Investigation of Vibration properties of Aluminium, Silicon carbide

Transcription

International Journal of Latest Trends in Engineering and Technology (IJLTET)
Investigation of Vibration properties of
Aluminium, Silicon carbide, Mica a Hybrid
Metal Matrix Composite
R Raghuram
Department of Mechanical Engineering,
Sri Muthukumaran Institute of Technology, Chennai, Tamil Nadu, India
S Sharath Kumar
M Shanmuga Priyan
P Saravanan
T Anand
Associate professor, Department of Mechanical Engineering,
Abstract- Vibration is an important mechanical phenomenon where oscillation takes place about an equilibrium point.
It is desirable in some cases such as tuning fork, mobile phones and loud speakers whereas the vibrational motions of
engines, motors or any mechanical devices are undesirable. In metals it is an undesirable property which produces
unwanted motions, wastage of energy and noises. Aluminium which is an abundant material which is widely used in
structural applications because of its light weight, high tensile strength etc. if alloyed, and is easily fabricated .In recent
trends, many composites of aluminium have been developed and their damping characteristics have superior property
when compared to its base alloy. This project focuses on investigating the damping characteristics of aluminium silicon
carbide mica a hybrid metal matrix composite which is formed by stir casting method. Three different compositions are
taken by varying the percentage of mica as 1%, 2%&3%. The advantage of this composite is that it offers high damping
ratio when compared to its base metal which is aluminium. The damping behavior is studied by the use of a accelerometer
and data acquisition software in cantilever beam conditions. It is found that the damping ratio increases as the percentage
of mica increases.
Keywords – aluminium, silicon carbide, mica, vibration, stir casting, damping ratio
I.
INTRODUCTION
Improved fuel efficiency and demand for high-strength lightweight material is increasing the demand for composites
as a result of which it has started to penetrate the field of material science. This is particularly true for automotive
and aerospace sectors. Wind energy suppliers, industrial suppliers etc are also increasing their use of composites.
Composite materials have an increasingly important role to play in achieving the targets for fuel efficiency and
reduced carbon dioxide emissions that leading automakers are aiming for. Composite material is composed of two or
more distinct phases (matrix phase and dispersed phase) and has properties significantly different from those of its
constituents. Many of common materials also have a small amount of dispersed phases in their structures, even so
they are not referred to as composite materials since their properties are similar to those of their base constituents
Vol. 5 Issue 2 March 2015
402
ISSN: 2278-621X
(physical properties of steel are similar to those of pure iron).Among the three different composites namely Metal
Matrix Composites (MMC), Ceramic Matrix Composites (CMC), Polymer Matrix Composites (PMC), the hybrid
metal matrix composite offers more advantages than the others. Aluminium matrix composites (AMCs) refer to the
class of light weight high performance aluminium centric material systems. It fulfills the requirement of Greater
strength, low density, Controlled thermal expansion coefficient, improved damping capabilities, improved abrasion
and wear resistance. AMCs are intended to substitute monolithic materials including aluminium alloys, titanium
alloys, polymer based composites; ferrous alloys are used in several applications in automotive, aerospace, rail
engineering, military, marine and industrial fields.
II.
EXPERIMENTAL WORK
A. Materials –
Metal matrix composites (MMCs) are one of the most important innovations in the development of advanced
material sciences. Aluminium and its alloys are widely used in the fabrication of MMCs among the various matrix
materials available.
Black silicon carbide and muscovite mica are selected as reinforcement materials. Silicon carbide is selected as it is
an important structural ceramic material due to its unique combination of properties such as excellent oxidation
resistance, high wear resistance, high thermal conductivity, good thermal shock resistance. Muscovite mica is used
as second reinforcement material as it is flexible, tough having high tensile strength; it can also withstand substantial
mechanical pressure perpendicular to the plane. While mica is flexible, elastic and tough, it is very soft. Mica has
zero moisture absorption.
This study concerns the effect of damping resistance when the content of mica is increased. Therefore 3 different
compositions are formed keeping the percentage of silicon carbide (4%) constant and varying mica percentage as 1,
2 and 3 in each composition.
B.
Specimen preparation –
The fabrication of metal matrix composites can done using various methods, stir casting technique is one such
method. This technique offers wide range of shapes, larger size particles and can with stand up to up to 500 kg load,
and is the least expensive method when compared to Squeeze Casting, powder metallurgy and spray casting
techniques
In stir casting process, the reinforcing phases are distributed into molten matrix by means of mechanical stirring.
The weighed aluminium 6061ingots is taken in a graphite crucible of number 6 and size 2Kg capacity and is heated
using an electric resistance furnace of 4kw power capacity at a temperature of 850°C. The required quantity of
reinforcement materials are weighed in a digital weighing machine and are also kept inside the furnace, in order to
increase the intermolecular bonding with aluminium.
(a)
(b)
(c)
(d)
Figure.1 (a) aluminium 6061 (b) stir casting equipment (c) mica (d) silicon carbide
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Plate die of length 150mm and thickness 5mm were taken so as to prepare the specimens for vibrational analysis as
per ASTM standards. The dies were cleaned using emery paper, and graphite was applied along with kerosene to
prevent the cast from sticking to the dies surface. The dies were preheated to a temperature of 500°C to reduce
shrinkage loss and blow holes formation when molten metal matrix was poured into it.
1% Pure Magnesium powder was added to the molten metal to compensate for the loss during heating and also to
increase the wetability between the materials. By improving the wetting we can (i) increase the surface energies of
the solids, (ii) decrease the surface tension of matrix alloy, and (iii) decreasing the solid/liquid interfacial energy at
the dispersed matrix interface. As the temperature set in the furnace was achieved the crucible was taken out by
using steel tongs, degasser powder was added to remove the impurities in the molten metal and coverall is sprinkled
over the aluminium to prevent oxidization). If by any chance oxygen enters the molten aluminium during pouring
into the mould, then the final casting will have bubbles which can ruin the finish of the cast shape.
Figure 2. specimen for free vibration test
The reinforcement materials were then added with the molten aluminium in the crucible and were manually stirred.
It is then again kept inside the furnace to obtain a temperature of 850°C. After achieving the temperature a
mechanical stirrer was introduced inside the furnace which rotates at 300rpm so as to distribute the reinforcement
equally. The stirring was done keeping the temperature constant and was carried out for approximately 10minutes.
Then the molten metal matrix composite obtained was poured into preheated die and was set to cool off for three
hours. The die was then opened to obtain the sample. This procedure was repeated for the 3 different compositions
and the specimens required for the vibration analysis are thus obtained.
C. Testing for vibration properties –
Free vibration occurs when a system is initially loaded and then even after the load is removed the body tends to
vibrate until it reaches zero value. The resistance towards such vibrations is known as damping. Damping factor of a
material can be determined by knowing its natural frequency along with some other parameters such as logarithmic
decrement, damping ratio and critical damping coefficient.
The specimen required for testing free vibration is cut out from a large plate die cast sample as per the ASTM
standard. The dimensions of the specimen are as follows, length 150mm, width 20mm and thickness 5mm.
ATALON free vibration testing machine is used to determine the free vibration of the material.
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Figure.3 free vibration test apparatus
The apparatus consists of a Cantilever beam with mounting arrangements to hold the specimen, NI / DEWESoft
Data Acquisition System – DAQ in order to input the values from the sensor to the computer in a graphical format,
Accelerometer with 5 meter cable with Wax Mount which is the sensor used to detect the vibrations of the
specimen.
The sample is initialed weighed and is fixed in the cantilever mounting arrangement such that 30mm of the beams
length is fixed at one end. The wax mount accelerometer is attached to the other end of the sample. An impact
hammer is taken and is struck against the sample in order to produce vibrations. The vibrations are sensed and
recorded using the accelerometer sensor A&D 3101 having sensitivity 9.8mV/g which converts the excitation into
electrical signal and feeds it to the computer and the data acquisition software plots the graph between amplitude vs.
time and amplitude vs. frequency based on the signal by the accelerometer sensor. After a certain time interval the
vibration in the specimen comes to zero, this is due to the damping property of the material.
Three sample specimens were subjected to testing in each composition and their average value was taken to
compute the damping coefficient of the composites. The Logarithmic decrement is computed from the amplitudes
using the following Equation
Logarithmic decrement
Where, X1 and X2 are the first two successive amplitudes and n is the number of cycles.
The damping ratio is determined by using the Equation,
In order to find out the value of damping coefficient, we need to know the values critical damping coefficient and
damping ratio. The critical damping coefficient can be found by the equation
is the circular frequency.
fn= Natural frequency of the material which is obtained from the peak value of amplitude vs. frequency
graph.
The damping coefficient C is found by the equation,
From the above equation, the damping coefficient for all the 3 samples of each composition is found out and there
aggregate value is taken.
III. RESULTS AND DISCUSSIONS
A. Vibration test –
Three different compositions are taken in order to determine the effect of increase in mica on the vibrational
property of aluminium silicon carbide composite and their values are given below:
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Figure.4 DEWESoft Data Acquisition System
The damping ratio, coefficient and other parameters are calculated using the values obtained from the free vibration
test and a table containing the results of the test is made.
Table -1 Variation in damping effect for different compositions
s.no
Compositions
Natural
frequency
Damping ratio
Damping
coefficient
1
Al+SiC(4%)+mica(1%)
232
0.01075
1.35
2
Al+SiC(4%)+mica(2%)
201
0.017
1.762
3
Al+SiC(4%)+mica(3%)
208
0.0215
2.33
Graph.1 shows compositions vs. damping coefficient
The damping ratio, coefficient and other parameters are calculated using the values obtained from the free vibration
test and a table containing the results of the test is made. From Table.1 we can see that the damping coefficient
increases in each successive composition.
The graphical representation in variation of damping coefficient for all three compositions clearly indicates that the
value of damping coefficient increases with each composition. This is because in each successive composition the
percentage of mica is increased.
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B. SEM Analysis –
In order to know about the microstructure of the made aluminium silicon carbide mica composite Scanning Electron
Microscope study is conducted. Before conducting the microstructure study, the surface of the specimen is to be
cleaned and polished. The specimen is then etched using hydrogen fluoride (HF) just an hour before the SEM study.
(a)
(b)
Figure.5 (a) Scanning electron microscope (b) etched specimen
(a)
(b)
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Silicon carbide
mica
(c)
Figure.6 (a) Al + SiC (4%) + mica (1%) (b) Al + SiC (4%) + mica (2%) (c) Al + SiC (4%) + mica (3%)
The SEM analysis clearly shows the distribution of silicon carbide and mica particles in aluminium. It can be
observed that the mica concentration has increased in each successive composition.
IV. CONCLUSION
It is observed that the aluminium metal matrix composites can be fabricated using stir casting method. It is subjected
to free vibration test to evaluate the damping behavior and natural frequency of the composites. From the SEM
photos it is clear that the reinforcements have been uniformly distributed in all the three compositions Thus it is
proved that mica has an effect on vibrational property in aluminium metal matrix composites, such that increasing
the mica content reduces the vibration of the material, thereby minimizing the energy loss and noise.
REFERENCES
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K. S. Uma Shankar, K. V. Gangadharan, Vijay Desai, B. Shivamurthy, ”Fabrication and Investigation of Damping Properties of Nano
Particulate Composites” Journal of Minerals & Materials Characterization & Engineering.
Lihua Liao, Xiuqing Zhang, Haowei Wang, Xianfeng Li, Naiheng Ma, “The characteristic of damping peak in Mg–9Al–Si Alloys”, Journal
of Alloys and Compounds 429 (2007) 163–166.
Hui Lu, Xianping Wang, Tao Zhang, Zhijun Cheng and Qianfeng Fang “Design, Fabrication, and Properties of High Damping Metal Matrix
Composites—A Review “Materials 2009.
Wu, G.H. Dou, Z.Y. Jiang, L.T. Cao, J.H. “Damping properties of aluminum matrix-fly ash composites”. Mater. Lett. 2006.
Gowri Shankar M.C, Jayashree P.k, Raviraj Shetty, Achutha Kini, Sharma S.S, “Individual and Combined Effect of Reinforcements on Stir
Cast Aluminium Metal Matrix Composites-A Review” International Journal of Current Engineering and Technology.
Deonath, R. T. Bhat, P. K. Rohatgi, Preparation of cast aluminium alloy-mica particle composites, Science May 1980, Volume 15, Issue
5, pp 1241- 1251
Manoj Singla, D. Deepak Dwivedi1, Lakhvir Singh, Vikas Chawla, Development of Aluminium Based Silicon Carbide Particulate Metal
Matrix Composite, Journal of Minerals and Materials Characterization and Engineering, vol.8, no.6
408
ISSN: 2278-621X

Investigation of Vibration properties of Aluminium, Silicon carbide

Transcription

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