Cracking caused by the combined action of a tensile stress and a corrosive environment.
Neither the stress nor the chemical alone would cause failure. Together they crack the part, often at a stress well below yield and in a chemical that has no effect on unstressed specimens.
Amorphous plastics are highly susceptible: polycarbonate, acrylic and PEI crack at press fits and threads after cleaning with a solvent. In metals, austenitic stainless cracks in chloride environments at elevated temperature, which is why duplex and super-austenitic grades exist.
Designing from a chemical compatibility table alone. Those ratings assume an unstressed specimen; stress makes a chemical that is rated acceptable fail in practice.
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