|
Description:
|
In polymer matrix composites (PMCs ) manufacturing processes can induce de -
fects , e .g . , voids , fiber misalignment , irregular fiber distribution in the cross -section
and broken fibers . The effects of such defects can be beneficial or deleterious de -
pending on whether they cause failure suppression or enhancement by localized de -
formation processes e .g . , crazing , shear yielding and fiber -matrix debonding . In this
study , a computational approach is formulated and implemented to develop solu -
tions for general boundary -value problems for PMC microstructures that accounts
for micromechanics -based constitutive relations including fine scale mechanisms of
material failure . The defects considered are voids , and the microstructure is explic -
itly represented by a distribution of fibers and voids embedded in a polymer matrix .
Fiber is modeled as a linearly elastic material while the polymer matrix is mod -
eled as an elastic -viscoplastic material . Two distinct models for the matrix behavior
are implemented : (i ) Druckerâ  Prager type Bodner model that accounts for rate and
pressure -sensitivity , and (ii ) improved macromolecular constitutive model that also
accounts for temperature dependence , small -strain softening and large -strain harden -
ing . Damage is simulated by the Gearing -Anand craze model as a reference model and by a new micromechanical craze model , developed to account for craze initiation ,
growth and breakdown . Critical dilatational energy density criterion is utilized to
predict fiber -matrix debonding through cavitation induced matrix cracking .
An extensive parametric study is conducted in which the roles of void shape ,
size and distribution relative to fiber in determining damage initiation and evolution
are investigated under imposed temperature and strain rate conditions . Results show
there are significant effects of voids on microstructural damage as well as on the
overall deformational and failure response of composites . |