THE ULTRASONIC NONDESTRUCTIVE EVALUATION OF MATERIALS AND ITS PROSPECTS

The evolution of making techniques, the increase in the quality standard of mechanical Parts, as well as the use of new materials (new alloys, composite materials, ceramics, ...) require more and more often performing non destructive evaluation in order to get more performing system as well as to lighten structures. These evaluations are used for either achievement of the processes, or initial as well as maintenance testing. They must adapt to new techniques and new problems and they are asked more and more quantitative results (quantitative evaluation of flaw nocivity and no more only detection) The methods appealing to ultrasonics, and above all ultrasonic echography which is the main topic tackled here, are among the most widely used testing methods behind X rays radiography. These methods exhibit several advantages upon this last one, involving inocuity for man (i.e. no particular precaution during utilization) and relatively low costs. Due to their nature, ultrasounds interact with matter much more strongly than X rays. This fact often leads the detected signal from ultrasounds to contain more informations than the signal coming from X rays Nevertheless in some cases the problem is to manage to separate or sort these informations in order to reach the desired information. An important evolution of ultrasonic methods has emphasized the last ten years, noticeable improvements have been brought to equipment, to Measuring methods, as well as to information processing. This permitted to improve testing resolution, to detect smaller defects, to better evaluate defects and to automate testings, the latter point in the aim to increase productivity and to set free from human errors. Some technical improvements are not yet made used in an industrial context but point out interesting prospects; some other are yet to be waited for, in particular thanks to the improvements in electronics, transducers and probes technology and to a more systematic use of data and information processing. Electronic systems and simple or array transducers will permit on the one hand to better control the shape of ultrasonic signals by mean of the adaptation of electrical excitation and on the other hand to control electronically the shape of ultrasound beam to increase resolution and to adapt it quickly to the tested piece and to the performed test. The signal and data processing, currently possible at a much wider scale thanks to the constant increase of mint and micro computing performances, will permit on one hand to reduce noise, specially structure noise, and on the other hand to much better exploit information in order to evaluate the defects more precisely All the improvements however will be fully exploited only by mean of developing models permitting the simulation of the responses of these new systems in versatile cases and so the interpretation of results. The modelling will concern in particular ultrasound propagation and acoustic beam forming in complex cases such as anisotropic or inhomogeneous materials or special geometrical configurations. ft will concern as well the diffraction diffusion upon spread on located defects.