Under impact conditions, chain scission is likely to become important (37), thus it can be speculated that crazing
will be favored and voiding and fibrillation will be aided by the scission processes rather than by viscous disentanglement via repetition, as occurred in slow strain-rate tests such as tensile test.
However, it is noted that while crazing
evidence was observed in each of the pressure deflection tests, ultimate failure occurred by yielding and drawing of remaining material ahead of the notch.
As the constraint was reduced, multiple crazing
continued to blunt the tip but it was also accompanied by the formation of large voids.
, the energy barrier comes from the requirement of the polymer molecules to slide past one another (via reptation) and to undergo conformational changes.
The first analysis was performed with a constant crazing
stress of 40 MPa and included experimental variables of relative craze density and strain rate.
Among processes of craze initiation to breakdown, craze tip advance and craze thickening are especially important since they are responsible for the major part of the energy dissipation during crazing
and thus directly influence polymer toughness.
The technique to be described in the present work is an in-situ, quantitative, non-subjective, direct measurement of craze density (amount of surface crazing
per unit surface area).
This article examines whether Izod impact strength can be improved by lowering the crosslinking degree of the rubber of MOD in a PVC/MOD molded product to make rubber void at the time of formation of the first craze, followed by a suppression of the final crack formation, and also whether Lzod impact strength can be improved by initially making rubber particles in MOD void to facilitate crazing
and shear yield, followed by a suppression of the final crack formation.
Also, it is possible to learn whether or not limited crazing
can trigger massive shear banding in the polymer matrix.
Largely deformed rubber particles and crazing
were observed near the surface of the whitened fractured section nearest the notch (Fig.
Qualitatively, the essential micro-mechanisms of yielding and fracture in rubber-modified polystyrene include: craze nucleation, rubber cavitation, formation of elastomeric fibrils, which prevent the crazing
from coalescing, and, finally, fibril breakdown, which leads to macroscopic crack propagation.
13) found that crazing
occurred at a lower strain for annealed or slowly cooled samples than for freshly quenched samples.