Study on identification of critical Weibull stress distribution by using miniature specimen

Abstract

Weibull stress criterion based on the “Local Approach” is applied for rational brittle fracture assessment of steel components taking account of the plastic constraint effect on fracture resistance. Once the cumulative distribution of critical Weibull stress is identified for the material itself, that is Weibull shape parameter m as a material constant independent of size/shape of components, loading mode and temperature, fracture toughness can be corrected to the fracture resistance of structural components on the basis of the Weibull stress criterion. On the other hand, a miniature fracture toughness specimen is useful for evaluating the toughness of local area of the component and limited material such as irradiated test sample. Then, this study focuses on developing a method for identification of shape parameter m of critical Weibull stress distribution using miniature specimens. Two types of miniature 3PB (3-point bend) specimen with thickness B=1.65mm that has different crack depth are used to identify the m-value. The m-value determined from the two types of miniature specimen is found to be almost the same as that obtained from normal size specimens with thickness B=15mm, whereas both testing are conducted at different temperature. It is demonstrated that the fracture toughness of the steel at the other temperature can be precisely corrected to the fracture resistance of the cracked component with lower crack-tip plastic constraint by means of the m-value identified from test results for two types of miniature specimen.

Keywords

• fracture toughness test
• miniature specimen
• brittle fracture
• local-approach
• weibull stress