Defect identification in GRID-LOCK® joints

Damage detection in aircraft structures is conducted using a variety of nondestructive evaluation (NDE) techniques, including visual inspection, ultrasonic inspection, eddy current inspection, radiography and optical methods. These techniques are well established and have distinct advantages and limitations. Optical NDE methods show significant promise for variety of aerospace structural components, including inspection of bonded metallic GRID-LOCK® structures. In this paper, a full-field surface slope measurement technique (shearography) is utilized to confirm the effectiveness of optical NDE. Two bond defects (one disbond and one weak bond) are incorporated into a GRID-LOCK® test structure and internal pressurization results in qualitative indications of damage on the shearograms. Because accurate characterization of structural defects is critical for flight safety, a quantitative nondestructive evaluation (QNDE) method using a scanning optical probe is also explored. This QNDE method involves use of radial basis function networks (RBFNs) trained and validated using finite element analysis nodal displacements.