Abstract: Aluminium matrix composites with alumina
reinforcements give superior mechanical & physical properties. Their
applications in several fields like automobile, aerospace, defense,
sports, electronics, bio-medical and other industrial purposes are
becoming essential for the last several decades. In the present work,
fabrication of hybrid composite was done by Stir casting technique
using Al 6061 as a matrix with alumina and silicon carbide (SiC) as
reinforcement materials. The weight percentage of alumina is varied
from 2 to 4% and the silicon carbide weight percentage is maintained
constant at 2%. Hardness and wear tests are performed in the as cast
and heat treated conditions. Age hardening treatment was performed
on the specimen with solutionizing at 550°C, aging at two
temperatures (150 and 200°C) for different time durations. Hardness
distribution curves are drawn and peak hardness values are recorded.
Hardness increase was very sensitive with respect to the decrease in
aging temperature. There was an improvement in wear resistance of
the peak aged material when aged at lower temperature. Also
increase in weight percent of alumina, increases wear resistance at
lower temperature but opposite behavior was seen when aged at
higher temperature.
Abstract: The nanoindentation behaviour and phase
transformation of annealed single-crystal silicon wafers are examined.
The silicon specimens are annealed at temperatures of 250, 350 and
450ºC, respectively, for 15 minutes and are then indented to maximum
loads of 30, 50 and 70 mN. The phase changes induced in the indented
specimens are observed using transmission electron microscopy
(TEM) and micro-Raman scattering spectroscopy (RSS). For all
annealing temperatures, an elbow feature is observed in the unloading
curve following indentation to a maximum load of 30 mN. Under
higher loads of 50 mN and 70 mN, respectively, the elbow feature is
replaced by a pop-out event. The elbow feature reveals a complete
amorphous phase transformation within the indented zone, whereas
the pop-out event indicates the formation of Si XII and Si III phases.
The experimental results show that the formation of these crystalline
silicon phases increases with an increasing annealing temperature and
indentation load. The hardness and Young’s modulus both decrease as
the annealing temperature and indentation load are increased.
Abstract: In the past decade, the use of digital image correlation
(DIC) techniques has increased significantly in the area of
experimental mechanics, especially for materials behavior
characterization. This non-contact tool enables full field displacement
and strain measurements over a complete region of interest. The DIC
algorithm requires a random contrast pattern on the surface of the
specimen in order to perform properly. To create this pattern, the
specimen is usually first coated using a white matt paint. Next, a
black random speckle pattern is applied using any suitable method. If
the applied paint coating is too thick, its top surface may not be able
to exactly follow the deformation of the specimen, and consequently,
the strain measurement might be underestimated. In the present
article, a study of the influence of the paint thickness on the strain
underestimation is performed for different strain levels. The results
are then compared to typical paint coating thicknesses applied by
experienced DIC users. A slight strain underestimation was observed
for paint coatings thicker than about 30μm. On the other hand, this
value was found to be uncommonly high compared to coating
thicknesses applied by DIC users.
Abstract: This paper presents the results of an experimental
study undertaken to evaluate the local bond stress-slip response of
short embedment of reinforcing bars in normal concrete (NC) and
high performance fiber reinforced cement composites (HPFRCC)
blocks. Long embedment was investigated as well to gain insights on
the distribution of strain, slip, bar stress and bond stress along the bar
especially in post-yield range. A total of 12 specimens were tested,
by means of pull-out of the reinforcing bars from concrete blocks. It
was found that the enhancement of local bond strength can be
reached up to 50% and ductility of the bond behavior was improved
significantly if HPFRCC is used. Also, under a constant strain at
loaded end, HPFRCC has delayed yielding of bars at other location
from the loaded end. Hence, the reduction of bond stress was slower
for HPFRCC in comparison with NC. Due to the same reason, the
total slips at loaded end for HPFRCC was smaller than NC as
expected. Test results indicated that HPFRCC has better bond slip
behavior which makes it a suitable material to be employed in
anchorage zone such as beam-column joints.
Abstract: Intermetallic materials are among advanced
technology materials that have outstanding mechanical and physical
properties for high temperature applications. Especially creep
resistance, low density and high hardness properties stand out in such
intermetallics. The microstructure, mechanical properties of %88Ni-
%10Cr and %2Mn powders were investigated using specimens
produced by tube furnace sintering at 900-1300°C temperature. A
composite consisting of ternary additions, a metallic phase, Fe, Cr
and Mn have been prepared under Ar shroud and then tube furnace
sintered. XRD, SEM (Scanning Electron Microscope), were
investigated to characterize the properties of the specimens.
Experimental results carried out for composition %88Ni-%10Cr and
%2Mn at 1300°C suggest that the best properties as 138,80HV and
6,269/cm3 density were obtained at 1300°C.
Abstract: The aim of this study is to investigate formability of
Al based closed cell metallic foams at high temperature. The foam
specimens with rectangular section were produced from
AlMg1Si0.6TiH20.8 alloy preform material. Bending and free
bending tests based on gravity effect were applied to foam specimens
at high temperatures. During the tests, the time-angular deformation
relationships with various temperatures were determined.
Deformation types formed in cell walls were investigated by means
of Scanning Electron Microscopy (SEM) and optical microscopy.
Bending deformation about 90° was achieved without any defect at
high temperatures. The importance of a critical temperature and
deformation rate was emphasized in maintaining the deformation.
Significant slip lines on surface of cell walls at tensile zones of
bending specimen were observed. At high strain rates, the microcrack
formation in boundaries of elongated grains was determined.
Abstract: Microstructural and hardening changes of
Fe-0.2wt.%V alloy and pure Fe irradiated with 100 keV hydrogen ions
at room temperature were investigated. It was found that dislocation
density varies dramatically after irradiation, ranging from dislocation
free to dense areas with tangled and complex dislocation
configuration. As the irradiated Fe-0.2wt.%V samples were annealed
at 773 K, the irradiation-induced dislocation loops disappear, while
many small precipitates with enriched C distribute in the matrix. Some
large precipitates with enriched V were also observed. The hardness of
Fe-0.2wt.%V alloy and pure Fe increases after irradiation, which
ascribes to the formation of dislocation loops in the irradiated
specimens. Compared with pure Fe, the size of the
irradiation-introduced dislocation loops in Fe-0.2wt.%V alloy
decreases and the density increases, the change of the hardness also
decreases.
Abstract: Failure of typical seismic frames has been found by
plastic hinge occurring on beams section near column faces. On the
other hand, the seismic capacity of the frames can be enhanced if the
plastic hinges of the beams are shifted away from the column faces.
This paper presents detailing of reinforcements in the interior beam–
column connections aiming to relocate the plastic hinge of reinforced
concrete and precast concrete frames. Four specimens were tested
under quasi-static cyclic load including two monolithic specimens
and two precast specimens. For one monolithic specimen, typical
seismic reinforcement was provided and considered as a reference
specimen named M1. The other reinforced concrete frame M2
contained additional intermediate steel in the connection area
compared with the specimen M1. For the precast specimens,
embedded T-section steels in joint were provided, with and without
diagonal bars in the connection area for specimen P1 and P2,
respectively. The test results indicated the ductile failure with beam
flexural failure in monolithic specimen M1 and the intermediate steel
increased strength and improved joint performance of specimen M2.
For the precast specimens, cracks generated at the end of the steel
inserts. However, slipping of reinforcing steel lapped in top of the
beams was seen before yielding of the main bars leading to the brittle
failure. The diagonal bars in precast specimens P2 improved the
connection stiffness and the energy dissipation capacity.
Abstract: An experimental and analytical research on shear
buckling of a comparably large polymer composite I-section is
presented. It is known that shear buckling load of a large span
composite beam is difficult to determine experimentally. In order to
sensitively detect shear buckling of the tested I-section, twenty strain
rosettes and eight displacement sensors were applied and attached on
the web and flange surfaces. The tested specimen was a pultruded
composite beam made of vinylester resin, E-glass, carbon fibers and
micro-fillers. Various coupon tests were performed before the shear
buckling test to obtain fundamental material properties of the Isection.
An asymmetric four-point bending loading scheme was
utilized for the shear test. The loading scheme resulted in a high shear
and almost zero moment condition at the center of the web panel. The
shear buckling load was successfully determined after analyzing the
obtained test data from strain rosettes and displacement sensors. An
analytical approach was also performed to verify the experimental
results and to support the discussed experimental program.
Abstract: This study is about the structural transformations of
aluminium examining with the Dynamic Mechanical Thermal
Analyzer (DMTA). It is a faster and simpler measuring method to
make consequence about the metal’s structural transformations. The
device measures the changing of the mechanical characteristics
depending on the heating rate, and concludes certain transformations.
This measuring method fast and shows clean-cut results comparing
the conventional ways.
Applying polymer measuring devices for metal investigations is
not widespread method. One of the adaptable ways is shown in this
study. The article compares the results of the small specimen test and
the DMTA method, considering the temperature and the forming
dependence of recrystallization temperature.
Abstract: The Aptima® HIV-1 Quant Dx Assay is a fully
automated assay on the Panther system. It is based on Transcription-
Mediated Amplification and real time detection technologies. This
assay is intended for monitoring HIV-1 viral load in plasma
specimens and for the detection of HIV-1 in plasma and serum
specimens.
Nine-hundred and seventy nine specimens selected at random
from routine testing at St Thomas’ Hospital, London were
anonymised and used to compare the performance of the Aptima
HIV-1 Quant Dx assay and Roche COBAS® AmpliPrep/COBAS®
TaqMan® HIV-1 Test, v2.0. Two-hundred and thirty four specimens
gave quantitative HIV-1 viral load results in both assays. The
quantitative results reported by the Aptima Assay were comparable to
those reported by the Roche COBAS AmpliPrep/COBAS TaqMan
HIV-1 Test, v2.0 with a linear regression slope of 1.04 and an
intercept on -0.097.
The Aptima assay detected HIV-1 in more samples than the
COBAS assay. This was not due to lack of specificity of the Aptima
assay because this assay gave 99.83% specificity on testing plasma
specimens from 600 HIV-1 negative individuals. To understand the
reason for this higher detection rate a side-by-side comparison of low
level panels made from the HIV-1 3rd international standard
(NIBSC10/152) and clinical samples of various subtypes were tested
in both assays. The Aptima assay was more sensitive than the
COBAS assay.
The good sensitivity, specificity and agreement with other
commercial assays make the HIV-1 Quant Dx Assay appropriate for
both viral load monitoring and detection of HIV-1 infections.
Abstract: In this paper, the effects of fiber types and elevated
temperatures on compressive strength, modulus of rapture and the
bond characteristics of fiber reinforced concretes (FRC) are
presented. By using the three different types of fibers (steel fiber-SF,
polypropylene-PPF and polyvinyl alcohol-PVA), FRC specimens
were produced and exposed to elevated temperatures up to 800 ºC for
1.5 hours. In addition, a plain concrete (without fiber) was produced
and used as a control. Test results obtained showed that the steel fiber
reinforced concrete (SFRC) had the highest compressive strength,
modulus of rapture and bond stress values at room temperatures, the
residual bond, flexural and compressive strengths of both FRC and
plain concrete dropped sharply after exposure to high temperatures.
The results also indicated that the reduction of bond, flexural and
compressive strengths with increasing the exposed temperature was
relatively less for SFRC than for plain, and FRC with PPF and PVA.
Abstract: Dental porcelain composites reinforced and toughened
by 20 wt.% tetragonal zirconia (3Y-TZP) were processed by hot
pressing at 1000°C. Two types of particles were tested: yttriastabilized
zirconia (ZrO2–3%Y2O3) agglomerates and pre-sintered
yttria-stabilized zirconia (ZrO2–3%Y2O3) particles. The composites
as well as the reinforcing particles were analyzed by the means of
optical and Scanning Electron Microscopy (SEM), Energy Dispersion
Spectroscopy (EDS) and X-Ray Diffraction (XRD). The mechanical
properties were obtained by the transverse rupture strength test. Wear
tests were also performed on the composites and monolithic
porcelain. The best mechanical results were displayed by the
porcelain reinforced with the pre-sintered ZrO2–3%Y2O3
agglomerates.
Abstract: The flora of Bozdağ (Konya) and its surroundings
were investigated between 2003 and 2005 years; 700 herbarium
specimens belonging to 482 taxa, 257 genera and 57 families were
collected and identified from the area. The families which have the
most taxa in research area are Asteraceae 67 (14.0%), Fabaceae 60
(12.6%), Lamiaceae 57 (11.9%), Brassicaceae 34 (7.1%), Poaceae
30 (6.3%), Rosaceae 24 (5.0%), Caryophyllaceae 23 (4.8%),
Liliaceae 19 (4.0%), Boraginaceae 17 (3.6%), and Apiaceae 13
(2.7%).
The research area is in the district of Konya and is in the B4
square according to the Grid System. The phytogeographic elements
are represented in the study area as follows; Irano-Turanian 91
(18.9%), Mediterranean 72 (14.9%), Euro-Siberian 21 (4.3%). The
phytogeographic regions of 273 (56.6%) taxa are either multi-regional
or unknown. The number of endemic taxa is 79 (16.3%).
Abstract: In review the generalized data about biological
activity of anthraquinone-containing plants and specimens on their
basis is presented. Data of traditional medicine, results of
bioscreening and clinical researches of specimens are analyzed.
Abstract: The main aim of the presented experiments is to
improve behaviour of sandwich structures under dynamic loading,
such as crash or explosion. This paper describes experimental
investigation on the response of new advanced materials to low and
high velocity load. Blast wave energy absorbers were designed using
two types of porous lightweight raw particle materials based on
expanded glass and ceramics with dimensions of 0.5-1 mm,
combined with polymeric binder. The effect of binder amount on the
static and dynamic properties of designed materials was observed.
Prism shaped specimens were prepared and loaded to obtain physicomechanical
parameters – bulk density, compressive and flexural
strength under quasistatic load, the dynamic response was determined
using Split Hopkinson Pressure bar apparatus. Numerical
investigation of the material behaviour in sandwich structure was
performed using implicit/explicit solver LS-Dyna. As the last step,
the developed material was used as the interlayer of blast resistant
litter bin, and it´s functionality was verified by real field blast tests.
Abstract: In the present work, fly ash geopolymer based
composites including polyester (PES) waste were studied. Specimens
of three compositions were prepared: (a) fly ash geopolymer with 5%
PES waste; (b) fly ash geopolymer mortar with 5% PES waste; (c) fly
ash geopolymer mortar with 6.25% PES waste. Compressive and
bending strength measurements, water absorption test and
determination of thermal conductivity coefficient were performed.
The results showed that the addition of sand in a mixture of
geopolymer with 5% PES content led to higher compressive strength,
while it increased water absorption and reduced thermal conductivity
coefficient. The increase of PES addition in geopolymer mortars
resulted in a more dense structure, indicated by the increase of
strength and thermal conductivity and the decrease of water
absorption.
Abstract: Over the past four decades, the fatigue behavior of
nickel-based alloys has been widely studied. However, in recent
years, significant advances in the fabrication process leading to grain
size reduction have been made in order to improve fatigue properties
of aircraft turbine discs. Indeed, a change in particle size affects the
initiation mode of fatigue cracks as well as the fatigue life of the
material. The present study aims to investigate the fatigue behavior of
a newly developed nickel-based superalloy under biaxial-planar
loading. Low Cycle Fatigue (LCF) tests are performed at different
stress ratios so as to study the influence of the multiaxial stress state
on the fatigue life of the material. Full-field displacement and strain
measurements as well as crack initiation detection are obtained using
Digital Image Correlation (DIC) techniques. The aim of this
presentation is first to provide an in-depth description of both the
experimental set-up and protocol: the multiaxial testing machine, the
specific design of the cruciform specimen and performances of the
DIC code are introduced. Second, results for sixteen specimens
related to different load ratios are presented. Crack detection, strain
amplitude and number of cycles to crack initiation vs. triaxial stress
ratio for each loading case are given. Third, from fractographic
investigations by scanning electron microscopy it is found that the
mechanism of fatigue crack initiation does not depend on the triaxial
stress ratio and that most fatigue cracks initiate from subsurface
carbides.
Abstract: Mechanical stress has a strong effect on the magnitude
of the Barkhausen-noise in structural steels. Because the
measurements are performed at the surface of the material, for a
sample sheet, the full effect can be described by a biaxial stress field.
The measured Barkhausen-noise is dependent on the orientation of
the exciting magnetic field relative to the axis of the stress tensor.
The sample inhomogenities including the residual stress also
modifies the angular dependence of the measured Barkhausen-noise.
We have developed a laboratory device with a cross like specimen
for bi-axial bending. The measuring head allowed performing
excitations in two orthogonal directions. We could excite the two
directions independently or simultaneously with different amplitudes.
The simultaneous excitation of the two coils could be performed in
phase or with a 90 degree phase shift. In principle this allows to
measure the Barkhausen-noise at an arbitrary direction without
moving the head, or to measure the Barkhausen-noise induced by a
rotating magnetic field if a linear superposition of the two fields can
be assumed.
Abstract: Concrete is found to undergo degradation when
subjected to elevated temperatures and loose substantial amount of its
strength. The loss of strength in concrete is mainly attributed to
decomposition of C-S-H and release of physically and chemically
bound water, which begins when the exposure temperature exceeds
100°C. When such a concrete comes in contact with moisture, the
cement paste is found rehydrate and considerable amount of strength
lost is found to recover. This paper presents results of an
experimental program carried out to investigate the effect of recuring
on strength gain of OPC concrete specimens subjected to elevated
temperatures from 200°C to 800°C, which were subjected to
retention time of two hours and four hours at the designated
temperature. Strength recoveries for concrete subjected to 7
designated elevated temperatures are compared. It is found that the
efficacy of recuring as a measure of strength recovery reduces with
increase in exposure temperature.