The micromechanisms of deformation and recovery in thermoplastic vulcanizat
es (TPVs) are studied using a series of micromechanical models. TPVs are a
class of composite material consisting of a relatively large volume fractio
n of elastomeric particles (upsilon (p) = 0.40-0.90) in a thermoplastic mat
rix, A representative TPV with upsilon (p) = 0.77 is selected for the study
. Six five-particle representative volume element (RVE) models are construc
ted where the symmetry of particle distribution and the relative thickness
of the matrix ligament bridging particles are systematically varied. The ma
croscopic stress-strain behavior of the TPV during loading and unloading is
successfully predicted by the simulation study as shown by direct comparis
on with experimental data. The simulation study reveals the important role
of relative matrix ligament thickness as well as geometric asymmetry in the
formation of a pseudo-continuous rubber phase which provides the rubber-li
ke behavior of TPVs during loading. The study shows the important role of m
atrix ligament thickness in controlling the initial stiffness and flow stre
ss of the TPV; thinner ligaments lead to earlier matrix yielding and thus e
arlier formation of the pseudo-continuous rubber phase. Upon formation of t
he pseudo-continuous rubber phase, the matrix material is seen to accommoda
te the large straining of the rubber phase by nearly rigid body motion (rot
ation and translation) of the bulky domains of the matrix; the rubber phase
is seen to undergo large contortions as it attempts to deform as an almost
continuous network around the "rigid" domains of matrix material. Furtherm
ore, the asymmetry together with the thin matrix ligaments greatly aids the
recovery of the material during unloading. Upon unloading, the rubber phas
e attempts recovery in a rubber-like manner. The bulkier regions of matrix
material simply rotate and translate with the recovering rubber domains. Th
e thin ligaments also rotate, but eventually also undergo bending and buckl
ing which enables the large amount of recovery observed in thermoplastic vu
lcanizates. (C) 2001 Elsevier Science Ltd. All rights reserved.