Experimental analysis and FEA modeling of sensor response in composites for structural health monitoring

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University of Alabama Libraries

Reliable damage detection is crucial for assessing the integrity of a structure. A structural health monitoring (SHM) system reduces the chances of fatal accidents by performing continuous monitoring of a structure. In this thesis, a well-established SHM technique, the Lamb wave-based approach, is used for damage detection in composite materials. Composite coupons are fabricated using a vacuum assisted resin transfer molding (VARTM) process. The damage to be detected is a pre-existing transverse crack in the coupon. Surface mounted piezoelectric actuators are used to generate Lamb waves in the composite coupon. Experiments were carried out on a composite coupon with a manufactured embedded crack-like defect in the middle four plies for two different orientations, [016]_T and [0_6/90_4/0_6]_T and a composite coupon with a surface crack with [016]_T orientation. The response from both undamaged and damaged (simulated crack) coupons is obtained using surface mounted piezoelectric sensors. A numerical study of the composite coupon with the simulated crack was conducted using finite element methods (FEM) and the model was verified using the experimental results. The FEM model is validated for crack modeling using static shear lag analysis applied at the crack as well as for dynamic loading. The active Lamb wave method, using the anti-symmetric mode, could detect a surface crack but was insensitive to the embedded crack. The effect of crack depth and crack location on damage detection efficiency was also studied. FEM models were also used for sensor placement optimization.

Electronic Thesis or Dissertation
Electrical engineering, Aerospace engineering