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The effect of cross-section and type of alloy on the performance of aluminum extrusions as door beams was investigated. As a result, aluminum door beams were developed which have bending properties comparing favorably with those of door beams made of high tensile strength steel with a tensile strength of 1470 N/mm2. Furthermore, a technology to design door beams with the required performance and bending properties dealing with various car models was developed by making the most of the versatility of aluminum extrusions produced in various types of cross-sections.

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 studies the influence of welding parameters on the mechanical properties of butt joints, using aluminum plates, extrusion and casting by CO2 laser. As a result of this study, good welds have been obtained by optimum power output of laser and welding speed for each material. It also shows that the feeding of filler metal can improve joint efficiency and can perform tensile failure position away from weld metal and can extend the tolerance of root gap for butt joints. These technique lead to improve joint strength of laser welds as strong as that of arc welds. Also bending property and fatigue strength are equal to that of other conventional welds. This investigation confirms that laser welding for joining of aluminum alloys can be used, and that the techniques in this study will be able to be applied for automobile structures.

Door guard beams have been developed through the utilization of ultra high strength steel (tensile strength>100 kg/mm2). At first, the sheet metal gauge was reduced in proportion to the strength of the ultra high strength without changing the shape of the beam section. This caused beam buckling and did not meet guard beam specifications. Analyzing this phenomena in accordance with the buckling theory of thin plates, a design criteria that makes effective use of the advantages of ultra high strength was developed. As a result, our newly designed small vehicle door guard beams are 20% lighter and 26% thinner than conventional ones. This makes it possible to reduce door thickness while increasing interior volume.

A new variable compression turbo (VC-Turbo) engine, which has a multi-link system for controlling the compression ratio from 8:1 to 14:1, requires high axial force for fastening the multi-links because of high input loads and the downsizing requirement. Therefore, it was necessary to develop a 1.6-GPa tensile strength bolt with plastic region tightening. One of the biggest technical concerns is delayed fracture. In this study, quenched and tempered alloy steels were chosen for the 1.6-GPa tensile strength bolt.

Mo-free 1.6-GPa bolt was developed for a Variable Compression Turbo (VC-Turbo) engine, which is environment friendly and improves fuel efficiency and output. Mo contributes to the improvement of delayed fracture resistance; therefore, the main objective is to achieve both high strength and delayed fracture resistance. Therefore, Si is added to the developed steel to achieve high strength and delayed fracture resistance. The delayed fracture tests were performed employing the Hc/He method. Hc is the limit of the diffusible hydrogen content without causing a delayed fracture under tightening, and He is the diffusible hydrogen content entering under a hydrogen-charging condition equivalent to the actual environment. The delayed fracture resistance is compared between the developed steel and the SCM440 utilized for 1.2-GPa class bolt as a representative of the current high-strength bolts.