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This paper presents the results of a strength analysis of a newly developed steel structure featuring a special cross section achieved with the hydroforming process that minimizes the influence of springback. This structure has been developed in pursuit of further weight reductions for the steel body in white. A steel tube with tensile strength of 590 MPa was fabricated in a low-pressure hydroforming operation, resulting in thicker side walls. The results of a three-point bending test showed that the bending strength of the new steel structure with thicker side walls was substantially increased. A finite element crush analysis based on the results of a forming analysis was shown to be effective in predicting the strength of the structure, including the effect of work hardening.

This paper presents a new material technology that can achieve both crashworthiness and weight reduction of the vehicle body. This new technology is based on three fundamental approaches. One is a technique for evaluating high-speed material deformation characteristics related to the crush behavior of energy-absorbing structures. A second is the material concept of high tensile steel featuring both increased material strength and higher strain-rate sensitivity in order to improve its energy-absorbing capacity. We have found 590N/mm2-class dual-phase (DP) steel consistent with this concept. The third is a technique for estimating the crush behavior of body structures, taking into account the plate thickness reduction and work hardening distribution resulting from the press-forming process. Finally, it was shown that the use of DP steel results in a 15% reduction in the weight of absorbing structures without affecting crashworthiness.

A study was made of the possibility of using an acoustic emission (AE) technique to estimate the maximum load applied to automotive carburized gears under actual operating conditions. Three-point bending tests done on carburized steel specimens showed that, provided a small crack was induced in the material, AE was not generated until the material was subjected to a higher bending load than the maximum load previously applied. Using this effect, the maximum load applied to gears, in which a crack had been induced during endurance testing, was estimated. Although the estimated maximum load was about 14% higher than the actual load, the AE technique appears to be a promising method for use in the design and durability assurance of carburized parts of automotive powertrains.