Internal material “architecture” for a kink-resistant metal tube

Catastrophic irreversible kink failure of a tubular geometry places considerable constraint on the design of metal structures and forming processes. A solution that postpones or eliminates such failure can be expected to significantly improve performance. The present study presents one possible solution: a tube with an internal “architecture” of alternating material properties along the axial direction. The influence of different geometries and material combinations on bending properties is investigated. Numerical analysis shows that the proposed solution provides better kinking resistance for certain geometries and material combinations. Such improvement is obtained through changes in deformation mechanism where softer regions bulge out during bending and prevent the creation of an inward kink. This allows higher bending curvatures to be reached. A small set of steel tubes was treated by carburization to test the concept. The experiments confirm the potential of the proposed architecture.