Application of Reference Stress and Probabilistic Methodologies to Assessing Creep Crack Growth

2009 ◽  
pp. 54-54-20 ◽  
Author(s):  
GG Chell ◽  
CJ Kuhlman ◽  
HR Millwater ◽  
DS Riha
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Creep Crack ◽  
Reference Stress

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.

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.

Use of the reference stress concept to assess the effect of crack growth increment size on the accuracy of creep crack grow predictions

1986 ◽  
Vol 21 (2) ◽  
pp. 109-115
Author(s):  
T H Hyde ◽  
K C Low
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Growth Increment ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Moving Crack ◽  
Critical Crack ◽  
Creep Crack ◽  
Reference Stress

An approximate method, based on the reference stress concept, for carrying out ‘moving-crack’ calculations, under creep conditions, is presented. Creep crack growth is assumed to be related to the C∗ parameter. The predictions obtained correlate well with detailed, ‘moving-crack’, finite element calculations. Preliminary calculations, to assess the adequacy of finite element meshes and the effect of variations in material properties on the accuracy of predictions, can be carried out quickly and relatively cheaply. The usefulness of the technique is illustrated by using it to show the effect of the magnitude of the crack growth increment assumed and of the value of critical crack tip opening displacement (the initiation parameter assumed) used.

Numerical Prediction of Constraint Effect of Creep Crack Growth

2009 ◽  
Author(s):  
Masataka Yatomi ◽  
Kamran M. Nikbin
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Creep Crack Growth ◽  
Constraint Effect ◽  
Three Point Bending ◽  
Creep Crack ◽  
Reference Stress ◽  
Edge Notch ◽  
Stress And Strain Rate

This paper presents the effect of constraint on creep crack growth (CCG) using FE analysis based on the stress and strain rate state at the crack tip. The comparison is made by modelling C(T) specimen tests under plane stress and plane strain conditions using creep properties of three different steels (C-Mn steel, P91 steel, and 316H austenitic steel). In addition, in order to examine the constraint effect on CCG due to geometry single edge notch specimen (SENT), centre cracked tension specimen (CCT) and three point bending (3PB) specimen have also been analysed. In all cases it is found that when the reference stress under plane strain conditions is higher than the yield stress, there is little difference between CCG rates under plane stress and plane strain.

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.

Relationship between Creep Crack Propagation Rates of P92 Steel and Welding HAZ and High Temperature Creep Fracture Parameter C* Based on Reference Stress Method

2014 ◽  
Vol 915-916 ◽  
pp. 612-618
Author(s):  
Li Xin Wang ◽  
Chang Ming Sun ◽  
Yan Bo Wang ◽  
Lian Yong Xu
Keyword(s):  
High Temperature ◽  
Crack Growth ◽  
Base Metal ◽  
Creep Crack Growth ◽  
Fracture Parameter ◽  
P92 Steel ◽  
Creep Crack ◽  
Reference Stress ◽  
Steel Base ◽  
Creep Crack Growth Rate

Uniaxial creep tests on micro-regions of P92 steel base metal and welding HAZ specimens were carried out at 923 K and under different stress levels. The creep equation of index of B and n was obtained from the test data fitted by using least square method. Then, creep crack growth tests based on the reference stress method on P92 steel base metal and welding HAZ compact tensile samples were carried out at 923 K and under stress intensity factor K of 18 MPa·m1/2. From the calculated and experimental data, it was found that a good relationship existed between the creep crack growth rate da/dc and high temperature creep fracture parameter C*. The reference stress method was verified to calculate the C* of compact tension specimens and can predict the creep crack growth rate of the P92 steel base metal and welding HAZ materials under steady state creep conditions. At the same time, high temperature defect evaluation parameters of D0 and Φ were obtained by fitting the linear parts in the relation curves using the log-log method. This study provides tests data on the defects evaluation and life prediction of P92 steel welding materials.

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