High Temperature Component Life Assessment

This paper presents a numerical study of creep crack growth in a fracture mechanics specimen. The material properties used are representative of a carbon-manganese steel at 360 o C and the constitutive behaviour of the steel is described by a power law creep model. A damage-based approach is used to predict the crack propagation rate in a compact tension specimen. Elastic-creep and elastic-plastic-creep analyses are performed using two different crack growth criteria to predict crack extension under plane stress and plane strain conditions. The plane strain crack growth rate predicted from the numerical analysis is found to be lower than that predicted from ductility exhaustion plane strain model (known as the NSW model), which uses the creep fracture mechanics parameter C* and the development of creep damage directly ahead of the crack tip to predict creep crack growth rates under plane strain/plane stress conditions. A modified NSW model (NSW-MOD) is presented in which the effect of the damage angle at the crack tip is considered in order to predict this difference. In the model it is assumed that fracture occurs first at the value of the crack tip angle, at which the creep strain, reaches its maximum value. It is found that the new NSW-MOD gives a better prediction of the plane strain upper-bound of the experimental data.

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“…(1) or (2), the stress and strain rate in the vicinity of a sharp crack tip are given by (see e.g. [17]),…”

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confidence: 99%

Theoretical and numerical modelling of creep crack growth in a carbon–manganese steel

Yatomi

O’Dowd

Nikbin

et al. 2006

Engineering Fracture Mechanics

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“…The results of fatigue tests were then used to describe the fatigue life as a function of P parameter defined by equation (1). The following diagrams (Figs.…”

Section: Modified Methods Of the Fatigue Life Description At Elevated mentioning

confidence: 99%

“…There are studies on creep processes of materials, their durability and methods of assessing the degree of material damage caused by long-term effects of load and temperature [1][2][3][4][5]. Many studies concentrate on the issue of initiation and growth of cracks both at room temperature and at elevated temperatures [1,[6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

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The Attempt of the Low-Cycle Fatigue Life Description of Chosen Creep-Resistant Steels Under Mechanical and Thermal Interactions

Okrajni

Marek

2017

Archives of Metallurgy and Materials

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The study focuses on the problem of determination of low-cycle fatigue properties for the chosen group of creep-resistant steels used in the power and chemical industries. It tries to find the parameter which would describe well the fatigue life and take into account mechanical loads and temperature. The results of LCF tests have been presented in the paper. New parameter P has been introduced. This parameter joins a plastic strain range, a stress range and temperature. The fatigue life has been predicted versus parameter P. The comparison of the predicted and observed values of fatigue life shows the agreement between these values. The method of fatigue life prediction formulated in this way is expected to describe the behavior of materials under thermo-mechanical fatigue.

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“…11. This is to be expected whilst damage is building up at a crack tip during the early stage of cracking [23].…”

Section: Crack Growth Analysismentioning

confidence: 96%

Creep crack initiation and growth in thick section steel pipes under internal pressure

Wasmer

Nikbin

Webster

2003

International Journal of Pressure Vessels and Piping

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In this study, creep crack growth in pre-cracked straight and bent pipes of a 9% Cr-steel, containing multiple cracks and tested at 625°C under static and slow cyclic pressure loading, is investigated. The results have been interpreted in terms of the creep fracture mechanics parameter C* and compared with data obtained on standard compact tension (CT) specimens of the same material and batch. In making the assessments, reference stress methods have been used to determine C* for the pipes. Several formulae can be employed for calculating reference stress depending on whether it is based on a 'global' or a 'local' collapse mechanism. When using this approach, it is shown that the values obtained for C* are sensitive to the material properties, geometric dimensions and crack lengths chosen in the analysis. However, it has been found that, the most satisfactory comparison of crack growth rates with standard CT specimen data is obtained when the 'global' reference stress solution is used in conjunction with the nominal thickness of a pipe and the mean parent uniaxial creep properties. Also, no difference has been observed between the crack growth rates measured in the straight and bent pipes. The main effect of the slow pressure cycling was to cause an acceleration in the early stages of cracking.

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High Temperature Component Life Assessment

Cited by 271 publications

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Theoretical and numerical modelling of creep crack growth in a carbon–manganese steel

Theoretical and numerical modelling of creep crack growth in a carbon–manganese steel

The Attempt of the Low-Cycle Fatigue Life Description of Chosen Creep-Resistant Steels Under Mechanical and Thermal Interactions

Creep crack initiation and growth in thick section steel pipes under internal pressure

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