User Contributed Dictionary
Verb
crazing- present participle of craze
Extensive Definition
Crazing is a network of fine cracks inside a
surface or glaze of a surface.
Crazing is a phenomenon that frequently precedes
fracture in some glassy
thermoplastic
polymers. 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.
Polymers
A craze is different from a crack in that 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. The initial energy absorption per square meter in a craze region has been found to be up to several hundred times that of the uncrazed region, but quickly decreases and levels off. Crazes form at highly stressed regions associated with scratches, flaws, Stress concentrations and molecular inhomogeneities. Crazes generally propagate perpendicular to the applied tension. Crazing occurs mostly in amorphous, brittle polymers like PS, PMMA and polycarbonate; it is typified by a whitening of the crazed region. The white colour is caused by light-scattering from the crazes.One of the main differences between crazing and
shear
banding, another form of stress deformation, is that crazing
occurs with an increase in volume, which shear banding does not.
This means that under compression, many of these brittle, amorphous
polymers will shear band rather than craze, as there is a
contraction of volume instead of an increase. In addition, when
crazing occurs, one will typically not observe "necking," or
concentration of force upon one spot in a material. Rather, crazing
will occur homogeneously throughout the material.
Rubber toughening
Crazing occurs in some thermoplastics such as
ABS
plastic when stressed. It is a typical response rubber
toughening where crazes are initiated at the surfaces of the
rubber particles added to toughen the material.
Ceramics
Crazing is also seen with some glazes used
on pottery, on single ply roofing membranes and may be seen on
concrete when good
concrete practices are not followed.