Micromachining of glassy carbon toolsets for micro embossing applications

Laser micro machining is fast gaining popularity as a method of fabricating micro scale structures. Lasers have been utilised for micro structuring of metals, ceramics and glass composites and with advances in material science, new materials are being developed for micro/nano products used in medical, optical, and chemical industries. Due to its favourable strength to weight ratio and extreme resistance to chemical attack, glassy carbon is a new material that offers many unique properties for micro devices. The laser machining of SIGRADUR® G grade glassy carbon was characterised using a 1065 nm wavelength Ytterbium doped pulsed fiber laser. The laser system has a selection of 25 preset waveforms with optimised peak powers for different pulsing frequencies. The optics provide spot diameter of 40 μm at the focus. The effect of fluence, transverse overlap and pulsing frequency (as waveform) on glassy carbon was investigated. Depth of removal and surface roughness were measured as machining quality indicators. The damage threshold fluence was determined to be 0.29 J/cm2 using a pulsing frequency of 250 kHz and a pulse width of 18 ns (waveform 3). Ablation rates of 17 < V < 300 μm3/pulse were observed within a fluence range of 0.98 < F < 2.98 J/cm2. For the same fluence variation, 0.6 μm to 6.8 μm deep trenches were machined. Trench widths varied from 29 μm at lower fluence to 47 μm at the higher fluence. Square pockets, 1 mm wide, were machined to understand the surface machining or milling. The depth of removal using both waveform 3 and 5 showed positive correlation with fluence, with waveform 5 causing more removal than waveform 3 for the same fluence. Machined depths varied from less than 1 μm to nearly 40 μm. For transverse overlap variation using waveform 3, the best surface finish with Rz = 1.1 μm was obtained for fluence 0.792 J/cm2 for transverse overlap of 1 μm, 6 μm, and 9 μm at machined depths of 22.9 μm, 6.6 μm, and 4.6 μm respectively. For fluence of 1.426 J/cm2, the best surface finish with Rz = 1.2 μm was obtained for transverse overlap of 6 μm, and 9 μm at machined depths of 12.46 μm, and 8.6 μm respectively. The experimental data was compiled as machining charts and utilised for fabricating a micro-embossing glassy carbon master toolsets as a capability demonstration.

Towards a fast electro-thermo-mechanical IGBT/Diode simulation framework for design of reliable power electronic converters

This paper describes a methodology that enables fast and reasonably accurate prediction of the reliability of power electronic modules featuring IGBTs and p-i-n diodes, by taking into account thermo-mechanical failure mechanisms of the devices and their associated packaging. In brief, the proposed simulation framework performs two main tasks which are tightly linked together: (i) the generation of the power devices' transient thermal response for realistic long load cycles and (ii) the prediction of the power modules' lifetime based on the obtained temperature profiles. In doing so the first task employs compact, physics-based device models, power losses lookup tables and polynomials and combined material-failure and thermal modelling, while the second task uses advanced reliability tests for failure mode and time-to-failure estimation. The proposed technique is intended to be utilised as a design/optimisation tool for reliable power electronic converters, since it allows easy and fast investigation of the effects that changes in circuit topology or devices' characteristics and packaging have on the reliability of the employed power electronic modules. © 2012 IEEE.

Unattended ground sensor system based on fiber optic disk accelerometer

The basic principle and critical characteristics of unattended ground sensors (UGS) based on fiber optic disk accelerometers are introduced. Mechanical principles of fiber optic disk accelerometers (FODA) and calculation methods are presented. An FODA with a high sensitivity of 120rad/g and a resonance frequency of 300Hz is designed and used for detection in military affair.

Real-time far distance micro-vibration measurement using an external cavity semiconductor laser interferometer with a feedback control system

An external cavity semiconductor laser interferometer used to measure far distance micro-vibration in real time is proposed. In the interferometer, a single longitudinal mode and excellent coherent characteristic grating external cavity semiconductor laser is constructed and acted as a light source and a phase compensator. Its coherent length exceeds 200 meters. The angle between normal and incidence beam of the far object is allowed to change in definite range during the measurement with this interferometer, and this makes the far distance interference measurement easier and more convenient. Also, it is not required to keep the amplitudes of the first and second harmonic components equal, and then the dynamic range is increased. A feedback control system is used to compensate the phase disturbance between the two interference beams introduced by environmental vibration.

Structure and mechanical properties of Mg-Zn-RE system alloys

The lightest density of Mg has stimulated renewed interest in Mg based alloys for applications in the automotive, aerospace and communications industries. However, Mg in the pure form has relatively low strength, limited ductility and is susceptible to corrosion. Great efforts have been made to improve the mechanical properties of Mg alloys. Alloying Mg with other elements is one of the most important methods. An important class of Mg alloys is the Mg-Zn-RE system (RE = rare earth elements). In recent few decades, a series of new Mg-Zn-RE system alloys have been obtained, and detailed the structure and mechanical properties of the alloys. In this paper, the structure and mechanical properties of the Mg-Zn-RE alloys have been summarized. It showed that these alloys have high strength and they are prospected to be widely used in the future.

Evaluation and application of micro-sampling system for inductively coupled plasma mass spectrometry

Two Meinhard microconcentric nebulizers, model AR30-07-FM02 and AR 30-07-FM005, were employed as a self-installed micro-sampling system for inductively coupled plasma-mass spectrometry (ICP-MS). The FM02 nebulizer at 22 muL/min of solution uptake rate gave the relative standard deviations of 7.6%, 3.0%, 2.7%, 1.8% for determinations (n = 10) of 20 mug/L Be, Co, In and Bi, respectively, and the detection limits (3s) of 0.14, 0.10, 0.02 and 0.01 mug/L for Be, Co In and Bi, respectively. The mass intensity of In-115 obtained by this micro-sampling system was 60% of that by conventional pneumatic nebulizer system at 1.3 mL/min. The analytical results for La, Ce, Pr and Nd in 20 muL Wistar rat amniotic fluid obtained by the present micro-sampling system were precisely in good agreement with those obtained using conventional pneumatic nebulization system.

Thermal, mechanical and ionic conductive behaviour of gamma-radiation induced PEO/PVDF(SIN)-LiClO4 polymer electrolyte system

An effort has been made to modify the mechanical behaviour of our previously reported gel-type gamma-radiation crosslinked polyethylene oxide (PEO)-LiClO4 polymer electrolyte. A highly polar and gamma-radiation crosslinkable crystalline polymer, polyvinylidene fluoride (PVDF), was selected to blend with PEO and then subjected to gamma-irradiation in order to make an simultaneous interpenetrating network (SIN), which was used as a polymer host to impart stiffness to the plasticized system. Experimental results have shown that the presence of PVDF in the system, through gamma-radiation induced SIN formation, could not only give a rather high mechanical modulus of 10(7) Pa at ambient temperature, but also maintain the room temperature ionic conductivity at a high level (greater than 10(-4) S/cm). DSC, DMA and conductivity measurement techniques were used to examine the effects of blending, gamma-irradiation and plasticization on the variations of glass transition and melting endotherm, on the appearance of high elastic plateau and on the temperature dependence of ionic conductivity: In addition, it was found that, in contrast with the unplasticized system, the ionic conductivity mechanism of this gel-type electrolyte seems to conform to the Arrhenius model, suggesting that, as a result of the high degree of plasticization, the polymer chains act mainly as the skeleton of the networks or polymer cages to immobilize the liquid electrolyte solution, whereas the ionic species migrate as if they were in a liquid medium. (C) 1997 Elsevier Science Ltd.

IONIC-CONDUCTIVITY AND DYNAMIC MECHANICAL RELAXATION OF A 2-COMPONENT EPOXY NETWORK-LICLO4 ELECTROLYTE SYSTEM

The correlation between mechanical relaxation and ionic conductivity was investigated in a two-component epoxy network-LiClO4 electrolyte system. The network was composed of diglycidyl ether of polyethylene glycol (DGEPEG) and triglycidyl ether of glycerol (TGEG). The effects of salt concentration, molecular weight of PEG in DGEPEG and the proportion of DGEPEG (1000) in DGEPEG/TGEG ratio on the ionic conductivity and the mechanical relaxation of the system were studied. It was found that, among the three influential factors, the former reinforces the network chains, reduces the free volume fraction and thus increases the relaxation time of the segmental motion, which in turn lowers the ionic conductivity of the specimen. Conversely, the latter two increase the free volume and thus the chain flexibility, showing an opposite effect. From the iso-free-volume plot of the shift factor log at and reduced ionic conductivity, it is noted that the plot can be used to examine the temperature dependence of segmental mobility and seems to be useful to judge whether the incorporated salt has been dissociated completely. Besides, the ionic conductivity and relaxation time at constant reference temperature are linearly correlated with each other in all the three cases. This result gives an additional experimental confirmation of the coordinated motion model of the ionic hopping with the moving polymer chain segment, which is generally used to explain the ionic conduction in non-glassy amorphous polymer electrolytes.

The Design of a Mechanical Assembly System

This thesis describes a mechanical assembly system called LAMA (Language for Automatic Mechanical Assembly). The goal of the work was to create a mechanical assembly system that transforms a high-level description of an automatic assembly operation into a program or execution by a computer controlled manipulator. This system allows the initial description of the assembly to be in terms of the desired effects on the parts being assembled. Languages such as WAVE [Bolles & Paul] and MINI [Silver] fail to meet this goal by requiring the assembly operation to be described in terms of manipulator motions. This research concentrates on the spatial complexity of mechanical assembly operations. The assembly problem is seen as the problem of achieving a certain set of geometrical constraints between basic objects while avoiding unwanted collisions. The thesis explores how these two facets, desired constraints and unwanted collisions, affect the primitive operations of the domain.

A LabVIEW Platform for Preclinical Imaging Using Digital Subtraction Angiography and Micro-CT.

CT and digital subtraction angiography (DSA) are ubiquitous in the clinic. Their preclinical equivalents are valuable imaging methods for studying disease models and treatment. We have developed a dual source/detector X-ray imaging system that we have used for both micro-CT and DSA studies in rodents. The control of such a complex imaging system requires substantial software development for which we use the graphical language LabVIEW (National Instruments, Austin, TX, USA). This paper focuses on a LabVIEW platform that we have developed to enable anatomical and functional imaging with micro-CT and DSA. Our LabVIEW applications integrate and control all the elements of our system including a dual source/detector X-ray system, a mechanical ventilator, a physiological monitor, and a power microinjector for the vascular delivery of X-ray contrast agents. Various applications allow cardiac- and respiratory-gated acquisitions for both DSA and micro-CT studies. Our results illustrate the application of DSA for cardiopulmonary studies and vascular imaging of the liver and coronary arteries. We also show how DSA can be used for functional imaging of the kidney. Finally, the power of 4D micro-CT imaging using both prospective and retrospective gating is shown for cardiac imaging.

Micro-mechanical parameterisations for continuum modelling of granular material using the discrete element method

The present work uses the discrete element method (DEM) to describe assemblies of particulate bulk materials. Working numerical descriptions of entire processes using this scheme are infeasible because of the very large number of elements (1012 or more in a moderately sized industrial silo). However it is possible to capture much of the essential bulk mechanics through selective DEM on important regions of an assembly, thereafter using the information in continuum numerical descriptions of particulate processes. The continuum numerical model uses population balances of the various components in bulk solid mixtures. It depends on constitutive relationships for the internal transfer, creation and/or destruction of components within the mixture. In this paper we show the means of generating such relationships for two important flow phenomena – segregation whereby particles differing in some important property (often size) separate into discrete phases, and degradation, whereby particles break into sub-elements, through impact on each other or shearing. We perform DEM simulations under a range of representative conditions, extracting the important parameters for the relevant transfer, creation and/or destruction of particles in certain classes within the assembly over time. Continuum predictions of segregation and degradation using this scheme are currently being successfully validated against bulk experimental data and are beginning to be used in schemes to improve the design and operation of bulk solids process plant.

Use of a coupled mechanical-acoustic computational model to identify failure mechanisms in paper production

In this paper, a couple mechanical-acoustic system of equations is solved to determine the relationship between emitted sound and damage mechanisims in paper under controlled stress conditions. The simple classical expression describing the frequency of a plucked string to its material properties is used to generate a numberical representation of the microscopic structue of the paper, and the resulting numerical model is then used to simulate the vibration of a range of simple fibre structures when undergoing two distinct types of damange mechanisms: (a)fibre/fibre bond failure, (b) fibre failure. The numercial results are analysed to determine whether there is any detectable systematic difference between the resulting acoustic emissions of the two damage processes. Fourier techniques are then used to compare th computeed results against experimental measurements. Distinct frequency components identifying each type of damage are shown to exist, and in this respect theory and experiments show good correspondece. Hence, it is shown, that althrough the mathematical model represents a grossly-simplified view of the complex structure of the paper, it nevertheless provides a good understanding of the underlying micro-mechanisms characterising its proeperties as a stress-resisting structure. Use of the model and acoompanying software will enable operators to identify approaching failure conditions in the continuous production of paper from emitted sound signals and take preventative action.

Thermo-mechanical analysis of the packaging process for micro-electronic displays

Micro-electronic displays are sensitive devices and its performance is easily affected by external environmental factors. To enable the display to perform in extreme conditions, the device must be structurally strengthened, the effects of this packaging process was investigated. A thermo-mechanical finite element analysis was used to discover potential problems in the packaging process and to improve the overall design of the device. The main concern from the analysis predicted that displacement of the borosilicate glass and the Y stress of the adhesive are important. Using this information a design which reduced the variation of displacement and kept the stress to a minimum was suggested

Reliability based design optimisation for system-in-package

This paper discusses a reliability based optimisation modelling approach demonstrated for the design of a SiP structure integrated by stacking dies one upon the other. In this investigation the focus is on the strategy for handling the uncertainties in the package design inputs and their implementation into the design optimisation modelling framework. The analysis of fhermo-mechanical behaviour of the package is utilised to predict the fatigue life-time of the lead-free board level solder interconnects and warpage of the package under thermal cycling. The SiP characterisation is obtained through the exploitation of Reduced Order Models (ROM) constructed using high fidelity analysis and Design of Experiments (DoE) methods. The design task is to identify the optimal SiP design specification by varying several package input parameters so that a specified target reliability of the solder joints is achieved and in the same time design requirements and package performance criteria are met