Effect of Corroded Surface Morphology on Ultra-Low Cycle Fatigue of Steel Bridge Piers

Abstract

Corrosion is a common form of durability degradation of steel bridges. Corrosion morphology affects stress distribution under cyclic loads and causes strain concentrations in pits, thus affecting the mechanical properties of steel structures, including ultra-low cycle fatigue (ULCF). To precisely simulate corrosion morphology and investigate the ULCF failure mechanism of corroded steel piers, a sculpting method was applied to mesh units using three-dimensional surface morphology data of corroded steel specimens. Moreover, the ULCF crack-initiation life was numerically predicted using the finite element model based on the cyclic void growth model (CVGM). The cumulative equivalent plastic strain, cyclic void growth index, and critical void growth index of corroded steel piers with different corroded morphologies were compared. Results reveal that, regardless of whether the pier is corroded, fatigue cracks tend to initiate at the weld toe at corners when exposed to cyclic loads under an oblique direction at the pier top. Additionally, the ULCF crack-initiation life in a corroded pier is less than that in an uncorroded pier, and it is significantly affected by a reduction in the pier wall thickness. Corrosion pits affect the position of ULCF crack initiation in a steel pier and cracks tend to initiate at the bottom of pits with large depth-to-diameter ratios. In the case of minor corrosion, the corrosion morphology affects the seismic performance of piers to a small extent.

Development of ultra-low cycle fatigue life prediction model for structural steel considering the effects of surface roughness, loading frequency, and loading amplitude

“…At a higher displacement amplitude of 5 mm, the fatigue life decreased by about 45% from 33.5 to 18.5 cycles with an increase in surface roughness from 20 to 100 μm. Song et al, (2021a) observed a similar reduction effect in the ULCF life of steel bridge piers with the increase in corrosion level. In another study by Song et al, (2021b), it was investigated that corrosion induced surface roughness has a dominant impact on the ULCF life of steel specimens.…”

“…McKelvey and Fatemi (2012) checked the fatigue life of forged steel and developed life curves as a function of hardness based on their experimental findings. Song et al, (2021aSong et al, ( , 2021b) investigated the ULCF properties and fracture process of corroded steel and found that fatigue life is significantly reduced by the increasing level of surface roughness induced by the corrosion process. Additionally, processing parameters are known to have a strong impact on fatigue life, and variation in surface morphology largely affects the LCF life (Hasunuma et al, 2019).…”

Study on Degradation Law and the Equivalent Thickness Model of Steel Subjected to Sulfate Corrosion

“…When the corrosion rate γ ≤ 10%, the number of pits increases with the corrosion rate, and the distribution of the pits became denser which caused the pits larger and deeper. When the corrosion rate is 15% ≤ γ ≤ 25%, the corrosion pits became clear and denser, and the corrosion pits are assumed as hemispherical [ 35 ].…”

“…Equation (23) illustrates the loss of dissipation energy due to electrochemical corrosion. It can be clearly seen in Figure 9 and Figure 10 that the corrosion pit distributes on the surface of the whole specimen, and the shape of the corrosion pit is presented as a hemisphere or semi-ellipsoid [ 35 , 39 ]. It assumes that the density of steel keeps constant.…”

“…According to meso-damage mechanics, the porosity of steel after sulfate corrosion can be defined as [ 35 ] where P v is the porosity of steel after sulfate corrosion; V vo is the void volume of steel; V 0 is the volume of the steel coupons.…”