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Yonemura S.,Kimitsu R and D Laboratory | Uenishi A.,Steel Research Laboratories | Kosugi S.,Mathematical Science and Technology Research Laboratory | Yoshida T.,A-D Technologies | And 2 more authors.
Nippon Steel Technical Report | Year: 2013

Bake-hardenable steel sheets are often used in exterior automotive body panels, such as doors, hoods, and fenders, because these applications require high strength for dent resistance as well as low yield strength for surface deflection. The dent resistance depends on the yield strength of materials after work hardening by forming and strain ageing by paint baking. In this study, the anisotropy of yield strength has been investigated in a uniaxially prestrained and baked bakehardenable steel. On the other hand, surface deflection is investigated by press forming experiments and their numerical simulations of the exterior door panel model. Emphasis is placed on the effects of mechanical properties and press forming condition on surface deflection are discussed. Furthermore, a new system for evaluation and visualization of surface deflection using Gaussian curvature is presented. 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


Hirose S.,A-D Technologies | Yonemura S.,Kimitsu R and D Laboratory | Uenishi A.,Steel Research Laboratories | Hiwatashi S.,Nagoya R and D Laboratory
Nippon Steel Technical Report | Year: 2013

The accuracy of crash analysis is important for design of car body with crashworthiness and depends on some properties of applied material. Strain rate dependency of flow stress and bake hardenability caused by painting process of car body are of particular significance to crash analysis. Here, developed technologies for evaluation of their properties were introduced. Source


Yoshida H.,A-D Technologies | Sato K.,Nagoya R and D Laboratory | Matsuno T.,A-D Technologies | Yoshida T.,A-D Technologies | And 2 more authors.
Nippon Steel Technical Report | Year: 2013

By using of high strength steel sheets for autobody parts and chassis parts, crack initiation of burring process and stretched flange is one of the most important problems in sheet metal forming. Although the factor of crack initiation is complicated procedure due to various cutting conditions and inhomogeneous distribution of stress or strain, we could evaluate this phenomenon by developing forming method of the parts, side bending test method and "limit diagram of stretch flange-ability". To prevent from crack initiation of burring process, we also developed original die shape and piercing methods for improving condition of the cutting edge. 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

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