Abstract: The prepreg process among the CFRP (Carbon Fiber
Reinforced Plastic) forming methods is the short term of
‘Pre-impregnation’, which is widely used for aerospace composites
that require a high quality property such as a fiber-reinforced woven
fabric, in which an epoxy hardening resin is impregnated the reality.
However, that this process requires continuous researches and
developments for its commercialization because the delamination
characteristically develops between the layers when a great weight is
loaded from outside to supplement such demerit, three lamination
methods among the prepreg lamination methods of CFRP were
designed to minimize the delamination between the layers due to
external impacts. Further, the newly designed methods and the
existing lamination methods were analyzed through a mechanical
characteristic test, Interlaminar Shear Strength test. The Interlaminar
Shear Strength test result confirmed that the newly proposed three
lamination methods, i.e. the Roll, Half and Zigzag laminations,
presented more excellent strengths compared to the conventional Ply
lamination. The interlaminar shear strength in the roll method with
relatively dense fiber distribution was approximately 1.75% higher
than that in the existing ply lamination method, and in the half method,
it was approximately 0.78% higher.
Abstract: Rotary draw bending is a method which is being used
in tube forming. In the tube bending process, the neutral axis moves
towards the inner arc and the wall thickness distribution changes for
tube’s cross section. Thinning takes place in the outer arc of the tube
(extrados) due to the stretching of the material, whereas thickening
occurs in the inner arc of the tube (intrados) due to the comparison of
the material. The calculations of the wall thickness distribution,
neutral axis shifting, and strain distribution have not been accurate
enough, so far. The previous model (the geometrical model)
describes the neutral axis shifting and wall thickness distribution. The
geometrical of the tube, bending radius and bending angle are
considered in the geometrical model, while the influence of the
material properties of the tube forming are ignored. The advanced
model is a modification of the previous model using material
properties that depends on the correction factor. The correction factor
is a purely empirically determined factor. The advanced model was
compared with the Finite element simulation (FE simulation) using a
different bending factor (Bf =bending radius/ diameter of the tube),
wall thickness (Wf = diameter of the tube/ wall thickness), and
material properties (strain hardening exponent). Finite element model
of rotary draw bending has been performed in PAM-TUBE program
(version: 2012). Results from the advanced model resemble the FE
simulation and the experimental test.
Abstract: The impact deformation and fracture behaviour of cobalt-based Haynes 188 superalloy are investigated by means of a split Hopkinson pressure bar. Impact tests are performed at strain rates ranging from 1×103 s-1 to 5×103 s-1 and temperatures between 25°C and 800°C. The experimental results indicate that the flow response and fracture characteristics of cobalt-based Haynes 188 superalloy are significantly dependent on the strain rate and temperature. The flow stress, work hardening rate and strain rate sensitivity all increase with increasing strain rate or decreasing temperature. It is shown that the impact response of the Haynes 188 specimens is adequately described by the Zerilli-Armstrong fcc model. The fracture analysis results indicate that the Haynes 188 specimens fail predominantly as the result of intensive localised shearing. Furthermore, it is shown that the flow localisation effect leads to the formation of adiabatic shear bands. The fracture surfaces of the deformed Haynes 188 specimens are characterised by dimple- and / or cleavage-like structure with knobby features. The knobby features are thought to be the result of a rise in the local temperature to a value greater than the melting point.
Abstract: In this paper, the elasto-plastic and cyclic torsion of a shaft is studied using a finite element method. The Prager kinematic hardening theory of plasticity with the Ramberg and Osgood stress-strain equation is used to evaluate the cyclic loading behavior of the shaft under the torsional loading. The material of shaft is assumed to follow the non-linear strain hardening property based on the Prager model. The finite element method with C1 continuity is developed and used for solution of the governing equations of the problem. The successive substitution iterative method is used to calculate the distribution of stresses and plastic strains in the shaft due to cyclic loads. The shear stress, effective stress, residual stress and elastic and plastic shear strain distribution are presented in the numerical results.
Abstract: The possibility of using industrial hemp as a source of natural fibers for purpose of construction, mainly for the preparation of lightweight composites based on hemp hurds is described. In this article, an overview of measurement results of important technical parameters (compressive strength, density, thermal conductivity) of composites based on organic filler - chemically modified hemp hurds in three solutions (EDTA, NaOH and Ca(OH)2) and inorganic binder MgO-cement after 7, 28, 60, 90 and 180 days of hardening is given. The results of long-term water storage of 28 days hardened composites at room temperature were investigated. Changes in the properties of composites caused by chemical treatment of hemp material are discussed.
Abstract: Economic development and globalization of international markets have created a favourable atmosphere for the emergence of new forms of crime such as money laundering or financing of terrorism, which may contribute to destabilized and damage economic systems. In particular, money laundering have acquired great importance since the 11S attacks, what has caused on the one hand, the establishment and development of preventive measures and, on the other hand, a progressive hardening of penal measures. Since then, the regulations imposed to fight against money laundering have been viewed as key components also in the fight against terrorist financing. Terrorism, at the beginning, was a “national” crime connected with internal problems of the State (for instance the RAF in Germany or ETA in Spain) but in the last 20 years has started to be an international problem that is connected with the defence and security of the States. Therefore, the new strategic concept for the defense and security of NATO has a comprehensive list of security threats to the Alliance, such as terrorism, international instability, money laundering or attacks on cyberspace, among others. With this new concept, money laundering and terrorism has become a priority in the national defense.
In this work we will analyze the methods to combat these new threats to the national security. We will study the preventive legislations to combat money laundering and financing of terrorism, the UIF that exchange information between States, and the hawala-Banking.
Abstract: The material properties of OFHC copper film was investigated with the High-Speed Material Micro Testing Machine (HSMMTM) at the high strain rates. The rate-dependent stress-strain curves from the experiment and the Johnson−Cook curve fitting showed large discrepancies as the plastic strain increases since the constitutive model implies no rate-dependent strain hardening effect. A new constitutive model was proposed in consideration of rate-dependent strain hardening effect. The strain rate hardening term in the new constitutive model consists of the strain rate sensitivity coefficients of the yield strength and strain hardening.
Abstract: 2024 Aluminum alloy was squeezed cast by the Gas Induced Semi Solid (GISS) process. Effect of artificial aging on microstructure and mechanical properties of this alloy was studied in the present work. The solutionized specimens were aged hardened at temperatures of 175°C, 200°C, and 225°C under various time durations. The highest hardness of about 77.7 HRE was attained from specimen aged at the temperature of 175°C for 36h. Upon investigation the microstructure by using transmission electron microscopy (TEM), the S’ phase was mainly attributed to the strengthening effect in the aged alloy. The apparent activation energy for precipitation hardening of the alloy was calculated as 133,805 J/mol.
Abstract: Constitutive modeling of material behavior is becoming increasingly important in prediction of possible failures in highly loaded engineering components, and consequently, optimization of their design. In order to account for large number of phenomena that occur in the material during operation, such as kinematic hardening effect in low cycle fatigue behavior of steels, complex nonlinear material models are used ever more frequently, despite of the complexity of determination of their parameters. As a method for the determination of these parameters, genetic algorithm is good choice because of its capability to provide very good approximation of the solution in systems with large number of unknown variables. For the application of genetic algorithm to parameter identification, inverse analysis must be primarily defined. It is used as a tool to fine-tune calculated stress-strain values with experimental ones. In order to choose proper objective function for inverse analysis among already existent and newly developed functions, the research is performed to investigate its influence on material behavior modeling.
Abstract: Ageing of 75% cold rolled Al-6Mg alloy with ternary 0.4 wt% scandium and quaternary zirconium and titanium has been carried out. Alloy samples are naturally, isochronally and isothermally aged for different time and temperatures. Hardness values of the differently processed alloys have been measured to understand the ageing behavior of Al-6Mg alloy with scandium and quaternary zirconium and titanium addition. Resistivity changes with annealing time and temperature were measured to understand the precipitation behavior and recovery of strain of the alloy. Attempts were also made to understand the grain refining effect of scandium in Al-6Mg alloy. It is observed that significant hardening takes place in the aged alloys due to the precipitation of scandium aluminides and the dendrites of the Al-6Mg alloy have been refined significantly due to addition of scandium.
Abstract: Metal matrix composites consists of a metallic matrix combined with dispersed particulate phase as reinforcement. Aluminum alloys have been the primary material of choice for structural components of aircraft since about 1930. Well known performance characteristics, known fabrication costs, design experience, and established manufacturing methods and facilities, are just a few of the reasons for the continued confidence in 7XXX Al alloys that will ensure their use in significant quantities for the time to come. Particulate MMCs are of special interest owing to the low cost of their raw materials (primarily natural river sand here) and their ease of fabrication, making them suitable for applications requiring relatively high volume production. 7XXX Al alloys are precipitation hardenable and therefore amenable for thermomechanical treatment. Al–Zn alloys reinforced with particulate materials are used in aerospace industries in spite of the drawbacks of susceptibility to stress corrosion, poor wettability, poor weldability and poor fatigue resistance. The resistance offered by these particulates for the moving dislocations impart secondary hardening in turn contributes strain hardening. Cold deformation increases lattice defects, which in turn improves the properties of solution treated alloy. In view of this, six different Al–Zn–Mg alloy composites reinforced with silica (3 wt. % and 5 wt. %) are prepared by conventional semisolid synthesizing process. The cast alloys are solution treated and aged. The solution treated alloys are further severely cold rolled to enhance the properties. The hardness and strength values are analyzed and compared with silica free Al – Zn-Mg alloys. Precipitation hardening phenomena is accelerated due to the increased number of potential sites for precipitation. Higher peak hardness and lesser aging time are the characteristics of thermo mechanically treated samples. For obtaining maximum hardness, optimum number and volume of precipitate particles are required. The Al-5Zn-1Mg with 5% SiO2 alloy composite shows better result.
Abstract: The effect of autofrettage process in strain hardened
thick-walled pressure vessels has been investigated theoretically by
finite element modeling. Equivalent von Mises stress is used as yield
criterion to evaluate the optimum autofrettage pressure and the
optimum radius of elastic-plastic junction. It has been observed that
the optimum autofrettage pressure increases along with the working
pressure. For two different working pressures, the effect of the ratio
of outer to inner radius (b/a=k) value on the optimum autofrettage
pressure is also noticed. The Optimum autofrettage pressure solely
depends on K value rather than on the inner or outer radius.
Furthermore, percentage reduction of von Mises stresses is compared
for different working pressures and different k values. Maximum von
Mises stress developed at different autofrettage pressure is equated
for elastic perfectly plastic and elastic-plastic material with different
slope of strain hardening segment. Cylinder material having higher
slope of strain hardening segment provides better benedictions in the
autofrettage process.
Abstract: Atherosclerosis is the condition in which an artery
wall thickens as the result of a build-up of fatty materials such as
cholesterol. It is a syndrome affecting arterial blood vessels, a
chronic inflammatory response in the walls of arteries, in large part
due to the accumulation of macrophage white blood cells and
promoted by low density (especially small particle) lipoproteins
(plasma proteins that carry cholesterol and triglycerides) without
adequate removal of fats and cholesterol from the macrophages by
functional high density lipoproteins (HDL). It is commonly referred
to as a hardening or furring of the arteries. It is caused by the
formation of multiple plaques within the arteries.
Abstract: This paper presents a novel three-phase utility
frequency to high frequency soft switching power conversion circuit
with dual mode pulse width modulation and pulse density modulation
for high power induction heating applications as melting of steel and
non ferrous metals, annealing of metals, surface hardening of steel
and cast iron work pieces and hot water producers, steamers and
super heated steamers. This high frequency power conversion circuit
can operate from three-phase systems to produce high current for
high power induction heating applications under the principles of
ZVS and it can regulate its ac output power from the rated value to a
low power level. A dual mode modulation control scheme based on
high frequency PWM in synchronization with the utility frequency
positive and negative half cycles for the proposed high frequency
conversion circuit and utility frequency pulse density modulation is
produced to extend its soft switching operating range for wide ac
output power regulation. A dual packs heat exchanger assembly is
designed to be used in consumer and industrial fluid pipeline systems
and it is proved to be suitable for the hot water, steam and super
heated steam producers. Experiment and simulation results are given
in this paper to verify the operation principles of the proposed ac
conversion circuit and to evaluate its power regulation and
conversion efficiency. Also, the paper presents a mutual coupling
model of the induction heating load instead of equivalent transformer
circuit model.
Abstract: Lateral expansion is a factor defining the level of
confinement in reinforced concrete columns. Therefore, predicting
the lateral strain relationship with axial strain becomes an important
issue. Measuring lateral strains in experiments is difficult and only
few report experimental lateral strains. Among the existing analytical
formulations, two recent models are compared with available test
results in this paper with shortcomings highlighted. A new analytical
model is proposed here for lateral strain axial strain relationship and
is based on the supposition that the concrete behaves linear elastic in
the early stages of loading and then nonlinear hardening up to the
peak stress and then volumetric expansion. The proposal for the
lateral strain axial strain relationship after the peak stress is mainly
based on the hypothesis that the plastic lateral strain varies linearly
with the plastic axial strain and it is shown that this is related to the
lateral confinement level.
Abstract: In this paper fatigue crack initiation and propagation in notched plate under constant amplitude loading through tensile residual stress field of 2024 T351 Al-alloy plate were investigated. Residual stress field was generated by plastic deformation using finite element method (FEM) where isotropic hardening in Von Mises model was applied. Simulation of fatigue behavior was made on AFGROW code. It was shown that the fatigue crack initiation and propagation were affected by level of residual stress filed. In this investigation, the presence of tensile residual stresses at notch (hole) reduces considerably the total fatigue life. It was shown that the decreasing in stress reduces the fatigue crack growth rates.
Abstract: The induction hardening machines are utilized in
the industries which modify machine parts and tools needed to
achieve high ware resistance. This paper describes the model of
induction heating process design of inverter circuit and the results
of induction surface hardening of heating coil. In the design of
heating coil, the shape and the turn numbers of the coil are very
important design factors because they decide the overall operating
performance of induction heater including resonant frequency, Q
factor, efficiency and power factor. The performance will be tested
by experiments in some cases high frequency induction hardening
machine.
Abstract: The objective of the research was to evaluate the
quality of milk pomade sweet – sherbet packed in different packaging
materials (Multibarrier 60, met.BOPET/PE, Aluthen), by several
packaging technologies – active and modified atmosphere (MAP)
(consisting of 100% CO2), and control – in air ambiance.
Experiments were carried out at the Faculty of Food Technology of
Latvia University of Agriculture. Samples were stored at the room
temperature +21±1 °C. The physiochemical properties – weight
losses, moisture, hardening, colour and changes in headspace
atmosphere concentration (CO2 and O2) of packs were analysed
before packaging and after 2, 4, 6, 8, 10 and 12 storage weeks.
Abstract: In this paper back-propagation artificial neural
network (BPANN) is employed to predict the limiting drawing ratio
(LDR) of the deep drawing process. To prepare a training set for
BPANN, some finite element simulations were carried out. die and
punch radius, die arc radius, friction coefficient, thickness, yield
strength of sheet and strain hardening exponent were used as the
input data and the LDR as the specified output used in the training of
neural network. As a result of the specified parameters, the program
will be able to estimate the LDR for any new given condition.
Comparing FEM and BPANN results, an acceptable correlation was
found.
Abstract: As the material used for fuselage structure must
possess low density, high strength to weight ratio, the selection of
appropriate materials for fuselage structure is one of the most
important tasks. Aluminum metal itself is soft and low in strength. It
can be made stronger by giving proper combination of suitable alloy
addition, mechanical treatment and thermal treatment. The usual
thermal treatment given to aluminum alloys is called age-hardening
or precipitation hardening. In this paper, the studies are carried out on
7075 aluminum alloy which is how to improve strength level for
fuselage structure. The marked effect of the strength on the ternary
alloy is clearly demonstrated at several ageing times and
temperatures. It is concluded that aluminum-zinc-magnesium alloy
can get the highest strength level in natural ageing.