TOTAL ASSESMENT OF THE CHARACTERISTICS OF SMALL CRACK PROPAGATION IN THE MATERIAL FOR STRUCTURAL USE

结构用材料中小裂纹扩展特性的总体评估

• 批准号: 62420024
• 负责人: SHIMIZU Masao
• 金额: $ 18.69万
• 依托单位: Keio University
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for General Scientific Research (A)
• 财政年份: 1987
• 资助国家: 日本
• 起止时间: 1987 至 1989
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-62420024/
• 关键词: FATIGUE STRENGTH; SMALL CRACK; CARBON STEEL; ALUMINUM ALLOY; MANSON-COFFIN LAW; MINER'S RULE; NON-METALLIC INCLUSION; MICROSTRUCTURE; 低サイクル疲労; 高サイクル疲労; マイナー則

Reassessment of the structural integrity of the machine-structure system has revealed that there are still critical problems to be solved for the total safety of the system. Total assesment of the behavior of small crack initiation and propagation in structural steel under low and high cycle fatigue regime is among these problems. In the series of present research project, special attention was paid to the following three topics. (1) Characteristics of near threshold propagation of small crack. (2) Microdefects and the nature of fatigue process in high hardened steel. (3) Fatigue fracture under extremely low cycle fatigue.Results obtained are summarized in the followings. (1) Near threshold propagation behavior of small crack in dual phase microstructure of unnotched specimen can be under the control of not only the crack growth resistance of the second phase microstructure during the process of conventional growth of single crack but also the condition of coalescence of multiple crack … More s near by the main crack. In addition, this coalescence becomes the causes of high structure sensitivity during crack propagation of relatively large crack. (2) Fatigue fracture of high hardened steel can be characterized by the concept that the matrix material can be regarded as the material having a number of small pits corresponding to small non-metallic inclusion. The level of fatigue strength can be under the control of the maximum sized inclusion in the surface layer of specimen so that the upper limit of the fatigue strength of material can be attained by the inclusion free microstructure. Furthermore, a reduction of fatigue strength of nitrided titanium can be explained to be due to possible defects in the hardened layer of the specimen. (3) Fatigue life of structural steel in extremely low cycle fatigue range can be under the control of two fracture criteria which are related to the difference of crack nucleation site in the material, i.e., the internal cracking and surface cracking, respectively.This is typical phenomenon for dual phase microstructure having relatively large brittle second phase and ductile matrix. Less

对机器-结构系统结构完整性的重新评估表明，对于系统的总体安全而言，仍有一些关键问题需要解决。对结构钢在低周和高周疲劳状态下的小裂纹萌生和扩展行为的全面评估就是这些问题之一。在本系列研究项目中，特别关注了以下三个主题。(1)小裂纹的近门槛扩展特性。(2)高硬钢的微观缺陷和疲劳过程的本质。(3)极低周疲劳下的疲劳断裂。(1)小裂纹在无缺口双相组织中的近门槛扩展行为不仅受常规单裂纹扩展过程中第二相组织的裂纹扩展阻力控制，而且还受多裂纹…合并条件的控制。更多的S靠近主缝。此外，在相对较大的裂纹扩展过程中，这种聚结成为高结构敏感性的原因。(2)高硬化钢的疲劳断裂可以用这样的概念来描述，即母材可以看作是具有许多与微小非金属夹杂物相对应的小凹坑的材料。疲劳强度水平可以通过控制试件表层夹杂物的最大尺寸来控制，从而通过无夹杂物组织达到材料疲劳强度的上限。此外，氮化钛疲劳强度的降低可以解释为可能是由于试件硬化层中的缺陷造成的。(3)结构钢在极低周疲劳范围内的疲劳寿命受两种断裂准则的控制，这两种断裂准则分别与材料中裂纹形核位置的不同有关，即内部裂纹和表面裂纹，这是典型的双相组织具有较大的脆性第二相和韧性基体的现象。较少

项目成果

黒島義人・ほか2名: "シミュレ-トョンによる疲労破壊起点の介在物寸法の評価" 日本機械学会論文集(A編)投稿中.

黑岛义人等2人：“通过模拟评估疲劳断裂起点处夹杂物的尺寸”，目前正在向日本机械工程学会会刊（A部分）提交。

森田辰郎・ほか3名: "窒化処理を施した純チタンの疲労挙動" 日本機械学会論文集(A編)投稿中.

森田达郎等3人：“氮化纯钛的疲劳行为”，目前正在向日本机械工程学会会刊（A版）提交。

Yoshito Kurosima et.al.: "Relationship between Critical Size of Inclusions Responsible for Fatigue Failure and Inclusion Size Distribution" Trans.JSME.

Yoshito Kurosima 等人：“导致疲劳失效的夹杂物的临界尺寸与夹杂物尺寸分布之间的关系”Trans.JSME。

小茂鳥潤 他: 機論. 54. 1731-1734 (1988)

Jun Komotori 等人：机制。54。1731-1734 (1988)

Katsunori Shimada et.al.: "Facture Mode Transition and Damage in Extremely Low Cycle Fatigue" Proc.of The Second Int.Conf.on Low Cycle Fatigue and Elasto-plastic Behavior of Materials Ed.K.T.Rie.,Elsever Applied Science.680-686 (1987)

Katsunori Shimada 等人：“极低循环疲劳中的断裂模式转变和损坏”Proc.of 第二届国际会议关于材料的低循环疲劳和弹塑性行为 Ed.K.T.Rie.，Elsever Applied Science.680