The interlocked carcass layers of unbonded flexible pipes are designed to resist the radial compression failure due to installation,storage and transportation. A three dimensional finite element model is developed to simulate the radial compression behavior of the carcass under radial forces. At the same time,by simplifying the carcass into a ring,an analytic formula of the radial compression stiffness of a ring under radial force is deduced for the carcass. A testing rig is also established for the radial ...