Effect of surface roughness on tensile ductility of artificially corroded steel plates

Abstract

Physically, corrosion damage results in a reduction in thickness and a change in surface geometry due to differential corrosion rates on the surface of a steel member. The effects of thickness reduction on the mechanical characteristics of structural steel have been investigated intensively, but the same cannot be said for the surface configuration. This study investigated the variation of corrosion thickness and surface roughness characteristics with increasing corrosion degradation and their contribution to a reduction in the tensile ductility of corroded steel. Twenty-two SS400 type steel plates were corroded by an underwater accelerated exposure (bubbling) test. Specimens were exposed for a varying number of days after which measurement and evaluation of thickness reduction and surface roughness characteristics were conducted. Then, the remaining load and elongation capacity were determined experimentally from the standard uniaxial tensile test. The distribution of the surface strains was studied employing digital image correlation techniques. Findings from this work revealed that surface unevenness due to corrosion causes stress concentration and uneven yielding, and strain localization after yielding during the tensile test. This translated to an early attainment of maximum load, resulting in reduced ductility in corroded specimens. A general trend is such that ductility decreases with increasing surface roughness. A plastic ductility loss of up to 80% is experienced when maximum surface height ratio, ζsz ≥ 0.9 and average surface height ratio, ζsa ≥ 0.15. Finally, empirical equations for estimating the remaining tensile ductility of corroded steel based on surface roughness characteristics were proposed.