Which mechanism caused repeated failures in early cast iron railway bridges despite apparent safety margins?

💡 Explanation

When subject to cyclical loading, cast iron railway bridges experienced fatigue crack growth because micro-cracks propagated with each train passage, leading to sudden catastrophic failures. Therefore progressive fatigue crack growth results, rather than embrittlement, expansion, or erosion which involve different material degradation mechanisms.

• Which factor most directly limits the height of pre-Columbian terraced agricultural systems in the Andes?
• Which defensive outcome resulted from counterweight trebuchets during medieval sieges against fortifications?
• Which condition necessitates terraces incorporating specific drainage systems in pre-Columbian Andean agriculture?
• Which structural enhancement during 18th-century ship construction primarily reduced the risk of hogging under wave stress?
• Which benefit did the 'chinampa' system provide for Aztec agriculture in Tenochtitlan's marshy environment?
• Which environmental risk increased with development constraints on Aztec chinampa cultivation expansions?