The use of the C∗ parameter in predicting creep crack propagation rates

1977 ◽  
Vol 12 (3) ◽  
pp. 167-179 ◽  
Author(s):  
M P Harper ◽  
E G Ellison
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Single Edge ◽  
Single Edge Notch ◽  
Creep Crack ◽  
Edge Notch ◽  
Single Edge Notch Bend ◽  
Good Agreement

The applicability of the C∗ parameter for the prediction of creep crack propagation rates is considered. A new method for estimating C∗ is presented, the results from which show good agreement with those from an existing technique. Experimental results from creep crack growth tests, conducted on a 1 Cr Mo V steel using both compact tension and single edge notch bend specimens, indicate that good correlation with C∗ is obtained once the effects of stress redistribution become negligible. Finally, comparisons are drawn between C∗ and other possible correlating parameters, and the limitations of each approach are discussed.

Comparison of Fatigue Crack Growth Rates Between Different Specimen Geometries

2021 ◽  
Author(s):  
Yan-Hui Zhang ◽  
Matthew Doré
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Literature Review ◽  
Crack Growth ◽  
Compact Tension ◽  
Specimen Geometry ◽  
Single Edge ◽  
Single Edge Notch ◽  
Advantages And Disadvantages ◽  
Edge Notch

Abstract Most engineering components are subjected to cyclic loading in service and design against fatigue failure is often a key consideration in design. For fracture mechanics fatigue analysis, fatigue crack growth (FCG) tests are often required to determine the relevant Paris power law parameters for the material under the environment concerned. Standards allow use of different specimen geometries for FCG tests such as compact tension (CT), centre crack tension (CCT), single edge notch bend (SENB) and single edge notch tension (SENT). However, when selecting specimen geometry for fatigue crack growth rate (FCGR) testing, there is often doubt about which specimen geometry is more appropriate and whether they give similar FCGR. There is limited work to compare the FCGR between different specimen geometries. This paper first briefly introduces the guidance on FCG test specimen geometries in standards and compares the advantages and disadvantages of these specimen geometries. A comprehensive literature review is carried out to compare the FCGR data between different specimen geometries. FCGR tests are conducted on SENB, SENT and CCT specimens of C-Mn steel to investigate any effects of specimen symmetry/asymmetry and crack constraint on FCGR. Based on the literature review and test data, it is concluded that FCGR is independent of the specimen geometries examined.

Influence of Prior Deformation on Creep Crack Growth Behaviour of 316H Austenitic Steels

2012 ◽  
Author(s):  
Hamed Yazdani Nezhad ◽  
Noel P. O’Dowd ◽  
Catrin M. Davies ◽  
Ali N. Mehmanparast ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Fe Analysis ◽  
Austenitic Steels ◽  
Creep Data ◽  
Growth Behaviour ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Good Agreement

The influence of pre-strain and pre-stress on creep crack growth behaviour of 316H austenitic steels is studied experimentally and numerically in this paper. Compact tension, C(T), specimens (25mm thickness) have been extracted from two steam headers, one as-received and one uniformly compressed to the strain value of 8%. The C(T) specimen extracted from the as-received header was compressed, introducing a non-uniform strain field. Creep crack growth (CCG) tests were performed at 550°C. Comparisons have been provided with the results from as-received C(T) specimens. Finite element (FE) analysis has been carried out to simulate the CCG behaviour of the C(T) specimens. By choosing the problem parameters appropriately, good agreement may be achieved between the FE predictions and the creep data.

Three Dimensional Criterion for Creep Crack Propagation in C(T) Specimen

2016 ◽  
Vol 853 ◽  
pp. 142-147
Author(s):  
Wen Ming Ye ◽  
Xu Teng Hu ◽  
Wan Lin Guo ◽  
Ying Dong Song
Keyword(s):  
Crack Propagation ◽  
Crack Growth ◽  
Growth Rates ◽  
Three Dimensional ◽  
Creep Crack Growth ◽  
Growth Control ◽  
Compact Tension ◽  
Thickness Effect ◽  
Creep Crack ◽  
Crack Growth Rates

Experimental of two kinds of compact tension (CT) specimens’ creep crack propagation are carried out in this paper. Traditional fracture mechanics and three-dimensional fracture theory are compared and the results show that: The K-Tz two-parameter model can eliminate the thickness-effect on the crack growth rates in the relatively low K range, however when K exceed certain values the effect of thickness for crack growth rates still exists; The Ct and Ct-Tz model can describe the thickness-effect of creep crack growth rates in regions of high Ct; When the crack tip stress intensity factor K of the two kinds of thickness (B=5 mm, B=10 mm) specimens equal to 35 and 31 respectively, this material’s creep crack growth control parameter change from K to Ct.

Acoustic Emission Monitoring During Fatigue Crack Growth in Standard C(T) and Miniature Single Edge Notch Tension Specimens

2020 ◽  
Author(s):  
Raghu V. Prakash ◽  
Chandan K. Mukhopadhyay ◽  
Prathmesh Pokharkar ◽  
Manuel Thomas
Keyword(s):  
Growth Rate ◽  
Acoustic Emission ◽  
Fatigue Crack ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Compact Tension ◽  
Single Edge ◽  
Single Edge Notch ◽  
Edge Notch

Abstract The fatigue crack growth rate studies in a structural alloy has been carried out using ASTM E-647 standard compact tension (C(T)) specimens and miniature single edge notch tension specimens (SEN(T)) at two different stress ratios of 0.1 and 0.7. Standard C(T) specimen had a dimension of 63.5 × 61 × 8 mm thickness while the miniature SEN(T) specimen had a size of 20 mm effective length × 10 mm wide and 0.7 mm thickness. A starter notch of 0.5 mm was cut using wire EDM process to initiate fatigue crack growth in miniature SEN(T) specimen. A special fixture was designed for testing the miniature SEN(T) specimen. During the fatigue crack growth experiments, Acoustic Emission (AE) activity was monitored on-line using AE sensors from Physical Acoustics, Mistras Group, USA. For the experiments on standard C(T) specimens, a standard probe (R15A) of 15 mm diameter was used, while for small size compact tension specimen, a Nano30 AE probe was used. The crack growth was monitored by visual methods as well as by compliance technique. The cumulative counts and absolute energy information obtained during fatigue crack growth testing was used to correlate the crack growth rate with acoustic emission activity. Empirical fit of data was used to obtain cross-correlation between crack growth rate and AE parameters for both the specimen geometries. The study suggested that suitable selection and placement of sensors is essential to obtain good results using AE sensor technique.

scholarly journals Modelling the Variability and the Anisotropic Behaviour of Crack Growth in SLM Ti-6Al-4V

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1400
Author(s):  
Rhys Jones ◽  
Calvin Rans ◽  
Athanasios P. Iliopoulos ◽  
John G. Michopoulos ◽  
Nam Phan ◽  
...  
Keyword(s):  
Crack Growth ◽  
The United States ◽  
Fatigue Threshold ◽  
Growth Equation ◽  
Single Edge ◽  
Test Program ◽  
Large Variability ◽  
Single Edge Notch ◽  
Anisotropic Behaviour ◽  
Edge Notch

The United States Air Force (USAF) Guidelines for the Durability and Damage Tolerance (DADT) certification of Additive Manufactured (AM) parts states that the most difficult challenge for the certification of an AM part is to establish an accurate prediction of its DADT. How to address this challenge is the focus of the present paper. To this end this paper examines the variability in crack growth in tests on additively manufactured (AM) Ti-6Al-4V specimens built using selective layer melting (SLM). One series of tests analysed involves thirty single edge notch tension specimens with five build orientations and two different post heat treatments. The other test program analysed involved ASTM standard single edge notch specimens with three different build directions. The results of this study highlight the ability of the Hartman–Schijve crack growth equation to capture the variability and the anisotropic behaviour of crack growth in SLM Ti-6Al-4V. It is thus shown that, despite the large variability in crack growth, the intrinsic crack growth equation remains unchanged and that the variability and the anisotropic nature of crack growth in this test program is captured by allowing for changes in both the fatigue threshold and the cyclic fracture toughness.

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.

Warm Pre-Stressing and Leaks in Pipelines

2014 ◽  
Author(s):  
Andrew Cosham ◽  
Phil Hopkins ◽  
David G. Jones ◽  
Julian Barnett
Keyword(s):  
Beneficial Effect ◽  
Pipe Steel ◽  
Theoretical Models ◽  
Manganese Steel ◽  
Single Edge ◽  
Line Pipe ◽  
Single Edge Notch ◽  
Edge Notch ◽  
Line Pipe Steel ◽  
Single Edge Notch Bend

Line pipe steel is a carbon manganese steel. The toughness of line pipe steel undergoes a transition from high toughness (on the upper shelf) to low toughness (on the lower shelf) as the temperature decreases. A fluid will cool significantly as it expands through a leak in a pipeline. This has led to the suggestion that localised cooling of the material surrounding the leak might be sufficient to cool the material down to below the ductile to brittle transition temperature and cause a brittle fracture. Warm pre-stressing occurs when a load is applied to a structure containing a defect and then the temperature of the structure is reduced. Warm pre-stressing causes the defect in the structure to fail at a higher load at the lower temperature than if it had not experienced this prior loading at the previously higher temperature. A programme of single edge notch bend tests has been conducted on behalf of National Grid Carbon to demonstrate the beneficial effect of warm pre-stressing in a line pipe steel. The material tested was a sample of 914.4 mm outside diameter, 19.1 mm wall thickness, Grade API 5L X60 line pipe. Single edge notch bend specimens were subject to the ‘load-cool-fail’ cycle and the ‘load-unload-cool-fail’ cycle. The effect of different levels of stable ductile crack growth during the pre-load was also investigated. Warm pre-stressing is shown to have a beneficial effect. The load at failure in the specimens that had been subject to warm pre-stressing was higher than those that had not been subject to warm pre-stressing, and, in most cases, it was higher than the pre-load. The fracture toughness (in terms of the stress intensity factor) of the specimens that had been subject to warm pre-stressing was 1.4 to 1.7 times higher than that of those that had not been subject to warm pre-stressing. The results of the tests were conservatively predicted using the theoretical models. Also, the results are consistent with previous tests on structural steels. Therefore, localised cooling of the material around a leak in a pipeline is not predicted to result in a failure.

Fracture Toughness Estimation for Pipeline Girth Welds

2002 ◽  
Author(s):  
Henryk G. Pisarski ◽  
Colin M. Wignall
Keyword(s):  
Fracture Toughness ◽  
Weld Metal ◽  
Specimen Geometry ◽  
Single Edge ◽  
Single Edge Notch ◽  
Edge Notch ◽  
Loading Modes ◽  
Girth Welds ◽  
The Relationship ◽  
Single Edge Notch Bend

The relationship between fracture toughness estimated using standard single edge notch bend (SENB), single edge notch tension (SENT) test specimens and fracture toughness associated with a circumferential flaw in a pipe girth weld is explored in terms of constraint using the Q parameter. It is shown that in the elastic-plastic regime, use of standard deeply notched SENB specimens provides a conservative assessment of fracture toughness, for both weld metal and HAZ, because of the high constraint associated with this specimen geometry. Use of specimen geometries and loading modes associated with lower constraint (e.g. SENT and shallowed notched SENB specimens), allow for improved estimates of fracture toughness to be made that are appropriate for the assessment of circumferential flaws in pipe girth welds. Recommendations are given on the specimen designs and notch orientations to be employed when evaluating weld metal and HAZ fracture toughness.

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