Influence of net section damage on creep crack growth

1989 ◽  
Vol 24 (2) ◽  
pp. 75-82 ◽  
Author(s):  
K Nishida ◽  
K M Nikbin ◽  
G A Webster
Keyword(s):  
Crack Growth ◽  
Residual Life ◽  
Process Zone ◽  
Creep Crack Growth ◽  
Appreciable Effect ◽  
Creep Crack ◽  
Short Cracks ◽  
Significant Damage ◽  
Mechanics Concepts ◽  
Uncracked Ligament

Fracture mechanics concepts for describing creep crack growth in terms of ductility exhaustion in a process zone at the crack tip are reviewed and extended to include damage accumulation in the ligament ahead of a crack. Applications are considered which show that net section damage has most influence for short cracks and plane stress conditions where significant damage can develop in the uncracked ligament. It is shown that, under plane strain loading, insufficient ligament damage occurs during the crack growth phase for it to have an appreciable effect on failure times. A method is also presented for accounting for the influence of an incubation period prior to the onset of cracking and for making residual life estimates.

Prediction of creep crack growth from uniaxial creep data

1984 ◽  
Vol 396 (1810) ◽  
pp. 183-197 ◽  
Keyword(s):  
Crack Growth ◽  
Growth Rates ◽  
Process Zone ◽  
Creep Crack Growth ◽  
Creep Process ◽  
Uniaxial Tensile ◽  
Creep Data ◽  
Creep Ductility ◽  
Creep Crack ◽  
Crack Growth Rates

In this paper uniaxial tensile creep data are used in conjunction with fracture mechanics concepts to predict creep crack growth rates in materials having a wide range of creep ductilities. A model is proposed of creep damage accumulation in a process zone ahead of the crack tip. The model allows all stages of creep to be incorporated in an approximate manner and creep ductility to be stress and stress-state sensitive. Good agreement is obtained with experimental crack growth data on a range of low alloy steels, a stainless steel, an aluminium alloy and a nickel-base superalloy. It is found that cracking rate is insensitive to the creep process zone size but inversely proportional to creep ductility. Crack growth rates under plane strain conditions are shown to be about fifty times those for plane stress loading.

A Sensitivity Study of Creep Crack Growth in Pipes

2002 ◽  
Author(s):  
K. Wasmer ◽  
K. M. Nikbin ◽  
G. A. Webster
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Creep Crack Growth ◽  
Sensitivity Study ◽  
Pressure Vessels ◽  
Materials Properties ◽  
Creep Crack ◽  
Piping Systems ◽  
Mechanics Concepts ◽  
Assessment Procedures

Failure of pressure vessels and piping systems that operate at high temperatures can occur by net section rupture, creep crack growth or a combination of both processes. Several design and assessment procedures are available for dealing with this situation. These include the ASME Pressure Vessel and Piping, French RCC-MR (Appendix 16) and British R5 and BS7910 codes. Each of these procedures uses a combination of continuum mechanics and fracture mechanics concepts to make an assessment. Although the procedures adopt the same basic principles, often different formulae are employed to make an assessment. The main parameters that are used are reference stress, σref, stress intensity factor, K, and the creep fracture mechanics term C*. In this paper, an analysis is performed to estimate the sensitivity of the predictions of creep crack growth in a pressurised pipe to the choice of formulae used and materials properties employed. It is shown that most sensitivity is obtained to choice of expression employed for calculating σref and to whether batch specific or more generic materials properties data are selected.

scholarly journals Creep crack growth assessment in terms of continuum damage mechanics

2018 ◽  
Vol 165 ◽  
pp. 19003
Author(s):  
Valery Shlyannikov ◽  
Andrey Tumanov
Keyword(s):  
Growth Rate ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Process Zone ◽  
Creep Crack Growth ◽  
Intensity Factors ◽  
Stress Strain ◽  
Creep Crack ◽  
Creep Stress

The stress, strain rate, and process zone with respect to the creep-crack growth in compacttension C(T) specimen is analyzed by employing damage-evolution equations. The damage model for the fracture of the process zone is represented using a stress based formulation. Both damage free and defective creeping solids have been studied. The variations in the creep stress/strain and crack-tip governing parameter in terms of the creep stress intensity factors with respect to time and the evolution of creep damage are analyzed using an FE model for C(T) specimen. The creep-fatigue crack growth rate tests were performed on special designed program test-cycle. The interpretation of the experimental creep crack growth rate data was given in terms of introduced creep stress intensity factors based on undamaged and damaged stress/strain fields.

Fracture mechanics in the creep range

1994 ◽  
Vol 29 (3) ◽  
pp. 215-223 ◽  
Author(s):  
G A Webster
Keyword(s):  
Experimental Data ◽  
High Temperature ◽  
Fracture Mechanics ◽  
Crack Growth ◽  
Limit Analysis ◽  
Process Zone ◽  
Creep Data ◽  
High Temperature Components ◽  
Mechanics Concepts ◽  
Uncracked Ligament

Cracked high temperature components may fail by crack growth, net-section rupture, or some combination of both processes. This paper reviews the fracture mechanics concepts required to describe this behaviour. Procedures are presented for evaluating relevant characterizing parameters using experimental, numerical and limit analysis methods. Models for predicting crack propagation rates from uni-axial creep data involving ductility exhaustion in a process zone at a crack tip are outlined. Both the influence of build-up of damage in the process zone and material deterioration in the uncracked ligament are considered. It is shown that the models give satisfactory correlations with experimental data.

An Engineering Approach to the Prediction of Creep Crack Growth

1986 ◽  
Vol 108 (2) ◽  
pp. 186-191 ◽  
Author(s):  
K. M. Nikbin ◽  
D. J. Smith ◽  
G. A. Webster
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Elevated Temperatures ◽  
Process Zone ◽  
Creep Crack Growth ◽  
Crack Tip ◽  
Creep Damage ◽  
Creep Ductility ◽  
Creep Crack

This paper is concerned with assessing the integrity of cracked engineering components which operate at elevated temperatures. Fracture mechanics parameters are discussed for describing creep crack growth. A model is presented for expressing growth rate in terms of creep damage accumulation in a process zone ahead of the crack tip. Correlations are made with a broad range of materials exhibiting a wide spread of creep ductilities. It is found that individual propagation rates can be predicted with reasonable accuracy from a knowledge only of the material uni-axial creep ductility. An engineering creep crack growth assessment diagram is proposed which is independent of material properties but which is sensitive to the state of stress at the crack tip. Approximate bounds are presented for plane stress and plane strain situations and it is shown that crack growth rates about fifty times faster are expected under plane strain conditions than when plane stress prevails.

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