Characterizations of creep crack growth in 1 per cent Cr Mo V steel

1981 ◽  
Vol 16 (2) ◽  
pp. 137-143 ◽  
Author(s):  
D J Smith ◽  
G A Webster
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Growth Data ◽  
Creep Crack ◽  
Test Pieces ◽  
Reference Stress ◽  
Collapse Mode ◽  
Two Parameters ◽  
Creep Deformations

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.

Experimental Investigation of Constraint Effects on Creep Crack Growth

2002 ◽  
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.

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

1999 ◽  
Vol 122 (1) ◽  
pp. 40-44 ◽  
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]

C∗ correlations for creep crack growth in weld metals

1986 ◽  
Vol 21 (4) ◽  
pp. 231-242 ◽  
Author(s):  
D J Gooch ◽  
S T Kimmins
Keyword(s):  
Crack Growth ◽  
Deformation Behaviour ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Compact Tension Specimen ◽  
Primary Creep ◽  
Creep Crack ◽  
Weld Metals ◽  
Reference Stress ◽  
Aisi 316

Creep crack growth tests have been performed on compact tension specimens of 2 1/4CrlMo, C—Mn, and AISI 316 weld metals at 565°C, at 360 and 390°C, and at 600°C, respectively. The data have been analysed in terms of the C∗ creep parameter obtained directly from experimental measurements and by use of estimation formulae which depend on uniaxial creep data and evaluation of a reference stress. When expressed in the form d a/d t = D C∗ q the two approaches result in correlations which differ both in the constant, D, and in the exponent, q. The differences in the constant may be largely rationalized in terms of the constraint on deformation appropriate to the test conditions and the effects of this on the reference stress. The exponent, q, was generally lower when the estimation formulae were used than when C∗ was calculated from measured displacement rates. This was attributed to the lower stress dependence of the load-line displacement rates of the compact tension specimens compared with that of the uniaxial minimum creep rate at similar stress levels. This arises because primary creep strains may dominate the overall deformation behaviour of a compact tension specimen for many practical circumstances.

Modeling and Simulation of Creep Crack Growth in High Chromium Steels

2014 ◽  
Author(s):  
Nicola Bonora ◽  
Luca Esposito ◽  
Simone Dichiaro ◽  
Paolo Folgarait
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Chromium Steel ◽  
Creep Model ◽  
Model Parameters ◽  
Approximate Methods ◽  
High Chromium ◽  
Creep Crack ◽  
Wide Range

Safe and accurate methods to predict creep crack growth (CCG) are required in order to assess the reliability of power generation plants components. With advances in finite element (FE) methods, more complex models incorporating damage can be applied in the study of CCG where simple analytical solutions or approximate methods are no longer applicable. The possibility to accurately simulate CCG depends not only on the damage formulation but also on the creep model since stress relaxation, occurring in the near tip region, controls the resulting creep rate and, therefore, crack initiation and growth. In this perspective, primary and tertiary creep regimes, usually neglected in simplified creep models, plays a relevant role and need to be taken into account. In this paper, an advanced multiaxial creep model [1], which incorporates damage effects, has been used to predict CCG in P91 high chromium steel. The model parameters have been determined based on uniaxial and multiaxial (round notched bar) creep data over a wide range of stress and temperature. Successively, the creep crack growth in standard compact tension sample was predicted and compared with available experimental data.

Elastic Follow-Up Factors to Estimate C(t) Under Secondary Loading

2012 ◽  
Author(s):  
Kuk-Hee Lee ◽  
Yun-Jae Kim ◽  
Robert A. Ainsworth ◽  
David Dean
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Transient Creep ◽  
Independent Method ◽  
Finite Element Analyses ◽  
Creep Crack ◽  
Reference Stress ◽  
Growth Increase ◽  
Plastic Creep

This paper proposes a method to determine the elastic follow-up factors for C(t)-integral under secondary stress. The rate of creep crack growth for transient creep is correlated with C(t)-integral. The elastic follow-up behaviour, which occurs in structures under secondary loading, prevents a relaxation of stress during transient creep. Thus, both the value of C(t) and creep crack growth increase with an increasing elastic follow-up. An estimation solution for C(t) has been proposed by Ainsworth and Dean based on the reference stress method. In order to predict the value of C(t) using this solution, an independent method to determine the elastic follow-up factors for cracked bodies is required. This paper proposes that the elastic follow-up factors for C(t) can be determined by elastic-plastic analyses by using the plastic-creep analogy. Finite element analyses have been performed to verify this method.

The Influence of Specimen Geometry and Test Times on High Temperature Crack Growth Behaviour in Parent and Welded 316H Stainless Steel

2008 ◽  
Author(s):  
Catrin M. Davies ◽  
Robert C. Wimpory ◽  
Masaakai Tabuchi ◽  
David W. Dean ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Large Fraction ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Parent Material ◽  
Test Duration ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Order Of Magnitude ◽  
Fracture Specimens

Experimental crack growth testing has been performed at 550 °C on a range of fracture specimens including sections taken from a 316 steel weldment. These specimens include the compact tension, C(T), and circumferentially cracked notched bar, CCB, geometries of various sizes. Results are presented from two creep crack growth (CCG) tests on a large and a small CCB weldment specimen. The creep crack initiation (CCI) and growth (CCG) behavior of the CCB weldments has been compared to that of homogeneous parent material (PM) CCB and C(T) specimens and to C(T) weldment specimen data. The data has been analyzed in terms of the C* parameter. The initiation period is found to occupy a large fraction of the test duration for weldments. The CCG rates in the larger CCB weldment test is on the order of six times faster, for a given value of C*, compared to the smaller specimen, indicating a specimen size effect. The CCI times are around an order of magnitude greater for the CCB weldment specimens compared to C(T) weldment data and are higher than that of the PM CCB data. It is recommended that further testing on weldment specimens is performed to affirm the apparent trends.

Intercomparison of Creep Crack Growth Data

1992 ◽  
pp. 211-240
Author(s):  
A. Saxena ◽  
T. Hollstein ◽  
G. A. Webster ◽  
T. Yokobori
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Growth Data ◽  
Creep Crack
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