Análise dos danos em arames da armadura de tração de umbilicais submarinos submetidos à fadiga por fricção

Abstract

The thesis addresses the analysis of friction-induced fatigue in submarine umbilicals, which are composite cables used in offshore operations. The armor wires of umbilicals are susceptible to fatigue failure, which may be associated with the friction wear phenomenon. Initially, wires containing actual friction-induced damage during full-scale fatigue tests of the umbilical were studied. These damages exhibited an elliptical shape with two defined zones: the adhesion zone and the sliding zone. The S-N diagrams of wires containing damage showed that minor defects did not affect fatigue behavior compared to smooth wires without prior damage. On the other hand, it was observed that larger defects could impact the fatigue life of the wires. Subsequently, methodologies were applied to analyze the fatigue life of damaged wires using the critical distance theory and continuous damage mechanics. The results indicated that the predictions provided appropriate approximations compared to literature data. Furthermore, the use of continuous damage mechanics allowed determining a minimum critical depth of 0.16 mm required to compromise the fatigue behavior of the material without the need to model the defect. The other part of the study involved designing a device and applying it in fatigue tests of umbilical wire friction. The results indicated that the proposed device could cause severe damage, although these damages were still not sufficient to significantly compromise the fatigue life of the component.