2011年12月　技術情報協会から『MATERIAL STAGE』が発行されました！

☆衝撃吸収マテリアルのトレンドの中で，”強靭性材料に関する研究　〜強くて壊れにくいフェールセーフ鋼を目指して〜”を紹介しています☆

2011年8月　アグネ技術センターから『金属』が発行されました！

☆超鉄鋼プロジェクト後の新しい展開が特集で組まれています☆

2011年1月5日　執筆，監修した書籍が技術評論社から発行されました！

☆2010年9月　Finite Element Analysis, edited by David MoratalがSCIYOから発刊されました！

フリーダウンロードサイトはこちら！ Strain Variations on Rolling Condition in Accumulative Roll-Bonding by Finite Element Analysis by Tadanobu INOUE

Static fracture toughness of fail-safe steel

A 1800 MPa class steel with ultrafine elongated grain structures were fabricated by multi-pass caliber rolling and a static three-point bending test was conducted. The strength ? toughness balance of the developed steel was remarkably improved compared with conventionally quenched and tempered steel with a martensitic structure. The static fracture toughness of the developed steel was about 40 times higher than that of the conventional steel. The microstructural design that improves toughness in ultrahigh-strength steels is clarified.

Delamination effect on impact properties of ultrafine-grained low carbon steel processed by warm caliber rolling

Bulk ultrafine-grained (UFG) low carbon steel bars were produced by caliber rolling, and the impact and tensile properties were investigated. Initial samples with two different microstructures, ferrite-pearlite and martensite (and/or bainite), were prepared and then caliber rolling was conducted at 500℃. The microstructures in the rolled bars consisted of an elongated UFG structure with a strong a-fiber texture. The rolled bar consisting of spheroidal cementite particles that distributed uniformly in the elongated ferrite matrix of transverse grain size of 0.8-1.0mm exhibited the best strength-ductility balance and impact properties. Although the yield strength in the rolled bar increased 2.4 times by grain refinement, the upper-shelf energy did not change, and its value was maintained from 100°C to -40°C. In the rolled bars, cracks during an impact test branched parallel to the longitudinal direction of the test samples as temperatures decreased. Delamination caused by such crack branching remarkably appeared near the ductile-to-brittle transition temperature. The effect of delamination on impact properties was associated with crack propagation on the basis of the microstructural features in the rolled bars. In conclusion, the strength-toughness balance is improved by refining crystal grains and controlling their shape and orientation; in addition, delamination effectively enhances the low-temperature toughness.

Hardness Variation and Strain Distribution in Magnesium Alloy AZ31 Processed by Multi-pass Caliber Rolling

The evolution of microstructure and hardness with equivalent strain was studied in magnesium alloy AZ31 bars fabricated using a process of multi-pass caliber rolling based on multidirectional deformation at warm working temperatures. The strain imposed was predicted by three-dimensional finite element simulation. The microstructure was observed using the electron back-scattered diffraction method. The strain predicted is larger than strain calculated simply from shape change of rolled bar and had a distribution with a maximum around corners in rolled bars.? The inhomogeneity of hardness throughout the cross section in the rolled bars was very similar to that of the strain predicted from the simulation. The caliber rolling produced a fine-grain structure below 2.5 mm in a bulk sample with a length of over 1000 mm. Caliber rolling can be applied as a new processing method for obtaining bulk ultrafine-grained magnesium.

Quantification of strain in accumulative roll-bonding under unlubricated condition by finite element analysis

The each strain component and equivalent strain in rolled materials were quantified using finite element analysis (FEA) that takes the deformation history into account. FE simulations were carried out considering stress-strain relations that depend on strain rate and friction between rolls and sheet. Rolling condition of accumulative roll-bonding (ARB) where introduction of a very large shear strain in the surface layer of rolled sheet had been verified through the embedded-pin method was employed in FEA. The histories of total shear strain, total strain in rolling direction, and equivalent strain during rolling were studied, and the magnitude and distribution of each of them through sheet thickness after rolling were shown. The problems associated with the experimental determination from an embedded-pin method were clarified through the present analysis. The equivalent strain at the surface in the 1100 Al processed by one ARB cycle without lubricant corresponded to the equivalent strain in the material processed by five ARB cycles with lubricant. These quantitative strain analyses would be useful for analyzing the evolution of microstructures in the ARB process as well as the conventional rolling deformation under high friction conditions.

結晶粒の形態と方位を制御した高強度高靭性鋼の破壊挙動解明

期間

H23(2011).4〜H26(2014).3

内容：

本研究では，新しい着想に基づいて開発した800MPa級および1800MPa級の壊れにくい高強度鋼を創製し（�@材料創製），-197℃から室温の温度範囲における静的なき裂感受性試験（�A特性試験）と数値解析（�B有限要素シミュレーション）を通じ，き裂の発生条件，およびその後の進展という破壊挙動と組織（�C組織解析）の関係を明確にし，破壊のメカニズム解明とともに，さらなる特性向上に向けた最適な組織設計指針を提示（�Dまとめ）することを目的にする．

対象材料

低炭素鋼，中炭素鋼

バルクナノメタル創製の計算機・物理シミュレーション

A02エ班研究代表者：柳本潤（東大），分担者：井上忠信（NIMS），土田紀之（兵庫県立大），柳田明（横浜国大）

期間

H22(2010).4〜H27(2015).3

内容：

本研究では，相変態を含む加工・熱処理プロセスによるバルクナノメタルの超微細粒組織形成を，計算機シミュレーション及び加工熱処理再現試験装置などを駆使した物理シミュレーションによって解明する．出口として，「多様なプロセスによるバルクナノメタルの製造手法の確立」を目指す

加工ひずみ制御による微細粒組織創成の定量的予測技術の構築

期間

H21(2008).4〜H23(2010).3→実績報告はこちらへ

内容：

本研究の目的は，計算科学と実験科学を結合した研究手法により，加工の進行に伴うひずみの蓄積とその空間分布による組織の変化を定量的に明らかにし，微細粒組織形成の予測技術を構築することである．

対象材料

低炭素鋼，純アルミニウム