Advanced Materials Research
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Advanced Materials Research Vols. 41-42
Paper Title Page
Abstract: Nano-scale Au/Cu multilayers were investigated by nano/microindentation. It was found
that the hardness of the multilayers increases with decreasing individual layer thickness (λ), and
shear band deformation can occur more easily in the multilayer with small λ. For comparison, the
same experiments were also performed on Cr/Cu multilayers with the same layer structure. The
results show that the Cr/Cu multilayer can be more effective in resisting shear band deformation
than the Au/Cu multilayer. Finally, the λ dependence of shear band deformation and the difference
between plastic deformation behaviors of the two multilayers were analyzed based on dislocation
plasticity.
3
Abstract: Articular cartilage is a semitransparent elastic material that covers on the two articulating
bones in synovial joints. It acts as a cushion between the bones that transfers loads from one to
another while attenuating dynamic stresses and providing almost frictionless contact surfaces for
normal use of synovial joints without pains. Osteoarthritis causes a chronic joint pain and it is
mainly due to malfunction of articular cartilage. The mechanical function of articular cartilage is
derived from its unique microstructure. Therefore, study of the relationship between the mechanical
function and microstructure of articular cartilage comprehends the aetiology and pathology of
osteoarthritis. Confocal microscopy permits studying the internal microstructure of buck biological
tissues without tissue sectioning and dehydration. This provides a way to study the relationship
between the mechanical function and microstructure of articular cartilage. Using a fibre optic laser
scanning confocal microscope, this study examines the pathological status of articular cartilage in
relation to the mechanical function and 3D collagen network of articular cartilage. The results show
that the 3D collagen structure and the mechanical function are different between normal and
arthritic cartilage. Loss of the integrity of the 3D collagen network is closely related to cartilage
softening.
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Abstract: In this work, deformation of monocrystalline silicon (Si) under nanoscratching was
investigated using transmission electron microscopy (TEM). The results indicated that no fracture
occurred during nanoscratching with loads ranging from 1 to 6 mN. The damaged regions induced
by nanoscratching included an amorphous Si region and a damaged crystalline Si region. Detailed
TEM analyses revealed that at the lowest load of 1 mN no dislocation was observed in the damaged
crystalline region, and only stacking faults were observed at the boundary between the damaged
crystalline Si and amorphous Si. Dislocations started to nucleate along (111) planes and penetrated
into the bulk Si when the normal load was increased to 2 mN and above. Defects perpendicular to
the scratched surface were initiated when the load was greater than 4 mN. The density of
dislocations also increased rapidly with the increase of the applied load.
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Abstract: The effects of cyclic loading on contact damage in curved bi-layer systems are
investigated. Dome structures consisting of glass shells, filled with epoxy resin, simulate the
essential structure of monolithic all-ceramic dental crowns on natural tooth dentine. Cyclic loading,
with only a vertical component, was carried out with the Multi-Functional Chewing Simulator
(Willytec. Munich, Germany). The specimens were tested by indentation with hard spheres of
tungsten carbide, with the load applied axially at the apex of the dome. This project reports some
new results on the effect of cyclic loading on curved bi-layer systems. In addition, the effect of
aqueous environments is addressed. In both air and water tests, observations taken throughout the
cyclic loading course indicated that the outer cone cracks inhibited the propagation of radial cracks.
Results confirm that crack initiation occurred more rapidly in wet conditions of testing,
emphasizing the influences of the moist environment of the oral cavity. Furthermore, the
experiments took into account the evolution of inner cone cracks observed in wet cyclic loading
tests. The new results are important since nearly all-dental crowns exhibit some curvature. The
implications of the results on the failure of dental crowns are discussed.
21
Abstract: Two available strength data sets of single-walled and multi-walled carbon nanotubes are
analysed, and the effects of sample sizes on their tensile strengths are investigated. A minimum
information criterion is applied to determine the optimal strength distribution. The results show that,
in contrast to a two-parameter Weibull distribution, lognormal distribution seems to be a more
suitable choice. A simple extrapolation of classical Weibull statistics to nanoscales may result in
overestimation on the tensile strength of carbon nanotubes.
27
Abstract: This paper summarizes some of the recent advances that have been made as a result of
contact damage tests on bi-layer structures containing one brittle layer on a polymeric support base.
The effects of indenter modulus (hard/soft indenters) and of the sate of loading (load location
reference to the specimen axis of symmetry) on contact damage in bi-layer systems were
investigated. Convex specimens having curvature of 12 mm inner coating diameter and 1mm thick
were produced, and loaded along the axis of symmetry and off axis at 45o using flat indenters of six
different moduli. The influence of indenter modulus on radial crack initiation and damage evolution
was examined in respect to the load location, with particular attention paid to the relevance of such
damage to lifetime-limiting failures of biomechanical layered systems. The results of this study
illustrates that the fracture behaviour of brittle layered structures is not dominated by certain
parameters. Critical loads for initiation of radial cracks are sensitive to indenter modulus (hardness)
but not sensitive to load location. Load location plays an important role in crack propagation and
subsequent damage patterns, especially at specimen margins.
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Abstract: Hydroxyapatite (HA) powder was synthesized by a sol-gel method with Ca(OH)2 and
H3PO4 as reactants. The HA granules were then coated with TiH2 powder using a mechanical
mixing method. The HA-TiH2 material system produced HA-Ti composites after hot-pressing at
1050°C. The HA-Ti composites are mainly composed of HA and Ti, with small amounts of Ca2P2O7
and Ca3(PO4)2 phases. Fracture toughness and bending strength are 2.4 MPa·m1/2 and 54.3 MPa,
respectively for the HA-20vol%Ti composite, higher than those of the pure HA ceramic. The
improvement in properties is because of the unique 3D network structure of Ti, which is an ideal
reinforcement structure for the weak and brittle HA. According to ISO/TR 7405-1984, hemolysis
test was performed to evaluate the blood compatibility of the material. The results show that the
hemolysis rate of the HA-20vol%Ti composite is 0.56%. Relative growth rates (RGR) of L-929
cells soaked after 6 days in the HA-20vol%Ti group, pure Ti group, black group and pure Pb group
were 132%, 100%, 90% and 6% respectively, while the level of cytotoxicity was grade 0 in HA-Ti
composite group. These results imply that the HA-20vol%Ti composite has good biocompatibility
and bioactivity.
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