A plastic part fails at a fraction of its rated strength, with no chemical attack and no visible degradation — because ESC does not need to degrade the polymer to destroy it.
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Environmental stress cracking looks like chemical attack and is not one. ESC needs three things at once — a susceptible polymer, a tensile or residual stress, and a surface-active agent that is often nothing more aggressive than a household detergent, an oil, or an alcohol — and none of them alone will fracture the part. The agent lowers the polymer’s surface energy enough for a craze to nucleate and grow at a stress far below the material’s rated strength, and it does this by chain disentanglement rather than chemical attack: FTIR on an ESC fracture typically shows no new chemical species and no measurable change in molecular weight, which is exactly what separates it from true chemical attack and is often the crux of a liability dispute over whether the part or the fluid was at fault.
ESC requires a specific combination of conditions to occur — removing any one of them stops it, which is exactly how the mechanism is confirmed.
Molded-in stress, a sharp corner, a scratch, or an assembly stress concentrating tensile stress to the level ESC requires to begin.
A wetting agent — detergent, oil, alcohol, or adhesive solvent — lowering the polymer’s surface energy at the crack tip without chemically attacking it.
Fibrils bridging the craze eventually rupture, converting a stable, load-bearing craze into a propagating crack.
Stress frozen into the part at processing — gate location, cooling rate, mold design — that adds directly to the applied or service stress.
Over-torqued fasteners, press-fits, and snap-fits imposing sustained tensile stress at a joint long after assembly is complete.
Some resins and grades — certain polycarbonates, ABS, and HDPE formulations — are markedly more ESC-susceptible than others under identical service conditions.
Confirming ESC means proving the combination of stress, agent, and susceptible resin — and ruling out true chemical attack.
An ESC finding raises the same set of questions almost every time:
The cleaning fluid, adhesive, lubricant, or chemical the part contacted is often the other half of the evidence. Do not clean the part or discard the suspected agent.
It is a brittle fracture mechanism unique to certain polymers, occurring when a sustained tensile stress and a surface-active chemical agent act on the material together. Neither one alone is enough — the same part under the same stress with no agent present, or exposed to the same agent with no significant stress, generally will not crack. The agent lowers the polymer’s surface energy enough for a craze to nucleate and grow at a stress well below the material’s rated strength, and the mechanism proceeds by chain disentanglement rather than by chemically attacking the polymer.
The polymer’s chemistry. In true chemical attack, FTIR and molecular-weight analysis show measurable change — new chemical species, chain scission, a shift in molecular weight. In ESC, those same tests typically show none: the resin is essentially unchanged chemically, and the failure is a physical response to stress and a wetting agent rather than a chemical reaction. That distinction is the crux of most ESC-versus-chemical-attack disputes, because it usually determines whether the part, the fluid, or the design carrying the stress is responsible.
Yes. ESC agents do not need to be aggressive chemicals — detergents, oils, alcohols, adhesives, and even some hand lotions are well-documented ESC agents for susceptible resins like certain grades of polycarbonate, ABS, and polyethylene. What matters is the combination of that agent with a part already under sustained tensile stress, whether from molded-in residual stress, an assembly fit, or an applied load. A fluid that is completely benign against an unstressed sample can still crack the same resin once stress is present.
By reproducing the mechanism and by the fracture morphology. SEM fractography of an ESC failure shows a characteristic craze and fibril pattern distinct from the shear lips and elongation of a ductile overload fracture or the flat, radial pattern of a brittle mechanical fracture. Bent-strip or constant-strain testing under ASTM D1693 or an equivalent protocol, using an exemplar part, the suspected fluid, and a comparable stress level, can reproduce the failure directly — which is usually the most persuasive evidence in a dispute.
The cracked part without cleaning, and a sample of every fluid, chemical, lubricant, or cleaning agent the part is known or suspected to have contacted, with quantities and dates if available. Also preserve exemplar unused parts from the same production lot — comparing molded-in stress between the failed part and an unused one is often what establishes whether the part itself, not just the fluid, contributed to the failure.
Technical briefings from our work in this area.
Reproducing a stress-cracking failure under controlled conditions is the most persuasive evidence available in these matters — provided the test conditions are defensible and the limits are stated.
readESC cannot happen without sustained tensile stress, and that stress is often nowhere in the design load case. Moulded-in stress, assembly stress and service load each leave a different trace.
readEnvironmental stress cracking and chemical attack look alike on a broken part and separate cleanly in the laboratory. The discriminator is whether the polymer's chemistry changed at all.
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