Over recent years the development of the use of composite materials has led to growing activity in the nondestructive testing field. Widely known techniques such as acoustic emission and ultra-sound have found a new field of application here and new techniques such as acousto-ultrasonics which have recently appeared have shown some interesting results in detecting defects in composite structures. However, acoustic emission for defect localisation and acousto-ultrasonics have sometimes shown a lack of reliability; very little is known about theoretical aspects of wave propagation in these materials, nor about the interaction existing in the material between acoustic waves and defects as the wave propagates. On the basis of some assumptions, theoretical calculations have been made on the prop agation of a steady wave in unidirectional composite plates and compared successfully to experimental results found in the literature.

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Monitoring cutting tools is a strong need in automated un-manned production systems. However tool breakage detection should be separated from tool wear monitoring. The works presented in this paper show that Acoustic Emission (AE) can be used for detecting tool breakage in most conditions and an industrial system is available. Tool wear monitoring is much more complex. As demonstrated by some results in turning and milling, there are a great number of influencing parameters. It appears that AE has also capabilities for tool wear monitoring but no industrial system is presently available. Expert system or intelligent system such as Neural Networks using multiparameter appear to be the best solution for the future.

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