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Shock Propagation in Aluminum Open-Cell Foam Under Impact

Andrew Barnes (), Krishnaswamy Ravi-Chandar (Univeristy of Texas at Austin), Stelios Kyriakides (University of Texas at Austin)

Instability in Solids and Structures

Mon 2:40 - 4:00

Barus-Holley 190

Lightweight cellular materials such as foams exhibit excellent energy absorption characteristics imparted by a low compressive stress plateau that can extend to average strains as high as 60%. In the Al-alloy open-cell foam of interest here, this stress plateau starts with the initiation of localized buckling and crushing of a band of cells. The crushed zone gradually spreads throughout the material while the stress remains relatively unchanged. When all the material is so affected, further deformation, or densification, occurs uniformly with a rising stress. Under impact, this type of behavior, in particular the convex densification regime makes the foam prone to developing shocks. This paper reports results from a series of impact tests on Al-6101-T6 open-cell foam that enable direct measurement of the shock characteristics. Both direct and stationary impact tests on cylindrical foam specimen are performed at impacts speeds in the range of 20-160 m/s using a gas gun. The stress in either the distal or proximal end is recorded using a pressure bar while the deformation of the foam is monitored with high-speed photography. Specimens impacted at velocities above approximately 45 m/s were found to develop nearly planar shocks that propagate at well-defined velocities crushing the specimen. Synchronization of the data acquisition with the digital video recording enables measurement of the relevant shock parameters and the establishment of shock Hugoniots for this material without resorting to a constitutive model. The paper will present details of this shock induced crushing behavior and contrast it with quasi-static crushing.