site. At first, the effect of different parameters such as repair patch material and Young’s modulus and thickness of the adhesive on the efficiency and durability of the patch is investigated. Then, the effect of the disbond site on the stress intensity factor (patch efficiency) and adhesive stress (patch durability) is analyzed in both modes I and II. The results show that disbond at the crack site leads to a further reduction in patch efficiency compared to the patch edge disbond, but when separation occurs at the patch edge, the adhesive stress and the disbond growth rate are higher. Also, when 15% of the patch is separated in the crack site, for the longitudinal and transverse disbond modes, the mean KI is increased by 8 and 4%, respectively, compared to the state without disbond. Thus, the longitudinal disbond mode is more critical.
