Evaluation and modeling of fracture toughness based on the mezzo-scopic elastic-plastic fracture mechanics

基于中观弹塑性断裂力学的断裂韧性评估和建模

基本信息

批准号：
11450262
负责人：
MIYATA Takashi
金额：
$ 9.28万
依托单位：
NAGOYA UNIVERSITY
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
1999
资助国家：
日本
起止时间：
1999 至 2001
项目状态：
已结题

项目摘要

Cleavage fracture toughness of steels was mezzo-scopically analyzed on the basis of the statistical local fracture criterion approach. The statistical Weibull stress criterion at the crack tip region suggests that the cleavage fracture toughness of steels can be described as a function of the yield stress, and other mechanical properties of the materials. Formulation of the cleavage fracture toughness was first examined through an investigation on correlation between the cleavage fracture toughness and the cleavage fracture stress obtained in notched round bar specimens in accordance with the theoretical prediction. Then, scatter of the toughness, strain rate and specimen thickness effect on the toughness, deterioration of the toughness due to cold working and irradiation, and improvement of the toughness caused by the Ni addition, were analyzed through the formulation above.The specimen size requirements in toughness qualification are also discussed on the basis of statistical local fracture criterion approach. The Weibull stress criterion for cleavage fracture is applied to the constraint loss field at the crack tip described with the toughness scaling model (TSM). The new model proposed demon strates that the TSM is a particular case for a material with a particular combination of the Weibull shape parameter, m and the strain hardening exponent, n. Analytical prediction indicates that the specimen size re quirements in toughness must be significantly depending on the value of n and m of the material. The 2-and 3- dimensional FE analysis were performed to confirm above analytical prediction.

基于统计局部断裂准则方法对钢的解理断裂韧性进行了细观分析。裂纹尖端区域的统计威布尔应力准则表明，钢的解理断裂韧性可以描述为屈服应力和材料其他机械性能的函数。首先，根据理论预测，通过研究在缺口圆棒样品中获得的解理断裂韧性和解理断裂应力之间的相关性，来检验解理断裂韧性的公式。然后，通过上述公式分析了韧性、应变速率和试样厚度对韧性影响的分散性、冷加工和辐照引起的韧性劣化以及添加Ni引起的韧性提高。试样尺寸要求还讨论了基于统计局部断裂准则方法的韧性鉴定。解理断裂的威布尔应力准则应用于用韧性标度模型（TSM）描述的裂纹尖端的约束损失场。提出的新模型表明，TSM 是具有威布尔形状参数 m 和应变硬化指数 n 特定组合的材料的特例。分析预测表明，试样尺寸对韧性的要求必须显着取决于材料的n和m值。进行 2 维和 3 维有限元分析以证实上述分析预测。