Title of Experiment: TENSILE TESTING (UNIVERSAL TESTER)Course
and Course Code: MECHANICS AND MATERIALS LAB (MEMB221)Semester and
Academy Year : SEM 1 2015/2016Day and Date ofExperiment Performed:
17th JUNE 2015Due Date: 22ND JUNE 2015Group Members: 1. RAJKUMAR
BALAKRISHNAN (ME093045) 2. KIRIBANATH GANESH (ME093041) 3.
SURENDERAN LOGAN (ME093015) 4. ANANTHAKUMAR MARIAPPAN (ME093037) 5.
DIVEYAA GOVINDARAJU (ME093023)Section and Group Number: SECTION 06
, GROUP 01Instructor Name: NURASLINDA BINTI ANUAR
TABLE OF CONTENT
CONTENT PAGES
Summary/ Abstract
Objective
Theory
Description of Apparatus
Procedure
Observations
Analysis and Results
Discussions
Conclusions
References
Appendices
SUMMARY
The objective of this experiment is to understand the principles
of tensile testing. Besides to investigate stress-strain
relationship of two types of materials specimens under a tensile
test. Materials that been investigated are aluminum and brass. By
doing the tensile test, we can determine the elongation at
fracture, tensile strength, yield strength and modulus of
elasticity. This experiment is used to determine the materials
properties and is used in very wide range of industries.
The experimental procedures are then followed. Readings of
elongation and its corresponding force are taken and tabulated. The
stress-strain values are calculated and a graph of load against
elongation is plotted. From this graph, the mechanical properties
such as modulus of elasticity, yield strength, tensile strength and
elongation at fracture are determined.
THEORY
If a load is static or changed relatively slowly with time and
is applied uniformly over a cross section /surface of a member, the
mechanical behaviour may be ascertained by a simple stress-strain
test. These tests are most commonly conducted for metals at room
temperature. There are three principal ways in which the load may
be applied: tension, compression and shear. Tension is one of the
most common mechanical stress-strain tests. The stress-strain
diagram shows the different behaviour of the individual materials
particularly clearly. Each material has a characteristic pattern of
stress and strain. A standard specimen is deformed, usually to
fracture with a gradually increasing tensile load that is applied
uniaxially along the long axis of a specimen. Most of the tension
tests for metals are conducted according to the ASTM Standard E 8
and E 8M, Standard Test Methods for Tension Testing of Metallic
Materials.
a) Fundamental Principles of the Tensile Test
Figure 1
The tensile test is the best known test in material testing. It
determines tensile strength, one of the most important properties
of material. Furthermore, it is also possible to determine
elongation at fracture as a toughness measurement of the
material.
In the tensile test, a mono-axial stress is generated in a
material sample. This stress is included via external loading of
the sample in a longitudinal direction via a tensile force. There
is then an even distribution of direct stress in the test
cross-section of the sample. (Figure 1)
In order to determine the strength of the material, loading of
the sample is slowly and continuously increased until it fails. The
maximum test force occurring is a measurement of the strength of
the material. The so-called tensile strength, RM is calculated from
the maximum test force, FB and the initial cross-section area, A0
of the sample:-
The simplest way to of determining the maximum test force is via
the maximum pointer on the force display. In the tensile test
itself, the cross-section of the sample is reduced it is
constricted and the actual stresses are considerably higher.
The elongation at fracture, A refers to the change in length of
the sample compared with its original length, L0 and is calculated
using the length, LU of the sample after fracture:-
In order to measure the lengths, two measuring marks are applied
to the test bar. After fracture, two ends of the sample are placed
together neatly at the fracture point and the distance between the
two measuring marks is measured.
b) Fundamental Principles of Stress-Strain Diagram
Figure 2
The stress-strain diagram (Figure 2) shows the different
behaviour of the individual materials particularly clearly. Each
material has a characteristic pattern of stress and strain.
Important material data can be read from the stress-strain
diagram. In addition to tensile strength, RM, the limit
proportionality, RP is particularly interesting. Beneath this
limit, the material conforms to Hookes Law with the Modulus of
Elasticity, E: Strain, is proportional to stress, :-
When this stress is exceeded, deformation is no longer
proportional to the load.
One particular important parameter from technical point of view
is the yield point, RE. From this point onwards, the material
becomes continuously plastically deformed. Deformation remains when
load is relieved. To safeguard the function of the component, it
should not be loaded any further.
With some materials, such as annealed soft steel, pronounced
creeping occurs from the yield onwards. The sample is elongated
without the load being increased further. In materials without
pronounced creeping, the proof stress Rp0.2 is specified. In such a
case, the material has a permanent elongation of 0.2% which remains
after relief of the loadThe diagram (Figure 3) shows the curves of
mild steel and an aluminium alloy.
Figure 3
The mild steel ruptures virtually without plastic deformation
but has a very high tensile strength .In the aluminium alloy, the
stress-strain curve rises less steeply in the elastic zone than the
other steel materials because of the lower modulus of
elasticity.
Figure 4
The stress-strain diagram (Figure 4) is produced from the values
for force and the elongation recorded during the tensile test.
And
Alternatively, the load extension diagram may be drawn directly
for pre-determined sample dimensions. In such a case, the
characteristic remain unaltered, but the time-consuming conversion
of measurements into strain and stress is unnecessary.
Poissons Ration
Poissons ration is defined as Wherex = the strain perpendicular
to the tensile axisz = the longitudinal strain
In general increases during the run, starting about 0.3 in the
elastic region and about 0.5 after the material begins to deform
plastically.
PROCEDURE
Set up test device as following:
1. The hand wheel on the master cylinder is untwisted as far as
it will go and the load frame is moved down to its lowest
position.1. The gripping heads in the upper cross-member and
cross-head is inserted.1. The gripping heads is screwed down with
the short bolt at the bottom and with pressure pad. 1. Gripping
head with the long bolt is screwed at the top 1. The required
tensile sample is inserted. 1. The test length LO of the sample is
measured and noted down between two marks. 1. The sample is screwed
by hand into the lower gripping head as far as the end stop. 1. The
sample is screwed into the upper gripping head as far as the end
stop, by rotating the gripping head itself. 1. The nut on the upper
gripping head is tighten by hand until he gripping head is seated
without slack in the upper cross-member. 1. The dial gauge is
adjusted1. The dial gauge is pushed upwards on the support bar
until the tracer pin is touching the drive.1. The rotating scale on
the dial gauge is set to zero.1. The maximum pointer on the force
display is set to zero.
Experimental steps
1. Slowly and constantly loaded by rotating the hand wheel.1.
Application of the force should spread over a time interval of 5-10
minutes.1. It is important to avoid sudden, jerky force
application.1. Observe the dial gauge and the sample. 1. Read the
force from the display every 0.1 mm and make note of it with the
corresponding extension. From 1 mm extension the reading interval
can be extended to 0.2 mm.1. Monitor the sample and note when
constriction begins. From now on, the force will no longer
increase, but instead will tend to decrease.1. ATTENTION: Do not be
startled. Particularly with some material, fracture will occur with
a loud bang.1. Read the maximum test force from the maximum pointer
and make note of it.1. Remove the sample from the gripping heads.1.
Twist back the hand wheel on the master cylinder as far as it will
go and move the load frame down.1. Repeat the same procedures with
the other specimen.
Data and ObservationData collected for the elongation of the
aluminum specimen
Extension(mm)Force (kN)
0.10
0.20
0.30.1
0.40.2
0.50.3
0.60.4
0.70.5
0.80.6
0.90.8
11
1.21.4
1.41.8
1.62.2
1.82.6
23
2.23.5
2.44
2.64.5
2.85
35.5
3.26
3.46.5
3.66.8
3.87.2
47.4
4.27.5
4.47.6
4.67.7
4.87.8
57.8
5.27.8
5.47.8
5.67.8
5.87.8
67.8
6.27.8
6.47.8
6.67.8
6.87.8
77.8
7.27.8
7.47.8
7.67.8
7.87.8
87.8
8.27.8
8.47.8
8.67.9
8.87.9
97.9
9.27.9
9.47.9
9.67.9
9.87.9
107.9
10.27.9
10.48
10.68
10.88
118
11.28
11.48
11.68
11.88
128
12.28
12.48
12.68
12.88
138
13.28
13.48.1
13.68.1
13.88.1
148.1
14.28.1
14.48.1
14.68.1
14.88.1
158.1
15.28.1
15.48.1
15.68.1
15.88.1
168.1
16.28.1
16.48.1
16.68.1
16.88.1
178.1
17.28.1
17.48.1
17.68.1
17.88.1
188.1
18.28.2
18.48.2
18.68.2
18.88.3
198.3
19.28.3
19.48.3
19.68.4
19.88.4
208.5
20.28.5
20.48.5
20.68.5
20.88.5
218.5
21.28.5
21.48.5
21.68.5
21.88.5
228.5
22.28.5
22.48.5
22.68.5
22.88.5
238.5
23.28.5
23.48.5
23.68.5
23.88.5
248.5
24.28.5
24.48.5
24.68.5
24.88.5
258.5
25.28.5
25.48.5
25.68.5
25.88.5
268.5
26.28.5
26.48.5
26.68.5
26.88.5
278.5
27.28.5
27.48.5
27.68.5
27.88.6
288.6
28.28.6
28.48.6
28.68.6
28.88.6
298.6
29.28.6
29.48.6
29.68.6
29.88.6
308.7
30.28.7
30.48.7
30.68.7
30.88.7
318.7
31.28.7
31.48.7
31.68.7
31.88.7
328.7
32.28.7
32.48.7
32.68.7
32.88.7
338.7
33.28.7
33.48.7
33.68.7
33.88.7
348.7
34.28.7
34.48.7
34.68.7
34.88.7
358.7
35.28.7
35.48.7
35.68.7
35.88.7
368.7
36.28.7
36.48.7
36.68.6
36.88.6
378.6
37.28.6
37.48.6
37.68.6
37.88.6
388.6
38.28.6
38.48.6
38.68.6
38.88.6
398.6
39.28.6
39.48.6
39.68.6
39.88.6
408.6
40.28.6
40.48.6
40.68.6
40.88.6
418.6
41.28.6
41.48.6
41.68.6
41.88.6
428.6
42.28.6
42.48.6
42.68.6
42.88.6
438.5
43.28.5
43.48.5
43.68.5
43.88.5
448.5
44.28.5
44.48.4
44.68.4
44.88.4
458.4
45.28.4
45.48.4
45.68.4
45.88.4
468.4
46.28.4
46.48.3
46.68.3
46.88.3
478.3
47.28.3
47.48.3
47.68.2
47.88.2
488.2
48.28.1
48.48.1
48.68.1
48.88
498
49.28
49.48
49.68
49.87.8
507.8
50.27.8
50.47.8
50.67.8
50.87.6
517.6
51.27.6
51.47.6
51.67.5
51.87.5
527.5
52.27.5
52.47.4
52.67.4
52.87.4
537.4
53.27.4
53.47.2
53.67.2
53.87.2
547.2
54.27.2
54.47.2
54.67.2
54.87
557
55.27
55.47
55.67
55.87
566.7
56.26.7
56.46.7
56.66.7
56.86.7
576.7
57.26.7
57.46.7
57.66.5
57.86.5
586.5
58.26.2
58.46.2
58.66.2
58.86.2
596.2
59.26.2
59.46
59.66
59.8
Data collected for the elongation of the brass specimen
Extension(mm)Force (kN)
0.10.1
0.20.2
0.30.4
0.40.5
0.50.8
0.61
0.71.3
0.81.5
0.91.7
11.9
1.22.4
1.42.9
1.63.4
1.83.9
24.4
2.25
2.45.5
2.66
2.86.5
37
3.27.5
3.47.9
3.68.1
3.88.4
48.6
4.28.8
4.48.9
4.69
4.89.05
59.1
5.29.1
5.49.1
5.69.1
5.89.1
69
6.29
6.49
6.69
6.89
79
7.29
7.49
7.69
7.89
89
8.29
8.49
8.69
8.89
99
9.29
9.49
9.69.2
9.89.2
109.2
10.29.2
10.49.2
10.69.2
10.89.2
119.2
11.29.2
11.49.2
11.69.2
11.89.2
129.2
12.29.2
12.49.2
12.69.1
12.89.1
139.1
13.29.1
13.49.1
13.69.1
13.89.1
149.1
14.29.1
14.49
14.69
14.89
159
15.29
15.49
15.69
15.89
169
16.29
16.49
16.69
16.89
179
17.29
17.49
17.69
17.89
188.9
18.28.9
18.48.9
18.68.8
18.88.8
198.8
19.28.8
19.48.6
19.68.6
19.88.6
208.6
20.28.6
20.48.6
20.68.6
20.88.6
218.6
21.28.6
21.48.6
21.68.6
21.88.6
228.6
22.28.5
22.48.5
22.68.5
22.88.5
238.5
23.28.5
23.48.5
23.68.5
23.88.5
248.5
24.28.5
24.48.5
24.68.5
24.88.5
258.5
25.28.5
25.48.5
25.68.5
25.88.5
268.5
26.28.5
26.48.5
26.68.5
26.88.5
278.5
27.28.5
27.48.5
27.68.5
27.88.5
288.5
28.28.4
28.48.4
28.68.4
28.88.3
298.3
29.28.3
29.48.2
29.68.2
29.88.2
308.2
30.28.2
30.48.2
30.68.2
30.88.1
318.1
31.28.1
31.48.1
31.68.1
31.88.1
328.1
32.28.1
32.48.1
32.68.1
32.88.1
338
33.28
33.48
33.68
33.88
348
34.28
34.47.9
34.67.9
34.87.9
357.8
35.27.8
35.47.7
35.67.7
35.87.7
367.6
36.27.6
36.47.6
36.67.6
36.87.6
377.6
37.27.5
37.47.5
37.67.5
37.87.4
387.4
38.27.4
38.47.3
38.67.3
38.87.2
397.2
39.27.1
39.47.1
39.67.1
39.87.2
407
40.26.9
40.46.9
40.66.8
40.86.7
416.6
41.26.6
41.46.6
41.66.6
41.86.6
426.5
42.26.5
42.46.4
42.66.4
42.86.3
436.3
43.26.2
43.46.2
43.66.2
43.86.1
446.1
44.26.1
44.46.1
44.66.1
44.86.1
456
45.26
45.4
Observations:
For the brass specimen, when the specimen was about to rupture,
there was a necking phenomenon which occurred. The specimen did not
break with a loud sound. Whereas for the aluminum specimen, there
was little necking and the specimen made a loud bang sound when the
specimen ruptured.
Analysis
Below are the graphs of the force applied versus the extension
of the metal.
Graph 1: Stress Strain Diagram for the Aluminum Specimen
Graph 2: Stress Strain Diagram for the Brass Specimen
Calculations:
307699556.6 Pa
285981538.4 Pa