A pulsed thermoelastic analysis of photothermal surface displacements in layered materials

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Abstract
A pulsed photothermal method is proposed for the detection of delaminations in layered materials. The surface of the material is heated by a focused laser pulse to a few degrees above the ambient temperature, and the induced thermoelastic displacement is detected by a laser interferometer. Unbonded areas are characterized by their thermoelastic bending behavior, in addition to their thermal expansion, because of the induced temperature gradients both in the radial and axial directions. A theoretical analysis and an experimental investigation of this behavior are described in order to point out the most significant parameters. An application of the nondestructive inspection of Al-epoxy honeycomb panels is presented.