Mechanical Properties of Polyurethane-Foam Impact Limiters

Rigid, closed-cell, polyurethane foams possess excellent energy-absorbing properties and are used as impact limiters for various packaging applications. They can absorb large quantities of energy as they transmit a stress equal to their crushing strength. Recently, their mechanical properties have come under increased scrutiny due to applications in nuclear-waste shipment packages. In such an application, the material is subjected to multiaxial state of stress. Strain-rate effects due to the dynamic nature of the loading in an hypothetical accident situation is also likely to be encountered. This paper describes a number of tests performed on polyurethane foams of various densities along several loading paths. These include uniaxial, hydrostatic and triaxial compression. Strain-rate effects were also studied under compressive loading. Since the material is significantly anisotropic, the experimental data are used to infer elasticity parameters and the shape of the anisotropic yield surface. Some strain-rate effects are also examined.