Internal deformation and velocity field measurements by use of digital speckle radiography

Using X-rays as information carriers it is possible to obtain data about motion inside an object that is opaque to visible light. An image correlation algorithm can be applied to a set of two X-ray images taken sequentially during a process, where the interior of the object is in motion. A displacement field describing the projected intermediate motion is thus obtained to sub-pixel accuracy. If this image set is expanded to contain several pictures separated in time, together describing the whole process, the images can be sequentially correlated to obtain a dynamic displacement field. In this paper, dynamical displacement field measurements have been carried out on two different objects, the first being a silo, where the motion of the flowing material in the centre plane is investigated. In the second case, the motion in a layer of glue between two wooden plates is examined during a process where a shearing force acts on the system. The plane in which the measurements are carried out is defined by the use of a contrast agent, usually a tungsten powder seeding. The obtained displacement field, together with the known intermediate time interval between exposures, gives the velocity field in the seeded plane. The results show good agreement with the expected motion in the respective processes, but also provide evidence of behaviour that would be undetectable using other existing techniques. A third experiment has also been carried out on a material requiring no contrast enhancing media. These measurements were performed on a chicken thigh being deformed by an external force. The results will be discussed in relation to their reliability and applicability. Further, the direction of future research will be indicated.