Damages such as a crackotch and delamination in aerospace, mechanical and offshore structures due to fatigue, corrosion or ac- cidence are inevitable during services. Such damages will grow at an alarming rate due to the stress/strain concentration around the dam- age locations and cause possible failures of structures [1-4]. Thus, the structural repair has become an important and practical research topic since the last several decades and attracted much attention in academy and industry. A key objective in a repair design is to lessen the stress/ strain concentration at the damaged part of a structure, e.g. the tips of the notch/crack and delamination, to reinforce the damaged structure. Structural repair with bonded materials has been the most traditionally used technology to increase the service life of damaged structures [5]. The traditional method was to meld or mount additional high stiffness patches onto the damaged area to improve the mechanical function of a damaged structure. In 2002, a patch repair of cracks in the longeron of an F16 aircraft was reported by Hart and Boogers [6]. The main cause for cracking was the occurrence of assembly stresses due to an improp- erly repaired access panel 2408. Since a conventional mechanical repair could not be done, a cost effective bonded patch repair was evaluated and applied to the cracked longeron. Titanium 6A14 V sheet was used for repair of the 2 mm thick 2024-T62 aluminium longeron flange. A symmetric bonded repair was done with a room temperature curing acrylate based adhesive. The feasibility of the proposed repair geom- etry was determined by periodic inspections to check on de-bonding and fatigue crack propagation. However, it was noted that the repair process was designed for an air craft with a limited service life (400 flight hours). A major problem is that additional stress concentration may possibly be induced at the bonding area [7]. Moreover, the repair method using normal additional patch cannot adjust itself to newly in- duced damage due to unexpected external loadings.
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