Increased ductility in high velocity electromagnetic ring expansion

Dynamic necking in materials with strain induced martensitic transformation

“…Therefore one should expect that, as the loading rate increases, the necking strains also do. This behavior finds good agreement with the experimental evidences reported for a number of metals and alloys in Grady and Benson (1983), Regazzoni and Montheillet (1985), Altynova et al (1996), and provides further validation to the role played by inertia in neck retardation predicted by stability analysis and finite element simulations, as discussed in forthcoming sections of the paper. Now, we pay attention to the differences between the η þ c À ɛ 1 curves corresponding to each material considered in this analysis.…”

Identification of the critical wavelength responsible for the fragmentation of ductile rings expanding at very high strain rates

“…Niordson (1965) developed a device for the rapid expansion of thin rings to determine materials properties at high strain rates. Compared to the uniaxial impact tensile test (K arman and Duwez, 1950;Clark and Wood, 1950) wave disturbances are eliminated due to the symmetry of the problem (Fyfe and Rajendran, 1980;Hu and Daehn, 1996;Altynova et al, 1996). The material stretches during loading until homogeneous deformation fails at large strain, leading to flow localization in the form of multiple necking and subsequent fragmentation.…”

“…From the pioneering work of Niordson (1965), the capability of the expanding rings method to determine fragmentation characteristics of ductile materials has been exploited by several laboratories (Grady and Brenson, 1983;Gourdin, 1989;Altynova et al, 1996;Hu and Daehn, 1996;Juanicotena and Llorca, 1997;Grady and Olsen, 2003;Ravi-Chandar, 2006, 2008;Janiszewski and Pichola, 2009;Janiszewski, 2012). Within the typical range of expansion velocities attained in this test -from 50 to 300 m/s -the experimental results show that the strain to failure of ductile materials is enhanced by the expansion velocity Altynova et al, 1996;Janiszewski, 2012). Moreover, the failure pattern is revealed velocity dependent too, leading to an increasing number of necks and fragments with testing velocity.…”

“…This leads to the selection of a dominant wavelength at each time of the deformation process which dictates the necking spacing. In recent works Mercier and Molinari (2004) and Mercier et al (2010) applied stability analyses to capture the number of fragments and necks observed experimentally (Altynova et al, 1996;Mercier et al, 2010) in the rapid expansion of rings and hemispheres. Within the higher loading velocities for which there were available data -$ 300 m=s -the perturbation analyses produced results in rather good agreement with the experimental evidence.…”

Temperature measurements on ES steel sheets subjected to perforation by hemispherical projectiles

“…Previous observations may be tied to the role that deformation rate has on the material behaviour [19,34]. Therefore, in order to provide a proper interpretation of the experimental temperature dependent measurements, it is necessary to estimate the strain rate level induced in the target material by the impact.…”