Application of a Novel Load Line Displacement Partitioning Technique to Creep Crack Growth Tests on Sen(t) Geometries of Type 316h Stainless Steel

2021 ◽  
Author(s):  
Jorge De-Andres ◽  
Michael Jones ◽  
Catrin Mair Davies
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Creep Crack ◽  
Load Line ◽  
Load Line Displacement ◽  
Partitioning Technique

Experimental Determination of Elastic and Plastic LLD Rates During Creep Crack Growth Testing

2017 ◽  
Author(s):  
K. M. Tarnowski ◽  
C. M. Davies ◽  
K. M. Nikbin ◽  
D. W. Dean
Keyword(s):  
Finite Element ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Current Method ◽  
Creep Crack ◽  
Load Line ◽  
Load Line Displacement ◽  
Final Failure ◽  
Complex Crack

Elastic and plastic load line displacement (LLD) rates are often ignored when analyzing Creep Crack Growth (CCG) tests due to difficulties in accurately determining their value for complex crack morphologies typical of creep. Instead, the total LLD rate is assumed to be entirely due to creep. This simplistic approach overestimates the crack tip characterizing parameter C* which is non-conservative. This paper presents a review of the current method of interpreting CCG test data in ASTM E1457 and proposes an improved approach which accounts for the elastic and plastic LLD rates. Estimations of the elastic and plastic LLD rate are obtained from a partial unload immediately after load-up and a full unload, at the end of the test, prior to final failure. Some finite element validation of this method is presented. Implementing this approach will facilitate more realistic CCG laws.

Analysis of Creep Crack Growth by Intelligent Phased Array Ultrasonic Inspection

2004 ◽  
Vol 261-263 ◽  
pp. 1319-1324 ◽  
Author(s):  
C.S. Jeong ◽  
Byeong Soo Lim
Keyword(s):  
Growth Rate ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Phased Array ◽  
Critical Role ◽  
Creep Crack Growth ◽  
Displacement Rate ◽  
Creep Crack ◽  
Load Line ◽  
Load Line Displacement

At high temperatures typical for service conditions in fossil power plants, the creep fracture is dominated by the formation, growth and coalescence of cavities. Using high temperature pipe materials, P92 and P122, the characteristics of creep crack growth were analyzed in this study according to the cavities. The characteristics of cavities play a critical role in creep crack propagation and load line displacement. The effect of the load line displacement rate(dv/dt) and crack growth rate(da/dt) on the da/dt–Ct relation of creep crack growth was evaluated at different temperatures and Ki(initial stress intensity factor) values. The number of cavities increased with increasing temperature and Ki. The crack growth rate and load line displacement rate increased with the increase in the cavity numbers. The kind and distribution of these internal flaws were investigated by an intelligent phased array ultrasonic method and they were utilized in deriving the relationship with the creep crack growth rate, which will predict the creep characteristics of these materials.

Load Line Displacement Partitioning in Creep Crack Growth Analyses of 316H Stainless Steel

2018 ◽  
Author(s):  
Michael D. Jones ◽  
Kamran M. Nikbin ◽  
Catrin M. Davies
Keyword(s):  
Crack Growth ◽  
Creep Crack Growth ◽  
Displacement Rate ◽  
Uniaxial Tensile ◽  
Growth Data ◽  
Creep Crack ◽  
Load Line ◽  
Load Line Displacement ◽  
Accelerated Creep ◽  
Tensile Data

Accelerated creep crack growth tests in the laboratory can lead to greater levels of plasticity at the tip of a creep crack than would be experienced in service. This is problematic when trying to determine C* which is used to model the stress field ahead of a crack. Deflection partitioning methods must be used in order to determine the contribution to the load line displacement rate as a result of creep which in turn is used to calculate C*. This partitioning can lead to negative values of the creep load line displacement rate due to the high contribution from plasticity. The amount of assumed plasticity is likely to be erroneously high as it is currently assumed that the material behaviour fits a Ramberg-Osgood model, when in reality such a fit does not predict the behaviour well over a large range of stress. This work compares the load line displacement determined from solutions based on a Ramberg-Osgood model with those calculated from finite element simulations using uniaxial tensile data to model the plasticity. The simulations formulated crack growth by means of a crack length vs time criterion using experimental crack growth data. It is found that the theoretical solutions do over predict the amount of plastic deformation compared to the numerical results. It is also found that for the short term test considered, the load-line displacement due to creep deformation was small compared to that from crack growth.

Life Estimation of Cracked Stainless Steel Components Under Creep Conditions

1991 ◽  
Vol 113 (3) ◽  
pp. 303-306 ◽  
Author(s):  
V. M. Radhakrishnan ◽  
M. Kamaraj ◽  
V. V. Balasubramaniam
Keyword(s):  
Stainless Steel ◽  
Crack Growth ◽  
Nuclear Power ◽  
State Energy ◽  
Creep Crack Growth ◽  
Experimental Investigations ◽  
Plane Stress Condition ◽  
Line Integral ◽  
Energy Rate ◽  
Creep Crack

Experimental investigations have been carried out to study the creep crack growth in types 316, 308 Cb, and 304 L stainless steel in the temperature range of 873–1073 K under plane stress condition. Testings have been carried out with both the base metal and the welded composite joints, because such joints are commonly used in nuclear power industries. Among the various parameters tried to correlate the creep crack growth, the energy rate line integral has been found to give the best description of the crack growth rate. The steady-state energy rate line integral has been found to correlate well with the rupture time. Based on this observation, life estimations are presented for thin components containing various initial defect sizes.

Numerical Simulation of Creep Crack Propagation for Austenitic Stainless Steel 0Cr18Ni9 at 550°C

2011 ◽  
Vol 230-232 ◽  
pp. 596-599
Author(s):  
Li Jie Chen ◽  
Zun Qun Gong ◽  
Qi Zhao
Keyword(s):  
Stainless Steel ◽  
Austenitic Stainless Steel ◽  
Crack Propagation ◽  
Crack Growth ◽  
Elevated Temperatures ◽  
Creep Crack Growth ◽  
Tensile Creep ◽  
Computational Error ◽  
Propagation Length ◽  
Creep Crack

First, tensile creep curve and creep propagation tests are conducted for austenitic stainless steel 0Cr18Ni9, i.e. 304 stainless steel at 550°C. The corresponding time hardening creep law is given for stresses ranging from 240 to 320 Mpa and the creep crack propagation length under a tension load of 10kN is measured by using QUESTAR long focus microscope system. Second, with the commercial finite element (FE) code ANSYS, the critical crack tip opening displacement (CTOD) is considered as crack propagation criterion to simulate the creep crack growth in the standard compact tension (CT) specimen. The FE predictions of the creep crack length in the primary and secondary stages are found to agree reasonably with the experimental results. The maximum computational error between the predictions and the experiment results is within 10%. Hence, the critical CTOD is a feasible criterion for crack growth simulations at elevated temperatures.

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.

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