Microwave Drilling: Future Possibilities and Challenges Based on Experimental Studies

Transcription

1 Microwave Drilling: Future Possibilities and Challenges Based on Experimental Studies Titto John George #*, Apurbba Kumar Sharma *, Pradeep Kumar *, Shantunu Das $, Rajesh Kumar $ # Department of Mechanical Engineering, Viswajyothi College of Engineering and Technology Muvattupuzha, Kerala, India * Department of Mechanical and Industrial Engineering, Indian Institute of Technology Roorkee, India 1 titto84886@gmail.com, 2 akshafme@iitr.ernet.in, 3 kumarfme@gmail.com $ Reactor Control Division, Baba Atomic Research Centre, Mumbai, India 4 shantanu@magnum.barc.gov.in Abstract Microwave material processing is getting more importance due to environmental concerns energy scarcity. It s an energy efficient process in which microwaves are used to heat the materials for different applications which provides the advantage of volumetric heating, selective heating based on the material-microwave interaction rather than the conventional heating which uses conductive and radiative heat transfer methods. This paper gives a brief report of the works carried out in applying microwave energy in machining area and intends to check the feasibility of microwave machining, especially in drilling of materials. Some studies were conducted using a setup developed for drilling of materials inside a microwave oven along with plasma formation in open atmosphere. This paper explains development of equipment for concentrating microwave to a small area like a beam and heating that area to produce a hole. This was tested in wood, glass and in aluminium specimens. The concept was also successfully used in drilling of raw animal bones obtained as a food-waste with an aim to use for medical applications. Details of the microwave drilling experiments conducted along with the results were discussed in the paper and it concludes with exploring the future possibilities and scope of further research in this process. Keywords Microwaves, Selective heating, Drilling, Material Processing I INTRODUCTION Microwaves belong to the portion of the electromagnetic spectrum with wavelengths from 1mm to 1m with corresponding frequencies between 300 MHz and 300 GHz. For microwave heating, two frequencies and 2.45 GHz were reserved by the Federal Communications Commission (FCC) for industrial, scientific, and medical (ISM) purposes are commonly used for microwave heating. The theoretical analysis of each of these microwave components is governed by appropriate boundary conditions and the Maxwell equations [1]-[3]. Significant research has been carried out to explore the possibilities of using microwave in applications like heating, sintering, bonding, welding, cladding and other areas of material processing. In the recent years, application of microwave in machining of materials has also been attempted. Due to its special properties microwave processing has given better results in comparison to conventional methods in all fields where it was applied. The studies done with microwave drilling has proved its ability in differentiating the materials and drill accordingly which is even impossible by any other techniques including laser drilling. This paper discuss the possibilities and challenges in developing a drilling process using microwave energy based on experimental studies conducted in various materials. II SIGNIFICANCE OF MICROWAVE PROCESSING Microwaves have some special properties in material interaction energy transfer which makes it useful in processing different types of materials. Energy is transferred to materials by interaction of the electromagnetic fields at the molecular level, and the dielectric properties ultimately determine the effect of the electromagnetic field on the material. Two fundamental mechanisms for energy transfer are dipole rotation and the ionic conduction. The interaction of microwaves with materials can be classified into three categories as shown in Fig. 1. Absorbing materials with properties ranging from conductors to insulators are usually high dielectric loss materials, which absorb electromagnetic energy readily and convert it to heat. Transparent materials are low dielectric loss materials or insulating materials, such as glass, ceramics and air which allow microwaves to pass through easily with little attenuation. Opaque materials are typically conducting materials with free electron, such as metals, that reflects microwave at room temperature [1]-[4]. Fig. 1 Schematic of microwave material interaction

2 Microwave heating possess some special characteristics like penetrating radiation, rapid heating, controllable field distributions, selective heating of materials and self-limiting which are not usually possible with conventional heating techniques. The term microwave effects has been proposed to describe anomalies that cannot be predicted or easily explained with present understanding of the electromagnetic theory [1]-[2]. For experimental works two different methods of microwave heating are generally used: direct microwave heating (DMH), and microwave hybrid heating (MHH). III BACKGROUND OF MICROWAVE DRILLING A method for drilling/cutting using microwave discharge was suggested by Kozyrev et al. [5] but further studies were not reported. A novel method for drilling hard non-conductive materials by localized application of microwave energy was introduced by Jerby et al. [6]-[8]. Titto et al. [9], [10] made some feasibility studies on drilling of metals with microwave hybrid heating. Highlights of these initial attempts are briefly discussed in this section and the latest studies were given in the remaining sections. A. Microwave Discharge Machining Kozyrev et al. [5] studied the combined action of microwave electric field and focused laser radiation on dielectrics to develop discharge technique for machining of certain kind of dielectrics. The concept was based on the local absorption of microwave power by dielectrics followed by its damage due to intensive heating. Localization of microwave absorption was made by heating a small area using thermal pulse such as laser. The basis of the process is dependence of microwave absorption coefficient by dielectrics on its temperature. Some experiments were performed and it was proved that application of microwave field increased the volume of removed material at least 8 times at 1 min exposure. However, the profile was not good and the complexity of set up may be the hindrance in conducting more studies in that. B. Microwave Drilling of Non Conducting Materials with a Near Field Concentrator The concentration of the microwave energy into a small spot is the key principle underlying the microwave-drill invention [6]-[8]. The near field microwave radiator illustrated in Fig. 2 is constructed as a coaxial waveguide ended with an extendable monopole antenna, which functions also as the drill bit with a movable centre conductor sustaining high temperatures. Initially, the microwave energy deposition rate is high at the material near the antenna. The subsurface tends to increase to a slightly higher temperature than the spontaneously cooled surface. A hot spot is created, and the material becomes soft or molten. The coaxial centre electrode is then inserted into this molten hot spot and shapes its boundaries. Finally, the electrode is pulled out from the hole, while the material cools down in its new shape. This microwave drill was effective for drilling and cutting in a variety of hard non-conductive dielectric materials, but not in metals due to reflection of microwaves [6]-[8]. It was also useful to insert and join metallic or ceramic nails into these materials. 1) Application on Drilling of Ceramic Thermal-Barrier Coatings: Its the inherent material selectivity makes microwave drill ideally suited for the controlled removal of ceramic coatings from underlying metallic substrates. TBC consists of two layers: a metallic oxidation-resistant bond coat and a thermally insulating layer. When the applicator is brought into contact with a metal, the microwave energy is reflected and little or no localized heating is obtained. Thus, the process has the inherent feature of materials selectivity. Drilling was stopped after reaching the surface of the metal plate. In all holes examined, the microwave drill process did not affect the microstructure of the underlying substrate [11]. Fig. 2 Scheme illustrating the principle of microwave drilling [6] IV FEASIBILITY STUDIES AND FABRICATION OF SETUP Some initial trials were conducted to study the possibility of drilling metallic materials through microwave heating. It is a known fact that bulk metals reflect microwaves at room temperature. The heating of metals has been achieved by using microwave hybrid heating technique by using a suitable susceptor and for non metallic materials microwave generated plasma was used. From the results of initial feasibility study a modified setup was made with which drilling of metals and non metals were performed. A. Fabrication of a Setup for Drilling Inside Microwave Oven The schematic diagram of the setup developed to perform microwave drilling inside a microwave oven is shown in Fig. 3. A spring of required stiffness was fixed to the bolt at the top of setup. The drill bit was fixed at the bottom end of the spring as shown in the schematic diagram. The spring and the drill bit were covered by microwave friendly materials to avoid reflection of microwave by metallic materials. The strength of the beam structure which is holding the spring should be sufficient to withstand the load. The specimen was placed at the base of the setup and was covered at the top by susceptor material in case of metallic materials. The fixture was made in

3 such a way that once the whole setup was put inside the microwave cavity and power is switched on the specimen becomes heated by microwave. The drill bit attached to the spring will apply a small force on the specimen which will be in a softened state due to heating. The preset force can be increased or decreased by adjusting the height of the base plate on which specimen was placed. All experiments were performed at 2.45 GHz frequency inside a multimode cavity of a domestic microwave oven. magnetron, a cooling fan of 20 W power was put near the magnetron and it was connected to the magnetron circuit by using another circuit containing a transformer to adjust voltage and diodes to make it working in AC. 5) Coaxial Cable with Monopole Antenna: The microwaves coming out from the coaxial adapter is transmitted to the applicator by a coaxial cable. These cables were good for using in low power and non heating applications, but for getting flexibility and ease of fabrication of setup, coaxial cables were used temporarily. The applicator, which emits microwave to the object to be heated, was a unidirectional monopole antenna made of copper and was attached to the end of the coaxial cable and this acts as the drill bit too. The length of antenna was 32.5 mm which was the standard size antenna for transmitting microwave of 2.45 GHz frequency and the diameter of the tip was 1.5 mm and 2 mm in all cases. Photograph of antenna used is given in Fig. 4. Fig. 3 Schematic diagram of microwave drilling setup for drilling inside oven B. Setup for Drilling with Concentrated Microwave Energy Based on the results of the previous setup for drilling, a new setup was made to perform drilling of both metallic and non metallic materials outside microwave oven by concentrating the microwave energy at the tip of the drill bit. The schematic block diagram of the setup with circuit is given in Fig. 5 and the various components are explained below. 1) Magnetron and its Circuit: A Panasonic (Model 2M211AM2) magnetron was used as a source of generating microwave at a constant a frequency of 2.45 GHz. Magnetron need a high voltage for accelerating the electron particles which was given using a circuit having a capacitor and a step up transformer. The output power of magnetron and the time of heating were controlled by an electronic circuit. 2) Waveguide Launcher: The output waves from magnetron will come to the atmosphere were collected and directed to flow in a required direction using a waveguide launcher which is also a rectangular waveguide of WR 340 standard for frequency of 2.45 GHz. This launcher was designed to match with the size of magnetron. The launcher was made of stainless steel sheet of 3mm thickness with the rectangular cross section of size 43 mm X 86 mm and the length of wave guide was 90mm. Fig. 4 Photograph of the antenna attached to the coaxial cable The components were assembled in a similar way as shown in the schematic block diagram given in Fig. 5. Coaxial cable was connected to the adapter by a male connector attached to it. Magnetron was place above the launcher and the cooling fan was placed near to the magnetron. The coaxial cable of length 1m was fixed into the metallic box where experiments were done to prevent human exposure to microwave in case of leakage. But the cable was free to move up and down. Proper earthing was provided to whole setup. There was a provision for inserting a thermocouple wire, in case of working with metallic materials. The photograph of the assembled setup is given in Fig. 6. 3) Rectangular to Coaxial Adapter: This was a standard waveguide of WR 340 standard used to convert the rectangular wave guide to coaxial waveguide/adapter. 4) Cooling Fan: The magnetron use to get heated up during operation and is prone to damage if the temperature goes beyond certain level. So to provide proper cooling to the Fig. 5 Connection diagram of the concentrated microwave drilling setup

4 Fig. 6 Photograph of the assembled setup to perform microwave drilling by concentrating microwave energy V EXPERIMENTAL PROCEDURE A. Drilling of Metals inside Microwave Oven Trials were conducted to study drilling of metallic material through MHH. The specimen was placed at the base of the set up and was covered at the top by a concrete plate and with graphite sheets as required to prevent reflection of microwaves by the metallic specimen. The force was applied by lifting the specimen above its position against the spring pressure on tungsten rod which, in turn, will apply force on the workpiece. The charcoal powder susceptor was directly placed above the workpiece where we want to drill. Once the whole set up was put inside the microwave cavity, the exposure was initiated as per the parameters described in Table 1. The red hot susceptor supplies heat to the metal beneath it by conventional mode of heat transfer, and at high temperature, metal starts absorbing microwave. Once the metal gets softened, the drill feature is pushed downwards due to force applied by the spring and a hole is formed in the workpiece. Experiments were performed with an Al sheet of 1 mm thickness, Cu and MS sheets of 0.5 mm thickness. The drill bit used was tungsten rod of 2 mm in all cases. Also, stainless steel rod of 0.8 mm diameter was used for drilling another aluminium specimen. All specimens were exposed to microwave of frequency 2.45 GHz in a multimode applicator with 900 W power. TABLE I PARAMETERS USED IN THE MICROWAVE DRILLING TRIALS Material Output Thickness (mm) power of microwave Time of exposure (s) Drill Feature (diameter in mm) Aluminium W 120 Tungsten (2) Copper W 150 Tungsten (2) Mild steel W 240 Tungsten (2) Aluminium W 60 SS (0.8) The specimens were then cut along the drilled hole using a Baincut Low Speed Saw and then polished with emery papers of fine grades and alumina powder. Then it was etched with proper acid solutions. Later the drilled specimens were characterized in scanning electron microscope (SEM) to see the micro structure. B. Drilling of Glass and Bone Inside Microwave Oven The procedure was almost same as that followed for metals. Here specimens were not covered to prevent reflection as non metals will not reflect microwaves. Also susceptor was not needed as a metallic drill touches the glass in presence of microwave a spark initiates and it continues to become a plasma formation. Here the tungsten rod itself will acts as a receiving and transmitting antenna for microwaves so that all the charge will concentrate at the tip of the drill feature. The temperature due to plasma is sufficient to drill the glass without any preloaded force from the spring. Self weight of the drill bit is sufficient to deform the glass. Experiments were performed with microwaves of frequency 2.45 GHz at 700 W power for glass and 600 W power for bone in a multimode applicator. Experiments were done with borosilicate glass of 1.5 mm and 4 mm thickness and the hole was drilled in 3 and 6 seconds respectively. Bone used was rib bone of cow which is taken from food waste, is about 6 mm in thickness and it took 10 seconds to make a hole in the bone. When the time or power is more, the glass breaks due to high temperature or thermal shock. The photograph of plasma formed in glass drilling is given in Fig. 7. Fig. 7 Plasma formation in drilling glass inside oven C. Drilling with the Setup to Concentrate Microwave In this setup, microwave generated in the magnetron will pass through the rectangular waveguide and enter the coaxial adapter from which it is transferred through a coaxial cable and come out through the monopole antenna attached to the end of the cable. The microwave coming out from the tip of monopole antenna will be propagating in a single direction.

5 To avoid complexity of the setup microwaves tuners were not used in the experiment for impedance matching. Microwaves were concentrated to a point on the specimen to be drilled and the spread will be more if the distance between the specimen and tip of antenna is more. The specimen will get heated up by microwave. First trials were performed in open atmosphere by putting the specimens in a flat surface, but microwaves were leaking and the side spread of microwaves was more due the absence of impedance matching. Later the experiments were conducted inside a metallic box to protect the operator from exposing to microwave. Experiments with the concentrated microwave drilling setup were performed on borosilicate glass, wood (deodar) and animal bone. Also drilling in Aluminium was tried with microwave hybrid heating by covering the metal with charcoal powder around the point of contact with antenna to prevent reflection and to start initial heating. A spark was observed similar to the plasma formation in drilling of glass with previous setup, at the point of contact between the drill bit (antenna) and the specimen in case of non metals. This spark was sufficient to heat the specimen to a molten or burning stage and the drill bit was pushed downward manually to complete the hole. The parameters used in drilling with concentrated microwave setup and the time taken to form hole is given in Table 2. Also some trials were performed after soaking the specimen in water to reduce the burnt area or the heat affected zone in case of wood and bone. As coaxial cable is not suitable for using in microwave heating applications, due to easiness of design and fabrication in comparison with coaxial wave guide it was used. Coaxial cable provides flexibility in moving the applicator to any position as needed. During experiments the covering of the cable was burned due to high temperature so that the experiments were difficult to perform continuously for more than 15 seconds. TABLE II PARAMETERS USED IN DRILLING WITH CONCENTRATED MICROWAVE Material Thickness Power Time (s) (mm) (W) Borosilicate glass Glass Bone Bone (wet) Wood Wood (wet) Wood (wet) Aluminium VI RESULTS AND DISCUSSIONS A. Drilling of Metals inside Microwave Oven The first Al specimen was drilled with 2 mm tool was melted and burned partially due to overheating. But a hole was formed and is given in Fig. 8(a). The time was 2 minutes but the charcoal started complete coupling in 30 s. The Al plate no 1 shows overheating on the area near to hole. This is due to low melting temperature of Al (about C) and non uniformity in placing the charcoal at the target area. The mild steel specimen was pierced partially with 2 mm diameter tool. Even after 4 minutes of exposure, though it got red hot, yet the temperature rise was not sufficient to form a hole. The photograph of the partially drilled mild steel specimen is given in Fig. 8 (b). The photograph of the drilled copper strip is given in Fig. 9 (b). Aluminium specimen 2 was drilled with a stainless steel rod of 0.8 mm diameter was drilled with heating in 60 seconds which is shown in Fig. 9 (a). SEM image of the 0.8 mm hole drilled in Aluminium specimen is given in Fig. 10. The profile of the hole is having good finish and shape. Fig. 8 (a) Al specimen partially burnt, with a 2 mm diameter hole. (b) Partially drilled stainless steel specimen. Fig. 9 (a) Aluminium with 0.8mm hole (b) Copper strip with 2 mm diameter hole In order to study the surface microstructure, SEM micrographs of the specimens were taken before and after drilling. No variation was observed in the surface structure of Aluminium and the SEM image of surface before and after microwave drilling is given in Fig. 11. Very small variation in grain size of copper as per Fig. 12 was observed where as the increase in grain size comparatively more in case of mild steel as given in Fig. 13. This may be due to overall heating of the specimen with charcoal and the time of heating was more in case of copper and mild steel. This can be minimized by

6 proper concentration of microwave to the drilling point and reducing the amount of susceptor to be used. Fig. 10 SEM image of a 0.8mm diameter hole drilled in Aluminium of 1mm thickness Fig. 12 SEM micrograph of the copper specimen (a) before microwave drilling (b) after drilling (grain coarsening) Fig. 11 SEM micrograph showing surface structure of Aluminium specimen (a) before microwave drilling (b) after microwave drilling B. Drilling of Non Metallic Materials inside Oven Photograph of a drilled glass specimen is given in Fig. 14(a). The plasma formation was very large and sudden in case of drilling of glass. Most of the specimens were broken suddenly after exposing to microwave along with applying a load by the drill feature. The surface finish is not good and some cracks were visible around the hole. These problems can be reduced by optimizing the parameters like power, time and by selecting a drill bit of suitable metal. As glass is very brittle the application of force on the glass must be minimized to prevent the breakage. SEM image of the edge of a hole drilled on glass specimen is given in Fig. 14(b). Fig. 13 SEM micrograph showing surface structure of MS specimen (a) before microwave drilling (b) after microwave drilling (grain coarsening) In case of drilling bone the plasma formation was comparative less than that in glass but it result in burning of the specimen in fire. The holes formed were not of good finish and the heat affected zone was much more in this case due to the fire caused by plasma. The photograph of bone drilled with this setup is given in Fig. 15.

7 specimen was split in to two pieces instead of forming a hole by localized heating. Fig. 14 (a) Photograph of the drilled glass specimen (b) SEM image of the edge of hole Fig. 16 Hole drilled on a borosilicate glass by concentrated microwave setup Fig. 15 Photograph of the hole drilled in bone C. Results of Drilling with Concentrated Microwave Trials were conducted in open atmosphere and inside a metallic box also. There was no difference in the hole drilled in both cases. The temperature inside the closed box was very high and this resulted in more damage of coaxial cable in the form of melting of the covering. The tendency of the cable and specimen to catch fire was also large inside the closed box. Due to this reason it was difficult to drill for more than 10 seconds continuously inside the metal box. The time taken in drilling was less than that in the previous setup for drilling inside microwave oven for the same power. But the overall efficiency was much less due transmission through various lengthy components in comparison with microwave oven. Also lack of tuning and spread of microwave were responsible for less efficiency. 1) Drilling of Glass: During drilling of borosilicate glass at high power the glass was broken suddenly after switching on the power. So the power used was 360 W in further trials. So it takes approximately 8 seconds to drill a glass plate of thickness 1.5 mm and the plasma formation was very less. The picture of a drilled hole in borosilicate glass is given in Fig. 16. In some cases, the portion which is drilled stick to the drill feature due to high temperature and melting. Such a drilled hole is removed from the drill bit after cooling and the SEM image of that drilled hole is given in Fig. 17. In case of the trials with glass of 8 mm thickness no spark was coming at 360 W so the power used was 500 W. In all the trials the Fig. 17 SEM image of the 1.5 mm diameter hole drilled on glass 2) Drilling of Bone: In case of drilling bones, some trials were performed with dry bones. In this case, the heat affected zone was much higher but less than that in comparison with that of the bones drilled with the previous setup. Then the experiments were conducted with wet bone by soaking the bone in water for 10 seconds. This is more similar to the real life situation where bones are always wet with blood. In this case the burning around the drilled hole was much less than previous case. The photographs of the drilled bone in dry and wet conditions were given in Fig. 18 and the SEM image of drilled hole in bone is given in Fig. 19. Fig. 18 Photograph of the hole drilled in bone without and with wetting 3) Drilling of Wood: During drilling of wood the plasma formation was almost absent and there was no fire in the specimen. But the specimen was burnt only at the portion

8 which is in contact with the drill and it was easy to make the hole by inserting the drill bit. In case of drilling dry wood, the heat affected zone was more than that in case of wet wood. But it was less compared to bone in corresponding cases. The photograph of 5 mm thick wood with a 2 mm diameter hole drilled with and without wetting is given in Fig. 20. The SEM image of the hole made in woods shown good finish of the edges and is given in Fig ) Drilling of Aluminium: In case of drilling Aluminium the specimen was covered with charcoal powder around the point of contact with antenna to prevent reflection. Here also small spark was developed at the point of contact and an indentation mark was formed in Aluminium specimen. Due to high temperature at the drill bit, the coaxial cable in was burned after 5 seconds of operation. The photograph of the indentation mark on specimen is given in Fig. 22(a) and its SEM image is given in Fig. 22(b). This gives the possibility of drilling metals with this setup with a coaxial cable which can sustain high temperature or with a coaxial wave guide. Fig. 19 SEM image of drilled bone Fig. 20 Photograph of the hole drilled in wood without and with wetting Fig. 21 (a) SEM image of the 2 mm diameter hole drilled in a wet wood (b) enlarged view of the edge Fig. 22 (a): Photograph of the Aluminium specimen having small deformation due to microwave concentrated drilling (b) SEM image of the indentation made my microwave drill in Aluminium specimen VIII. CONCLUSIONS Drilling of metals by microwave hybrid heating and prosthetic load was done inside oven. Microwave drilling of glass and bone was done with microwave generated plasma inside an oven. A setup capable of concentrating microwave to a small area was developed for microwave drilling. Microwave drilling of engineering materials such as glass and wood were done by concentrating microwave to a small area along for localized heating along with formation of plasma. Drilling of biological materials like bone was performed by concentrating microwave which can be applied for medical applications. Feasibility of drilling metallic materials with concentrated microwave energy was proved. Drilling of wood and bone was performed in dry and wet conditions in which the latter gives better results. Material destruction was much reduced in wet materials. In both the drilling setups plasma ball formation was observed in normal atmosphere, which heats up the material locally to a high

9 temperature. Even though microwave drilling and heating is competitive with laser in many aspects like cost, efficiency and simplicity of operational equipment, it is lacking accuracy and precision in comparison with laser. Use of concentrated microwave for drilling is limited to millimetre range where as laser can be easily focused to microns and the accuracy of microwave drilling is very less. IX SCOPE OF FUTURE WORK The present studies show less accuracy and efficiency due to leakage and spreading of microwave. This can be rectified to certain extent by proper tuning and impedance matching. This can be achieved by adding a three stub tuner and reflection measuring equipments to the present system. Also, the antenna and coaxial wave guide/cable design need to be improved in order to get accurate focusing of microwave. Usage of an EH tuner will help in processing materials with separate electric and magnetic fields depending on their properties as materials have different characteristic in heating with electric and magnetic part of microwave. A model of such a setup by modifying the present one is given in Fig. 23. Fig. 24 Microwave assisted metal forming system Fig. 25 Microwave heating of tumour inside flesh Fig. 23 Suggested setup for microwave drilling and concentrated heating Drilling inside the microwave oven shows the feasibility of developing this technique for gang/multiple drilling. Cutting of hard and brittle materials can also be made possible by further development of plasma formation in drilling. The device for concentrating microwave is having the potential to be developed as a heat source similar to a welding electrode in process like joining, cladding, and hardfacing. The plastic deformation observed during drilling of metals opens up the beginning of a new technology of microwave assisted metal forming. A setup which can be used in a production line where continuous flow of materials along with microwave heating for metal forming is given in Fig. 24. Concentrated microwave drill with coaxial cable can be developed further for medical applications like concentrated heating of small points to destroy the cells of tumours or cancer inside the flesh. Heating profile of such an application is given in Fig. 25. ACKNOWLEDGEMENT The financial support received for the present works from the BRNS, Govt. of India vide Project Grant No. 2010/36/60- BRNS/2048 has been duly acknowledged. Authors gratefully acknowledge the inputs received from Dr. K P Ray of SAMEER institute Mumbai and research students Amit Bansal and Manjot Singh Cheema. REFERENCES [1] E.T. Thostenson, T.W. Chou, Composites: Part A 30 (1999) [2] David E. Clark, Diane C. Folz, Jon K. West, Materials Science and Engineering A287 (2000) [3] H. S. Ku, E. Siores, A. Taube, Computers & Industrial engineering 42(2002) [4] Jiping Cheng, Rustum Roy, Dinesh Agrawal, Mat Res Innovat (2002) 5: [5] S.P. Kozyrev, V.A. Nevrovsky, L.L. Sukhikh, V.A. Vasin, Yu. M. Yashnov, XVIIth International Symposium on Discharges and Electrical Insulation in Vacuum-Berkeley-1996 [6] E. Jerby, V. Dikhtyar, 8th Ampere Proc., Bayreuth, Sept [7] E. Jerby, V. Dikhtyar, O. Aktushev, Published in Ceramic Bulletin 82(2003) 35. [8] E. Jerby, V. Dikhtyar, O. Aktushev, U. Grosglick, SCIENCE VOL OCTOBER 2002 [9] Titto John George, Apurbba Kumar Sharma, Pradeep Kumar, i- manager s Journal on Mechanical Engineering, Vol. 2 No. 2 February - April 2012, pages 1-6 [10] Titto John George, Amit Bansal, Apurbba Kumar Sharma, Pradeep Kumar, Proceedings of International Conference on Mechanical Engineering Technology, Kerala (ICOMET 2012), January 2012, pages [11] Eli Jerby, J. Am. Ceram. Soc., 87 [2] (2004)