Intercomparison of Creep Crack Growth Data

Estimates of stress intensity factor, K, reference stress, σref, and creep parameter, C∗, have been made for compact tension (CT) and double cantilever beam (DCB) test-pieces containing side grooves. Limit analysis techniques were used to determine the latter two parameters. It is shown that the expressions developed for σref are sensitive to the collapse mode proposed, whereas those for C∗ are largely independent. Comparisons of predictions of creep crack growth data on CT and DCB specimens of a 1 per cent CrMoV steel in terms of K and σref have revealed different dependences for the two geometries, suggesting that neither parameter gives satisfactory correlations. Better overall agreement is obtained with the C∗ parameter, even though gross creep deformations were not observed. It is suggested that further improvement may be gained with this parameter if more accurate estimates of C∗, which allow the inclusion of elastic terms, are used.

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Experimental Investigation of Constraint Effects on Creep Crack Growth

Computational Weld Mechanics, Constraint, and Weld Fracture ◽

10.1115/pvp2002-1117 ◽

2002 ◽

Cited By ~ 21

Author(s):

Adam D. Bettinson ◽

Noel P. O’Dowd ◽

Kamran M. Nikbin ◽

George A. Webster

Keyword(s):

Stainless Steel ◽

Crack Growth ◽

Creep Crack Growth ◽

Compact Tension ◽

Growth Data ◽

Creep Crack ◽

Low Constraint ◽

Constraint Effects ◽

Crack Growth Model ◽

Crack Growth Rates

In this work the effects of specimen size and type on creep crack growth rates in stainless steel are examined. Experiments have been carried out on high constraint compact tension specimens (CT) and low constraint centre cracked panels (CCP) of ex-service 316H stainless steel. All testing was carried out at 550°C. Constraint effects have been observed in the data, with the large CT specimens having the fastest crack growth rate and the small CCP specimens the slowest. These trends are consistent with those that would be predicted from two parameter (C*–Q) theories. However, it is found that a constraint dependent creep crack growth model based on ductility exhaustion overpredicts the constraint dependence of the crack growth data.

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Comparison Between Crack Growth in Fracture Mechanics Specimens and Feature Component Tests Carried Out in a Low-Alloy Steel

Journal of Pressure Vessel Technology ◽

10.1115/1.556147 ◽

1999 ◽

Vol 122 (1) ◽

pp. 40-44 ◽

Cited By ~ 1

Author(s):

Kamran Nikbin

Keyword(s):

Fracture Mechanics ◽

Crack Growth ◽

Creep Crack Growth ◽

Compact Tension ◽

Growth Data ◽

Good Correspondence ◽

Creep Crack ◽

Growth Properties ◽

Circumferential Defects ◽

Testing Condition

In both power generation plants and the chemical industries, there is a need to assess the significance of defects which may exist in high-temperature equipment operating in the creep range. This paper examines the methods of analysis used in laboratory creep crack growth data and their relevance to crack growth data derived from feature component tests which best simulate actual components under controlled testing condition. The material examined was a 214 Cr 1 Mo steel in the new condition at 550 and 600°C. The creep crack growth properties were determined on compact tension specimens. The data were compared with representative crack growth data from feature test components. These consisted of cracked rings, thick-walled cylinders, and thin-walled tubes containing axial or circumferential defects under combinations of axial and internal pressure loading. Little influence of size or temperature on the measured crack propagation rates was observed when the results were plotted against the creep fracture mechanics parameter C*. This is shown to be because the relevant condition had little effect on the appropriate crack tip creep ductilities of the material. Good correspondence was observed between the compact tension and the feature component tests, suggesting the feasibility of the C* method for predicting short-term laboratory tests using different geometries. [S0094-9930(00)01001-5]

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