Guided Wave-Based Assessment of Bonded Composite Joints

We present a numerical and experimental framework for the inspection of double cantilever beam composite coupons that are fabricated by bonding two composite laminates. The method is based on a mode-matching procedure in which the experimental dispersion curves of guided wave modes supported by the coupons are compared with those computed by a numerical model in which the bond strength is progressively updated until a match is achieved. Specifically, guided waves are generated in the coupons in the 0–250 kHz range by direct contact excitation with a wedge beam transducer. Their corresponding velocity field is recorded using infrared laser vibrometry. From the measured velocity arrays, the dispersion curves of several higher order modes are extracted and subsequently used to match a semi-analytical finite element model of the coupons. The updating procedure is based on two steps. In the first step, the dispersion data of a coupon with a known pristine bond are used to determine the orthotropic elastic coefficients of the composite laminae. In the second step, these coefficients are fixed and only the bond equivalent Young’s modulus is updated by using the experimental dispersion curves. Analyses performed on coupons with three different level of seeded contamination indicate that our proposed method can quantify their reduction with good accuracy, which makes the method suitable for the efficient non-destructive inspection of structural components.