Microstructure evolution of 6061 O Al alloy during ultrasonic consolidation:An insight from electron backscatter diffraction

6061 O Al alloy foils were welded to form monolithic and SiC fibre-embedded samples using the ultrasonic consolidation (UC) process. Contact pressures of 135, 155 and 175 MPa were investigated at 20 kHz frequency, 50% of the oscillation amplitude, 34.5 mm s sonotrode velocity and 20 °C. Deformed microstructures were analysed using electron backscatter diffraction (EBSD). At all contact pressures deformation occurs by non-steady state dislocation glide. Dynamic recovery is active in the upper and lower foils. Friction at the welding interface, instantaneous internal temperatures (0.5-0.8 of the melting temperature, T), contact pressure and fast strain rates result in transient microstructures and grain size reduction by continuous dynamic recrystallization (CDRX) within the bonding zone. Bonding occurs by local grain boundary migration, which allows diffusion and atom interlocking across the contact between two clean surfaces. Textures weaken with increasing contact pressure due to increased strain hardening and different grain rotation rates. High contact pressures enhance dynamic recovery and CDRX. Deformation around the fibre is intense within 50 μm and extends to 450 μm from it. © 2009 Acta Materialia Inc.

Modelling and characterization of ultrasonic consolidation process of Aluminium alloys

Ultrasonic consolidation process is a rapid manufacturing process used to join thin layers of metal at low temperatures and low energy consumption. In this work, finite element method has been used to simulate the ultrasonic consolidation of Aluminium alloys 6061 (AA-6061) and 3003 (AA-3003). A thermomechanical material model has been developed in the framework of continuum cyclic plasticity theory which takes into account both volume (acoustic softening) and surface (thermal softening due to friction) effects. A friction model based on experimental studies has been developed, which takes into account the dependence of coefficient of friction upon contact pressure, amount of slip, temperature and number of cycles. Using the developed material and friction model ultrasonic consolidation (UC) process has been simulated for various combinations of process parameters involved. Experimental observations are explained on the basis of the results obtained in the present study. The current research provides the opportunity to explain the differences of the behaviour of AA-6061 and AA-3003 during the ultrasonic consolidation process. Finally, trends of the experimentally measured fracture energies of the bonded specimen are compared to the predicted friction work at the weld interface resulted from the simulation at similar process condition. Similarity of the trends indicates the validity of the developed model in its predictive capability of the process. © 2008 Materials Research Society.

Microstructure and microtexture evolution of aluminum alloy 3003 under ultrasonic welding process for embedding SiC fibre

Ultrasonic welding process can be used for bonding metal foils which is the fundament of ultrasonic consolidation (UC). UC process can be used to embed reinforcement fibres such as SiC fibres within an aluminum matrix materials. In this research we are investigating the phenomena occurring in the microstructure of the parts during ultrasonic welding process to obtain better understanding about how and why the process works. High-resolution electron backscatter diffraction (EBSD) is used to study the effects of the vibration on the evolution of microstructure in AA3003. The inverse pole figures (IPF) and the correlated misorientation angle distribution of the mentioned samples are obtained. The characteristics of the crystallographic orientation, the grain structure and the grain boundary are analyzed to find the effect of ultrasonic vibration on the microstructure and microtexture of the bond. The ultrasonic vibration will lead to exceptional refinement of grains to a micron level along the bond area and affect the crystallographic orientation. Ultrasonic vibration results in a very weak texture. Plastic flow occurs in the grain after welding process and there is additional plastic flow around the fibre which leads to the fibre embedding. © 2009 Editorial Board of CHINA WELDING.

Microstructure evolution of AA6061 under ultrasonic welding

Ultrasonic metal welding can be used to join two metal foils. There are two different effects under ultrasonic welding. They are surface effect and volume effect. These two effects were validated under macro experiments. Then how to validate in micro test is seldom researched. EBSD method was used to research the microstructure evolution of AA6061 under ultrasonic welding. The image maps indicating all Euler angle and the correlated misorientation angle distribution of both original foil and welding sample were got by EBSD in order to understand how ultrasonic welding affect the grain orientation and microstructure. The test shows that after ultrasonic vibration, the grain size has little change. And ultrasonic vibration results in a very weak texture. FEM results also validate these conclusions.

3D coupled thermomechanical finite element analysis of ultrasonic consolidation

A 3-D coupled temperature-displacement finite element analysis is performed to study an ultrasonic consolidation process. Results show that ultrasonic wave is effective in causing deformation in aluminum foils. Ultrasonic vibration leads to an oscillating stress field. The oscillation of stress in substrate lags behind the ultrasonic vibration by about 0.1 cycle of ultrasonic wave. The upper foil, which is in contact with the substrate, has the most severe deformation. The substrate undergoes little deformation. Apparent material softening by ultrasonic wave, which is of great concern for decades, is successfully simulated. The higher the friction coefficient, the more obvious the apparent material softening effect.

Microstrcutural evolution of SiC fibre embedded AA6061 matrix induced by ultrasonic consolidation

Ultrasonic consolidation (UC) uses high frequency (20-40KHz) mechanical vibrations to produce a solid-state metallurgical bond (weld) between metal foils. UC as a novel layered manufacturing technique is used in this research to embed reinforcing members such as silicon carbide fibers into the aluminium alloy 6061's matrices. It is known that UC induce volume and surface effect in the material it is acting on. Both effects are employed in embedding active/passive elements in the metal matrix. Whilst the process and the two effects are used and identified at macro level, what is happening at micro level is unknown and hardly studied. In this research we are investigating the phenomena occurring in the microstructure of the parts during UC process to obtain better understanding about how and why the process works. In this research, high-resolution electron backscatter diffraction is used to study the effects of the UC process on the evolution of microstructure in AA6061 with and without fibre elements. The inverse pole figures (IPF), pole figures (PF) and the correlated misorientation angle distribution of the mentioned samples are obtained. The characteristics of the crystallographic orientation, the grain structure and the grain boundary are analysed to find the effect of ultrasonic vibration and embedding fibre on the microstructure and texture of the bond. The ultrasonic vibration will lead to exceptional refinement of grains to a micron level along the bond area and affect the crystallographic orientation. Additional plastic flow occurs around the fibre which leads to the fibre embedding. © 2008 Materials Research Society.

Finite element analysis of ultrasonic insertion of SiC fibre in aluminium alloy 6061

In this work, a computational framework has been proposed to successfully simulate the fibre embedding using ultrasonic consolidation process. The main components of the proposed computational approach are a developed constitutive model and a friction model which are especially suitable for the condition of ultrasonic process. The effect of different process parameters, such as velocity of sonotrode, displacement amplitude of ultrasonic vibration and applied loads are studied. The presented work especially focuses on the quality of the developed weld and the fibre coverage due to the plastic flow around the fibre. The areas of maximum plastic flow predicted by the simulation are confirmed by the EBSD microstructural studies. © 2011 Inderscience Enterprises Ltd.

Critical evaluation of pulse-echo ultrasonic test method for the determination of setting and mechanical properties of acrylic bone cement: Influence of mixing technique

Currently there is no reliable objective method to quantify the setting properties of acrylic bone cements within an operating theatre environment. Ultrasonic technology can be used to determine the acoustic properties of the polymerising bone cement, which are linked to material properties and provide indications of the physical and chemical changes occurring within the cement. The focus of this study was the critical evaluation of pulse-echo ultrasonic test method in determining the setting and mechanical properties of three different acrylic bone cement when prepared under atmospheric and vacuum mixing conditions. Results indicated that the ultrasonic pulse-echo technique provided a highly reproducible and accurate method of monitoring the polymerisation reaction and indicating the principal setting parameters when compared to ISO 5833 standard, irrespective of the acrylic bone cement or mixing method used. However, applying the same test method to predict the final mechanical properties of acrylic bone cement did not prove a wholly accurate approach. Inhomogeneities within the cement microstructure and specimen geometry were found to have a significant influence on mechanical property predictions. Consideration of all the results suggests that the non-invasive and non-destructive pulse-echo ultrasonic test method is an effective and reliable method for following the full polymerisation reaction of acrylic bone cement in real-time and then determining the setting properties within a surgical theatre environment. However the application of similar technology for predicting the final mechanical properties of acrylic bone cement on a consistent basis may prove difficult.

An Ultrasonic Relaxation Study of 1-Alkyl-3-Methylmidazolium-Based Room Temperature Ionic Liquids: Probing the Role of Alkyl Chain Length in the Cation

Ultrasound absorption spectra of four 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide were determined as a function of the alkyl chain length on the cation from 1-propyl- to 1-hexyl- from 293.15 to 323.15 K at ambient pressure. Herein, the ultrasound absorption measurements were carried out using a standard pulse technique within a frequency range from 10 to 300 MHz. Additionally the speed of sound, density and viscosity have been measured. The presence of strong dissipative processes during the ultrasound wave propagation was found experimentally, i.e. relaxation processes in the megahertz range were observed for all compounds over the whole temperature range. The relaxation spectra (both relaxation amplitude and relaxation frequency) were shown to be dependent on the alkyl side chain length of the 1-alkyl-3-methylimidazolium ring. In most cases, a single Debye model described the absorption spectra very well. However, a comparison of the determined spectra with the spectra of a few other imidazolium-based ionic liquids reported in the literature (in part recalculated in this work) shows that the complexity of the spectra increases rapidly with the elongation of the alkyl chain length on the cation. This complexity indicates that both the volume viscosity and the shear viscosity are involved in relaxation processes even in relatively low frequency ranges. As a consequence, the sound velocity dispersion is present at relatively low megahertz frequencies.

Ultrasonic location system

Esta tese apresenta um sistema de localização baseado exclusivamente em ultrassons, não necessitando de recorrer a qualquer outra tecnologia. Este sistema de localização foi concebido para poder operar em ambientes onde qualquer outra tecnologia não pode ser utilizada ou o seu uso está condicionado, como são exemplo aplicações subaquáticas ou ambientes hospitalares. O sistema de localização proposto faz uso de uma rede de faróis fixos permitindo que estações móveis se localizem. Devido à necessidade de transmissão de dados e medição de distâncias foi desenvolvido um pulso de ultrassons robusto a ecos que permite realizar ambas as tarefas com sucesso. O sistema de localização permite que as estações móveis se localizem escutando apenas a informação em pulsos de ultrassons enviados pelos faróis usando para tal um algoritmo baseado em diferenças de tempo de chegada. Desta forma a privacidade dos utilizadores é garantida e o sistema torna-se completamente independente do número de utilizadores. Por forma a facilitar a implementação da rede de faróis apenas será necessário determinar manualmente a posição de alguns dos faróis, designados por faróis âncora. Estes irão permitir que os restantes faróis, completamente autónomos, se possam localizar através de um algoritmo iterativo de localização baseado na minimização de uma função de custo. Para que este sistema possa funcionar como previsto será necessário que os faróis possam sincronizar os seus relógios e medir a distância entre eles. Para tal, esta tese propõe um protocolo de sincronização de relógio que permite também obter as medidas de distância entre os faróis trocando somente três mensagens de ultrassons. Adicionalmente, o sistema de localização permite que faróis danificados possam ser substituídos sem comprometer a operabilidade da rede reduzindo a complexidade na manutenção. Para além do mencionado, foi igualmente implementado um simulador de ultrassons para ambientes fechados, o qual provou ser bastante preciso e uma ferramenta de elevado valor para simular o comportamento do sistema de localização sobre condições controladas.

Open source data sensing software for ultrasonic non-invasive temperature estimation

In this paper, an open source solution for measurement of temperature and ultrasonic signals (RF-lines) is proposed. This software is an alternative to the expensive commercial data acquisition software, enabling the user to tune applications to particular acquisition architectures. The collected ultrasonic and temperature signals were used for non-invasive temperature estimation using neural networks. The existence of precise temperature estimators is an essential point aiming at the secure and effective applica tion of thermal therapies in humans. If such estimators exist then effective controllers could be developed for the therapeutic instrumentation. In previous works the time-shift between RF-lines echoes were extracted, and used for creation of neural networks estimators. The obtained estimators successfully represent the temperature in the time-space domain, achieving a maximum absolute error inferior to the threshold value defined for hyperthermia/diathermia applications.

Albuterol delivery in an in vitro pediatric ventilator lung model: comparison of jet, ultrasonic, and mesh nebulizers.

OBJECTIVE: : To determine the influence of nebulizer types and nebulization modes on bronchodilator delivery in a mechanically ventilated pediatric lung model. DESIGN: : In vitro, laboratory study. SETTING: : Research laboratory of a university hospital. INTERVENTIONS: : Using albuterol as a marker, three nebulizer types (jet nebulizer, ultrasonic nebulizer, and vibrating-mesh nebulizer) were tested in three nebulization modes in a nonhumidified bench model mimicking the ventilatory pattern of a 10-kg infant. The amounts of albuterol deposited on the inspiratory filters (inhaled drug) at the end of the endotracheal tube, on the expiratory filters, and remaining in the nebulizers or in the ventilator circuit were determined. Particle size distribution of the nebulizers was also measured. MEASUREMENTS AND MAIN RESULTS: : The inhaled drug was 2.8% ± 0.5% for the jet nebulizer, 10.5% ± 2.3% for the ultrasonic nebulizer, and 5.4% ± 2.7% for the vibrating-mesh nebulizer in intermittent nebulization during the inspiratory phase (p < 0.01). The most efficient nebulizer was the vibrating-mesh nebulizer in continuous nebulization (13.3% ± 4.6%, p < 0.01). Depending on the nebulizers, a variable but important part of albuterol was observed as remaining in the nebulizers (jet and ultrasonic nebulizers), or being expired or lost in the ventilator circuit (all nebulizers). Only small particles (range 2.39-2.70 µm) reached the end of the endotracheal tube. CONCLUSIONS: : Important differences between nebulizer types and nebulization modes were seen for albuterol deposition at the end of the endotracheal tube in an in vitro pediatric ventilator-lung model. New aerosol devices, such as ultrasonic and vibrating-mesh nebulizers, were more efficient than the jet nebulizer.

Ultrasonic attenuation in layered superconductors /

We study the ultrasonic attenuation in layered superconductors using the Green's function formalism. General expressions are derived analytically and then calculated numerically by taking the nearest and next-nearest interactions in a disordered layered superconductor with random hoppings. Our results show huge anisotropics of ultrasonic attenuation in the superconductors and the strong dependence of ultrasonic attenuation on the temperature and the direction of polarization of the sound wave.

Activity of brainstem cholinergic neurons during 22 kHz ultrasonic vocalization in rats /

Adult rats emit 22 kHz ultrasonic alann calls in aversive situations. This type of call IS a component of defensive behaviour and it functions predominantly to warn conspecifics about predators. Production of these calls is dependent on the central cholinergic system. The laterodorsal tegmental nucleus (LDT) and pedunculopontine tegmental nucleus (PPT) contain largely cholinergic neurons, which create a continuous column in the brainstem. The LDT projects to structures in the forebrain, and it has been implicated in the initiation of 22 kHz alarm calls. It was hypothesized that release of acetylcholine from the ascending LDT terminals in mesencephalic and diencephalic areas initiates 22 kHz alarm vocalization. Therefore, the tegmental cholinergic neurons should be more active during emission of alarm calls. The aim of this study was to demonstrate increased activity of LDT cholinergic neurons during emission of 22 kHz calls induced by air puff stimuli. Immunohistochemical staining of the enzyme choline acetyltransferase identified cell bodies of cholinergic neurons, and c-Fos immunolabeling identified active cells. Double labeled cells were regarded as active cholinergic cells. There were significantly more (p

The role of the dopaminergic system in the production of ultrasonic calls in adult rats /

Ultrasonic vocalizations (USV) are emitted by rats in a number of social situations such as aggressive encounters, during sexual behavior, and during play in young rats, situations which are predominantly associated with strong emotional responses. These USV typically involve two distinct types of calls: 22 kHz calls, which are emitted in aversive situations and 50 kHz calls, which are emitted in non-aversive, appetitive situation. The 50 kHz calls are the focus of the present study and to date both the glutamatergic and the dopaminergic systems have been independently implicated in the production of these 50 kHz calls. The present study was conducted to examine a possible relationship between glutamate (GLU) and dopamine (DA) in mediating 50 kHz calls. It was hypothesized that the dopaminergic system plays a mediating role in 50 kHz calls induced by injections ofGLU into the anterior hypothalamic/preoptic area (AHPOA) in adult rats. A total of 68 adult male rats were used in this study. Rats' USV were recorded and analyzed in five experiments that were designed to test the hypothesis: in experiment 1, rats were treated with systemic amphetamine (AMPH) alone; in experiment 2, intra- AHPOA GLU was pretreated with systemic AMPH; in experiment 3, intra-AHPOA GLU was pretreated with intra-AHPOA AMPH; in experiment 4, rats were treated with high and low doses of intra-AHPOA AMPH only; in experiment 5, rats were treated with systemic haloperidol (HAL) as a pretreatment for intra-AHPOA GLU. Analysis of the results indicated that AMPH has a facilitatory effect on 50 kHz USV and that a relationship between DA and GLU in inducing 50 kHz calls does exist. The effect, however, was only observed when DA receptors were antagonized with HAL and was not seen with systemic AMPH pretreatments of intra-AHPOA GLU. The DAGLU relationship at the AHPOA was unclear.