An Approach to Account for Negative R-Ratio Effects in Fatigue Crack Growth Calculations for Pressure Vessels Based on Crack Closure Concepts

Abstract

Current fatigue crack growth procedures in the commercial nuclear industry do not clearly specify how compressive loads are to be handled and, therefore, regulatory agencies usually recommend a conservative approach requiring full consideration of the loads. This paper demonstrates that a more realistic approach to account for compressive loads can be formulated using crack closure concepts. Several empirical plasticity-induced crack closure models were evaluated. An approach in the Section XI ASME Code for tensile loading only has been extended and evaluated for negative R-ratios. However, the paper shows this approach to be overly conservative. The approaches using crack closure models are shown to be more accurate. An analytically based crack closure model, while more complicated, is shown to give a theoretical basis to the empirically derived crack closure models. The paper concludes with a recommendation for modifying the current ASME Code practices consistent with the crack closure models and fatigue crack growth data from negative R-ratio tests.

Simulation of the Propagation of Circumferential Crack in the Cylindrical Element Structure Exposed to Cyclic Loadings

“…Полученные результаты сравниваются с данными расчетов по методу Ньюмана [7], который позволяет учитывать асимметрию цикла нагружения и свойства материала, характеризующие зону пластичности. В соответствии с ним, расчетная формула для скорости роста трещины для рассматриваемого случая 846 , 3 10…”

“…При этом предполагается, что в полуцикле сжимающих нагрузок трещина не распространяется, а расчеты проводятся для отнулевого цикла [4][5][6]. Вместе с тем, ряд исследований по распространению трещины при знакопеременном цикле нагружения (как экспериментальных [3,7] так и численных [8]) показывают, что сжимающий полуцикл нагружения также влияет на развитие трещины.…”

Fatigue crack growth under remote and local compression – a state-of-the-art review

“…and Kmax, such as Forman's equation [34], the relationship proposed by McEvily et al [35] and a number of other authors. For a review of some of the famous fatigue crack growth rate equations see the works of Bloom [36] and Huang [37]. The equations are mainly based on empirical plasticity-induced crack closure models.…”

“…The equations are mainly based on empirical plasticity-induced crack closure models. Additional mechanisms include asperity-induced and oxide-induced closure [36]. The Two Parameter models, e.g.…”

Correlations between crack initiation and crack propagation lives of notched specimens under constant and variable amplitude loading

“…Leonetti et al 18 predicted cyclic R‐curves and respecting crack opening and closing effects useable for short and long cracks in welded components based only on the Vickers hardness HV using the ‐model in combination with approaches by McEvily 20 and Chapetti 21 . Liang et al 17 combined an effective stress intensity factor range Δ K eff (considering crack opening and closing effects) with the multi‐R‐ratio model by Bloom 15 . Using Neuber's Equation Liang et al calculated the effective stresses and strains in the notch from the nominal stresses using the plastic load factor K p and therefore identify Δ K eff .…”