Stress-whitening is where a white line appears along a bend or curve when a material is stressed by bending or punching operations.
The appearance of white line indicates that there is an onset of failure of the corresponding material. This phenomenon is known as "stress-whitening". This is more common in
amorphous
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal.
Etymology
The term comes from the Greek ''a'' ("wi ...
materials, and also in some brittle
polymer
A polymer (; Greek '' poly-'', "many" + ''-mer'', "part")
is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic a ...
s like
PS,
PMMA PMMA may refer to:
* para-Methoxymethamphetamine, a stimulant drug
* Philippine Merchant Marine Academy
The Philippine Merchant Marine Academy ( fil, Akademiya sa Bapor Pangkalakalan ng Pilipinas) also referred to by its acronym PMMA) is a ma ...
and
Polycarbonate
Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily work ...
. The white colour is because of the light scattering by the
crazes and changes in the
refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
of the area under stress.
References
* {{cite book , last1=International , first1=ASM , last2=Lampman , first2=S. , title=Characterization and Failure Analysis of Plastics , publisher=ASM International , year=2003 , isbn=978-1-61503-073-6 , url=https://books.google.com/books?id=RJWiilJLdxYC&pg=PA405 , access-date=2021-05-01
Machining