A local approach to cleavage fracture in ferritic steels following warm pre‐stressing

Quantification of the enhancement in cleavage fracture toughness of ferritic steels following warm pre-stressing has received great interest in light of its significance in the integrity assessment of such structures as pressure vessels. A Beremin type probability distribution model, i.e., a local stress-based approach to cleavage fracture, has been developed and used for estimating cleavage fracture following prior loading (or warm pre-stressing, WPS) in two ferritic steels with different geometry configurations. Firstly, the Weibull parameters required to match the experimental scatter in lower shelf toughness of the candidate steels are identified. These parameters are then used in two- and three-dimensional finite element simulations of prior loading on the upper shelf followed by unloading and cooling to lower shelf temperatures (WPS) to determine the probability of failure. Using both isotropic hardening and kinematic hardening material models, the effect of hardening response on the predictions obtained from the suggested approach has been examined. The predictions are consistent with experimental scatter in toughness following WPS and provide a means of determining the importance of the crack tip residual stresses. We demonstrate that for our steels the crack tip residual stress is the pivotal feature in improving the fracture toughness following WPS. Predictions are compared with the available experimental data. The paper finally discusses the results in the context of the non-uniqueness of the Weibull parameters and investigates the sensitivity of predictions to the Weibull exponent, m, and the relevance of m to the stress triaxiality factor as suggested in the literature.

[1]  J. H. Chen,et al.  Quantification of the Warm Prestressing Effect in a Shape Welded 10 MnMoNi 5-5 Material , 2000 .

[2]  Claudio Ruggieri,et al.  Transferability of elastic–plastic fracture toughness using the Weibull stress approach: significance of parameter calibration , 2000 .

[3]  Peter Williams,et al.  Mechanical Engineering Publications , 1989 .

[4]  S. Carassou.  Déclenchement du clivage dans un acier faiblement allié : rôle de l'endommagement ductile localisé autour des inclusions , 1999 .

[5]  D. A. Curry,et al.  A micromechanistic approach to the warm pre-stressing of ferritic steels , 1981 .

[6]  S. J. Garwood,et al.  Experimental study of effects of prior overload on fracture toughness of A533B steel , 1990 .

[7]  A. Pineau,et al.  A local criterion for cleavage fracture of a nuclear pressure vessel steel , 1983 .

[8]  B. Bergman,et al.  On the estimation of the Weibull modulus , 1984 .

[9]  D. Smith,et al.  The effects of warm pre-stressing on cleavage fracture. Part 2: finite element analysis , 2004 .

[10]  S Hadidi-Moud,et al.  Predicting How Crack Tip Residual Stresses Influence Brittle Fracture , 2002 .

[11]  Hamish Fowler.  The influence of warm prestressing and proof loading on the cleavage fracture toughness of ferritic steels , 1998 .

[12]  Nicola Bonora,et al.  On the dependence of the Weibull exponent on geometry and loading conditions and its implications on the fracture toughness probability curve using a local approach criterion , 2000 .

[13]  D. J. Smith,et al.  The significance of prior overload on fracture resistance: a critical review , 1990 .

[14]  Claudio Ruggieri,et al.  Calibration of Weibull stress parameters using fracture toughness data , 1998 .

[15]  A. Cowan,et al.  A review of warm prestressing studies , 1983 .

[16]  John R. Rice,et al.  ON THE RELATIONSHIP BETWEEN CRITICAL TENSILE STRESS AND FRACTURE TOUGHNESS IN MILD STEEL , 1973 .

[17]  S Hadidi-Moud,et al.  The effects of warm pre-stressing on cleavage fracture. Part 1: evaluation of experiments , 2004 .

[18]  Philippa A.S. Reed,et al.  INVESTIGATION OF THE ROLE OF RESIDUAL STRESSES IN THE WARM PRESTRESS (WPS) EFFECT. PART II—ANALYSIS , 1996 .