Composite Materials Research Progress

Preface xi
The analysis shows that some of the variables can indeed be used for assessing the
damage tolerance of the laminate. In single impact tests, results point out the existence of an
energy threshold at about 40-50% of the penetration energy, below which the damage threat
is quite negligible. Other variables are not directly related to the amount of damage induced in
the laminate but rather give an indication of the laminate efficiency of energy absorption.
The electromechanical field concentrations due to electrodes in piezoelectric composites
are investigated through numerical and experimental characterization. Chapter 8 consists of
two parts. In the first part, a nonlinear finite element analysis is carried out to discuss the
electromechanical fields in rectangular piezoelectric composite actuators with partial
electrodes, by introducing models for polarization switching in local areas of the field
concentrations. Two criteria based on the work done by electromechanical loads and the
internal energy density are used. Strain measurements are also presented for a four layered
piezoelectric actuator, and a comparison of the predictions with experimental data is
conducted. In the second part, the electromechanical fields in the neighborhood of circular
electrodes in piezoelectric disk composites are reported. Nonlinear disk device behavior
induced by localized polarization switching is discussed.
Aluminum-based alloys reinforced with ceramic microparticles are attractive materials
for many structural applications. However, large ceramic microparticles often act as stress
concentrators in the composites during mechanical loading, giving rise to failure of materials
via particle cracking. In recent years, increasing demand for high performance materials has
led to the development of aluminum-based nanocomposites having functions and properties
that are not achievable with monolithic materials and microcomposites. The incorporation of
very low volume contents of ceramic reinforcements on a nanometer scale into aluminumbased
alloys yields remarkable mechanical properties such as high tensile stiffness and
strength as well as excellent creep resistance. However, agglomeration of nanoparticles
occurs readily during the composite fabrication, leading to inferior mechanical performance
of nanocomposites with higher filler content. Cryomilling and severe plastic deformation
processes have emerged as the two important processes to form ultrafine grained composites
with homogeneous dispersion of reinforcing particles. In Chapter 9, recent development in the
processing, structure and mechanical properties of the aluminum-based nanocomposites are
addressed and discussed.