On the temperature independence of statistical model parameters for cleavage fracture in ferritic steels

Abstract

The work relates to the effect of temperature on the model parameters in local approaches (LAs) to cleavage fracture. According to a recently developed LA model, the physical consensus of plastic deformation being a prerequisite to cleavage fracture enforces any LA model of cleavage fracture to observe initial yielding of a volume element as its threshold stress state to incur cleavage fracture in addition to the conventional practice of confining the fracture process zone within the plastic deformation zone. The physical consistency of the new LA model to the basic LA methodology and the differences between the new LA model and other existing models are interpreted. Then this new LA model is adopted to investigate the temperature dependence of LA model parameters using circumferentially notched round tensile specimens. With the published strength data as input, finite element (FE) calculation is conducted for elastic-perfectly plastic deformation and the realistic elastic-plastic hardening, respectively, to provide stress distributions for model calibration. The calibration results in temperature independent model parameters. This leads to the establishment of a ‘master curve’ characteristic to synchronise the correlation between the nominal strength and the corresponding cleavage fracture probability at different temperatures. This ‘master curve’ behaviour is verified by strength data from three different steels, providing a new path to calculate cleavage fracture probability with significantly reduced FE efforts.

Keywords:

• Ferritic steels
• plastic yielding
• cleavage fracture
• statistical model
• temperature effect
• model calibration

Acknowledgements

The new local approach was initiated due to a research stay with Humboldt Research Fellowship in Institute of Ferrous Metallurgy (IEHK) at RWTH Aachen University. Wei-Sheng Lei is grateful to Professor Winfried Dahl and Professor Wolfgang Bleck for hosting the visit and the Alexander von Humboldt Foundation for the financial support. The support by the State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi’an Jiaotong University is greatly acknowledged.