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This paper presents the results of experimental analysis on the structural performance of steel, aluminum alloy and stampable sheets for bumper beams and the calculation results on the weight reduction of those bumper beams. Bending tests of straight beams, which were made of the three kinds of materials, were carried out in order to examine their structural performance. In consideration of failure modes, it was found that the maximum load and the absorbed energy of those beams can be evaluated by their material strength, their side-wall thickness and the height of their cross sections. Based on this evaluation method, the weight and the absorbed energy of the constant displacement were calculated using a common cross section. The weight reduction of aluminum alloy and stampable sheets is superior to 590MPa high tensile strength steel sheets.

In order to improve the capability of frontal or rear automotive members to absorb impact energy, a basic study was performed to evaluate the effect of strength, micro-structure, and plate thickness on dynamic deformation phenomena using tensile specimens and hat square columns. Tensile strengths of the materials were selected from 340 to 1180 MPa class steels. Five kinds of micro-structure, Ferrite, Ferrite + Bainite, Ferrite + Martensite, Ferrite + Pearlite, Ferrite + Bainite + γ, and Martensite, were investigated. Tensile tests were carried out under strain rates from 10-1 to 103 /sec. and crash tests of hat square columns were conducted under test speeds from 0.1 to 14.0 m/sec.

From the viewpoint of applying ERW (Electric Resistance Welded) steel tubes for automotive structural parts by means of hydroforming technology, a series of free-bulge experiments is carried out. Four kinds of mild and high tensile strength steel tubes are provided. Initial stress ratio, αm that represents an axial force level is adopted as an experimental parameter. Expansion limit increases with decrease of αm. The bulge shape and the expansion limit are also affected by the mechanical properties of tubes. The strain hardening property in bulge deformation is approximated by a parabolic equation.

The effect of a concentration of stress at a welded joint on the fatigue limit was investigated from the point of view of the effective design of automotive parts made of high strength hot rolled steel sheets. The stress concentration at the welded joint was evaluated using FEM analysis and the effect of stress concentration on endurance limit was investigated by fatigue tests using specimens of practical welded joints and specimens with the simulated configuration of welded joints. It is pointed out that another effect besides stress concentration and residual stress should be considered to evaluate the endurance limits for high tensile strength materials of over 590 N/mm2.

The Effects of microstructures on stretch flangeability and stretchability in hot rolled high strength steel was investigated. Stretch flangeability of multi-phase steels was inferior to that of single phase steels at a given tensile strength, although stretchability of the former was superior to that of the latter. In multi-phase steel, the main factor affecting stretch flangeability is the hardness ratio of ferrite to hard phase, on the other hand, that which most affects stretchability is the volume fraction of ferrite. According to these results, several types of high strength hot rolled steel sheets with excellent formability were developed.

The formability of electrodeposited Zn-SiO2 composite coating has been studied. Flaking of the coating and die pick-up were hardly observed during the draw bead simulation test. Powdering resistance of the coating were also better than that of galvannealed steel. Good formability of Zn-SiO2 composite coatings is attributed, primarily to the low friction coefficient of the coating, and secondly to the microcracking effect which release the forming stress.

Vibration Damping Steel Sheet (VDS), which is composed of two steel-sheet skin layers and a middle layer of viscoelastic polymer resin, has been applied to automotive parts. For application to body panels, VDS needs several superior characteristics, such as, high damping capacity at room temperature and spot weldability as well as press formability. VDS developed by sandwiching a thermosetting resin has the loss factor of 0.2 at room temperature, and can be press formed and spotwelded under the same conditions as for an conventional steel sheet.

Increase of load capacity for trucks by weight reduction of the body has been required to cut down transportation costs. The weight reduction of truck body is feasible in terms of the application of high-strength steel sheet to body. Especially, the application to truck frame is important because it is heavy. The required properties of steel sheet for truck frame use are press formability and fatigue strength. Press formability can be optimized based on the previous investigation results. On the other hand, investigations on fatigue strength are relatively few, and the value of fatigue strength is not sufficient. Accordingly, the fatigue strength of high-strength steel sheet for truck frame use was investigated in this study. As for fatigue strength, the fatigue strength of steel sheet with scale is significant because the steel sheet is painted without pickling to remove the surface scale.