Structural mechanics (CE-312)
Practical
Dr. Umbreen-Us-Sahar
Assistant Professor
Department of Civil Engineering
University of Engineering and Technology
1
EXPERIMENT # 1
To Perform Uni-axial Tension Test (BS 4449-1997,
BS 4461-1978, ASTM 615 ) on
1.Hot rolled deformed steel bar
2.Cold twisted Deformed steel bar
3. Cast iron
OBJECTIVES
1. To study uni-axial stress-strain behavior of steel bars
2. To check adequacy of specimens according to British
standards
3. To determine different mechanical properties of steel
bars . e.g., yield strength, tensile strength, modulus of
elasticity, ductility etc.
APPARATUS
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200 Tons Shimadzu Universal Testing Machine (UTM)
Extensometer.
Spring divider
Vernier caliper
Weighing balance
Steel tap
Gauge marking tools
STEEL
Steel is a metal alloy which is mainly composed of ion and
carbon.
IRON ORES
There are four main iron ores:
1. Magnetite (Fe3O4, 72.4% Fe)
2. Hematite (Fe2O3, 69.9% Fe)
3. Iron Pyrite (Fe S2, 45% Fe)
4. Siderite ( FeCO3, 40 % Fe)
Manufacturing of Steel
1. Oxides of iron + flux
2. Pig iron + Admixture
Coke 2300 0C
Pig iron +water
Steel (Molten form)
Billets/Ingots
An ingot is a piece of relatively pure material,
usually metal, that is cast into a shape suitable for further
processing.
75 x75 mm for Grade 40
100X100 mm for Grade 60
Classification of Steel
Classification of steel mainly depends on percentage of
carbon contents
1. Low carbon steel
0.05% to 0.29%
2. Medium carbon steel
0.30% to 0.59%
3. High carbon steel
0.60% to 0.99%
4. Ultra-High Carbon steel
1% to 2%
5. Mild steel
0.16% to 0.29%
Chemical composition of Mild steel
Various ingredients in steel and their functions
Heat treatment
Effect of change C on Mechanical Properties of steel
1)Decreases the ductility of steel.
2) Increases the tensile strength of steel
3) Increases the hardness of steel.
4) Decreases the ease with which steel can be machined.
5) Lowers the melting point of steel.
6) Makes steel easier to harden with heat treatments.
7) Lowers the temperature required to heat treat steel.
8) Increases the difficulty of welding steel.
After L.H. Van Vlack 1989
Mechanical properties of steel
1) Tensile strength
It is the maximum stress that a material can withstand while
being stretched or pulled before failing or breaking.
2) Hardness
This is the property of material that enable to resist plastic
deformation, usually by penetration.
Scratch hardness, Indentation hardness, Rebound hardness.
3)Ductility
This is a mechanical property indicating the extent to which
material can be deformed plastically without fracture.
Final strain < 5% -------Ductile material
Final Strain ≥ 5%-------- Brittle material
A typical Stress-Strain Curve for Mild Steel
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P.L
E.L
U.Y.P
L.Y.P
US
N.R.S
A.R.S
E
Modulus of Resilience
It is the amount of work done/energy absorbed per unit
volume of material as simple tensile force is increased from
zero to proportionality limit.
It is calculated as the area under the stress-strain curve from
0 to PL.
Modulus of Toughness
It is the amount of work done/energy absorbed per unit
volume of material as simple tensile force is increased from
zero to nominal rupture strength (failure).
It is calculated as the total area under the stress-strain curve.
% age elongation
The change in length per unit original length, expressed in
% age is called as % age elongation.
% age elongation =( Lf-Lo/Lo) x100
% Reduction in Cross sectional Area
The reduction in cross-sectional area per unit original area,
expressed in % age is called as % age reduction in x.sec
area.
% age reduction in area =( Af-Ao/Ao) x100
Gauge length (already discussed)
Tolerance on diameter/size
The change in length per unit original length, expressed in
% age is called as % age elongation.
% age difference in size =
( Standard dia-Actual dia/Standard dia) x100
Tolerance on M/L ratio
% age difference in M/L ratio =
( Standard M/L – Actual M/L/Standard M/L) x100
Standard values take from codes
Methods of finding Yield point
1. Halting of machine/drop of beam method
Mainly used for G-40 as yielding zone is greater as
compared to G-60.
2. Offset method
This method is used for the materials that don’t have
well-defined yield point. In this method a line is to be
drawn parallel to the initial tangent of the stress-strain
diagram at an offset of 0.2% strain.
Methods of finding Yield point
3. Specific strain method
According to this method, the yielding occurs at 0.5%
strain, i.e., yield stress (proof stress) is stress
corresponding to 0.5% strain.
Proof stress: It is the stress corresponding to yield strength
of material having no clear indication of yield point and
yield point is determined from graphical solutions of
stress-strain curve.
4. Luder line method
According to this method, yielding occurs when smaller
pieces of material (rust, chalk marking etc) fall off from
the specimen.
Cold formed/worked/twisted steel
By applying a pre-calculated twist to hot rolled deformed
steel, yielding portion is eliminated from stress-strain
diagram. A permanent set is provided in the material after
normal temperature.
Commercial name: Tor steel
The full strength of this steel can be utilized.
Failure is sudden as no yielding.
Cast Iron
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Carbon content varies from 2%-4.5%
It has coarse crystalline structure
It is brittle material
It can not be welded at normal temperature.
It does not rust.
Cast iron is not used in construction industry. It is used
for rain water pipes, manhole covers etc.