Abstract
The paper discusses and applies a statistical approach to correlate the fracture behavior of a notched and fracture mechanics specimen. The method can be used for fatigue analysis. The random nature of cleavage fracture process determines that both the microscopic fracture stress and the macroscopic properties including fracture load, fracture toughness and the ductile to brittle transition temperature are all stochastic parameters. This understanding leads to the proposal of statistical assessment of cleavage induced notch toughness of ferritic steels according to a new local approach to cleavage fracture. The temperature independence of the two Weibull parameters in the new model induces a master curve to correlate the fracture load at different temperatures. A normalized stress combining the two Weibull parameters and the yield stress is proposed as the deterministic index to measure notch toughness. This proposed index is applied to compare the notch toughness of a ferritic steel with two different microstructures.
Highlights
Ferritic steels are commonly used to fabricate reactor pressure vessels (RPVs) in the commercial light water reactors
The random nature of cleavage fracture process determines that both the microscopic fracture stress and the macroscopic properties including fracture load, fracture toughness and the ductile to brittle transition temperature are all stochastic parameters. This understanding leads to the proposal of statistical assessment of cleavage induced notch toughness of ferritic steels according to a new local approach to cleavage fracture
The temperature independence of the two Weibull parameters in the new model induces a master curve to correlate the fracture load at different temperatures
Summary
Ferritic steels are commonly used to fabricate reactor pressure vessels (RPVs) in the commercial light water reactors. 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. The maximum tensile principal stress criterion for cleavage fracture (Eq(8)) (5).The power-law distribution of microcrack size (Eq(9)) Basically, equations are defined in Table 1 to translate the five assumptions into mathematical formulations and check the validity of each step for formulating the Beremin model.
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