Abstract
It is important to protect assets located within cavities vulnerable to incident shock waves generated by explosions. The aim of the present work is to explore if closed cell aluminum foams can mediate and attenuate incident shocks experienced by cavities. A small cavity of 9 mm diameter and 2 mm length was created within the steel end-wall of a shock tube and exposed to shocks, directly or after isolating by aluminum foam liners. Shock waves with incident pressure of 9–10 bar travelling at a velocity of 1000–1050 m/s were generated in the shock tube. Compared to the no-foam condition, the pressure induced in the cavity was either equal or lower, depending on whether the foam density was low (0.28 g/cc) or high (0.31 to 0.49 g/cc), respectively. Moreover, the rate of pressure rise, which was very high without and with the low density foam barrier, reduced substantially with increasing foam density. Foams deformed plastically under shock loading, with the extent of deformation decreasing with increasing foam density. Some interesting responses such as perforation of cell walls in the front side and densification in the far side of the foam were observed by a combination of scanning electron microscopy and X-ray microscopy. The present work conclusively shows that shocks in cavities within rigid walls can be attenuated by using foam liners of sufficiently high densities, which resist densification and extrusion into the cavities. Even such relatively high-density foams would be much lighter than fully dense materials capable of protecting cavities from shocks.
Highlights
Closed cell aluminum foams are known to absorb a significant amount of energy during quasi-static compression by undergoing a large amount of plastic deformation at low transmitted stress [1].Plastic deformation occurs in bands of cells by cell wall bending and buckling, causing cell collapse and foam densification [2]
Mazor et al [3] and Ben-Dor et al [4] carried out mathematical analyses and limited experiments of head-on collisions of planar shock waves of Mach 1.08–1.41 in a rectangular shock tube with ultra-low density, (0.03 g/cc) polyurethane foams placed against the end-wall of a
The pressure generated by the wave after transmission through the foam, reflection from the end-wall, transmission back through the foam, and re-emergence from the front face was found to be more than the reflected pressure off the end-wall of the empty shock tube, which was termed as “shock amplification”
Summary
Closed cell aluminum foams are known to absorb a significant amount of energy during quasi-static compression by undergoing a large amount of plastic deformation at low transmitted stress [1].Plastic deformation occurs in bands of cells by cell wall bending and buckling, causing cell collapse and foam densification [2]. Mazor et al [3] and Ben-Dor et al [4] carried out mathematical analyses and limited experiments of head-on collisions of planar shock waves of Mach 1.08–1.41 in a rectangular shock tube with ultra-low density, (0.03 g/cc) polyurethane foams placed against the end-wall of a. They found that the reflected pressure from the front face of the foam was less than that from the end-wall of the empty shock tube, which was termed as “shock attenuation”. The pressure generated by the wave after transmission through the foam, reflection from the end-wall, transmission back through the foam, and re-emergence from the front face was found to be more than the reflected pressure off the end-wall of the empty shock tube, which was termed as “shock amplification”. Shock amplification occurs while the foam deformation is restricted to the plateau domain, i.e., the region in the compressive stress–strain relationship of foams in which large strains occur at low and near-constant stress, since under such conditions compression waves inside the foam can transform into shock waves
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