TDFAD Analysis of Creep Crack Initiation in Pre-Strained and As-Received Type 316H Stainless Steel

2012 ◽  
Author(s):  
C. M. Davies ◽  
D. W. Dean ◽  
A. Mehmanparast
Keyword(s):  
Stainless Steel ◽  
Crack Initiation ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Small Scale ◽  
Creep Crack ◽  
Material Condition ◽  
Failure Assessment ◽  
Dependent Failure ◽  
Tension Fracture

The time dependent failure assessment diagram (TDFAD), an extended form of the low temperature FAD used in the R6 procedure, has been developed to allow creep crack initiation to be predicted using a FAD-based approach. The TDFAD has a number of advantages compared to other methods for predicting creep crack initiation time: detailed calculations of crack tip parameters such as C* are not needed; it is not necessary to establish the fracture regime in advance and the TDFAD can indicate whether initiation occurs under small-scale or widespread creep conditions. The TDFAD approach relies on the availability of appropriate creep toughness, Kcmat, values. In this work, creep toughness data have been derived from experimental creep crack growth (CCG) tests on compact tension fracture mechanics specimens made of Type 316H stainless steel in as-received (AR) material and material that has been pre-compressed (PC) by up to 8% plastic strain. The influence of material pre-conditioning on creep toughness is examined. TDFADs are then constructed for each material condition and creep crack initiation (CCI) time predictions are obtained for the CCG tests performed on the Type 316H steel at 550 °C. The influence of material condition on the predicted CCI mode is examined and discussed.

TDFAD Analysis of Creep Crack Initiation in 0.5CMV/2.25CrMoV Steel Weldments

2019 ◽  
Author(s):  
M. Ejaz ◽  
C. M. Davies
Keyword(s):  
Crack Initiation ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Parent Material ◽  
Time Dependent ◽  
Creep Crack ◽  
Material Condition ◽  
Weld Material ◽  
Failure Assessment ◽  
Dependent Failure

Abstract The time dependent failure assessment diagram (TDFAD) is a convenient methodology to simultaneously assess whether a component is likely to fail by brittle, ductile or creep fracture, plastic collapse or creep rupture. In this work, creep toughness data, Kmatc, have been derived from experimental creep crack growth (CCG) tests on compact tension fracture mechanics specimens made of a weldment consisting of 0.5CMV parent material, 2.25CrMo, where the starter crack was located in the heat affected zone (HAZ). Time dependent failure assessment diagrams (TDFADs) are then constructed for each material condition and creep crack initiation (CCI) time predictions were obtained for the CCG tests performed on the weldment samples using both a TDFAD based on either parent and weld material data. The TDFAD based on the weld data provided the most conservative prediction of CCI times thus is recommended for use for weldment samples.

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.

Specimen Orientation and Constraint Effects on the Creep Crack Growth Behaviour of 316H Stainless Steel

2012 ◽  
Author(s):  
A. Mehmanparast ◽  
C. M. Davies ◽  
D. W. Dean ◽  
K. M. Nikbin
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Compact Tension ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Uniaxial Creep ◽  
Microstructural Effects ◽  
Specimen Orientation ◽  
Constraint Effects

Pre-compression (PC) is found to have strong effects on the tensile, uniaxial creep rupture and creep crack growth (CCG) behaviour of type 316H stainless steel at 550 °C. In this work, blocks of 316H steel have been pre-compressed to 8% plastic strain at room temperature and compact tension, C(T), specimens are extracted from the pre-strained blocks with loading directions parallel and normal to the PC axis. The influence of specimen orientation and thickness on the CCG behaviour of the PC material is examined. The results are compared to short term and long term CCG behaviour of 316H steel at the same temperature. Higher CCG rates and shorter CCI times have been found in PC material with a loading direction normal to the PC axis compared to that parallel to the PC axis. These observations are discussed with respect to the microstructural effects.

scholarly journals Failure assessment diagram analysis of creep crack initiation in 316H stainless steel

2003 ◽  
Vol 80 (7-8) ◽  
pp. 541-551 ◽  
Author(s):  
C.M. Davies ◽  
N.P. O'Dowd ◽  
D.W. Dean ◽  
K.M. Nikbin ◽  
R.A. Ainsworth
Keyword(s):  
Stainless Steel ◽  
Crack Initiation ◽  
Failure Assessment Diagram ◽  
Creep Crack ◽  
Failure Assessment ◽  
Diagram Analysis

Predictions of Creep Crack Initiation Periods in Pre-Compressed 316H Stainless Steel

2013 ◽  
Author(s):  
K. M. Tarnowski ◽  
C. M. Davies ◽  
G. A. Webster ◽  
D. W. Dean
Keyword(s):  
Stainless Steel ◽  
Crack Initiation ◽  
Crack Growth ◽  
Crack Opening ◽  
Creep Crack Growth ◽  
Prediction Methods ◽  
Opening Displacement ◽  
Crack Growth Behaviour ◽  
Creep Crack ◽  
Significant Difference

Pre-compression of 316H stainless steel significantly alters its tensile, uniaxial creep and crack growth behaviour. It has previously been shown that reliable and conservative creep crack initiation predictions can generally be obtained for as-received 316H stainless steel using a variety of prediction methods. Given the changes in material behaviour caused by pre-compression, this paper applies similar prediction methods to pre-compressed 316H stainless steel at 550°C. Several procedures are available for estimating creep crack initiation time periods. The suitability of a procedure depends on the availability of the necessary material data. The procedures considered in this paper include the use of the creep fracture mechanics parameter C*, the crack opening displacement concept, the sigma-d approach and the time dependent failure assessment diagram. Creep crack growth tests have been performed on compact tension specimens manufactured from 316H stainless steel which was uniformly pre-compressed by 4% and 8% at room temperature. For each test, the time for creep crack initiation to occur was recorded. Predicted creep crack initiation times have been compared with the experimentally determined values. Comparisons with as-received material are also included. For pre-compressed material, conservative creep crack initiation predictions were only consistently achieved using steady state creep crack growth rates predicted from C*. This is a significant difference to as-received material for which conservative predictions were generally obtained by a variety of methods. At this time, there is only a limited set of pre-compressed data making it difficult to draw firm conclusions about the appropriateness of the various creep crack initiation prediction methods. The differences in the results between the pre-compressed and as-received material do however highlight the need for further tests on pre-compressed material.

Correlation Analysis Between Time-Dependent Creep Crack-Tip Stress and Constraint Effect on Creep Crack Initiation Time

2020 ◽  
Author(s):  
Seung-Ho Lee ◽  
Hyun-Woo Jung ◽  
Yun-Jae Kim ◽  
Kamran Nikbin ◽  
Robert A. Ainsworth
Keyword(s):  
Crack Initiation ◽  
Correlation Analysis ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Compact Tension ◽  
Time Dependent ◽  
Initiation Time ◽  
Constraint Effect ◽  
Creep Crack ◽  
Crack Tip Stress

Abstract In this study, to qualify the constraint effect on creep crack initiation, the correlation analysis between proposed constraint parameter Q’ using time-dependent creep crack-tip stress and creep crack initiation time variable Ai was performed. Ai implies the influence of constraint effect on creep crack initiation. The procedure to calculate the Ai and the Q’-parameter was presented. To evaluate various status of constraint effect, creep crack growth tests for twenty-one compact tension specimens of Type 316H stainless steel at 550°C were investigated. The results of correlation analysis explain the reason for the different initiation time at the same C* level in respect of constraint effect.

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