Modelling of Fatigue Crack Propagation in Part-Through Cracked Pipes Using Gamma Function

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Mechanics, Materials Science & Engineering, September 2016

ISSN 2412-5954

Modelling of Fatigue Crack Propagation in Part-Through Cracked Pipes Using Gamma Function Pawan Kumar 1,a, Vaneshwar Kumar Sahu2, P.K.Ray2, B.B.Verma2 1

Institute For Frontier Materials, Deakin University, Australia

2

National Institute of Technology, Rourkela, India

a

pkumar@deakin.edu.au DOI 10.13140/RG.2.2.16973.03043

Keywords: fatigue crack propagation, part-through cracked pipes, gamma model.

ABSTRACT. In the present investigation a gamma model has been formulated to estimate the fatigue crack growth in part-through cracked pipe specimens. The main feature of the model is that the gamma function is correlated with various physical variables like crack driving parameters and materials properties in non-dimensional form so that the proposed model can be used for different loading conditions. The validation of model has been done with experimental data in order to compare its accuracy in predicting fatigue crack growth.

Introduction. The fatigue crack growth Nomenclature behaviour of surface crack in a pipe in a semi circumferential crack length; radial direction is one of the most serious problems associated with piping systems ai initial crack length (mm); as it is responsible for detection of leak aj final crack length (mm);; before break. There are different piping integrity systems used in aircrafts, A, B, C, D curve fitting constants offshore oil drilling, and coolant pipes in da/dN crack growth rate; high pressure nuclear reactors which encounter fluctuating loading condition. K stress intensity factor (MPa); Due to this kind of loading condition a new KC fracture toughness (MPa m); surface crack can generate or an existing K stress intensity factor range (MPa m); crack can propagate. This leads to damage in structure and integrity. Many M specific growth rate; researchers have studied fatigue crack growth problems in pipes. Different mij specific growth rate in interval( j-i); techniques like numerical analysis, finite N number of cycles; element method, boundary integral have P been used to address fatigue crack growth N j predicted fatigue life using exponential model; in pipes. Jhonson et al. [1] used boundary R load ratio; integral method for tension loading and providing a numerical solution to the Ri Internal radius of specimen; problem. Daond and Cartwright [2] t Thickness of specimen; applied strain energy release rate method w width of specimen in uniform tension as well as pure bending condition in pipes. Delate et al. [3] reported numerical results for exterior cracks of semi-elliptical shape using line spring model. In present research a modified gamma function is used to model fatigue crack growth in part- through cracked pipe in radial direction. MMSE Journal. Open Access www.mmse.xyz

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