Abstract: Abstract： In order to investigate the failure property of carcass layer, the lay angle, initial ovality and material nonlinearity of carcass layer were considered in this paper. Meanwhile, three kinds of contact conditions, i.e, bonded coupling, coulomb friction with friction coefficient, and smooth friction were adopted to simulate the contact between adjacent surfaces of carcass layer. Finally, failure properties of a typical carcass layer of unbonded flexible riser under uniform external pressure and two forces acting along a diameter were predicted by using ABAQUS. It is shown that the contact condition between adjacent surfaces of carcass layer has a great influence on failure property. The lay angle effect on failure property can be ignored. With initial ovality and material nonlinearity, the critical pressure of carcass layer under uniform external pressure is sharply decreased, while the radial displacement of carcass layer under crushing is greatly increased. The numerical method can remedy the flaw of analytical method which cannot take the above factors into consideration.

Key words: Key words： unbonded flexible risers, carcass, failure, material nonlinearity, initial ovality