A critical piece of information to assess the deformation behavior of the sandwich structure is the stress/strain responses of the core materials in uniaxial compression and shear at various strain rates. The "Dynamic Failure of Materials" subgroup has investigated the compressive behavior of various metallic cellular core materials, such as open cell aluminum alloy foams, stainless steel textile cores, stainless steel tetrahedral trusses, and pyramidal trusses, at three different strain rate regimes. A sub-miniature loading frame for quasi-static loading, a Kolsky bar for strain rates up to 100-700 s^-1, and a light gas gun for high strain rate up to 10⁴ s^-1 were employed. For all the tests, real time imaging of the specimen allows the determination of failure and deformation modes through digital image correlation.

The group also developed a fluid-structure interaction (FSI) experiment to determine the behavior of sandwich panels subjected to underwater blast. The set-up is a highly instrumented scaled model designed to characterize the underwater blast impulsive loading of structures, and to identify their failure by means of real time measurements of deflection profiles, deformation histories, and fracture. In the FSI setup, a water chamber made of a steel tube is incorporated into a gas gun apparatus. A scaled structure is fixed at one end of the steel tube and a water piston seals the other end. A flyer plate impacts the water piston and produces an exponentially-decaying pressure history in lieu of explosive detonation. The pressure induced by the flyer plate propagates and imposes an impulse to the structure (panel specimen), which response elicits bubble formation and water cavitations.

FSI Setup

Shadow Moiré and High-Speed Photography

Personnel

• H.D. Espinosa (PI)
• Felix Latourte (Postdoc)
• David Grégoire (Postdoc)

Collaborators

• Prof. J. W. Hutchinson (Harvard University)
• Prof. T. Belytschko (Northwestern University)
• Prof. A. G. Evans (UCSB)
• Prof. H. N. G. Wadley (University of Virginia)
• Prof. F. W. Zok (UCSB)
• Prof. N. A. Fleck (Cambridge University)
• Prof. V. Deshpande (Cambridge University)

• L.F. Mori, D.T. Queheillalt, H.N.G. Wadley, H.D. Espinosa, "Deformation and Failure Modes of I-Core Sandwich Structures Subjected to Underwater Impulsive Loads," Experimental Mechanics, August, 2008.
• L.F. Mori, S. Lee, Z.Y. Xue, A. Vaziri, D.T. Queheillalt, K.P. Dharmasena, H.N.G. Wadley, J.W. Hutchinson, H.D. Espinosa, "Deformation and Fracture Modes of Sandwich Structures Subjected to Underwater Impulsive Loads," Journal of Mechanics of Materials and Structures, Vol. 2, No. 10, p. 1981-2006, 2007.
• H.D. Espinosa, S. Lee, and N. Moldovan. "A Novel Fluid Structure Interaction Experiment to Investigate Deformation of Structural Elements Subjected to Impulsive Loading." Experimental Mechanics, Vol. 46, No. 6, p. 805-824, 2006.
• S. Lee, F. Barthelat, J.W. Hutchinson, and H.D. Espinosa. "Dynamic failure of metallic pyramidal truss core materials - Experiments and modeling." International Journal of Plasticity, Vol. 22, No. 11, p. 2118-2145, 2006.
• S. Lee, F. Barthelat, N. Moldovan, H.D. Espinosa, and H.N.G. Wadley, "Deformation Rate Effects on Failure Modes of Open-Cell Al Foams and Textile Cellular Materials," International Journal of Solids and Structures, Vol. 43, No.1, p. 53-73, 2006.
• S. Lee, F. Barthelat, and H.D. Espinosa. "Strain Rate Effects in Metallic Cellular Materials," Proceedings of the 2003 SEM Annual Conference and Exposition on Experimental and Applied Mechanics, June 2-4, Charlotte, North Carolina, Session 37, Paper 188, 2003.