A CONSTITUTIVE THEORY FOR RIGID POLYURETHANE FOAM

Rigid, closed-cell, polyurethane foam consists of interconnected polyu rethane plates that form cells. When this foam is compressed, it exhib its an initial elastic regime, which is followed by a plateau regime i n which the load required to compress the foam remains nearly constant . In the plateau regime, cell walls are damaged and large permanent vo lume changes are generated. As additional load is applied, cell walls are compressed against neighboring cell walls, and the stiffness of th e foam increases and approaches a value equal to that of solid polyure thane. When the foam is loaded in tension, the cell walls are damaged and the foam fractures. A constitutive theory for rigid polyurethane f oam has been developed. This theory is based on a decomposition of the foam in two parts: a skeleton and a nonlinear elastic continuum in pa rallel. The skeleton accounts for the foam behavior in the elastic and plateau regimes and is described using a coupled plasticity with cont inuum damage theory. The nonlinear elastic continuum accounts for the lock-up of the foam due to internal gas pressure and cell wall interac tions. This new constitutive theory has been implemented in both stati c and dynamic finite element codes. Numerical simulations performed us ing the new constitutive theory are presented.