Experimental study of dynamic periodic processes

In the field of experimental mechanics, X-ray computed tomography is a well-established method for non-destructive testing of a wide range of objects. It is quite common to employ digital volumetric correlation to evaluate the deformation of bodies by comparing their initial and current state. Time-dependent tomography, which works with tomographic data sets covering the entire process under investigation, has also been on the rise in recent years. However, we must keep in mind that a single tomographic data set represents thousands of X-ray images, making such measurements quite demanding in terms of instrumentation and subsequent data processing. For events taking minutes or longer, conventional laboratory X-ray computed tomography scanner can be used, while for faster events a very intense X-ray source is usually required, which typically leads to the use of a synchrotron. From a particular speed, even synchrotron sources may no more be enough. An exception is tomographic tracking of purely periodic events, such as the oscillation of a beam at its natural frequency. As will be shown, despite the relatively high velocity of motion, a good reconstruction can be achieved even with a conventional X-ray source. Thus, we obtain information not only about the intrinsic shape of a particular beam, but also about its internal structure. It will be possible, for example, to investigate how any local imperfections may affect the shape of the vibration, assuming that some defects may not be apparent under static loading. Specifically, this paper will show the results of a tomographic reconstruction of a slender beam oscillating at 4.15 Hz.