山陰地域中部，宍道低地帯東部の海域，美保湾で行った音波探査記録に基づき，同低地帯東部の中海から美保湾にかけての後期更新世以降の発達史を明らかにした．音波探査記録と既存ボーリングデータを比較した結果，縄文海進以前および後期更新世に形成された3つの顕著な反射面が認められた．これより，後期更新世以降の地史を5段階に区分した．ステージ1（MIS 6）は，最終間氷期前で，海水準が低下していた時代である．ステージ２（MIS 5）は海水準が現在とほぼ同じ時代で，旧弓ヶ浜砂州が現在とほぼ同じ位置に形成され，砂州先端では潮流により海釜地形が形成された．ステージ3（MIS 4-3）では，ステージ2で形成された海釜地形を埋める堆積が起こった．ステージ4（MIS 2）では海水準が大きく低下し，更新統上面に凹地形が形成された．ステージ5（MIS 1）では，縄文海進以降に現在の堆積地形が形成された．

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The basic objective of this study is to establish the material design concepts for the coexistence of good mechanical properties with super heat-resistance in the systems of ceramic/metal and ceramic/ceramic FGMs. Flexural and fracture toughness tests were conducted on gas-pressure combustion sintered Cr₃C₂ ceramic and its composites with Ni and TiC (Cr₃C₂/Ni, Cr₃C₂/TiC) in a vacuum environment up to 1200°C using a newly developed materials testing system. Fracture characteristics were investigated on the basis of fracture mechanics and fractography. The toughness of Cr₃C₂ can be improved by the addition of metallic particles. It is found that the principal mechanism of toughness improvements in these composites (ductile-phase reinforced ceramic matrix composites) is attributed to crack tip blunting by a ductile metallic phase.

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It is still essential for high strength engineering ceramics to improve fracture toughness for a wide use in primary structural applications. The purposes of this paper are to apply the ductile metallic phase toughening mechanism proposed previously to ceramics/metals functionally gradient materials (FGMs) and to confirm the possibility of improvement of fracture toughness without the reduction of strength. Fracture characteristics were investigated for symmetrically step by step graded FGMs (Cr₃C₂/Ni, TiC/Ni) on the basis of fracture mechanics and fractography. It was found that the ductile metallic phase toughening mechanism has a good potential for ceramics/metals FGMs.

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