To design an optimized sandwich structure for energy absorption during impact loading, at least four different factors are important: 1) the component’s total weight, 2) the force transmitted to the underlying structure, 3) the component’s total energy absorption, and 4) the out-of-plane displacement of the back skin. Such sandwich structures could normally consist of two thin and stiff skins separated by a thicker foam core, and they are traditionally used as structural elements with high specific bending stiffness and strength. However, in many situations, such as in a car accident, one can sacrifice some of the structural integrity of the component for increased energy absorption. One option is then to remove the front skin to better activate the energy-absorbing foam core, while at the same time reduce the total weight of the component significantly.
This study is part of an ongoing research program  where low-velocity impact tests on sandwich structures consisting of steel skins and various low-density polymeric foams as core have been conducted in a drop tower. In the first test series, the foam core was covered by the steel skin, while in the second test series the front skin was removed. These skins represent 70-90 % of the total weight of the component. It is found that if the front skin is removed, the energy absorption is generally increased, while the resisting force is reduced, which are both beneficial. For low impact velocities, the displacement of the back skin is hardly affected, while for the highest impact velocity there is a marked difference in back-skin deflection between covered and uncovered components. The results indicate that the mechanical response of the front skin is not essential in order to make an efficient energy absorber as long as the back skin is strong enough to carry the loading.
 Reyes A, Børvik T (2018) Low velocity impact on crash components with steel skins and polymer foam cores. Submitted for possible journal publication.