Which mechanism involves the combination of mechanical stress with chemical attack to cause cracking in metals?

• A. Stress cracking
• B. Galvanic corrosion
• C. Pitting
• D. Erosion

Answer: (A)

Cracking caused by the joint action of mechanical stress and a chemical environment is stress-assisted cracking (often called stress corrosion cracking). The idea is that tensile or persistent stress creates or opens flaws, and the corrosive attack at those flaw sites weakens the material and promotes crack initiation and propagation. In this synergy, the environment lowers the stress needed to crack and helps the crack grow, which wouldn’t happen as readily with either factor alone. For example, a metal under chloride-containing conditions may develop cracks that advance under relatively modest applied stresses. This differs from galvanic corrosion, which is driven by electrochemical potential differences and may corrode surfaces without cracking; pitting, while a form of corrosion, produces pits rather than cracks; and erosion is physical removal by fluid flow without the chemical-attack-driven crack growth.