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]

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.

Modelling Crack Growth in the Life Assessment of Elevated Temperature Components

2007 ◽  
Vol 348-349 ◽  
pp. 709-712
Author(s):  
Kamran M. Nikbin
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Plane Strain ◽  
Elevated Temperatures ◽  
Creep Crack Growth ◽  
Crack Propagation Rate ◽  
Life Assessment ◽  
Manganese Steel ◽  
Growth Data ◽  
Creep Crack

Modelling of Creep Crack Growth (CCG) using analytical and numerical methods is relevant to life assessment procedures of components operating at elevated temperatures. This paper compares an analytical crack prediction and a numerical based virtual CCG technique used in fracture mechanics components with sample experimental results. Two approaches are presented. First the well developed strain exhaustion model called the NSW and the modified NSW-MOD models which predict plane stress/strain bound crack initiation and growth rates for engineering alloys and the second a damage-based approach used to numerically predict the crack propagation rate in Finite Element models of fracture mechanics specimens. The results from both methods are correlated against an independently determined C* parameter. As an example the NSW and the extended NSW-MOD strain exhaustion models are applied to compare to the experimental data and FE predictions for two steels at Carbon-Manganese steel tested at 360 oC and a weld 316H stainless steel at 550 oC. For values of C* within the limits of the present creep crack growth data presented the plane strain crack growth rate predicted from the numerical analysis is found to be less conservative than the plane strain NSW model but more conservative than plane strain NSW-MOD model.

Creep Crack Growth of P92 Welds

2008 ◽  
Author(s):  
Masataka Yatomi ◽  
Akio Fuji ◽  
Ken-ichi I. Kobayashi ◽  
Masaaki Tabuchi ◽  
Takeo Yokobori ◽  
...  
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Creep Model ◽  
Element Analysis ◽  
Creep Properties ◽  
Creep Crack ◽  
Type Iv ◽  
Growth Properties ◽  
Power Law Creep

This paper represents creep properties and creep crack growth properties for P92 welds. The CCG tests were carried out using cross-welded compact tension (C (T) specimens at several temperatures. The crack front was located at HAZ region to simulate Type IV crack. Finite element analysis was conducted to simulate multiaxiality in welded joints and compare the experimental results. The constitutive behaviour for these materials is described by a power law creep model.

Estimation of Creep Crack Growth Properties Using Circumferential Notched Round Bar Specimen for 12CrWCoB Rotor Steel

2005 ◽  
Vol 297-300 ◽  
pp. 397-402
Author(s):  
Je Chang Ha ◽  
Joon Hyun Lee ◽  
Masaaki Tabuchi ◽  
A.Toshimitsu Yokobori Jr.
Keyword(s):  
Crack Growth ◽  
Axial Stress ◽  
Creep Crack Growth ◽  
Turbine Rotor ◽  
Rotor Steel ◽  
Creep Ductility ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Round Bar ◽  
Growth Properties

Most heat resisting materials in structural components are used under multi-axial stress conditions and under such conditions ductile materials often exhibit brittle manner and low creep ductility at elevated temperature. Creep crack initiation and growth properties are also affected by multi-axial stress and it is important to evaluate these effects when laboratory data are applied to structural components. Creep crack growth tests using circumferential notched round bar specimens are a simple method to investigate multi-axial stress effects without using complicated test facilities. Creep crack growth tests have been performed using a 12CrWCoB turbine rotor steel. In order to investigate the effects of multi-axial stress on creep crack growth properties, the tests were conducted for various notch depths at 650°C. The circumferential notched round bar specimen showed brittle crack growth behaviour under multi-axial stress conditions. Creep crack growth rate was characterized in terms of the C* parameter. A 12CrWCoB turbine rotor steel has been tested using circumferential notched round bar specimens with different multi-axiality. Circumferential notched round bar specimens show increased brittle creep crack growth behaviour due to the multi-axial stress condition. Creep crack growth properties could be predicted by allowing for the decrease of creep ductility under multi-axial conditions.

scholarly journals Creep Crack Growth Test Method and Creep Crack Growth Properties for TiAl Intermetallic Compound.

2000 ◽  
Vol 49 (1) ◽  
pp. 80-85 ◽  
Author(s):  
Masaaki TABUCHI ◽  
Toshimitu YOKOBORI ◽  
Akio FUJI ◽  
Kiyoshi KUBO ◽  
Koichi YAGI ◽  
...  
Keyword(s):  
Intermetallic Compound ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Test Method ◽  
Creep Crack ◽  
Growth Test ◽  
Tial Intermetallic Compound ◽  
Growth Properties

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.

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