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In crack
formation and propagation in polymeric materials the macromolecules can form
"bridges" linking the two sides of the crack. Additional work has
to be done to break the backbone of these molecules or pull them out of the
opposite crack surface. This work increases the effective surface energy and
increases the polymers toughness. The photograph shows the crack tip region
in polypropylene oxide, the strands linking the sides of the crack in the
"craze" zone can be seen. The lower diagram illustrates the process
of micro-void coalescence and fracture of the fibrillar micro-bridges in this
craze zone as crack propagation progresses. |
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