The FMVSS 201 regulation requires that interior components in upper compartment of a passenger vehicle pass a head impact test using a Free Moving Head (FMH) model with a HIC(d) limit. In this type of test, most interior components themselves do not generate high HIC(d) numbers but the steel structures underneath these components do. In addition to normal functions, interior components need to absorb the kinetic energy of the FMH model such that the acceleration response of the FMH model does not generate a high HIC(d) number in the test.
This paper first reviews the existing work on the principles for the head impact protection and identifies limitations of the existing theory for the design of the interior components that are mounted on flexible structures. This paper discusses and proposes a design methodology for automotive interior components to ensure that they comply with FMVSS 201 head impact requirements. This paper identifies special considerations in the design of an energy absorbing layer on a flexible structure, which is common in automotive interior components. It is found conservative designing an energy absorbing layer on a flexible structure directly using existing methods from references. Also this paper discusses several typical deceleration behaviors of a constant force energy absorbing layer on a flexible structure and suggests the saturated design as an acceptable design. This paper further proposes design criteria and provides all equations for this design. Finally, this paper demonstrates a practical design case of an energy absorbing element on a cover of a seat belt slip ring. This design has reduced the HIC number by half with no change to the overall dimensions of the original cover.