An important technical subject in automotive design is the improvement of collision safety paralleled with weight reduction for economy of natural resources and energy.

Guard bearns, which are fitted inside the doors for improved side collision characteristics, not only increase vehicrle weight, but also restrict more effective use of limited vehicle space.

For further miniaturization and weight reduction, therefore, we attempted to design a door guard beam constructed of ultra high strength steel, the strength of which is several times greater than mild steel.

During the design stage, an analytical study was conducted on a cross section of the guard beam so as to determine whether buckling would occur following the reduction in thickness;​ and to make the most effective use of the properties of the high strength material.

Based on these analytical results, a performance test was conducted on a guard beam which was reduced 10 to 20 percent weight and 10 to 30 percent in beam-width. As a result of this test, we concluded that ultra high strength steel can be satisfactorily utilized to allow weight reduction and still be consistent with collision safety requirements.