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Elastic-plastic crack front fields in arc-shaped tension specimens (C-specimens) were analyzed by a three-dimensional finite element method. The effect of side grooves on the ductile fracture behavior was investigated by studying the J-integral distribution, plane-strain constraint parameter, and development of plastic zones and comparing to experimental data. The applicability of the η factor (derived for use with compact tension specimens) for the calculation of J-integral values for the C-specimen was also investigated. The results show that side grooves promote and establish near plane strain conditions at the crack front in sub-size specimens. It was also found that a two-dimensional plane-strain analysis in conjunction with the standard American Society for Testing and Materials (ASTM) tests was sufficient to determine the fracture toughness values from side-grooved C-specimen. The results indicate the η factor for compact tension specimen as specified in the ASTM standards appears to produce reliable results for the calculation of J of C-specimens.

A model is developed to quantify the effect of hydrogen on the critical stress intensity factor or fracture toughness of steels. The stress-assisted hydrogen diffusion model proposed by Liu (1970) is assumed and combined with the elastic stress field around the crack tip for quantifying the hydrogen concentration at the crack tip. Introducing a fracture criterion as the critical hydrogen concentration at a critical distance ahead of the crack tip, this model is successfully applied to the interpretation of hydrogen embrittlement behavior in a piping material. Experimental data at constant temperature were used to validate the model. With further development, the model has the potential to predict fracture toughness values at temperatures other than the test temperature.

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