Crash Behavior of Columns in Relation to Material Properties and Joining Techniques

The strain rate behavior of mild-steel and high-strength steel qualities has been investigated. The hardening as a function of the strain rate of a set of steel qualities was determined, and it was found that the gain in strength for high-strength steels is not in proportion to the static yield-strength. The absolute increase in strength for high-strength steel is often less than for mild steel (although this fact depends on the microstructure of the steel). This fact is reflected in the absorption of energy for square crash-columns that were tested on a sled-impact facility. Downgauging parts from mild-steel to high-strength steel must be therefore be done carefully to maintain its crashworthiness properties. Special attention should be given to the strain rate sensitivity of the next generation of high strength steel qualities. Moreover we have tested and simulated spotwelded columns to test the failure criterion for spotwelds. It appeared that using a failure criterion with standard tensile- and cross-tension forces for rupture of spot-welded specimens gives quite satisfactory results.