Crazing

Definition - What does Crazing mean?

Crazing is a network of checks or cracks appearing on a coated surface. Crazing is a phenomenon that frequently precedes fracture in some glassy thermoplastic polymers. Crazing happens when a glaze or coating is under tension.

Crazing occurs in some thermoplastics such as acrylonitrile butadiene styrene (ABS plastic) when stressed. It is a typical response in rubber toughening, where crazes are initiated at the surfaces of the rubber particles added to toughen the material. Crazing is also seen on single-ply roofing membranes, and on concrete when good concrete practices are not followed.

Crazing is also known as shallow map cracking or pattern cracking.


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Corrosionpedia explains Crazing

Crazing occurs in regions of high hydrostatic tension, or in regions of very localized yielding, which leads to the formation of interpenetrating microvoids and small fibrils. If an applied tensile load is sufficient, these bridges elongate and break, causing the microvoids to grow and coalesce; as microvoids coalesce, cracks begin to form. Crazing has no influence on corrosion resistance.

Generally, crazing is considered a glaze defect because the vessel can be significantly weaker than an uncrazed pot. Craze lines can also harbor bacteria or germs. Therefore, dinnerware pottery should be uncrazed ware.

In polymer, a craze is different from a crack in that it cannot be felt on the surface and it can continue to support a load. Furthermore, the process of craze growth prior to cracking absorbs fracture energy and effectively increases the fracture toughness of a polymer.

Crazing forms at highly stressed regions associated with scratches, flaws, stress concentrations and molecular inhomogeneities. Crazing generally propagates perpendicular to the applied tension, and occurs mostly in amorphous, brittle polymers like polystyrene (PS), acrylic (PMMA) and polycarbonate. It is typified by a whitening of the crazed region. The white color is caused by light-scattering from the crazes.

Crazing is a typical phenomenon on pre-anodized aluminum and is a micro-cracking of the anodic layer. It occurs after re-coiling the anodized aluminum, and the cracks form perpendicular to the rolling direction. The crazing, caused during re-coiling, is homogeneous and therefore less visible.

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