Effect of experimental sample size on local Weibull assessment of cleavage fracture for steel

Abstract

This paper examines the sample size of the experimental datasets in calibrating the Weibull parameters for the modified three‐parameter Weibull stress framework, so as to enhance the experimental strategy for cleavage assessment of ferritic steels based on a local approach. The present work generates a large number of random and independent subsets from the ‘Euro steel’ fracture toughness database for the calibration procedure. The calibration of the Weibull parameters utilizes a subset of high‐constraint specimens and a subset of low‐constraint specimens from the Euro steel database to resolve the uniqueness issue in the calibration procedure reported in previous studies. This investigation reveals strong dependence of the calibrated Weibull modulus on both the constraint differences between the high‐constraint subset and the low‐constraint subset and the size of the selected subsets. The scale fracture toughness value, however, does not exhibit significant dependence on the constraint difference between the two subsets of specimens. The confidence level of the scale fracture toughness, nevertheless, still exhibits strong dependence on the sample size of the experimental data.

Effects of Loading Frequency and Loading Type on High-Cycle and Very-High-Cycle Fatigue of a High-Strength Steel

“…Recently, Sun et al [ 43 ] proposed a statistical method to predict the fatigue strength under different control volumes, and the predicted results were in good agreement with experimental data. In the derivation of such a statistical method, data scattering was described by Weibull distribution, which is commonly used in the analysis of specimen size effect, e.g., a recent paper by Zhang et al [ 44 ] addressed the effect of sample size on Weibull parameters. It is clear that for the feature of stress gradient under RB, the control volume of the specimen is substantially smaller than that under AL; thus, the AL specimen has a higher risky possibility than the RB specimen, which leads to lower fatigue strength by the AL method than by the RB method.…”

Weibull stress analysis for the corner crack in reactor pressure vessel nozzle

“…The advantage of local approaches is that Weibull stress can be transferred from one constraint level to another according to the failure probability. 9 Therefore, the failure probability can be easily obtained by Weibull stress.…”

A new local approach model for cleavage fracture in ferritic steels and its validation

“…Ferritic steels have body centered cubic crystal structures that possess the ductile-to-brittle transition temperature (DBTT) characteristic [1,2]. This leads to the inherent susceptibility of RPVs to stochastic transgranular cleavage induced brittle fracture in the actual service temperature range due to geometrical discontinuities at notches and cracks, and in the occurrence of pressurized thermal shock loadings.…”