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Yoshida T.,A-D Technologies | Sato K.,Nagoya R and D Laboratory | Isogai E.,Hirohata R and D Laboratory | Hashimoto K.,A-D Technologies
Nippon Steel Technical Report | Year: 2013

Springback is one of the most difficult problems in applying high strength steel sheets to automotive body parts. The mechanism of springback behavior classified by the phenomenon and countermeasures based on each mechanism were reported. It was made clear that section opening of member parts was reduced by crash forming and wall tension control. And torsion and camber of complicated shape parts were possible to decrease by planer stress control using the developed analytical methods of CAE. In addition, about the buckling torsion of panels, the mechanism of the occurrence was studied and effects of countermeasures were reported. Basic concept of countermeasure for springback is expected to design the part high rigidity at first, utilize the stress control methods and minimize the compensation of die tools. Source

Fujita N.,Quality Management Div. | Matsumura K.-I.,Hirohata R and D Laboratory | Tomokiyo T.,Yawata Steel Works | Kusumi K.,Steel Research Laboratories | Nonaka T.,Nagoya R and D Laboratory
Nippon Steel Technical Report | Year: 2013

Application of ultra-high strength steel sheets is one of the most important methods to satisfy weight reduction and crash safety of a vehicle. Recently, there is a trend to apply ultra-high strength steel sheets widely to auto-body parts. In this report, present situation of ultra-high strength steel sheets, especially with tensile strength more than 980MPa and 1,470MPa by hot-stamping, have been introduced. Source

Yoshida T.,A-D Technologies | Uenishi A.,A-D Technologies | Isogai E.,Hirohata R and D Laboratory | Sato K.,Nagoya R and D Laboratory | Yonemura S.,Kimitsu R and D Laboratory
Nippon Steel Technical Report | Year: 2013

Improving the prediction accuracy of springback simulation are one of the most important problem because springback is major forming defect in sheet metal forming using high strength steel sheets. By applying the mixed hardening model by Lemaitre- Chaboche, which is possible to consider the Bauschinger effect under reverse loading path, prediction accuracy of springback were improved. And influences of material parameters of this model on springback deformation are investigated. To investigate the mechanism of the 3D springback, theoretical evaluation of simulation results before springback is carried out. It was found that 3D springback were reduced effectively by countermeasures obtained from that analytical results applied to the rear member model tests. Source

Uenishi A.,A-D Technologies | Isogai E.,Hirohata R and D Laboratory | Sugiura N.,Kimitsu R and D Laboratory | Ikematsu Y.,Hirohata R and D Laboratory | And 2 more authors.
Nippon Steel Technical Report | Year: 2013

The material behavior at large strains is one of the most important properties in sheet steel, for it undergoes severe plastic deformation in its use. We focus on the relationship between the work hardening behavior at large strains and the evolution of microstructure during deformation by experimental and numerical methods, with attention to the crystal orientation. The work hardening behavior of ferritic single crystal with different orientations has been characterized by simple shear experiments. At the same time, TEM observations have been performed to study microstructures after shear deformation. The work hardening behavior depends largely on the crystal orientation. The observed microstructures may be classified into three types. The work hardening behavior could be correlated to the type of microstructure via the activity of slip systems. Crystal plasticity analysis revealed that the behavior in macroscopic and microscopic scales could be attributed to the activity of slip systems and their interaction. Source

Tamaki T.,Hirohata R and D Laboratory | Murakami K.,Hirohata R and D Laboratory
Nippon Steel Technical Report | Year: 2013

A local curvature multi-vertex model was developed. This model is the straightforward two-dimensional topological network model based on the physical principles which consider the curvatures of grain boundaries and the grain boundary tensions at triple junctions. The simulator based on the physical model was developed and applied to the materials with an artificial random texture and an actual texture. As the results, the grain growth by simulation obeyed the 1/2 low of time which was derived from the classical curvature model. Moreover, the grain growth velocity and misorientation distribution was turned out to be changed by the grain boundary characteristics. The developed model was verified to simulate the experimental results quite well. Source

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