where [GAMMA] is the effective surface energy at the void tips for crazing
, [gamma] is the van der Waals surface energy, [v.sub.e] is the entanglement density, d is the entanglement distance, U is the energy for breaking a single backbone bond.
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.
By lowering the constraint, the degree of crack tip blunting increased via multiple crazing
. However, there were comparably fewer secondary crazes in the structure than those seen in PE80 but the crazes were thicker.
, 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.
If the toughness is improved mainly through crazing
, the toughener phase must exhibit good interfacial adhesion with the matrix , and acts not only as a stress concentrator but also as a craze stabilizer [2, 18].
Despite multiple crazing
in PE1, the overall break separation remains lower than that for PE2 due to the lower value of [lambda] of the fibrils in any given craze of PE1.
Largely deformed rubber particles and crazing
were observed near the surface of the whitened fractured section nearest the notch (Fig.