Optimising Plasma Cut-edge Properties for Improving the Durability of Bridge Structures

摘要

The qualities of plasma cut-edges generated on S355 structural steel were investigated to understand their effect on durability. These edges are left exposed in often critical areas after final assembly of bridge and load bearing applications, in which the damaging characteristic defects formed during the cutting process can act as initiation sites for fatigue cracks. Cuts were generated using oxygen and air at a range of commercial traverse cutting speeds that are used to fabricate structural components. A comparison of topographical properties and microstructural observations confirmed that the changes in the cut-edge surface and internal properties were significantly altered by the plasma gas type. Through the characterisation of cut-edges, optimum process parameters were determined that minimise the level of cut-edge microstructural and surface damage. An improvement in understanding the mechanisms that form irregularities on plasma cut-edge surfaces has been developed, so that damage inducing characteristic properties can be minimised. This has resulted in establishing the influence of characteristic properties on resulting fatigue life, as a means to generate plasma cut-edges that are near to optimum. This was tested using a representative tophat beam component, in order to validate these results and act as guidance towards the fabrication of structural steel which have optimum cut-edge durability.