Location

La Jolla, CA

Start Date

1-1-1998 12:00 AM

Description

The new structures developed in industry are more and more complex (special coatings, smart materials, etc⋯) and often need to be investigated by non-contact methods. Laser Based Ultrasound technique (LBU) offers for several years an efficient alternative to conventional ultrasound (piezoelectric transducers), especially for the nondestructive evaluation (NDE) and the material characterization [1]. Many structures encountered in aeronautics such as painted metals or composites are made of two layers of completely different materials and the control of such specimens may be intricate. Thus, it is useful to develop a theoretical model able to predict the laser induced acoustic response of a two-layered material [2,3]. So, this paper presents a new and original model adapted to that kind of structures which are homogeneous and transversely isotropic. The cylindrical symmetry of the model allows fast calculation and observation of the displacements over a long duration. The simulations are compared to the experimental results performed with a Nd: Yag laser for the generation and a heterodyne interferometer. Moreover, the NonDestructive Testing (NDT) of metallic structures is difficult because of the very large optical reflection coefficient of the laser light on the surface. A paint covering the surface of the metal allows to improve the ultrasound generation around the normal incidence and then improves the control of the material. The two-layer model is used to characterize this paint and to optimize its thickness in order to ensure the way of testing such as the detection of effects due to corrosion.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

17A

Chapter

Chapter 2: Emerging Technologies

Section

Laser/Optical Ultrasonics

Pages

651-658

DOI

10.1007/978-1-4615-5339-7_84

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Laser Ultrasonics NDE of Two-Layered Samples

La Jolla, CA

The new structures developed in industry are more and more complex (special coatings, smart materials, etc⋯) and often need to be investigated by non-contact methods. Laser Based Ultrasound technique (LBU) offers for several years an efficient alternative to conventional ultrasound (piezoelectric transducers), especially for the nondestructive evaluation (NDE) and the material characterization [1]. Many structures encountered in aeronautics such as painted metals or composites are made of two layers of completely different materials and the control of such specimens may be intricate. Thus, it is useful to develop a theoretical model able to predict the laser induced acoustic response of a two-layered material [2,3]. So, this paper presents a new and original model adapted to that kind of structures which are homogeneous and transversely isotropic. The cylindrical symmetry of the model allows fast calculation and observation of the displacements over a long duration. The simulations are compared to the experimental results performed with a Nd: Yag laser for the generation and a heterodyne interferometer. Moreover, the NonDestructive Testing (NDT) of metallic structures is difficult because of the very large optical reflection coefficient of the laser light on the surface. A paint covering the surface of the metal allows to improve the ultrasound generation around the normal incidence and then improves the control of the material. The two-layer model is used to characterize this paint and to optimize its thickness in order to ensure the way of testing such as the detection of effects due to corrosion.