Transcript Engineering Materials - USM :: Universiti Sains Malaysia

Engineering materials
Metal / Metallic materials
Generally classified as ferrous and nonferrous
Ferrous materials consist of steel and cast iron
Eg. Carbon steel, high alloy steel, stainless steel
Nonferrous materials consist of the rest of the
metals and alloys
Eg. Aluminum, magnesium, titanium & their
alloys
Materials from each group are further classified and
given certain designation according to the ASTM
standard
Engineering materials
Each has their own unique number/code that
represent main alloying elements, cast or wrought
and in case of plain carbon – amount of carbon.
Steel can be classified or grouped according to some
common characteristic.
The most common classification is by their
i. Composition
Example : 10xx, 15xx
ii. Strength
Most common material used in construction
of structure such as bridge, building and ships
Engineering materials
Low yield strength, less < 40 psi
Eg : A36 – Carbon steel plates, bars and shapes
High strength, between 40 psi and 120 psi
Eg. A440- Carbon steel plates, bars and shapes of
high tensile strength
Ultra-high strength > 200 psi
iii. Product shape, finish processing and quality
descriptors
Typical product classification of flat hot-rolled
carbon & low alloy steel
According to the thickness and width
Engineering materials
For ‘shape’ product forms
eg. I beam and special shapes ( designed for specific
application ), bar ( also included round, squares,
hexagon in cross section )
Finishing process
The last processing that the steel undergone.
The mot common are hot-rolled, cold—rolled or
cold finished, annealed, normalized, quenched and
tempered, coating process.
Engineering materials
Design and selection for metals
One of the major issues for structural components is
deflection under service load.
A function of the applied forces and geometry, and also
stiffness of material.
So suitable material and design are needed.
Load carrying capacity of component can be related to
the yield strength, fatigue strength or creep strength
depending on loading & service condition.
All are structure sensitive.
Changed, chemical composition of the alloy, method and
condition of manufacturing, as well as heat treatment
Engineering materials
Electrical & thermal conductivities
Thermal conductivity, K
Is measure of the rate at which heat is trnasfered through a
material
Q
T
k
A
x
Manufacture of component where electrical
conductivity is primary requirement
Al & Co
Corrosion resistance & specific gravity limits the
materials.
Engineering materials
Manufacturing consideration
Wrought m/str usu stronger and more ductile than cast.
Precision / size tolerances, surface finish, heat treatment
– stress relief etc., other secondary treatment &
finishing.
Weldability – a function of material composition. So
structure involve welding of the components need to
consider. Also for other joining means.
Machinability – improvement by heat treatment or
alloying elements.
Economic aspects - perform function at lowest cost.
Engineering materials
Design for polymer
Polymer – low density, good thermal & electrical insulation, high
resistance to most chemicals and ability to take colours and
opacities.
But if unreinforced bulk polymer are mechanically weaker, lower
elastic moduli & high thermal expansion coefficients.
Improvement – Reinforced variety of fibrous materials
Composites (PMC).
Advantages : ease of manufacturing & versatility.
Can manufacture into complicated shapes in one step with
little need for further processing or surface treatment.
Engineering materials
Versatility : ability to produce accurate component, with
excellent surface finish and attractive color, at low cost and
high speed
Basic manufacturing processes for polymer parts are extrusion,
molding, casting and forming of sheet.
Thermoset & thermoplastic
Differ in the degree of their inter-molecular bonding
Rubber are similar to plastic in structure and the difference is
largely based on the degree of extensibility or stretching.
Design : avoid limitations, must remember that strength &
stiffness vary with T, many have low impact strength, i.e brittle
so avoid stress raisers.
Engineering materials
Design consideration for polymer
Structural part
When the parts is to carry load
Should remember the strength and stiffness of
plastics vary with temperature.
Long term properties
Eg. Creep behavior
Stress raiser
Engineering materials
Design for ceramics
Ceramics – inorganic compounds of one or more metals with a
nonmetallic element. Eg Al2O3, SiC, Si2N3.
Crystal structure of ceramic are complex
They accommodate more than one element of widely
different atomic size.
The interatomic forces generally alternate between ionic &
covalent.
usually heat & electrical insulators.
Strong ionic & covalent bonds give high hardness, stiffness &
stability (thermal & hostile env.).
(1) Amorphous or glass, (2) crystalline (arrange) & (3) crystalline
bonded by glassy matrix.
Engineering materials
Whitewares, glass, refractories, structural clay products &
enamels.
Disadvantages
Brittleness, low mechanical & thermal shock
Design consideration for ceramics
Sensitive to stress concentration
Avoid stress raiser during design.
Dimensional change take place during drying and firing, should
be consider
Large flat surface can cause wrapping
Large changes in thickness of product can lead to nonuniform
drying and cracking.
Engineering materials
Design for composite
A composite material can be broadly defined as an assembly two
or more chemically distinct material, having distinct interface
between them and acting to produce desired set of properties
Composites – MMC, PMC & CMC.
The composite constituent divided into two
Matrix
Structural constituent / reinforcement
Properties / behavior depends on properties, size & distribution,
volume fraction & shape of the constituents, & the nature and
strength of bond between constituents.
Engineering materials
Mostly developed to improve mechanical properties i.e strength,
stiffness, creep resistance & toughness.
Three type of composite
(1) Dispersion-strengthened, (2) Reinforcement – continuous
& discontinuous (3) Laminated.
Designing with composite
A composite materials usually are more expensive on a cost.
Important factors when designing with composite materials is
that their high strength are obtained only as a result of large
elastics strains in the fiber
Fatigue behavior at low stress level because fibrous composites
may have many crack, which can be growing and propagate
through the matrix