Laser-ultrasonics semi-analytical model for two-layered samples

The early detection of corrosion in aging structures is probably one of the most important challenges of the aeronautic maintenance services. Laser-ultrasonics offers interesting characteristics to become an industrial technique able to solve this problem. Neverless, to become quantitative, this non-destructive method requires a precise description of the laser-ultrasonic generation. This paper presents a new and original model which takes into account the layered structure which is generally encountered in aeronautic materials subjected to impacts, fatigue and corrosion. This model solved the Christoffel equations in an axisymmetrical configuration over an infinite plate of finite thickness presenting a cylindrical orthotropy. The sample is a flat plate made of two layers of different materials and the laser impinges the sample normally to the surface. The method of resolution used allows fast calculation and observation of the displacements over a long time period. This is very useful in NDT, especially in the case of thick samples. Validations were conducted by comparing the results calculated by this model to the ones obtained with a previous model and with experimental measurement using a Nd:YAG pump laser and an interferometric detection.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.