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The aim of this communication is to compare different ultrasonic phased array imaging methods applied on carbon fiber composite structures. First, real time phased array methods as for example focused line scan, single plane wave imaging, dynamic depth focusing… were applied to the inspection of a composite plate and confronted in terms of sensitivity of detection, number of processed signals, acquisition time, total time of inspection and data processing. It was then possible to establish criteria, according to the defect sought and operating conditions, in order to favor the use of a specific imaging method over another by identifying the performances and limitations of each one of them. In case of thicker or more heterogeneous composite plates, it seemed useful to develop an ultrasonic imaging method taking into account the anisotropy and the attenuation of the composite material. Thus the Total Focusing Method and Plane Wave Imaging algorithms were modified by considering the effects of the composite material anisotropy and attenuation on the ultrasonic wave propagation, and thus on the ultrasonic imaging. These modified TFM and PWI algorithms were firstly validated on simulated data and then applied to image a 30-mm-thick carbon fiber composite plate with artificial defects. The performances and the limitations of these modified TFM and PWI algorithms are finally discussed in terms of reliability, resolution, robustness in function of the material properties characterization… and compared to conventional phased array imaging methods (Focused line scan…).

Sparse representation of signals has been subject of many advances during recent years especially in the field of applied physics. The problem is to search for the most compact representation of signals in terms of linear combinations of elementary waveforms in an over-complete dictionary. The underlying hypothesis in most of sparse representation problems is that if one can associate a sparse representation to a given signal, its structure reveals information directly linked to the physical nature of the addressed problem. From this point of view it has been shown that sparse representation problems have closed connexions with inverse problems and source separation problems. In this contribution, an application of sparse representation techniques to identify damage mechanisms from Acoustic Emission (AE) signals is presented. The sparse representation is which is based on the continues wavelet transform. All experiments concern investigations realized on glass fibre reinforced polymer composites (GFRP).

The present paper deals with the numerical study of scattering behavior of incident SH0 guided wave mode towards a point impacted damaged zone in a thin plate. A 3D finite element frequency domain model is used to simulate the scattering of an incident guided wave mode at a frequency below A1 cut-off and wavelength comparable to the size of the damaged zone. The later is modeled as a conical shaped geometry with decayed material stiffness properties. The directivity of the scattered fields for the SH0 Lamb wave mode predicted numerically for different depths and base diameters of damaged zone are shown graphically. The scattering results may provide some information related to the extent and depth of the conical damage zone caused due to a point impact inside the composite plate using guided wave sensors.

Abstract:
By their efficiency and non destructive character, ultrasonic methods have taken an important place in the mechanical characterisation field. The knowledge of the elastic constants is of great importance for the ultrasonic stress state determination. The second order elastic constants are determined with the linear elastic theory while the third order constants require the use of the acoustoelastic theory. As this latter describes the influence of the applied stress on ultrasonic waves velocities, the used specimen must be stressed.
For this, an experimental set which consists of a water-filled tank associated with a tensile machine has been conceived in order to characterise an isotropic material ( A37 Steel ). Two unfocused longitudinal-wave transducers were used in a through mode at 5 MHz operating frequency. The receiving transducer diameter, is big enough to inform us clearly about the ultrasonic waves attenuation, and hence the influence of the material texture when the incidence angle is changed. Agreement of the experiment with the acoustoelasticity predictions has been found.
1. Introduction:
In the quality testing, the detection