Energy dissipation of a system with foam to metal interfaces

Abstract

The physical mechanisms of energy dissipation in foam to metal interfaces must be understood in order to develop predictive models of systems with foam packaging common to many aerospace and aeronautical applications. Experimental data was obtained from hardware termed “Ministack”, which has large, unbonded interfaces held under compressive preload. This setup has a solid aluminum mass placed into two foam cups which are then inserted into an aluminum can and fastened with a known preload. Ministack was tested on a shaker using upward sine sweep base acceleration excitations to estimate the linearized natural frequency and energy dissipation of the first axial mode. The experimental system was disassembled and reassembled before each series of tests in order to observe the effects of the assembly to assembly variability on the dynamics. There are some important findings in the measured data: there is significant assembly to assembly variability, the order in which the sine sweeps are performed influence the dynamic response, and the system exhibits nontrivial damping and stiffness nonlinearities that must be accounted for in modeling efforts. A Craig-Bampton model connected with a four-parameter Iwan element and piecewise linear springs is developed and calibrated using test data with the intention of capturing the nonlinear energy dissipation and loss of stiffness observed in experiment.