Experimental study on the effects of corrosion on multi-scale crack propagation performance of a steel box girder structure

To accurately simulate engineering service conditions and evaluate the impact of corrosive environments on crack propagation in a steel box girder structure, this study conducted material- and structural-scale corrosion-environment and mechanical performance tests.

Material-level compact tension (CT) specimens and a steel box girder model were fabricated, with initial cracks introduced via artificial defects and fatigue loading. Corrosion tests were then conducted separately: CT specimens were exposed to a coastal field environment for three months to simulate marine atmospheric corrosion, whereas the box girder model underwent accelerated corrosion in a laboratory chamber for one month. Fracture toughness tests were performed on CT specimens before and after corrosion, and crack propagation tests were conducted on the box girder under cyclic fatigue loading.

Key findings include the following: (1) At the material scale, fracture toughness of the uncorroded welded CT specimens was $237.4\mathrm{M}\mathrm{P}\mathrm{a}\cdot {\mathrm{m}}^{\frac{1}{2}}$, which increased to $380.0\mathrm{M}\mathrm{P}\mathrm{a}\cdot {\mathrm{m}}^{\frac{1}{2}}$ (~60% increase) after three months of coastal exposure. This is attributed to corrosion-induced blunting of the sharp crack tip, which raised the energy required for crack re-initiation. (2) At the structural scale, after accelerated corrosion, only two of three pre-existing cracks on the box girder (at the #4 support point) propagated under cyclic loading, with a significant delay in crack initiation that further supports the crack-tip-blunting effect. Propagation paths traversed corrosion pits, where the crack rate slowed or briefly halted until a new sharp tip formed on the opposite side, rendering the paths more complex and discontinuous. (3) The two propagating cracks at the #4 support point grew essentially perpendicular to the primary load-bearing direction, predominantly as Mode Ⅰ (opening mode); the fastest crack (#4-V-b) propagated at 2.06×10^–3 mm/cycle along a largely linear a–N curve, indicating stable fatigue crack growth.

This study reveals dual effects of corrosive environments on crack propagation in steel box girder structures. Corrosion enhances fracture toughness by blunting the crack tip, inhibiting crack initiation. However, pre-existing corrosion pits can act as preferential propagation paths and cause growth fluctuations, increasing the risk of local failure.