Aluminum Strips Research Articles

Modelling and Experimental Testing of Hybrid Joints Made of: Aluminium Adherends, Adhesive Layers and Rivets for Aerospace Applications

AbstractThe contemporary demands in different branches of engineering require application of new multi-component materials and structural systems. Appropriately chosen joining technology can offer significant enhancement of structural system performance in terms of effectiveness, reliability, safety and other design criteria. The modern applications of complex joints are of great technological interest as they permit to combine and to enhance the individual effects of each kind of joint. This is of great importance for modern applications in different branches of engineering: aerospace, mechanical and civil. Therefore in this paper we will focus on the analysis of mechanical response of adhesive joint of aluminium strips reinforced by rivets. The aim of the paper is to investigate experimentally the mechanical behaviour of adhesive joint of aluminium strips reinforced by rivets for industrial applications in aerospace. The considered joint was subjected to uniaxial loading. The tests in this paper were performed for: • classical adhesive joint in order to investigate material parameters for numerical modelling of the hybrid joint • hybrid joining of the structural elements in order to investigate the reinforcement effect. The experiments with application of digital image ARAMIS system allowed for on-line monitoring of the deformation process of the considered joining elements. The particular distributions of displacement fields at the joint surface were estimated for any stage of loading process. Numerical modelling was performed for experimentally investigated specimens. The materials parameters, necessary for calculation, were estimated from experiments. FEA modelling was done with the help of ABAQUS code.

Coupled thermal-fluid-mechanics analysis of twin roll casting of A7075 aluminum alloy

Better understanding of temperature distribution and roll separation force during twin roll casting of aluminum alloys is critical to successfully fabricate good quality of aluminum strips. Therefore, the simulation techniques are widely applied to understand the twin roll casting process in a comprehensive way and to reduce the experimental time and cost of trial and error. However, most of the conventional approaches are considered thermally coupled flow, or thermally coupled mechanical behaviors. In this study, a fully coupled thermal-fluid-mechanical analysis of twin roll casting of A7075 aluminum strips was carried out using the finite element method. Temperature profile, liquid fraction and metal flow of aluminum strips with different thickness were predicted. Roll separation force and roll temperatures were experimentally obtained from a pilot-scale twin roll caster, and those results were compared with model predictions. Coupling the fluid of the liquid melt to the thermal and mechanical modeling reasonably predicted roll temperature distribution and roll separation force during twin roll casting.

Modular and efficient ozone systems based on massively parallel chemical processing in microchannel plasma arrays: performance and commercialization

Plasmachemical systems based on the production of a specific molecule (O3) in literally thousands of microchannel plasmas simultaneously have been demonstrated, developed and engineered over the past seven years, and commercialized. At the heart of this new plasma technology is the plasma chip, a flat aluminum strip fabricated by photolithographic and wet chemical processes and comprising 24–48 channels, micromachined into nanoporous aluminum oxide, with embedded electrodes. By integrating 4–6 chips into a module, the mass output of an ozone microplasma system is scaled linearly with the number of modules operating in parallel. A 115 g/hr (2.7 kg/day) ozone system, for example, is realized by the combined output of 18 modules comprising 72 chips and 1,800 microchannels. The implications of this plasma processing architecture for scaling ozone production capability, and reducing capital and service costs when introducing redundancy into the system, are profound. In contrast to conventional ozone generator technology, microplasma systems operate reliably (albeit with reduced output) in ambient air and humidity levels up to 90%, a characteristic attributable to the water adsorption/desorption properties and electrical breakdown strength of nanoporous alumina. Extensive testing has documented chip and system lifetimes (MTBF) beyond 5,000 hours, and efficiencies >130 g/kWh when oxygen is the feedstock gas. Furthermore, the weight and volume of microplasma systems are a factor of 3-10 lower than those for conventional ozone systems of comparable output. Massively-parallel plasmachemical processing offers functionality, performance, and commercial value beyond that afforded by conventional technology, and is currently in operation in more than 30 countries worldwide.

Thermal Treatment of Aviation Aluminum Alloys in Strip Processing Lines

For many years now the use of aluminum as a light weight construction material in the aviation and automotive industry is on the rise. Without the innovative aluminum materials the strategies of constructing in light-weight design cannot be implemented. Last but not least this trend is driven by official requirements directing the reduction of greenhouse gas emissions. Aluminum is used both for structural components as well as for external body parts. Aluminum products for these industries have to undergo a production process which includes homogenizing of the ingots, hot rolling and cold rolling. Subsequent to the cold rolling process, the aluminum sheets have to undergo a heat treatment process to regain formability as well as the required material strength. The material properties required by the aviation and automotive industry are achieved in the annealing furnace and downstream cooling equipment. Equal and well-aimed heating and cooling along the length and across the width provide the strips with the metallurgical properties with regard to hardness and grain size. Hence the annealing furnace and the downstream cooling equipment are the decisive process components and critical for the high quality of the end material. First the material is heated up to a temperature above 500 °C for the solution heat treatment process. The following process step foresees cooling down the material to ambient temperature. Especially 6xxx automotive-alloys as well as 2xxx and 7xxx aerospace-alloys require high cooling rates. Eventually, the material gets heated up again for a certain time to apply an artificial aging process. In floatation heat treatment furnaces the strip is guided sinusoidal and contactless by floatation nozzles through the furnace. The strip is heated up and kept at the required strip temperatures in time, so the aluminum-alloy obtains their structure. The cooling process with high cooling rates is executed as a combination of water and air cooling. A mathematical model calculates the necessary settings for the annealing and cooling process under consideration of the mechanical properties. Paper and presentation will introduce the furnace technology for aluminum strips. Especially, the heat treatment facilities for heat and chemical treatment lines will be presented. It will especially emphasize on heat treatment cycles, the materials and the applications.

Demonstration of a Pixel-Scale Superconducting Heat Switch for an Ideal Integrating Bolometer

The sensitivity of a bolometer is in principle limited by the phonon noise, which is a function of the conductance between its absorber and the thermal sink. However, practical issues limit the degree to which conductance can be minimized. For example, in a high-radiation environment, extremely low conductance, or, equivalently, long thermal recovery time, can lead to high data loss. To circumvent such limitations, we are developing a technique of modulating the conductance through the use of pixel-scale superconducting heat switches. We have fabricated bolometer-like test devices consisting of isolated regions connected to a thermal ground plane through narrow aluminum strips. Niobium coils are patterned around the aluminum strips. Flowing current through a coil allows the aluminum to be driven into the normal or high thermal conductance state. We have measured the conductance of these devices as a function of temperature and drive coil current.

Heat transfer enhancement of internal flow by inserting punched delta winglet vortex generators with various attack angles

Effects of punched delta winglet vortex generator inserts (PDWVGs) on single-phase forced convection heat transfer and friction loss of internal flow were experimentally investigated. The PDWVGs were manufactured by punching directly on aluminum strips with different attack angles (α) of 30°, 50° and 70°. Winglet-pitch ratio (Rp) and a winglet-width ratio (Rb) of PDWVGs were 1.05 and 0.42, respectively. Longitudinal strip and plain tube were also tested for comparison. The experiments were carried out under the conditions of Reynolds number from 5500 to 14500. Experimental results reveal that the PDWVG insert in a tube provided considerably higher heat transfer coefficient than the tube without the insert through pressure loss was also increased. The Nusselt number and friction factor increased with the increasing of α. The heat transfer enhancement by the PDWVGs with α of 30°, 50° and 70° provided higher than the plain tube in the range of 110–131%, 157–188% and 218–264%, respectively. The average friction factors in the inner tube generated by the PDWVGs with α of 30°, 50° and 70° were about 8.80, 10.21 and 11.87 times above the plain tube, respectively. The thermal enhancement factor was in the range of 0.91–1.22 for PDWVGs and 0.88–0.99 for L-S. In addition, the empirical correlations of Nusselt number, friction factor and thermal performance factor for PDWVGs were developed from the experimental results.

Essential work of fracture assessment for thin aluminium strips using finite element analysis

The fracture toughness of a commercial thin aluminium sheet (1.2mm) is measured by the essential work of fracture (EWF) method using a double-edge notch tension specimen. The EWF method is implemented at room temperature at a deformation speed of 2mm/min. The basics of the EWF method and its relation with J-integral are described in this paper. Ligament yielding is observed to occur at the peak of the load-displacement curve. Following this, necking and tearing occur in the softening region. The EWF for the thin aluminium sheet is measured as 51.5kJ/m2. However, the non-essential work of fracture is dissipated in the tearing process after yielding, causing expansion of the plastic region. In this work, two advanced finite element models, namely, non-linear and linear J-Integral finite element models, are implemented to simulate the essential work of fracture test. The results for the essential and non-essential fracture indicate good agreement with EWF fitting. The linear extended finite element (XFEM) model yields more accurate results than the J-integral method. Crack opening displacement is measured by the EWF method, and is compared with the results of the studied models.

Prevalence of proximal contact loss between implant‐supported fixed prostheses and adjacent natural teeth and its associated factors: a 7‐year prospective study

The aim was to analyze the prevalence rate of proximal contact loss (PCL) between implant-fixed prostheses (IFPs) and adjacent teeth and investigate the associated factors. One hundred fifty participants were recruited for this prospective study from January 2009 to December 2014. Two hundred thirty-four IFPs supported by 384 implants for the posterior region were followed up until June 2016. The contact tightness had been recorded using aluminum strips of different thicknesses with a regular interval after delivery. Proximal contact was considered as lost if the contact tightness was over 50μm, and statistical analyses were performed to estimate the prevalence rate of PCL and its influential factors. Among the total 299 proximal contacts of 234 IFPs, 179 were observed as a PCL (59.9%). Bone level and root configuration of the adjacent teeth, the proximal contact position and jaw position of the implant prostheses were statistically significant factors, when analyzed by the cumulative PCL rate using the log-rank test of the Kaplan-Meier method (P<0.05) According to the Cox proportional hazard regression analysis, the proximal contact position, bone level of adjacent teeth and jaw position were revealed to be statistically significant (P<0.05). PCL should be considered an implant prosthesis complication to which various associated factors could be related. This study revealed that the lower alveolar bone support level of the adjacent teeth, maxillary position of IFPs and mesial site of IFPs were significantly associated with a higher incidence of PCL.

Behavior of anodized aluminum strip under sine and square wave voltage

The purpose of this paper is to understand the pros and cons of aluminum conductors insulated with anodized aluminum for rotating machines used in aircraft. The investigation is focused on the breakdown voltage and partial discharge inception voltage of simple systems (crossed pairs, simplified coils). The results show that both breakdown voltage and partial discharge inception voltage are very sensitive to curvature radius and lower than those achieved using conventional copper conductors insulated with polymeric enamels. However, the operating temperature of the insulation (600 °C) is extremely appealing. Therefore, it could be interesting to devise high temperature fillers and suitable manufacturing procedures to exploit this insulation system in specific applications, where the weight of the machine is the key factor for material selection.

Assessment of human bones encompassing physiological decay and damage using piezo sensors in non-bonded configuration

In the recent years, several biomedical applications of lead zirconate titanate piezo-electric ceramic patches based on the electro-mechanical impedance technique have been reported in the literature. However, practical application of the technique on live subjects is severely hampered due to the requirement of bonding the patch with bone or cartilage with an adhesive. In addition, live subjects have skin cover over the bone. This article proposes and evaluates the feasibility of employing lead zirconate titanate patches as biomedical sensors in non-bonded configuration for assessing the physiological conditions of bones. For this purpose, a special design is proposed where the lead zirconate titanate patch is first bonded on a thin aluminum strip, which is in turn clamped securely on the biomedical subject. The proposed configuration is investigated both in vitro and in vivo. The non-bonded piezo sensors are first investigated to identify dynamic parameters of the bone through lab-based experimental study involving artificial bones. Thereafter, physiological damage and decay conditions are artificially simulated in the experimental bones and the same are correlated with changes in conductance signatures from the non-bonded piezo sensor as well as the lead zirconate titanate patch in the conventional adhesively bonded (direct bonding to the subject) configuration. The trend of the conductance signatures in the healthy and the damaged conditions from the non-bonded piezo sensor is found to correlate well with the corresponding signatures from the directly bonded piezo sensor. At the same time, the repeatability of the signatures is also found to be satisfactory. After success in bare bones, the non-bonded piezo sensor configuration is extended to monitor the condition of bones covered with skin and tissue, simulated in the lab with the aid of silicone-based coating. Finally, a proof-of-concept experiment on a live human subject is successfully demonstrated. The overall results of the study demonstrate very good prospects of employing lead zirconate titanate patches in non-bonded piezo sensor mode for monitoring the condition of human bones and other related biomedical subjects.

New method of producing tailored blanks with constant thickness

The concept of weight-saving in automotive manufacture by using tailored blanks is well established. The methods used to produce extra strength in particular areas of the blank can be based either on increasing material thickness in those areas or keeping the thickness constant but varying the material properties. Typically the first option is used by welding blank patches of different thickness. From the view point of forming blanks into sheet metal products uniform thickness is less problematic and it can be achieved by welding different materials of the same thickness or localised heat treatment. However, these approaches have major limitations: welding introduces discontinuity in material structure and properties while selective heat treatment is difficult to control. A new, original method presented here is based on a local shear deformation of the blank material. The particular process used is incremental equal channel angular pressing. The proposed approach is simulated using finite element modelling and then experimentally verified by producing a constant thickness pure aluminium strip with varying hardness. A discussion of different variants of this approach indicates its potential.

Uncertainty analysis of residual stresses measured by slitting method in equal-channel angular rolled Al-1060 strips

Residual stresses can meaningfully influence on the operation of a part. They are almost created by all fabrication processes. In this study, slitting method was used to obtain the residual stress profile through the thickness of equal-channel angular rolled aluminum strips. Furthermore, uncertainty analysis of the measured residual stresses was performed. The measurement and model uncertainties were considered in the uncertainty analysis, and the effect of each one on the total uncertainty was investigated. Besides, to study the through-depth residual stress distribution numerically, finite element simulation of equal-channel angular rolling process in route C was done. In route C, the strip should be rotated around the longitudinal axis by 180° after each successive pass. The results showed the important role of both measurement and model uncertainties in the calculation of total uncertainty. The maximum tensile residual stresses of the control, 1-pass and 2-pass samples were 7.59, 64.4 and 85.11 MPa, respectively, and the root mean square total uncertainty of them were 1.47, 2.43 and 5.12 MPa, respectively. There was a good agreement between experimental and numerical results.

Voltage distribution in inorganic insulation windings for high-temperature motors

Purpose The purpose of this paper is to present a method for computing voltage spikes endured by the insulation of the first coils of high-temperature (HT°) synchronous machines fed by PWM inverters that deliver fast-fronted voltage pulses. Design/methodology/approach The transient state following each steep edge is computed by SPICE using the global high-frequency (HF) equivalent circuit of the motor winding. This equivalent circuit is automatically built using the proposed elementary coil model. Two inorganic HT° technologies are compared: the first one uses a round copper wire insulated by a thin ceramic layer and the second one is made with an anodized aluminum strip. Findings The winding made with an anodized aluminum strip, which has a higher turn-to-turn capacitance, yields a better voltage distribution between coils of the machine. Research limitations/implications The elementary coil equivalent circuit is computed from impedance measurements performed on an elementary coil. Another starting point could be developed with an FE analysis to determine the parameters of the HF equivalent circuit, which would avoid the need for a prototype coil before the machine design. Practical implications For inorganic motors, the insulation layers have poorer electrical characteristics compared with standard organic ones. Therefore, the computation of voltage spikes distribution along the coils of each phase represents a major issue in the design of HT° machines. Originality/value The presented approach is a step toward the design of HT° (400-500°C) actuators fed by PWM inverters based on fast SiC electronic switches.

Dielectric characteristics of an anodized aluminum strip

The purpose of this work is to study the possibility to integrate aluminum strip in motor coils with only alumina, growth by anodization, as inter-turn insulation. This would allow making more lightweight and possibly high temperature running motors, as aluminum melting point is around 660 °C and alumina remains solid until 2072 °C. Partial discharge inception and extinction voltages and breakdown voltage are quantified under ambient conditions and then under increasing temperatures up to 600 °C. Different technologies are presented prior to the results to justify the choice of anodized aluminum strip. Dissipation factor of the insulation is also studied and shows the resistive behavior of the insulation above 400 °C.

Fabrication of manganese-aluminum bronze as a shape memory alloy by accumulative roll bonding process

Cu/Al/Mn nanocomposites were produced from copper and aluminum strips and manganese powder using Accumulative Roll Bonding (ARB) and then solid solution treatment was performed to produce shape memory alloy. Two solid solution treatment temperatures (850 and 950°C) were employed to evaluate the phase formation. Scanning electron microscopy, optical microscopy and X-ray diffraction were used for the microstructural and structural studies of the samples. The composition of the produced sample after solid solution treatment at 950°C was also evaluated by energy dispersive X-ray spectroscopy. The results showed that manganese-aluminum bronze, 83Cu-12Al-5Mn (wt.%), was successfully produced by the ARB process followed by heat treatment. The microstructure of the composite annealed at 950°C consisted of a fully martensitic phase after ice-water quenching. In addition, the electrochemical corrosion behavior of the produced nanocomposite and bronze was investigated in a 3.5wt.% NaCl solution by a potentiostat-galvanostat device. It was found that the corrosion resistance of the bronze alloy is higher than that of the composite due to having a single phase microstructure.

Ti–MgB 2 Conductor for Superconducting Space Magnets

Among the characteristics required by a spaceborne superconducting magnet, lightness and reliability are the most important. The use of titanium clad magnesium diboride conductors fulfills both the requirements: it allows avoiding helium cryogenics, it guarantees good stability, and it has density below 4500 kg/m 3 . A conductor based on a Ti-MgB 2 tape was developed in the framework of a study on superconducting shields to protect astronauts against cosmic rays, co-funded by the European Union (EU FP7 SR2S Project). The magnet is designed to operate at 10 K and below 4 T at the conductor. The prototype tape, manufactured via ex situ method, is 3 mm wide and 0.5 mm thick and has 19 MgB 2 filaments. According to the original design, a pure aluminum strip should be coupled to the tape in order to protect the conductor in case of quench. However, due to technical problems, the process was completed by soldering a copper strip on titanium. The conductor and its manufacture process are described in this paper.

DESIGN OF PRESS TOOL FOR BOTTOM TANK IN AN AIR CONDITION UNIT

Bottom tank (Heater core) is made up of multilayered Aluminium strip. The capacity was 25 tons mechanical press for all the tools. Even though the tonnage requirement of the tools are less, the available press was for 25 tonnes. The main objective of this work is to design press tool for 25 tonnage capacity of the machine. The different drawing tools required are draw tool, setting tool, trimming tool, skirt draw tool etc. so that component is formed in a single shot. Theoretical calculation has to be carried out before doing design analysis. Tonnage capacity must be checked with necessary equations. Tools has to be selected as per DME, HASCO standards.

Rolling of Flat Aluminum Strips with Tailored Mechanical Properties

In this study, the possibility of producing of flat aluminum strips with tailored mechanical properties across their width by means of rolling was examined. The aim of the work was an experimental analysis of the effect of cold rolling of the strips with a pre-profiled cross-section in flat rolls. Because of different work hardening of the various elements of the pre-profiled strips a characteristic profile of mechanical properties over the strips cross-section was created. The performed tensile tests and hardness measurements proved the possibility of setting of tailored properties in flat strips by means of rolling. The difference between the mechanical characteristics of various strip’s elements for the selected aluminum alloy can reach 40%.

Study of the Structural Properties and Segregation of Alloying Elements in Strips from the TRC Line

Twin roll casting (TRC) technology is becoming increasingly popular because of the opportunity to receive aluminum strips which may serve as input for direct cold rolling processes. Furthermore, these strips have a favourable combination of mechanical and electric properties as well as dimensional tolerances. TRC line strips show segregation of alloying elements and structure providing a combination of casting structure and wrought alloy. As part of this study, the structure of the strips from the TRC line has been analyzed as well as the segregation of the alloying elements.

Research of Spined Heat-Exchanging Pipes

Work is devoted to a research of spined heat-exchanging pipes that are assumed to use in air-cooler exchangers (ACE). The proposed new geometry of finning allows intensifying heat exchange and improving the efficiency of air coolers. It is caused by the increased area of finned surface with a value of finning ratio (the ratio of the area of the smooth pipe to a finned one) to 42.7, while in the commercially available ACE, the figure is 22. Besides, the geometrical arrangement of the pin fins turbulizes the airflow. It should be mentioned that an easier method of manufacturing of heat exchanging pipes is proposed to use, which will reduce their costs. The proposed heat exchange pipes are made by winding cut aluminum strip to the supporting pipe or stretching stamped blanks on it. To increase the efficiency of the heat exchange surface pin fins should be as thin and long as possible; however, their strength should be sufficient for deformation-free operation. Fins should be staggered to maximize the distance between them. Spined heat-exchange pipes are designed to operate in a commercially produced ACE and their service is carried out similarly to commercially produced transversely finned pipes.