Abstract: The device concerns a method for detecting the position of at least one point of the crack front within a part (4) subjected to fatique stresses or to a ductile rupture. An ultrasonic beam is used focused in the plane P of the crack growth; the axis of this beam forms an angle comprised between 50.degree. and 80.degree. with P. The beam is displaced until the echo passes through a maximum, in which case the focusing is situated at the tip of the crack in the plane of displacement. The invention also concerns a device for the implementation of the method.

Abstract: The fault-containing area to be inspected is insonified by means of an ultrasonic transducer with a space-limited beam which is displaced in stepwise manner, the signals coming from the successively insonified areas being detected by several receivers, the phases and amplitudes of the signals being determined and the reconstitution of the area to be inspected performed. There is a main image of the fault and also parasitic images thereof. The number of receivers is chosen in such a way that the distance between the parasitic images and the main image exceeds the width of the area insonified by the transmitter and the reconstitution is only carried out in the insonified areas having given rise to a signal in order to eliminate the parasitic images. Application to the non-destructive inspection of mechanical parts.