Seminar: «A general overview on multiple necking and fragmentation problems in ductile solids subjected to high strain rates»
Understanding the fragmentation of ductile solids and structures subjected to high velocity impacts or blast loadings has importance in aerospace industry, military applications, civil engineering and geophysical applications. Meteoric cratering, explosive behaviour of projectiles or orbital debris impact on spacecraft structures are examples of situations in which to preserve the integrity of structures subjected to strain rates within the range >104 s-1 becomes crucial. From the early studies in this area –dating in the late 18th century– to the present time, an intense debate on the causes which reside behind the fragmentation of ductile solids has been carried out. In this seminar we will discuss canonical problems of rings (bars) and cylinders (plates) subjected to dynamic radial expansion. The principal advantage of the rapidly expanding ring and cylinder tests is that, due to the symmetry of the problems, the effects of wave propagation are nearly eliminated before flow localization occurs in the form of multiple necks which ultimately lead to the fragmentation of the sample. Within this framework, we have developed a combined analytical / numerical methodology based on linear stability analyses and finite element calculations that provides new insights into the critical factors that control the processes of multiple necking and fragmentation. Our results suggest that the combination of inertia and stress multiaxiality effects inside a necked section lead to the promotion of a finite number of wavelengths that, at sufficiently high strain rates, determine/control, at least up to some extent, the neck spacing and fragments size. These results argue for the inclusion of a deterministic component within the fragmentation mechanisms and thus complement/enrich the statistical fragmentation theory developed by Mott in the 40s.
José A. Rodríguez-Martínez
Dr. Rodríguez-Martínez holds a position of Associate Professor at the Department of Continuum Mechanics and Structural Analysis of the University Carlos III of Madrid. He has co-authored over 40 per-reviewed papers that have been published in the most renowned journals of Solid Mechanics: JMPS, IJP, IJSS, MOM, IJES… and participated in numerous international conferences and workshops where he has delivered various invited lectures. Dr. Rodríguez-Martínez has been chairman of 2 international symposiums/conferences devoted to the dynamic behaviour of solids and structures. He has been the principal investigator of several National and European projects among which we must highlight the project OUTCOME granted by the European Commission and funded with 2M€. The main topics of research of Dr. Rodríguez-Martínez are the constitutive modelling of metallic materials at high strain rates, the analysis of plastic instabilities in ductile solids subjected to dynamic loading and the large amplitude vibrations of nonlinear elastic structures.