Abstract: This work is focused on the study of valuation of
recycled concrete aggregates, by measuring certain properties of
concrete in the fresh and hardened state. In this study, rheological
tests and physic-mechanical characterization on concretes and
mortars were conducted with recycled concrete whose geometric
properties were identified aggregates. Mortars were elaborated with
recycled fine aggregate (0/5mm) and concretes were manufactured
using recycled coarse aggregates (5/12.5 mm and 12.5/20 mm). First,
a study of the mortars was conducted to determine the effectiveness
of polycarboxylate superplasticizer on the workability of these and
their action deflocculating of the recycled sand. The rheological
behavior of mortars based on fine aggregate recycled was
characterized. The results confirm that the mortars composed of
different fractions of recycled sand (0 /5) have a better mechanical
properties (compressive and flexural strength) compared to normal
mortar. Also, the mechanical strengths of concretes made with
recycled aggregates (5/12.5 mm and 12.5/20 mm), are comparable to
those of conventional concrete with conventional aggregates,
provided that the implementation can be improved by the addition of
a superplasticizer.
Abstract: To elucidate the material characteristics of single
crystals of pure aluminum and copper, the respective relations between
crystallographic orientations and microstructures were examined,
along with bending and mechanical properties. The texture
distribution was also analysed. Bending tests were performed in a
SEM apparatus while its behaviors were observed. Some analytical
results related to crystal direction maps, inverse pole figures, and
textures were obtained from electron backscatter diffraction (EBSD)
analyses.
Abstract: Aluminum hybrid reinforcement technology is a
response to the dynamic ever increasing service requirements of such
industries as transportation, aerospace, automobile, marine, etc. It is
unique in that it offers a platform of almost unending combinations of
materials to produce various hybrid composites. This article reviews
the studies carried out on various combinations of aluminum hybrid
composite and the effects on mechanical, physical and chemical
properties. It is observed that the extent of enhancement of these
properties of hybrid composites is strongly dependent on the nature
of the reinforcement, its hardness, particle size, volume fraction,
uniformity of dispersion within the matrix and the method of hybrid
production.
Abstract: The influence of three different types of halloysite
nanotubes (HNTs) with different dimensions, namely as camel lake
(CLA), Jarrahdale (JA) and Matauri Bay (MB), on their reinforcing
ability of ethylene propylene dine monomer (EPDM) were
investigated by varying the HNTs loading (from 0-15 phr).
Mechanical properties of the nanocomposites improved with addition
of all three HNTs, but CLA based nanocomposites exhibited a
significant enhancement compared to the other HNTs. For instance,
tensile properties of EPDM nanocomposites increased by 120%,
256% and 340% for MB, JA and CLA, respectively, with addition of
15 phr of HNTs. This could be due to the higher aspect ratio and
higher surface area of CLA compared to others. Scanning electron
microscopy (SEM) of nanocomposites at 15 phr of HNT loadings
showed low amounts of pulled-out nanotubes which confirmed the
presence of more embedded nanotubes inside the EPDM matrix, as
well as aggregates within the fracture surface of EPDM/HNT
nanocomposites
Abstract: Two micromechanical models for 3D smart composite
with embedded periodic or nearly periodic network of generally
orthotropic reinforcements and actuators are developed and applied to
cubic structures with unidirectional orientation of constituents.
Analytical formulas for the effective piezothermoelastic coefficients
are derived using the Asymptotic Homogenization Method (AHM).
Finite Element Analysis (FEA) is subsequently developed and used
to examine the aforementioned periodic 3D network reinforced smart
structures. The deformation responses from the FE simulations are
used to extract effective coefficients. The results from both
techniques are compared. This work considers piezoelectric materials
that respond linearly to changes in electric field, electric
displacement, mechanical stress and strain and thermal effects. This
combination of electric fields and thermo-mechanical response in
smart composite structures is characterized by piezoelectric and
thermal expansion coefficients. The problem is represented by unitcell
and the models are developed using the AHM and the FEA to
determine the effective piezoelectric and thermal expansion
coefficients. Each unit cell contains a number of orthotropic
inclusions in the form of structural reinforcements and actuators.
Using matrix representation of the coupled response of the unit cell,
the effective piezoelectric and thermal expansion coefficients are
calculated and compared with results of the asymptotic
homogenization method. A very good agreement is shown between
these two approaches.
Abstract: Composites depending on the nature of their
constituents and mode of production are regarded as one of the
advanced materials that drive today’s technology. This paper
attempts a short review of the subject matter with a general aim of
pushing to the next level the frontier of knowledge as it impacts the
technology of nano-particles manufacturing. The objectives entail an
effort to; aggregate recent research efforts in this field, analyse
research findings and observations, streamline research efforts and
support industry in taking decision on areas of fund deployment. It is
envisaged that this work will serve as a quick hand-on compendium
material for researchers in this field and a guide to relevant
government departments wishing to fund a research whose outcomes
have the potential of improving the nation’s GDP.
Abstract: A series of polystyrene (PS) nanoparticles were
prepared by grafting polystyrene from both aggregated silica and
colloidally dispersed silica nanoparticles using atom-transfer radical
polymerisation (ATRP). Cross-linking and macroscopic gelation
were minimised by using a miniemulsion system. The thermal and
mechanical behaviour of the nanocomposites have been examined by
differential scanning calorimetry (DSC) and dynamic mechanical
thermal analysis (DMTA).
Abstract: The thermo-mechanical behaviour of concrete energy
pile foundations with different single and double U-tube shapes
incorporated was analysed using the Comsol Multi-physics package.
For the analysis, a 3D numerical model in real scale of the concrete
pile and surrounding soil was simulated regarding actual operation of
ground heat exchangers (GHE) and the surrounding ambient
temperature. Based on initial ground temperature profile measured in
situ, tube inlet temperature was considered to range from 6oC to 0oC
(during the contraction process) over a 30-day period. Extra thermal
stresses and deformations were calculated during the simulations and
differences arising from the use of two different systems (single-tube
and double-tube) were analysed. The results revealed no significant
difference for extra thermal stresses at the centre of the pile in either
system. However, displacements over the pile length were found to
be up to 1.5-fold higher in the double-tube system than the singletube
system.
Abstract: A new small–scale test rig developed for rolling
contact fatigue (RCF) investigations in wheel–rail material. This
paper presents the scaling strategy of the rig based on dimensional
analysis and mechanical modelling. The new experimental rig is
indeed a spinning frame structure with multiple wheel components
over a fixed rail-track ring, capable of simulating continuous wheelrail
contact in a laboratory scale. This paper describes the
dimensional design of the rig, to derive its overall scaling strategy
and to determine the key elements’ specifications. Finite element
(FE) modelling is used to simulate the mechanical behavior of the rig
with two sample scale factors of 1/5 and 1/7. The results of FE
models are compared with the actual railway system to observe the
effectiveness of the chosen scales. The mechanical properties of the
components and variables of the system are finally determined
through the design process.
Abstract: Aluminium and its alloys have excellent corrosion
resistant properties, ease of fabrication and high specific strength to
weight ratio. In this investigation an attempt has been made to study
the effect of different post weld heat treatment methods on the
mechanical and metallurgical properties of TIG welded joints of the
commercial aluminium alloy. Three different methods of post weld
heat treatments are solution heat treatment, artificial ageing and
combination of solution heat treatment and artificial aging are given
to TIG welded aluminium joints. Mechanical and metallurgical
properties of As welded joints of the aluminium alloys and post weld
heat treated joints of the aluminium alloys were examined.
Abstract: This work presents a Computational Fluid Dynamics
(CFD) simulation of a butterfly valve used to control the flow of
combustible gas mixture in an industrial process setting.The work
uses CFD simulation to analyze the flow characteristics in the
vicinity of the valve, including the pressure distributions and
Frequency spectrum of the pressure pulsations downstream the valves
and the vortex shedding allow predicting the torque fluctuations
acting on the valve shaft and the possibility of generating mechanical
vibration and resonance.These fluctuations are due to aerodynamic
torque resulting from fluid turbulence and vortex shedding in the
valve vicinity.
The valve analyzed is located in a pipeline between two opposing
90o elbows, which exposes the valve and the surrounding structure to
the turbulence generated upstream and downstream the elbows at
either end of the pipe.CFD simulations show that the best location for
the valve from a vibration point of view is in the middle of the pipe
joining the elbows.
Abstract: Kuosheng nuclear power plant (NPP) is a BWR/6 type
NPP and located on the northern coast of Taiwan. First, Kuosheng
NPP TRACE model were developed in this research. In order to assess
the system response of Kuosheng NPP TRACE model, startup tests
data were used to evaluate Kuosheng NPP TRACE model. Second, the
overpressurization transient analysis of Kuosheng NPP TRACE model
was performed. Besides, in order to confirm the mechanical property
and integrity of fuel rods, FRAPTRAN analysis was also performed in
this study.
Abstract: Bone properties and response behavior after static or
dynamic activation (loading) are still interesting topics in many fields
of the science especially in the biomechanical problems such as bone
loss of astronauts in space, osteoporosis, bone remodeling after
fracture or remodeling after surgery (endoprosthesis and implants)
and in osteointegration. This contribution deals with the relation
between physiological, demineralized and deproteinized state of the
turkey long bone – tibia. Three methods for comparison were used: 1)
densitometry, 2) three point bending and 3) frequency analysis. The
main goal of this work was to describe the decrease of the protein
(collagen) or mineral of the bone with relation to the fracture in three
point bending. The comparison is linked to the problem of different
bone mechanical behavior in physiological and osteoporotic state.
Abstract: This paper presents a method for the efficient
implementation of a unidirectional or bidirectional DC/DC converter.
The DC/DC converter is used essentially for energy exchange
between the low voltage service battery and a high voltage battery
commonly found in Electric Vehicle applications. In these
applications, apart from cost, efficiency of design is an important
characteristic. A useful way to reduce the size of electronic
equipment in the electric vehicles is proposed in this paper. The
technique simplifies the mechanical complexity and maximizes the
energy usage using the latest converter control techniques. Moreover
a bidirectional battery charger for hybrid electric vehicles is also
implemented in this paper. Several simulations on the test system
have been carried out in Matlab/Simulink environment. The results
exemplify the robustness of the proposed design methodology in case
of a 1.5 KW DC-DC converter.
Abstract: Nonstandard tests are necessary for analyses and
verification of new developed structural and technological solutions
with application of composite materials. One of the most critical
primary structural parts of a typical aerospace structure is T-joint.
This structural element is loaded mainly in shear, bending, peel and
tension. The paper is focused on the shear loading simulations. The
aim of the work is to obtain a representative uniform distribution of
shear loads along T-joint during the mechanical testing. A new
design of T-joint test procedure, numerical simulation and
optimization of representative boundary conditions are presented.
The different conditions and inaccuracies both in simulations and
experiments are discussed. The influence of different parameters on
stress and strain distributions is demonstrated on T-joint made of
CFRP (carbon fibre reinforced plastic). A special test rig designed by
VZLU (Aerospace Research and Test Establishment) for T-shear test
procedure is presented.
Abstract: This paper is concerning the issues of behaviour of
lightweight expanded clay aggregates concrete exposed to high
temperature. Lightweight aggregates from expanded clay are
produced by firing of row material up to temperature 1050°C.
Lightweight aggregates have suitable properties in terms of volume
stability, when exposed to temperatures up to 1050°C, which could
indicate their suitability for construction applications with higher risk
of fire. The test samples were exposed to heat by using the standard
temperature-time curve ISO 834. Negative changes in resulting
mechanical properties, such as compressive strength, tensile strength,
and flexural strength were evaluated. Also visual evaluation of the
specimen was performed. On specimen exposed to excessive heat, an
explosive spalling could be observed, due to evaporation of
considerable amount of unbounded water from the inner structure of
the concrete.
Abstract: In this paper, thick walled Cylindrical tanks or tubes
made of functionally graded material under internal pressure and
temperature gradient are studied. Material parameters have been
considered as power functions. They play important role in the
elastoplastic behavior of these materials. To clarify their role,
different materials with different parameters have been used under
temperature gradient. Finally, their effect and loading effect have
been determined in first yield point. Also, the important role of
temperature gradient was also shown. At the end the study has been
results obtained from changes in the elastic modulus and yield stress.
Also special attention is also given to the effects of this internal
pressure and temperature gradient in the creation of tensile and
compressive stresses.
Abstract: Polyethylene (PE), Polypropylene (PP), Polyethylene
(vinyl acetate) (EVA) and PE-ionomer nanocomposite samples were
prepared by mixing of the polymer with organofilized
montmorillonite fillers Cloisite 93A and Dellite 67G. The amount of
each modified montmorillonite (MMT) was fixed to 5% (w/w). The
twin-screw kneader was used for the compounding of polymer matrix
and chosen nanofillers. The level of MMT exfoliation was studied by
the transmission electron microscopy (TEM) observations. The
mechanical properties of prepared materials were evaluated by
dynamical mechanical analysis at 30°C and by the measurement of
tensile properties (stress and strain at break).
Abstract: Due to reduced stiffness, research on second
generation titanium alloys for implant applications, like the
metastable β-titanium alloy Ti-15Mo, become more and more
important in the recent years. The machinability of these alloys is
generally poor leading to problems during implant production and
comparably large production costs. Therefore, in the present study,
Ti-15Mo was alloyed with 0.8 wt.-% of the rare earth metals
lanthanum (Ti-15Mo+0.8La) and neodymium (Ti-15Mo+0.8Nd) to
improve its machinability. Their microstructure consisted of a
titanium matrix and micrometer-size particles of the rare earth metals
and two of their oxides. The particles stabilized the microstructure as
grain growth was minimized. As especially the ductility might be
affected by the precipitates, the behavior of Ti-15Mo+0.8La and Ti-
15Mo+0.8Nd was investigated during static and dynamic
deformation at elevated temperature to develop a processing route.
The resulting mechanical properties (static strength and ductility)
were similar in all investigated alloys.
Abstract: Copper being one of the major intrinsic residual
impurities in steel possesses the tendency to induce severe
microstructural distortions if not controlled within certain limits.
Hence, this paper investigates the effect of this element on the
mechanical properties of construction steel with a view to ascertain
its safe limits for effective control. The experiment entails collection
of statistically scheduled samples of hot rolled profiles with varied
copper concentrations in the range of 0.12-0.39 wt. %. From these
samples were prepared standard test specimens subjected to tensile,
impact, hardness and microstructural analyses. Results show a rather
huge compromise in mechanical properties as the specimens
demonstrated 54.3%, 74.2% and 64.9% reduction in tensile strength,
impact energy and hardness respectively as copper content increases
from 0.12 wt. % to 0.39 wt. %. The steel’s abysmal performance is
due to the severe distortion of the microstructure occasioned by the
development of incoherent complex compounds which weaken the
pearlite reinforcing phase. It is concluded that the presence of copper
above 0.22 wt. % is deleterious to construction steel performance.