1. 5. Engineering Materials
Materials and Civilization, Materials and Engineering,
Classification of Engineering Materials, Mechanical Properties
of Materials: elasticity, plasticity, strength, ductility, brittleness,
melleability, toughness, resilience, hardness, machinability,
formability, weldability. Properties, Composition, and Industrial
Applications of materials: metals (ferrous- cast iron, tool steels,
stainless steels and non ferrous- Aluminum, brass, bronze ),
polymers (natural and synthetic , thermoplastic and
thermosetting), ceramics (glass, optical fibre glass, cements),
composites ( fibre reinforced, metal matrix), smart materials
(piezoelectric, shape memory, thermochromic, photochromic,
magnetorheological), Conductors, Semiconductors and
insulators, Organic and Inorganic materials. Selection of
materials for engineering applications.
2. Materials and Civilization
Civilization comes from latin word civilis meaning civil and
civilas meaning city
# Civilization may be defined as the sum total of all progress
made by man in every sphere of action.
# Following are the sequences of civilization and happening in
their periods:
1. Stone age is associate with the use of stone as materials.
2.Bronze age, the innovation of smelting and casting of materials
started.
3. Iron age coincided with wide spread use iron or steel for their
cutting tools and weapons.
# We conclude that the progress of civilization is strongly
related to the development of materials and engg.
5. Mechanical Properties of Materials
Elasticity Elasticity (or stretchiness) is the physical property of a
material that returns to its original shape after the
external forces) that made it deform or distort is
removed. The relative amount of deformation is called
the strain.
plasticity describes the deformation of a material
undergoing non-reversible changes of shape in
response to applied forces.
Plasticity
6. Strength of a material is its ability to withstand an
applied load without failure. The applied load may be
tensile, compressive, or shear.
A load applied to a mechanical member will induce
internal forces within the member called stresses.
The stresses acting on the material cause deformation of
the material. Deformation of the material is called strain.
7. Ductility is a solid material's ability to deform under
tensile stress; this is often characterized by the material's
ability to be stretched into a wire.
Malleability, a similar property, is a material's ability
to deform under compressive stress; this is often
characterized by the material's ability to form a thin sheet
by hammering or rolling.
Both of these mechanical properties are aspects of plasticity,
the extent to which a solid material can be plastically
deformed without fracture.
8. Brittleness Tendency of a material to fracture or fail
upon the application of a relatively small amount of
force, impact, or shock.
Toughness Property of a material that enables it to
absorb and distribute within itself relatively large
amounts of energy (both stresses and strains) of
repeated impacts and/or shocks, and undergo
considerable deformation before fracturing or failing.
Toughness is Opposite of Brittleness.
9. Resilience is the property of a material to absorb energy
when it is deformed elastically and then, upon unloading to
have this energy recovered. In other words, it is the
maximum energy per unit volume that can be elastically
stored.
Hardness Resistance of a material to deformation,
indentation, or penetration by means such as abrasion,
drilling, impact, scratching, and/or wear.
Machinability refers to the ease with which a
metal can be machined to an acceptable surface finish.
Materials with good machinability require little power to
cut, can be cut quickly, easily obtain a good finish, and
do not wear the tooling much; such materials are said to
be free machining.
10. Formability is the ability for a given metal workpiece
to undergoing plastic deformation without damage.
Weldability, also known as joinability,of a
material refers to its ability to be welded. Many metals
and thermoplastics can be welded, but some are easier
to weld than others. A material's weldability is used to
determine the welding process and to compare the final
weld quality to other materials.
11. Stiffness is the resistance of an elastic body to
deformation by an applied force
Fatigue is the progressive and localized structural
damage that occurs when a material is subjected to
cyclic loading. The nominal maximum stress values are
less than the ultimate tensile stress limit, and may be
below the yield stress limit of the material.
Creep is the tendency of a solid material to slowly
move or deform permanently under the influence of
stresses. It occurs as a result of long term exposure to
high levels of stress that are below the yield strength of
the material. Creep is more severe in materials that are
subjected to heat for long periods, and near melting
point. Creep always increases with temperature.
12. Criteria for Selection of Material
# Design of any machine element begins with the selection
of a material.
# There are large number of engg. Materials available and
many more are adding up day by day.
Д Choice of material depends upon the following factors:
1. Availability of material
2. Cost of material
3. Manufacturing considerations
4. Material properties.
13. Material Selection Process
1. Analysis of desired material
properties
2. Screening of candidate materials
3. Selection of most suitable material
14. 6. Centroid, Centre of Gravity and Moment of
Inertia:
Difference between centre of gravity and centroid.
Determination of position of centroid of plane geometric
figures of I, U, H, L, T, C, Circular and Triangular Sections.
Centroid of Composite Areas. Determination of position of
Centre of Gravity (CG) of regular solids viz. Right Circular
Cone, Solid Hemisphere, thin Hollow Hemisphere. Area
moment of inertia & mass moment of inertia, Polar moment of
inertia, Parallel axes Theorem (or transfer formula),
Perpendicular axes Theorem, Radius of gyration,
determination of area Moment of Inertia of I, U, H, L, T, C,
Circular and Triangular Sections along various axes. Mass
moment of Inertia of Circular Ring, Disc, Cylinder, Sphere and
Cone about their axis of symmetry and other axes.
