Tensile Test

Tensile Test a. DATE: 2012.02.08 b. TITLE: Tensile Test c. AIM: To investigate the tensile properties of Mild Steel and Tor Steel Specimens using Hounsfield Tensometer. It is required to determine, I.For Mild Steel 1. Yield Stress (Upper and Lower) 2. Tensile Strength 3. Limit of Proportionality 4. Percentage elongation 5. Percentage reduction in area I.For Tor Steel 1. Tensile Strength 2. Percentage elongation 3. Percentage reduction in area 4. Prof Stress at 0.2 % strain d. TESTING APPARATUS: •

Hounsfield Tensometer

•

Universal Elongation Gauge

•

Universal Reduction in area Gauge

•

Vernier Caliper

e. INTRODUCTION: Mechanical testing plays an important role in evaluating basic properties of engineering materials (Metals, Plastics and composite materials) as well as in developing new materials and in controlling the quality of materials for use in design and construction purposes. The most common type of test used to measure the properties of a material is called the Tension Test. In this test, a piece of material is pulled until it fractures. Tension test is widely used to provide basic information on the strength of materials. The major parameters that describe the stress strain curve obtained during the tension test are the tensile strength (UTS), yield strength or yield point (σy), elastic modulus (E), percent elongation (ΔL%), The reduction in area (RA%), Modules of Toughness(UT), Modules of Resilience(UR), Poisson’s ratio (ν) also can be found by the using this testing method.

f. THEORY: basic definitions of tensile properties and their mathematical representations. •

Engineering Stress: Load or force per unit area which tends to deform the specimen on which it acts. Stress (σ) = Load (N)/ Initial cross section Area(mm2)

•

Engineering Strain: The change in specimen length divided by its original length. Strain (Ɛ) = {final length (Lf) – initial length (L0)} / initial length (L0) = Elongation (∆L) / initial length (L0)

•

Ultimate Tensile Strength (UTS): maximum load a material can bear without any fracture.

•

Yield Strength: stress applied to the material at which plastic deformation starts to occur while the specimen is loaded. Yield strength = Load (kN) at Yield point / Initial cross section Area 2

(mm ) •

Young’s modules (Elastic modules): Gradient of the Stress-Strain curve in elastic region. Young’s modules = Yield Stress (σy) / Yield Strain (Ɛy)

➢ Modules of Resilience: the amount of energy (or work) stored per unit volume at the

elastic limit. Equal to the area under the elastic portion of the stress-strain curve. Modules of Resilience (UR) = 1/2 {Yield Stress (σy) . Yield Strain (Ɛy)} •

Modules of toughness: the amount of energy stored per unit volume at fracture of the material. Total area under the stress-strain curve. Modules of toughness (UT) = whole area under stress- strain curve Owning of the plastic deformation a specimen also undergoes permanent increase in length and permanent decrease in cross sectional area.

•

Percentage elongation =

increase in length

x 100

Original gauge length •

Percentage reduction in area = Maximum decrease in area x 100 Original cross sectional area

g. DATA: Shape and Elements of the standard test specimen:

(L0)

(d)

Round Tensile Test piece

Corresponding Chucks

No.

11

12

Area (in2)

1/80

1/40

h. PROCEDURE •

Measured the gauge length, Diameter of specimen using a vernier caliper.

•

Placed the specimen at zero reading of the Universal Reduction in area Gauge and closed the two arms to touch and locked. After that removed the specimen.

•

Placed the specimen on the Universal Elongation Gauge, after the cradle at the appropriate gauge length. Then moved the pivoted arm to the left until its reading is zero and lock.

•

Placed the test piece in the Hounsfield tensometer through chucks.

•

Rotated the tensometer handle gradually to applied strain until the specimen failed.

•

Noted the number of revolutions and corresponding force from the mercury column at each revolution.

•

After the specimen failed moved a broken end towards the pivot in the Universal Reduction in area Gauge (until two arms touch it) and determined the percentage reduction in area.

•

Fitted the two broken ends of the specimen and pressed against the left side by the arm of the Universal Elongation Gauge and measured the percentage elongation of the specimen.

i. CALCULATIONS:

For Mild steel No. of rev 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36

Force (Ton) 0 0.015 0.03 0.06 0.09 0.13 0.17 0.22 0.27 0.32 0.36 0.42 0.47 0.52 0.57 0.61 0.64 0.66 0.66 0.68 0.7 0.73 0.75 0.77 0.79 0.81 0.82 0.83 0.84 0.86 0.87 0.88 0.89 0.9 0.91 0.92 0.92

No. of rev 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73

Force (Ton) 0.92 0.93 0.94 0.94 0.95 0.95 0.95 0.95 0.96 0.96 0.96 0.96 0.96 0.96 0.97 0.97 0.97 0.95 0.96 0.95 0.96 0.95 0.95 0.95 0.94 0.94 0.93 0.93 0.92 0.91 0.95 0.95 0.93 0.92 0.93 0.93 0.91

No. of rev 74 75

No. of rev

Force

For Tor Steel No. of rev

Force (Ton)

Force (Ton) 0.89 0.87

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

For mild steel,

0 0 0.01 0.01 0.02 0.1 0.14 0.19 0.24 0.29 0.34 0.39 0.45 0.5 0.55 0.6 0.64 0.67 0.69 0.73 0.74 0.76 0.79 0.81 0.83 0.85 0.86 0.88 0.89 0.89 0.9 0.91 0.92

33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

(Ton) 0.92 0.92 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.93 0.93 0.93 0.93 0.93 0.9 0.9 0.9 0.89 0.87 0.85 0.85 0.84 0.82 0.8 0.79 0.78 0.77 0.76

1. Yield Stress (Upper) = 0.66 x 1000 x 9.81N

16.33 mm2

= 396.48 N mm-2 Yield Stress (Lower) = 0.65 x 1000 x 9.81N 16.33 mm2 = 390.48 N mm-2 2. Maximum Stress = 0.97 x 1000 x 9.81N

16.33 mm2

= 582.71 N mm-2 3. Failure Stress = 0.87 x 1000 x 9.81N

16.33 mm2

= 522.64 N mm-2 For Tor Steel 1. Proof Stress = 0.89 x 1000 x 9.81N

16.33 mm2

= 534.65 N mm-2 2. Maximum Stress = 0.94 x 1000 x 9.81N

16.33 mm2

= 564.69 N mm-2 3. Failure Stress = 0.76 x 1000 x 9.81N

16.33 mm2

= 456.55 N mm-2

j. RESULTS:

Mild Steel (N mm-2)

Tor Steel (N mm-2)

Yield Stress (upper)

396.48

-

Yield Stress (Lower)

390.48

-

Maximum Stress

582.71

564.69

Failure Stress

522.64

456.55

-

534.65

Parameter

Proof Stress

k. DISCUSSION: 1. Comparison of stress-strain curves of the two metals and also of other materials. 2. Application of parameters obtained from the experiment. 3. Comparison of test results and the factors causing them. 4. Significance of the stress-strain curve of Mild Steel 5. Different types of specimens. 6. Other methods of determining the same parameters. 7. Comment on the particular method of testing. 8. A method to determine Young’s Modules and proof stress using the Hounsfield Tensometer.