PSI - Issue 13

Rodrygo Figueiredo Moço et al. / Procedia Structural Integrity 13 (2018) 1915–1923 Rodrygo F. Moço, Fábio G. Cavalcante and Gustavo H. B. Donato / Structural Integrity Procedia 00 (2018) 000–000 7 of prestrain levels, reaching between 14 and 33% reductions for prestrain levels between 4.3 and 14.7%. It is potentially interesting for optimized design, structural integrity assessments and life predictions.  In addition, the effect of plastic prestrain in reducing the fatigue crack growth rate is nonlinear for varying Δ K . The greater is imposed Δ K during cyclic loading, the more pronounced will be plastic prestrain effect.  Despite in this work the material was prestrained using a uniaxial stress fields prior to machining specimens in order to avoid residual stresses (different from most cases found in literature, where specimens are prestrained directly), the same trend was found – the larger is the prestrain, the lower will be the FCG rate. 1921

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Fig. 5. FEM simulation of calendering process and resulting strains during (a) initial curvature and (b-d) the evolution of the process .

 The FE models for UOE and calendaring processes revealed the significant strain variations imposed by such manufacturing processes along the structures. They also proved that strains varies along the pipe radius and angular positions, which, as a consequence, can influence, for example, the number of cycles that a crack take to propagate through the pipe thickness. This results reinforce the necessity to consider prestrain effects during design of components that are cold plastic formed. Acknowledgements  This investigation is supported by the Brazilian Council for Scientific and Technological Development - CNPQ (grant 486176/2013-4 ) and by Centro Universitário FEI, Brazil, through its laboratories and human resources