Purpose
The reinforced concrete
members, mild steel bars are used to resist tension. Tensile strength of bar
depends on the composition of the ingrediants. The results obtained through
test are useful while designing member and also for checking quality of bars
used in construction.
Objectives
1. To
observe behavior of mild steel on gradual axial tension.
2. To plot
and interpret the stress strain graph.
3. To
calculate various physical properties.
Reference
The test will be carried out as
per I.S. 1608 and results will be compared with I.S. 432 part-I
Apparatus
Universal testing machine with
tension grips, externsometer, vernier calipers, round bar specimen having 40
times diameter
The following physical
properties are determined
1. Elastic
limit
2. Yield
stress
3. Ultimate
stress
4. Breaking
stress
5. Percent
elongation
When the specimen is subject to
an axial load, it undergoes the deformation per unit length is known as strain
and intensity of internal resistance as strain and intensity of internal
resistance as stress. The material regains its original shape after removal of
load if it is loaded within elastic limit. The ratio of stress to strain is
constant within elastic limit and is known as modulus of elasticity.
Stress = б = load / original cross – section area
Strain = e = change in length / original length
Young’s modulus = stress / strain
Percentage elongation of material gives
certain measure of ductility and it is measured on standard gauge length.
Standard gauge length is taken as 5.65 (root of 50) where 50 is cross sectional area round
bars the gauge length is 5 times the diameter.
Diagram
Instruction
·
Mark the specimen by a punch with interval of 10
mm.
·
This marking should before the full length
between two grips.
·
The distance between two grips shall be 10 times
diameter.
·
Measure the diameter of given bar with the help
of vernier calliper.
·
Observe the adjusted loading range and note down
the same.
·
The zero is adjusted in load dial after switching
the machine on and then the machine is switched off.
·
Fix the specimen between the grips.
·
Adjust the gauge length on extensometer and fix
the same on middle portion of the bar. Note down the gauge length adjust the
zero of extensometer and zero of measuring device fixed on machine.
· Switch on the machine. Take the extensometer
readings for given interval of loading and record the same in observation
table.
· Observe the hesitation in the movement of
indicator on load dial and the indicator will move some what to and fro record
upper load and lower load at this movement. That gives upper yield point and
lower yield point respectively.
· Simultaneously observe now the extensometer is
showing rapid change in extension at constant loading. This shows, that specimen
has external in plastic range. Remove the extensometer.
· Record further extension on extension measuring
device fixed on machine. The stage from plastic range to ultimate load is known
as the strain hardening stage.
·
Observe neck formation of ultimate load and
observe how the main indicator is coming back.
·
Record breaking load switch OFF the machine.
·
Adjust the cup and cone by rejoining broken
pieces and find out final gauge length measure final diameter of fracture.
·
If the fracture is near the grip, the test is to
be repeated.
1. Least
count of extensometer.
2. Actual
diameter of specimen.
3. Gauge
length.
4. Initial
length.
5. Final
length.
According to I.S. 432 (part I)
the yield stress ultimate stress for bars upto 20 mm us yielding stress,
ultimate stress.
Percentage elongation for bars
upto 10 mm is – 25%
The stress as performed are
Yield stress = 29.11 N/mm2
Ultimate stress = 34.30 N/mm2
Percentage elongation = 6.19 %
The obtain value are more than
the standard values hence the specimen is good quality.
Observation table
δɻ
|
Load
|
Strain
|
Stress
(N/mm2)
|
1mm
|
520
|
1.76-3
|
51.8
|
2mm
|
760
|
3.5-3
|
76.7
|
3mm
|
1200
|
5.3-3
|
119.6
|
4mm
|
1720
|
7.07-3
|
171.5
|
5mm
|
2280
|
8.8-3
|
227.3
|
6mm
|
2840
|
10.61-3
|
283.2
|
7mm
|
2880
|
12.3-3
|
287.1
|
8mm
|
2900
|
14.15-3
|
291.1
|
9mm
|
2920
|
15.9-3
|
295.1
|
10mm
|
2920
|
17.6-3
|
295.1
|
11mm
|
2920
|
17.46-3
|
311.1
|
12mm
|
2960
|
21.2-3
|
319.0
|
13mm
|
3100
|
21.2-3
|
329.0
|
14mm
|
3200
|
23-3
|
323.0
|
15mm
|
3240
|
24.9-3
|
331.0
|
16mm
|
3320
|
26.5-3
|
331.0
|
17mm
|
3400
|
28.3-3
|
331.0
|
18mm
|
3460
|
30-3
|
343.0
|
19mm
|
3520
|
31.8-3
|
348.0
|
20mm
|
3580
|
33.62-3
|
351.0
|
21mm
|
3620
|
35.16-3
|
360.5
|
22mm
|
3660
|
37.16-3
|
364.6
|
23mm
|
3680
|
38.92-3
|
364.6
|
24mm
|
3720
|
40.70-3
|
366.9
|
25mm
|
3740
|
42.49-3
|
370.9
|
26mm
|
3780
|
44.42-3
|
372.9
|
27mm
|
3800
|
46.6-3
|
376.9
|
28mm
|
3820
|
47.78-3
|
378.9
|
29mm
|
3840
|
49.65-3
|
380.9
|
30mm
|
3860
|
51.22-3
|
382.9
|
31mm
|
3880
|
52.09-3
|
384.9
|
32mm
|
3820
|
54.80-3
|
384.9
|
33mm
|
3840
|
58.40-3
|
386.9
|
34mm
|
3920
|
60.17-3
|
390.9
|
35mm
|
3940
|
61.94-3
|
392.8
|
Observation
1. Least
count of extensometer
2. Actual
diameter at specimen = 1.139 cm
3. Gauge
length
Initial
length = 56.5 cm
Final
length = 60 cm
Acc to
I.S. 432 the yield stress ultimate stress for bar upto 20 mm
Yield
stress = 29.11 N/mm2
Ultimate
stress = 34.30 N/mm2
Percentage
elongation for bars upto 10mm to 25 %
The
stresses performed
1. Yield
stresses = 29.11 N/mm2
2. Ultimate
stresses = 34.30 N/mm2
3. Percent
of elongation 6.19 %
Result
The obtained values are more
than specified value. Hence the materials of good quality.
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