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Published April 25, 2010 | Published
Journal Article Open

Collapse of void arrays under stress wave loading


The interaction of an array of voids collapsing after passage of a stress wave is studied as a model problem relevant to porous materials, for example, to energy localization leading to hotspot formation in energetic materials. Dynamic experiments are designed to illuminate the hydrodynamic processes of collapsing void interactions for eventual input into device-scale initiation models. We examine a stress wave loading representative of accidental mechanical insult, for which the wave passage length scale is comparable with the void and inter-void length scales. A single void, two-void linear array, and a four-void staggered array are studied. Diagnostic techniques include high-speed imaging of cylindrical void collapse and the first particle image velocimetry measurements in the surrounding material. Voids exhibit an asymmetrical collapse process, with the formation of a high-speed internal jet. Volume and diameter versus time data for single void collapse under stress wave loading are compared with literature results for single voids under shock-wave loading. The internal volume history does not fall on a straight line and is in agreement with simulations, but in contrast to existing linear experimental data fits. The velocity field induced in the surrounding material is measured to quantify a region of influence at selected stages of single void collapse. In the case of multiple voids, the stress wave diffracts in response to the presence of the upstream void, affecting the loading condition on the downstream voids. Both collapse-inhibiting (shielding) and collapse-triggering effects are observed.

Additional Information

© 2010 Cambridge University Press. Received 6 April 2009; revised 17 November 2009; accepted 17 November 2009. Published online: 13 April 2010. The authors gratefully acknowledge Professor John Lambros for the generous loan of laboratory equipment and space which made this study possible. We thank Matthew Parker for his initial experiments, Professor Greg Elliott for valuable input in the PIV measurements, Professor Jonathan Freund, Dr Ratnesh Shukla, Professor Carlos Pantano and Professor Scott Stewart for useful discussions comparing experiments and simulations, and researchers in the DE-9 division at Los Alamos National Laboratories. We also thank Dr Eric Johnsen and Professor Tim Colonius for sharing their numerical data. This work was supported in part by the US Department of Energy through the University of California under subcontract B523819.

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