Abstract: Since, both the relative position of tunnels and the construction procedure affect the soil movement and internal forces in the lining, it is of major concern to study the influence of these factors on the tunnel design. Construction procedures of tunnels have considerable effects on the magnitude of surface movements and lining stresses. This paper describes numerical analysis of construction procedure of a three adjacent shallow tunnels at high groundwater levels using the commercial finite difference software (FLAC-3D). The aim of this study is to determinate the most suitable construction procedure for the three tunnels and the optimum excavation step in Tehran Metro tunnels in order to optimize the surface settlements and lining stresses.
Abstract: Thyristor based firing angle controlled voltage regulators are extensively used for speed control of single phase induction motors. This leads to power saving but the applied voltage and current waveforms become non-sinusoidal. These non-sinusoidal waveforms increase voltage and thermal stresses which result into accelerated insulation aging, thus reducing the motor life. Life models that allow predicting the capability of insulation under such multi-stress situations tend to be very complex and somewhat impractical. This paper presents the fuzzy logic application to investigate the synergic effect of voltage and thermal stresses on intrinsic aging of induction motor insulation. A fuzzy expert system is developed to estimate the life of induction motor insulation under multiple stresses. Three insulation degradation parameters, viz. peak modification factor, wave shape modification factor and thermal loss are experimentally obtained for different firing angles. Fuzzy expert system consists of fuzzyfication of the insulation degradation parameters, algorithms based on inverse power law to estimate the life and defuzzyficaton process to output the life. An electro-thermal life model is developed from the results of fuzzy expert system. This fuzzy logic based electro-thermal life model can be used for life estimation of induction motors operated with non-sinusoidal voltage and current waveforms.
Abstract: The results of an experimental program conducted on seventeen simply supported concrete beams to study the effect of transverse reinforcement on the behavior of lap splice of steel reinforcement in tension zones in high strength concrete beams, are presented. The parameters included in the experimental program were the concrete compressive strength, the lap splice length, the amount of transverse reinforcement provided within the splice region, and the shape of transverse reinforcement around spliced bars. The experimental results showed that the displacement ductility increased and the mode of failure changed from splitting bond failure to flexural failure when the amount of transverse reinforcement in splice region increased, and the compressive strength increased up to 100 MPa. The presence of transverse reinforcement around spliced bars had pronounced effect on increasing the ultimate load, the ultimate deflection, and the displacement ductility. The prediction of maximum steel stresses for spliced bars using ACI 318-05 building code was compared with the experimental results. The comparison showed that the effect of transverse reinforcement around spliced bars has to be considered into the design equations for lap splice length in high strength concrete beams.
Abstract: The functional performance of machined components, often, depends on surface topography, hardness, nature of stress and strain induced on the surface, etc. Invariably, surfaces of metallic components obtained by turning, milling, etc., consist of irregularities such as machining marks are responsible for the above. Surface finishing/coating processes used to produce improved surface quality/textures are classified as chip-removal and chip-less processes. Burnishing is chip-less cold working process carried out to improve surface finish, hardness and resistance to fatigue and corrosion; not obtainable by other surface coating and surface treatment processes. It is a very simple, but effective method which improves surface characteristics and is reported to introduce compressive stresses.
Of late, considerable attention is paid to post-machining, finishing operations, such as burnishing. During burnishing the micro-irregularities start to deform plastically, initially the crests are gradually flattened and zones of reduced deformation are formed. When all the crests are deformed, the valleys between the micro-irregularities start moving in the direction of the newly formed surface. The grain structure is then condensed, producing a smoother and harder surface with superior load-carrying and wear-resistant capabilities.
Burnishing can be performed on a lathe with a highly polished ball or roller type tool which is traversed under force over a rotating/stationary work piece. Often, several passes are used to obtain the work piece surface with the desired finish and hardness.
This paper presents the findings of an experimental investigation on the effect of ball burnishing parameters such as, burnishing speed, feed, force and number of passes; on surface roughness (Ra) and micro-hardness (Hv) of a 60/40 copper/zinc alloy, using a 2-level fractional factorial design of experiments (DoE). Mathematical models were developed to predict surface roughness and hardness generated by burnishing in terms of the above process parameters. A ball-type tool, designed and constructed from a high chrome steel material (HRC=63 and Ra=0.012 µm), was used for burnishing of fine-turned cylindrical bars (0.68-0.78µm and 145Hv). They are given by,
Ra= 0.305-0.005X1 - 0.0175X2 + 0.0525X4 + 0.0125X1X4 -0.02X2X4 - 0.0375X3X4
Hv=160.625 -2.37 5X1 + 5.125X2 + 1.875X3 + 4.375X4 - 1.625X1X4 + 4.375X2X4 - 2.375X3X4
High surface microhardness (175HV) was obtained at 400rpm, 2passes, 0.05mm/rev and 15kgf., and high surface finish (0.20µm) was achieved at 30kgf, 0.1mm/rev, 112rpm and single pass. In other words, surface finish improved by 350% and microhardness improved by 21% compared to as machined conditions.
Abstract: Springback is a significant problem in the sheet metal
forming process. When the tools are released after the stage of
forming, the product springs out, because of the action of the internal
stresses. In many cases the deviation of form is too large and the
compensation of the springback is necessary. The precise prediction
of the springback of product is increasingly significant for the design
of the tools and for compensation because of the higher ratio of the
yield stress to the elastic modulus.
The main object in this paper was to study the effect of the
anisotropy on the springback for three directions of rolling: 0°, 45°
and 90°. At the same time, we highlighted the influence of three
different metallic materials: Aluminum, Steel and Galvanized steel.
The original of our purpose consist on tests which are ensured by
adapting a U-type stretching-bending device on a tensile testing
machine, where we studied and quantified the variation of the
springback according to the direction of rolling. We also showed the
role of lubrication in the reduction of the springback.
Moreover, in this work, we have studied important characteristics
in deep drawing process which is a springback. We have presented
defaults that are showed in this process and many parameters
influenced a springback.
Finally, our results works lead us to understand the influence of
grains orientation with different metallic materials on the springback
and drawing some conclusions how to concept deep drawing tools. In
addition, the conducted work represents a fundamental contribution
in the discussion the industry application.
Abstract: Downward turbulent bubbly flows in pipes were
modeled using computational fluid dynamics tools. The
Hydrodynamics, phase distribution and turbulent structure of twophase
air-water flow in a 57.15 mm diameter and 3.06 m length
vertical pipe was modeled by using the 3-D Eulerian-Eulerian
multiphase flow approach. Void fraction, liquid velocity and
turbulent fluctuations profiles were calculated and compared against
experimental data. CFD results are in good agreement with
experimental data.
Abstract: Simulation of occlusal function during laboratory
material-s testing becomes essential in predicting long-term
performance before clinical usage. The aim of the study was to assess
the influence of chamfer preparation depth on failure risk of heat
pressed ceramic crowns with and without zirconia framework by
means of finite element analysis. 3D models of maxillary central
incisor, prepared for full ceramic crowns with different depths of the
chamfer margin (between 0.8 and 1.2 mm) and 6-degree tapered
walls together with the overlying crowns were generated using
literature data (Fig. 1, 2). The crowns were designed with and
without a zirconia framework with a thickness of 0.4 mm. For all
preparations and crowns, stresses in the pressed ceramic crown,
zirconia framework, pressed ceramic veneer, and dentin were
evaluated separately. The highest stresses were registered in the
dentin. The depth of the preparations had no significant influence on
the stress values of the teeth and pressed ceramics for the studied
cases, only for the zirconia framework. The zirconia framework
decreases the stress values in the veneer.
Abstract: Tensile armour wires provide a flexible pipe's
resistance to longitudinal stresses. Flexible pipe manufacturers need
to know the effect of defects such as scratches and cracks, with
dimensions less than 0.2mm which is the limit of the current nondestructive
detection technology, on the fracture stress and fracture
strain of the wire for quality assurance purposes. Recent research
involving the determination of the fracture strength of cracked wires
employed laboratory testing and classical fracture mechanics
approach using non-standardised fracture mechanics specimens
because standard test specimens could not be manufactured from the
wires owing to their sizes. In this work, the effect of miniature
cracks on the fracture properties of tensile armour wires was
investigated using laboratory and finite element tensile testing
simulations with the phenomenological shear fracture model. The
investigation revealed that the presence of cracks shallower than
0.2mm is worse on the fracture strain of the wire.
Abstract: The intention of this study to design the probability optimized sewing sack-s workstation based on ergonomics for productivity improvement and decreasing musculoskeletal disorders. The physical dimensions of two workers were using to design the new workstation. The physical dimensions are (1) sitting height, (2) mid shoulder height sitting, (3) shoulder breadth, (4) knee height, (5) popliteal height, (6) hip breadth and (7) buttock-knee length. The 5th percentile of buttock knee length sitting (51 cm), the 50th percentile of mid shoulder height sitting (62 cm) and the 95th percentile of popliteal height (43 cm) and hip breadth (45 cm) applied to design the workstation for sewing sack-s operator and the others used to adjust the components of this workstation. The risk assessment by RULA before and after using the probability optimized workstation were 7 and 7 scores and REBA scores were 11 and 5, respectively. Body discomfort-abnormal index was used to assess muscle fatigue of operators before adjustment workstation found that neck muscles, arm muscles area, muscles on the back and the lower back muscles fatigue. Therefore, the extension and flexion exercise was applied to relief musculoskeletal stresses. The workers exercised 15 minutes before the beginning and the end of work for 5 days. After that, the capability of flexion and extension muscles- workers were increasing in 3 muscles (arm, leg, and back muscles).
Abstract: This study deals with the phenomena of reflection and transmission (refraction) of qSV-waves, for an incident of quasi transverse vertically waves, at a plane interface of two semi-infinite piezoelectric elastic media under the influence of the initial stresses. The relations governing the reflection and transmission coefficients of these reflected waves for various suitable boundary conditions are derived. We have shown analytically that reflection and transmission coefficients of (qP) and (qSV) waves depend upon the angle of incidence, the parameters of electric potential, the material constants of the medium as will as the initial stresses presented in the media. The numerical calculations of the reflection and transmission amplitude ratios for different values of initial stresses have been carried out by computer for different materials as examples and the results are given in the form of graphs. Finally, some of particular cases are considered.
Abstract: In most wheat growing moderate regions and
especially in the north of Iran climate, is affected grain filling by
several physical and abiotic stresses. In this region, grain filling often
occurs when temperatures are increasing and moisture supply is
decreasing. The experiment was designed in RCBD with split plot
arrangements with four replications. Four irrigation treatments
included (I0) no irrigation (check); (I1) one irrigation (50 mm) at
heading stage; (I2) two irrigation (100 mm) at heading and anthesis
stage; and (I3) three irrigation (150 mm) at heading, anthesis and
early grain filling growth stage, two wheat cultivars (Milan and
Shanghai) were cultured in the experiment. Totally raining was 453
mm during the growth season. The result indicated that biological
yield, grain yield and harvest index were significantly affected by
irrigation levels. I3 treatment produced more tillers number in m2,
fertile tillers number in m2, harvest index and biological yield. Milan
produced more tillers number in m2, fertile tillers in m2, while
Shanghai produced heavier tillers and grain 1000 weight. Plant height
was significant in wheat varieties while were not statistically
significant in irrigation levels. Milan produced more grain yield,
harvest index and biological yield. Grain yield shown that I1, I2, and
I3 produced increasing of 5228 (21%), 5460 (27%) and 5670 (29%)
kg ha-1, respectively. There was an interaction of irrigation and
cultivar on grain yields. In the absence of the irrigation reduced grain
1000 weight from 45 to 40 g. No irrigation reduced soil moisture
extraction during the grain filling stage. Current assimilation as a
source of carbon for grain filling depends on the light intercepting
viable green surfaces of the plant after anthesis that due to natural
senescence and the effect of various stresses. At the same time the
demand by the growing grain is increasing. It is concluded from
research work that wheat crop irrigated Milan cultivar could increase
the grain yield in comparison with Shanghai cultivar. Although, the
grain yield of Shanghai under irrigation was slightly lower than
Milan. This grain yield also was related to weather condition, sowing
date, plant density and location conditions and management of
fertilizers, because there was not significant difference in biological
and straw yield. The best result was produced by I1 treatment. I2 and
I3 treatments were not significantly difference with I1 treatment.
Grain yield of I1 indicated that wheat is under soil moisture
deficiency. Therefore, I1 irrigation was better than I0.
Abstract: Power transformer consists of components which are
under consistent thermal and electrical stresses. The major
component which degrades under these stresses is the paper
insulation of the power transformer. At site, lightning impulses and
cable faults may cause the winding deformation. In addition, the
winding may deform due to impact during transportation. A
deformed winding will excite more stress to its insulating paper thus
will degrade it. Insulation degradation will shorten the life-span of
the transformer. Currently there are two methods of detecting the
winding deformation which are Sweep Frequency Response
Analysis (SFRA) and Low Voltage Impulse Test (LVI). The latter
injects current pulses to the winding and capture the admittance
plot. In this paper, a transformer which experienced overheating and
arcing was identified, and both SFRA and LVI were performed.
Next, the transformer was brought to the factory for untanking. The
untanking results revealed that the LVI is more accurate than the
SFRA method for this case study.
Abstract: In this paper are illustrated the principal aspects
connected with the numerical evaluation of thermal stress induced by high gradient temperature in the concrete beam. The reinforced concrete beam has many advantages over steel
beam, such as high resistance to high temperature, high resistance to thermal shock, Better resistance to fatigue and buckling, strong
resistance against, fire, explosion, etc.
The main drawback of the reinforced concrete beam is its poor resistance to tensile stresses. In order to investigate the thermal
induced tensile stresses, a numerical model of a transient thermal
analysis is presented for the evaluation of thermo-mechanical
response of concrete beam to the high temperature, taking into account the temperature dependence of the thermo physical properties of the concrete like thermal conductivity and specific heat.
Abstract: In this paper, the test purpose will be to assess
whether or not the accelerated model proposed by Eyring will be able
to translate results for the shape and scale parameters of an
underlying Weibull model, obtained under two accelerating using
conditions, to expected normal using condition results for these
parameters. The product being analyzed is a new type of insulate
fluid, and the accelerating factor is the voltage stresses applied to the
fluid at two different levels (30KV and 40KV). The normal operating
voltage is 25KV. In this case, it was possible to test the insulate fluid
at normal voltage using condition. Both results for the two
parameters of the Weibull model, obtained under normal using
condition and translated from accelerated using conditions to normal
conditions, will be compared to each other to assess the accuracy of
the Eyring model when the accelerating factor is only the voltage
stress.
Abstract: Power cables are vulnerable to failure due to aging or
defects that occur with the passage of time under continuous
operation and loading stresses. PD detection and characterization
provide information on the location, nature, form and extent of the
degradation. As a result, PD monitoring has become an important
part of condition based maintenance (CBM) program among power
utilities. Online partial discharge (PD) localization of defect sources
in power cable system is possible using the time of flight method.
The information regarding the time difference between the main and
reflected pulses and cable length can help in locating the partial
discharge source along the cable length. However, if the length of
the cable is not known and the defect source is located at the extreme
ends of the cable or in the middle of the cable, then double ended
measurement is required to indicate the location of PD source. Use of
multiple sensors can also help in discriminating the cable PD or local/
external PD. This paper presents the experience and results from
online partial discharge measurements conducted in the laboratory
and the challenges in partial discharge source localization.
Abstract: A Vehicle-s door wireing harness arrangement structure is provided. In vehicle-s door wiring harness(W/H) system is more toward to arrange a passenger compartment than a hinge and a weatherstrip. This article gives some insight into the dimensioning process, with special focus on large deflection analysis of wiring harness(W/H) in vehicle-s door structures for durability problem. An Finite elements analysis for door wiring harness(W/H) are used for residual stresses and dimensional stability with bending flexible. Durability test data for slim test specimens were compared with the numerical predicted fatigue life for verification. The final lifing of the component combines the effects of these microstructural features with the complex stress state arising from the combined service loading and residual stresses.
Abstract: Optimal selection of electrical insulations in electrical
machinery insures reliability during operation. From the insulation
studies of view for electrical machines, stator is the most important
part. This fact reveals the requirement for inspection of the electrical
machine insulation along with the electro-thermal stresses. In the
first step of the study, a part of the whole structure of machine in
which covers the general characteristics of the machine is chosen,
then based on the electromagnetic analysis (finite element method),
the machine operation is simulated. In the simulation results, the
temperature distribution of the total structure is presented
simultaneously by using electro-thermal analysis. The results of
electro-thermal analysis can be used for designing an optimal cooling
system. In order to design, review and comparing the cooling
systems, four wiring structures in the slots of Stator are presented.
The structures are compared to each other in terms of electrical,
thermal distribution and remaining life of insulation by using Finite
Element analysis. According to the steps of the study, an optimization
algorithm has been presented for selection of appropriate structure.
Abstract: Transition theory has been used to derive the elasticplastic
and transitional stresses. Results obtained have been discussed
numerically and depicted graphically. It is observed that the rotating
disk made of incompressible material with inclusion require higher
angular speed to yield at the internal surface as compared to disk
made of compressible material. It is seen that the radial and
circumferential stresses are maximum at the internal surface with and
without edge load (for flat disk). With the increase in thickness
parameter (k = 2, 4), the circumferential stress is maximum at the
external surface while the radial stress is maximum at the internal
surface. From the figures drawn the disk with exponentially varying
thickness (k = 2), high angular speed is required for initial yielding at
internal surface as compared to flat disk and exponentially varying
thickness for k = 4 onwards. It is concluded that the disk made of
isotropic compressible material is on the safer side of the design as
compared to disk made of isotropic incompressible material as it
requires higher percentage increase in an angular speed to become
fully plastic from its initial yielding.
Abstract: The heterotrophic seedling growth can be defined as a
product of two components: (1) the weight of mobilized seed reserve,
and (2) conversion efficiency of utilized seed reserve to seedling
tissue. The first component can be further divided into (1) initial seed
weight, and (2) the fraction of seed reserve, which is mobilized. The
objective of this study was the identification of the sensitive seedling
growth component(s) in response to drought and salinity stresses.
Two experiments were separately conducted using various salinity
levels (osmotic pressure) of 0, 0.25, 0.50, 0.75, 1, 1.25 and 1.5 MPa
created using NaCl as first experiment and by polyethylene glycol
(drought stress) of 0, 0.2, 0.4, 0.6, 0.8, 1, 1.2 and 1.4 MPa in second
experiment. Seeds of five crops species (Hordeum vulgare, Brassica
napus, Zea mays, Medicago sativa and Medicago scutellata) were
used in each experiment. In both experiments, seedling growth,
fraction of seed reserve utilization and weight of mobilized seed
reserve decreased with increasing drought and salt intensity.
However, drought and salinity stresses had no effect on the
conversion efficiency. It was concluded that the sensitive component
of seedling growth is the weight of mobilized seed reserve.
Abstract: This work presents a numerical model developed to
simulate the dynamics and vibrations of a multistage tractor gearbox.
The effect of time varying mesh stiffness, time varying frictional
torque on the gear teeth, lateral and torsional flexibility of the shafts
and flexibility of the bearings were included in the model. The model
was developed by using the Lagrangian method, and it was applied to
study the effect of three design variables on the vibration and stress
levels on the gears. The first design variable, module, had little effect
on the vibration levels but a higher module resulted to higher bending
stress levels. The second design variable, pressure angle, had little
effect on the vibration levels, but had a strong effect on the stress
levels on the pinion of a high reduction ratio gear pair. A pressure
angle of 25o resulted to lower stress levels for a pinion with 14 teeth
than a pressure angle of 20o. The third design variable, contact ratio,
had a very strong effect on both the vibration levels and bending
stress levels. Increasing the contact ratio to 2.0 reduced both the
vibration levels and bending stress levels significantly. For the gear
train design used in this study, a module of 2.5 and contact ratio of
2.0 for the various meshes was found to yield the best combination
of low vibration levels and low bending stresses. The model can
therefore be used as a tool for obtaining the optimum gear design
parameters for a given multistage spur gear train.