Three dimensional, flexural-torsional dynamic buckling of long wires after tensile fracture and implications on deep water riser dynamics

When a long slender structure such as a wire, strut or rope is loaded under tension all the way to fracture, upon failure an elastic unloading wave propagates down the wire and reflects as a compressive wave from the distant clamp end. The compressive effect of dynamic pulse buckling, amplitude and wave length depend on material properties and geometry features of the problem. Small scale experiments were performed on thin stainless steel wires of 0.127 mm diameter and varying lengths. The theory of dynamic pulse buckling, developed in the 1980s at the Stanford Research Institute, is used to study the initial phase of the deformation of the wire. In order to obtain a deeper insight in the mechanism of structural collapse, numerical simulations and high speed photography on small scale tests were employed. Both techniques revealed propagation of the bending disturbance (with increasing amplitude) and formation of the periodic helical shape wave with varying amplitude in space. A considerable axial momentum brings the wire into a complex process of elastic–plastic deformation with strain reversal. The numerical simulation was compared to high speed snapshots, showing good agreement. The implication of the presented results to structural integrity of deep water installations is also discussed.