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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