The purpose of the experiment discussed in the present paper is to study the deformation of a structure (here a copper
cylinder) induced by explosives. During its expansion, the (initially 3-mm thick) cylinder keeps on thinning until fracture
appears. Some tens of microseconds before failure, strain localization occurs, which induces mechanical necking. In
order to characterize the time for the onset of localization and the necking development, two diagnostic techniques are
designed to provide images: one based on X ray observations (for total thickness variations) and a second consisting in
25 stereoscopic acquisitions at about 400,000 frames per second. The latter enables us to estimate the three dimensional
shape changes of the cylinder with time.
The 3D reconstructions from the single X radiograph and stereoscopic films are described. Both techniques require
calibration as a first stage. For the X view, a self calibration is performed in order to convert X measurements (a
radiographic stack with 12 detection levels) to total dose in rad using a flashlight on a steel mock-up with calibrated
defects. For stereovision, a controlled calibration object is used. The second stage is the reconstruction. For X
radiographs, the results of a 2D hydrodynamic computation of the expansion at radiographic time coupled with an X
photon transport code provide us an estimate of the scatter field and allow us to perform attenuation evaluations of
copper alone, and to estimate its thickness. In stereovision, the reconstruction is achieved by an image correlation
software which exploits the random patterns marking on the object outer surface.
The purpose of this experiment is to study the behavior of expanding copper cylinder under explosive loading. The
apparatus is designed to submit the target to high strain, high stain rate in quasi-plane deformation constraints. Using
high-speed cinematography we evaluate the expansion characteristics and observe plastic instability and striction
phenomena. Stereoscopic observation is used to give us the possibility to reconstruct the 3D shape and to access to free
moving and strain fields. In order to measure the residual thickness and characterize striction patterns, we employ a flash
X-Ray imaging diagnostic. Experimental results are presented and compared with hydrocode calculations.