Various best match between the property-profiles of the materials.

Various kinds of materials
are being used in the different aspects of our life. Materials as a field
are most commonly represented by ceramics, metals, polymers and other
composites. While noted improvements have taken place in the area of ceramics
and metals, it is the field of polymers that has experienced an explosion in
progress. Polymers have gone from being cheap substitutes for natural products
to providing high quality options for a wide variety of applications. Material
selection involves seeking the best match between the property-profiles of the
materials. It is the foundation of all engineering applications and design.
To
avoid the drawbacks of intuitive approaches systematic methods must be applied.
The most important motive why material selection is performed is to ensure that
the component functions well such as failures do not occur too frequently.
Further reasons are to make full use of the materials and to obtain cost
effective components. In fact minimisation of cost is usually the main
objective in engineering design at the same time as a number of requirements
should be satisfied. Due consideration has also to be taken to the value of
weight savings in transport applications. In special cases other objectives
like the maximization of performance may be of importance. Systematic selection
of the best material for a given application begins with these objectives which
are illustrated below:

1. Functional
requirements

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

2. Operating parameters

3. Cost considerations

4. Manufacturing
process

 

Material selection
involves a complex interaction between component function, material process and
its shape. Selecting the optimum combination of material and process cannot be
performed at one certain stage in the history of a project. It should gradually
evolve during the different stages of product development. . Appropriate
selection of material is significant for the safe and reliable functioning of a
part or component.  After identifying the
application of the material, it is very important to keep in mind the primary
design and secondary requirements of the final product. There is always a close
connection between material selection and design configuration for any product.
Nowadays, testing a material has been made very easier with CAE software. The
testing of materials for use in crash and safety simulations and the conversion
of test data into material models manually is a process that is not well
standardized in the industry. Through these software an engineer can have a
look over wide area of properties of materials. Matereality is one of the
software among them which can save the properties, charts and test reports for
your material which helps you to have a clear view over a wide range of
materials that can be use or rejected as per their required characteristics.

 

                            FUNCTIONAL
REQUIREMENT

The correct combination
of mechanical, physical and chemical properties are considered to meet the
function and operating condition for any material. The first step in every
material selection task is to specify the requirements in terms of its properties.
During
primary selection, properties of a material play a magnificent role. These
properties distinguish materials in their usage. Among these properties some of
them are very effective which are:

1.     
Strength

2.     
Hardness

3.     
Rigidity

4.     
Toughness

5.     
Fatigue

6.     
Creep

no two materials can
have all same properties and the choice is usually decided by the best possible
combinations. This may need a great scientific approach so that the outcome
will be more convenient.

1. STRENGTH:

It is basically a
relation between internal forces, deformation and external loads. In general
method of analysis used in strength of materials the first step is to assume
that the member is in equilibrium. Important assumptions in strength of
materials are that the body which is being analyzed is continuous, homogenous
and isotropic. A continuous body is one which does not contain voids or empty
spaces of any kind. A body is homogenous if it has identical properties at all
points. A body is said to be isotropic with respect to some property when that
property does not vary with direction or orientation.

Engineering materials
such as steel, cast iron and aluminum may appear to meet these conditions when
viewed on gross scale. Most of the engineering metals are made up of different
mechanical properties so a test is performed on the sample of the component or
on the actual component to predict its strength behavior or its
susceptibility to various failure modes when the part is in service or in
operating conditions. The type of test is selected on the basis of
direction of acting forces on particular structures or components or
parts. The most common type of strength tests are Tensile and tension
tests – longitudinal, Transverse and ‘Z’ direction or through thickness tensile
test, Weld longitudinal and transverse tensile test, bond tension test,
adhesive tension test, Compression test, Shear test, Torque test, Torsion test,
Flexural test, Modulus of bending, bending moment test.  

 

 The stress and
strain initially increase with a linear relationship. This is the
linear-elastic portion of the curve and it indicates that no plastic
deformation has occurred.

2. HARDNESS:

 Hardness is the resistance of material to
permanent deformation of the surface. Hardness is not a fundamental property of
a material, but a combined effect of compressive, elastic and plastic
properties. It can be measured by nondestructive testing.

 Hardness measurement can be in Macro, Micro
& nano – scale.  Measurement of the
Macro-hardness of materials is a quick and simple method of obtaining
mechanical property data.  The
Macro-hardness measurement will be highly variable.  Micro-hardness measurements are appropriate.

Hardness Measurement
Methods are Rockwell hardness test, Brinell hardness, Vickers, Knoop hardness
and shore.

·        
The Rockwell Hardness Test and
Superficial Rockwell is performed on castings, forgings and other
relatively large metal products and samples because the tests produce a large
visible indentation.

The Brinell Hardness Test can
be applied to almost any metallic material and is the method
most commonly used to test castings and forgings that have a grain
structure too coarse for other metal hardness testing methods.
Micro hardness testing by
Knoop and Vickers Hardness Test methods measure small samples or
small regions in a sample. They are often used to measure
surface or coating hardness on carburized or case-hardened parts, as well
as surface conditions such as grinding burns or decarburization. (Vickers
is also available on the macro scale to 50 kg.)
The Shore Durometer Test measures
the hardness of polymeric materials.

 

3. RIGIDITY:

 Rigidity, also
known as “stiffness,” is generally measured using Young’s modulus. It
can be defined as the “force necessary to bend a material to a given
degree.”

For testing a material
according to its rigidity, torsion test is done in which measured modulus of
rigidity is termed “apparent” since it is the value obtained by measuring the
angular deflection occurring when the specimen is subjected to an applied
torque. Since it is possible that the specimen will be deflected beyond its
elastic limit, the calculated value will not always represent the true modulus
of rigidity within the elastic limit of the material the true modulus of rigidity
within the elastic limit of the material.

4. TOUGHNESS:

 Material
toughness is the amount of energy per unit volume that a material can absorb
before rupturing. It is also defined as a material’s resistance to
fracture when stressed. Toughness requires a balance of strength and
ductility.

The toughness of a
material can be measured using a small specimen of that material. A typical
testing machine uses a pendulum to strike a notched specimen of defined
cross-section and deform it. The height from which the pendulum fell, minus the
height to which it rose after deforming the specimen, multiplied by the weight
of the pendulum is a measure of the energy absorbed by the specimen as it was
deformed during the impact with the pendulum. The Charpy and Izod
notched impact strength tests are typical ASTM tests used to determine
toughness.

 

5. FATIGUE:

It is
the weakening of a material caused by repeatedly applied loads. It is the
progressive and localized structural damage that occurs when a material is
subjected to cyclic loading.

Fatigue occurs when a
material is subjected to repeat loading and unloading. If the loads are above a
certain threshold, microscopic cracks will begin to form at the stress
concentrators such as the surface, persistent slip bands (PSBs), interfaces of
constituents in the case of composites, and grain interfaces in the case of
metals.  Eventually a crack will reach a critical size, the
crack will propagate suddenly and the structure will fracture. The shape of the
structure will significantly affect the fatigue life, square holes or sharp
corners will lead to elevated local stresses where fatigue cracks can initiate.
Higher value fatigue materials can bear high stress which can be the key point
in selecting a material according to its loading.

              

 

6. CREEP:

It is the slow and
progressive deformation of a material with time at constant stress. Keeping in
mind that temperature, composition and grain size can affect the amount of
deformation.

Test for selecting a
material with respect to its creep can be done by following two tests which
are:

1. Creep test

2. Stress Rupture
Testing

A creep test involves a
tensile specimen under a constant load maintained at a constant temperature.
Measurements of strain are then recorded over a period of time.

Creep occurs in three stages that are Primary, Secondary and Tertiary. Creep
occurs at the beginning of the tests and is mostly transiently, not at a steady
rate.

Stress Rupture Testing involves a tensile specimen
under a constant load at a constant temperature. Stress rupture testing is like
creep testing aside from the stresses is being higher than those utilized
within a creep testing. Stress rupture tests are utilized to find out the time
it takes for failure so stress rupture testing is always continued until
failure of the material occurs.

 

                                                                                                          

                           MANUFACTURING
PROCESES

Manufacturing
process are the steps through which raw materials are transformed into a
final product. The manufacturing process begins with the product design, and
materials specification from which the product is made. These materials are
then modified through manufacturing processes to become the required part.

 

The basic manufacturing
process required for selection of materials is:

Plasticity
Malleability
Ductility
Machinability
Thermal
conductivity and diffusibility

 

PLASTICITY:

In materials
science, plasticity describes
the deformation of a solid material undergoing non-reversible changes
of shape in response to applied forces. For example, a solid piece of metal
being bent or pounded into a new shape displays plasticity as permanent changes
occur within the material itself.

PLASTICS:
Plastics
are increasingly being used to replace other materials like bronze, stainless
steel, aluminum and ceramics. The most popular reasons for switching to
plastics include:

Longer part life
Elimination of lubrication
Reduced wear on mating parts
Faster operation of equipment/line
speeds
Less power needed to run equipment
Corrosion resistance and inertness

 

MALLEABILITY

Malleability is a substance’s ability to deform
under pressure (compressive stress). If malleable, a material may be flattened
into thin sheets by hammering or rolling. Malleable materials can be flattened
into metal leaf

Malleability is mostly
tested as hardness. The most common hardness tests are Rockwell and Brinell
tests. They determine the resistance of a material to indentation. Ductility is
also similar to malleability. Ductility is usually measured by elongation and
reduction of area as determine in tensile test.
Malleability is a mechanical property of matter, but is most commonly used in
reference to metals.
This is important in metalworking, as materials that crack or break under
pressure cannot be hammered or rolled. One thing that brittle metal and plastic
are made by molded where malleable metals can be formed by using stamping or
pressing.

 

DUCTILITY

Ductility is defined as the ability of a material to deform to a greater
extent before the sign of crack, when it is subjected to tensile force. 

Testing parameters
affecting ductility

·        
 When
a specimen is pulled in tension to fracture, a region of local deformation
occurs, called the neck.  Necking occurs as the force begins to drop after
the maximum force has been reached on the stress strain curve. Up to the point
at which the maximum force occurs, the strain is uniform along the gage length,
meaning that the strain is independent of gage length. 
However, after necking starts, the gage length becomes important. When the gage
length is short, the necking region occupies a much larger portion of the gage
length. Conversely, for longer gage lengths, the necking occupies a smaller
portion of the gage length. As a rule, the larger the gage length, the smaller
the measured elongation for a given material.

·        
Specimen dimensions. The cross sectional
area of a specimen also has a significant effect on elongation measurements.
The slimness ratio, K, is defined as the gage length divided by the square root
of the cross sectional area.

     K = Lo/ ?Ao     Eq.3
where Lo is the original gage length.
Ao is the original cross sectional area of specimen.

Experiments have shown
that as the slimness ratio decreases, the measured elongation increases.
Holding the slimness ratio, K, constant will minimize the effect of changes in
specimen dimensions on elongation.

Reduction of area is normally measured only on round test specimens because the
shape of the reduced section in the neck remains essentially circular
throughout the test. With rectangular test pieces, the corners prevent uniform
flow from occurring, and consequently the shape in the neck is no longer rectangular.
In general, as reduction of area increases, the minimum allowable bend radius
for a sheet material decreases.

·        
Testing speed/strain rate. Generally,
higher strain rates have an adverse effect on the ductility of materials,
meaning that elongation values decrease as the strain rate increases. Metals
that are brittle are more sensitive to strain rate. Also, the strain rate
sensitivity of metals is quite low at room temperature but increases with
increasing temperature.

 

MACHINABILITY

It refers to the ease
with which a metal can be cut (machined) permitting the removal of the material
with a satisfactory finish at low cost.  Materials with good
machinability require little power to cut, can be cut quickly.

Machinability can be
difficult to predict because machining has so many variables. Two sets of
factors are the condition of work materials and the physical properties of work
materials. The condition of the work material includes eight
factors: microstructure, grain size, heat treatment, chemical composition,
fabrication, hardness, yield strength, and tensile strength.

These ratings were
established for materials with Brinell hardness numbers (BHN) as listed. When a
material listed is to be machined and is found to have a BHN different from
that shown in the table, a ratio is applied.

                       

THERMAL CONDUCTIVITY
AND DIFFUSIBILITY:

In
simple terms this is a measure of the capacity of a material to conduct heat
through its mass. Different insulating materials and other types of material
have specific thermal conductivity values that can be used to measure their
insulating effectiveness.

Thermal Conductivity
Meters measure thermal conductivity according to the ASTM E1530 guarded heat
flow meter method. In this technique, a sample of the material to be tested is
held under a compressive load between two surfaces, each controlled at a
different temperature. The lower surface is part of a calibrated heat flux
transducer. As heat is transferred from the upper surface through the sample to
the lower surface, an axial temperature gradient is established in the stack.
By measuring the temperature difference across the sample along with the output
from the heat flux transducer, thermal conductivity of the sample can be determined
when the thickness is known.

 

                                     OPERATING PARAMETER

 It is basically a limit
of material capability to standby it’s self under harsh environment conditions.
These environmental factors include pressure, temperature, corrosion and
biological effects. Almost every aspect of materials usage, from extraction and
production, through product design and ultimately disposal issues, is now
subject to environmental considerations. Furthermore there are many cases where
the development of ‘environmentally-friendly’ materials is providing new
challenges for materials scientists and engineers.

1. CONTACT WITH AIR:

The shiny surface of very
reactive metals soon becomes
dull when exposed to air.
The metal reacts with the
oxygen in air to give the metal oxide. 

Whereas, other
materials like polymers and ceramics doesn’t go with any prominent changes with
respect to air. Among the materials, most of the metals undergo corrosion when
suspended in air for long or short period of time depending upon the
characteristics of respective material.  Corrosion
makes the material gradually weak with time. Hence, for the satisfactory
operation, performance and life of engineering product, it becomes necessary
that material being selected for that product should have sufficient corrosion
resistance.

2. TEMPERATURE
AFFECT:

POLYMERS:
The temperature dependency of the properties of polymers is strongly correlated.
The saturated polymers are more sensitive to temperature changes than the
unsaturated polyester ones. The
unsaturated polyester samples present a less brittle behavior starting at 50 ºC.
From room temperature to 60 ºC, flexural and compressive strength decreases
drastically as temperature increases, a loss of more than 50% is reported.

•        
METALS:
Decrease in temperature there is an increase in the tensile strength and yield
strength of all metals. Alloys of nickel, copper and aluminum retain most of
their ductility and toughness at low temperature. For mild steel, the elongation
and reduction in cross sectional area is satisfactory up to – 180°c but after
that it goes down to a large extent. Near absolute zero temperature many metals
exhibit the phenomenon of super conductivity. Below 100°c non-ferrous metals
show better properties than Ferro metals.

                                    

Cold regions
engineering has a general need for the evaluation of materials at low
temperatures. Performance of many structures and components is seriously
affected when the weather becomes very cold. At low temperatures materials tend
to become hard and brittle which causes many difficulties in selecting a
material with respect to temperature change.

CERAMICS:
At elevated temperatures, two
factors become important to change the dependence of mechanical properties on
microstructure. First, dislocations become much higher and second, the
diffusion of point defects is enhanced.

3. BIOLIGICAL
EFFECTS:

A living organism has a
material structure to provide an environment for complicated chemistry of
living. Chemical and physical reactions provide energy to maintain living
functions and to renew structural material. Thus, consideration of biological
effect is a natural extension of physical and chemical properties.

METALS:
 Heavy metals constitute a very heterogeneous
group of elements widely varied in their chemical properties and biological
functions. Heavy metals are kept under environmental pollutant category due to
their toxic effects on plants, animals and human being. Heavy metal
contamination of soil results from anthropogenic as well as natural activities.

To a large extend,
biological functions of any materials are related to their chemical and
physical properties. However, reactions in biological systems are catalyzed by
enzymes. Furthermore, products of one reaction may be reactants for another in
a complicate scheme of reactions to maintain live. Malfunction of a reaction
causes trouble, leading to disease or death. Thus, biological effects deserve
special consideration.

POLYMERS:
Turning
to adverse effects of plastic on the human population, there is a growing rate
of potential health risks. A range of chemicals that are used in the
manufacture of polymers especially plastics are known to be toxic.
Biomonitoring provides an integrated measure of an organism’s exposure to
contaminants from multiple sources. This approach has shown that chemicals used
in the manufacture of polymers are present in the human population.

4. CONSIDERATION OF STANDARDS:

Metallic Material
Testing Standards focus on hardness, tensile, and fatigue testing, approaching
the issues from multiple angles to provide a range of information. In addition,
metallic material testing standards cover corrosion testing, weld testing, and other
areas of interest. Together, standardized testing provides valuable information
to determine the reliability of metallic materials and the products and
structures using them. Over 12,000 of ASTM standards are there to test different
materials. This may lead to the correct and exact selection of material you are
looking for.

5. WEAR RESISTANCE:

Wear is a problem when
the materials are contacting each other in a product. So it must be ensured
that the selected materials have sufficient wear resistance. There are many
production techniques available to improve the wear resistance and make the
material is more suitable for the application. This is also very important
factor to consider when selecting a material for a particular design. In the
engineering design process this has to be considered with great care. Especially,
in metal there are many wear loses. These
ceramics successfully resist various solid and liquid abrasive and corrosive
media transported at high velocities and pressures, and at cavitations. They
may replace hard metals widely used for wear- and corrosion-protection. The
features of the compositions, microstructure, and physical properties of these
ceramics, as well as the wear resistance test results, are much better than
metals. The factors affecting wear resistance of ceramics is may be subdivided
by the factors dealing with microstructure and properties of ceramics and by
the factors dealing with application conditions.

x

Hi!
I'm Homer!

Would you like to get a custom essay? How about receiving a customized one?

Check it out