Design, Analysis, and SHM of Bonded Composite Repair and Substructure

The behavior of bonded patch repaired composite laminates loaded in uniaxial in-plane tension or compression is examined. A nonlinear stress analysis is performed on a double-lap joint to identify critical joint parameters and design an efficient external patch repair. It is found that oversized patches not only increase the structure's weight but also increase the stress concentrations in the repaired region, which can cause premature failure. Reducing the patch thickness near the edges of the overlap and increasing the local adhesive thickness decreases the stress concentration in both shear and peel stresses. A three-dimensional finite element analysis is then performed to determine the stresses in the optimum repaired configuration and used with a stress-based failure criterion to predict the ultimate failure load. Experimental measurements show that carefully designed bonded patch repairs can recover up to 80% of the undamaged laminate strength. The integrity of the bonded repair in terms of crack growth underneath the patch, which can arise from fatigue loading, impact, improper surface preparation, or environmental exposures, can be successfully monitored by inserting two smart layers (an embedded network of piezoelectric actuators/sensors) into the repair patch. Keywords: composites; bonded patch repairs; external patches; analysis; design; finite element analysis; damage diagnosis; crack growth detection; smart repair patch; piezoelectric actuators/sensors; Lamb waves

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