Tracking the propagation of type B PLC bands

The Portevin-Le Châtelier (PLC) effect is a case of plastic instability that may occur during the deformation of ductile alloys. The phenomenon is usually investigated by means of tensile tests, in which, for certain ranges of temperature and strain rate, the plastic deformation of the material intermittently loses the uniformity and concentrates in narrow regions. These regions are referred to as PLC bands. In the recent years, great attention is given to the characteristics of these bands, which are often studied with optical methods. With the aim of improving the resolution of these observations, the employed camera should frame a small region of the material, but this leads to the drawback that the rest of the specimen is not considered. To overcome this limitation, the propagating nature of the bands can be profitable since one can predict the position and the time of the next event and then move the camera accordingly. In this paper an optical measuring system is presented, permitting the tracking and observation of a certain type of PLC bands. The system consists of two cameras, one for a global observation of the specimen and a real time detection of the emerging bands, and a second one for the detailed observation with a high resolution. This last camera is moved along the specimen in order to continuously image the propagation of the band.