Which structural weakness was a common failure mode in Roman ballista artillery pieces after prolonged use?

💡 Explanation

After repeated firing of a ballista, the energy stored is released through torsion. Cyclic twisting causes metal fatigue within the axle because the yield strength of metal is surpassed locally, resulting in shear failure. Therefore, axle shearing is the weakness rather than rope fraying, frame warping, or trigger slippage, which rely on other operational causes such as weathering or oxidation.

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