What is Mechatronics
Mechatronics is a concept of Japanese origin (1970’s) and can be defined as the application of electronics and computer technology to control the motions of mechanical systems (figure 1.1.1). Figure 1.1.1 Definition of Mechatronics It is a multidisciplinary approach to product and manufacturing system design (Figure 1.1.2). It involves application of electrical, mechanical, control and computer engineering to develop products, processes and systems with greater flexibility, ease in redesign and ability of reprogramming. It concurrently includes all these disciplines. Figure 1.1.2 Mechatronics: a multi-disciplinary approach Mechatronics can also be termed as replacement of mechanics with electronics or enhance mechanics with electronics. For example, in modern automobiles, mechanical fuel injection systems are now replaced with electronic fuel injection systems. This replacement made theautomobiles more efficient and less pollutant. With the help of microelectronics and sensor technology, mechatronics systems are providing high levels of precision and reliability. It is now possible to move (in x – y plane) the work table of a modern production machine tool in a step of 0.0001…
Corrosion of Ceramics
It is often said that one of the biggest advantages which ceramics have over other materials is their corrosion resistance, that is, their chemical inertness in corrosive environments. Is this always true? Corrosion is generally understood as property degradation due to environmental attack. As it will be shown in this section, there are a number of environments in which ceramics can degrade at a rapid rate. There exists a tremendous need for reliable and corrosion resistant structural ceramic or partly ceramic materials which can be used in aggressive environments such as: - high energy battery systems (such as sodium-sulphur): beta-alumina is being investigated - gas turbines: silicon nitride and/or carbide are being investigated - heat exchangers: SiC, composites are being investigated Ceramics are indeed much more environmentally stable, as compared to any other group of engineering materials, e.g. metals or plastics. Still, the potential for ceramics as corrosion resistant engineering structural materials are far from being fully realized, because of: - mechanical nonreliability of structural ceramic components - difficult design with brittle materials - a shortage of information and standardization of ceramics - human reluctance to use non-ductile materials Issues…
India’s Three-Stage Nuclear Power Programme
India’s three-stage nuclear power programme was formulated by Homi Bhabha in the 1950s to secure the country’s long term energy independence, through the use of uranium and thorium reserves found in the monazite sands of coastal regions of…
Crack Initiation and Propagation
Stages is fatigue failure: I. crack initiation at high stress points (stress raisers) II. propagation (incremental in each cycle) III. final failure by fracture Stage I - propagation • slow • along crystallographic planes of high shear stress • flat and featureless fatigue surface Stage II - propagation Crack propagates by repetitive plastic blunting and sharpening of the crack tip.
Types of Nuclear Reactors
Nuclear reactors serve three general purposes. Civilian reactors are used to generate energy for electricity and sometimes also steam for district heating; military reactors create materials that can be used in nuclear weapons; and research…
FATIGUE
Fatigue is the catastrophic failure due to dynamic (fluctuating) stresses. It can happen in bridges, airplanes, machine components, etc. The characteristics are: • long period of cyclic strain • the most usual (90%) of metallic failures (happens also in ceramics and polymers) • is brittle-like even in ductile metals, with little plastic deformation • it occurs in stages involving the initiation andpropagation of cracks. Cyclic Stresses These are characterized by maximum, minimum and mean stress, the stress amplitude, and the stress ratio.
FRACTURE
Fundamentals of Fracture Fracture is a form of failure where the material separates in pieces due to stress, at temperatures below the melting point. The fracture is termed ductile or brittle depending on whether the elongation is large or small. Steps in fracture (response to stress): • Crack formation • Crack propagation Ductile Fracture Stages of ductile fracture - Initial necking - Small cavity formation (micro voids) - Void growth (ellipsoid) by coalescence into a crack - Fast crack propagation around neck. Shear strain at 45o - Final shear fracture (cup and cone) The interior surface is fibrous, irregular, which signify plastic deformation. Brittle Fracture…
Nuclear fission
Nuclear fission, subdivision of a heavy atomic nucleus, such as that of uranium or plutonium, into two fragments of roughly equal mass. The process is accompanied by the release of a large amount…
Nano – Materials
Nanostructured materials are those materials whose structural elements—clusters, crystallites or molecules have dimensions in the range of 1-100 nm. These small groups of atoms, in general, go by different names such as nanoparticles, nanocrystals, quantum dots and quantum boxes. Substantial work is being carried out in the domain of nanostructured materials and nanotubes during the past decade since they were found to have potential for high technology engineering applications. One finds a remarkable variations in fundamental electrical, optical and magnetic properties that occur as one progresses from an ‘infinitely extended’ solid to a particle of material consisting of a countable number of atoms. The various types of nanostructured materials which has been considered for applications in opto-electronic devices and quantum- optic devices are nano-sized powders of silicon, silicon-nitride (SiN), silicon-carbide (SiC) and their thin films. Some of these are also used as advanced ceramics with controlled micro structures because their strength and toughness increase when the grain size diminishes. Carbon- based nanomaterials and nanostructures including fullerenes and nanotube plays an increasingly pervasive role in nanoscale science and technology. Today, nanotechnology is being heralded as the next enabling technology that will redesign the future of several technologies, products and markets.
Smart materials
Smart materials are designed materials that have one or more properties that can be significantly changed in a controlled fashion by external stimuli, such as stress, temperature, moisture, pH, electric or magnetic fields. Group of new and state-of-the-art materials now being developed, and expected to have significant influence on present-day technologies, especially in the fields of medicine, manufacturing and defense. Smart/Intelligent material system consists some type of sensor (detects an input) and an actuator (performs responsive and adaptive function). Actuators may be called upon to change shape, position, natural frequency, mechanical characteristics in response to changes in temperature, electric/magnetic fields, moisture, pH, etc. Four types of materials used as actuators: Shape memory alloys, Piezo-electric ceramics, Magnetostrictive materials, Electro-/Magneto-rheological fluids. Materials / Devices used as sensors: Optical fibers, Piezo-electric materials, Micro-electro-mechanical systems (MEMS), etc. Typical applications: By incorporating sensors, actuators and chip processors into system, researchers are able to stimulate biological human-like behavior; Fibers for bridges, buildings, and wood utility poles; They also help in fast moving and accurate robot parts, high speed helicopter rotor blades; Actuators that control chatter in precision machine tools; Small microelectronic circuits in machines ranging from computers to photolithography prints; Health monitoring detecting the success or failure of a product.
