Which mechanism explains the long-term structural weakening in wrought iron bridges from the 19th century carrying railway traffic?

💡 Explanation

When trains repeatedly cross wrought iron bridges, cyclic loading causes fatigue cracking because microscopic flaws grow under fluctuating stress, eventually leading to structural weakening and failure. Therefore fatigue cracking explains the weakening, rather than corrosion, embrittlement, or erosion which require different environmental or material conditions.

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