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Tensile test Report:Khurshidanjum Pathan, group (A1a)

Abstract:The purpose of tensile test is to calculate tensile strength; percentage elongation and percentage reduction of area after fracture through data analysis for Mild Steel, Copper and Aluminium by applying maximum load until it break. As a result it is possible to choose between the three different materials by the analysis and comparison of uncertainties, yield and tensile strength, ductility and stiffness. In this test sample of material to be tested is being set in tensile test machine and load being applied until it fractured and in between all the data were being recorded.

IntroductionIn this experiment specimen rod of Mild steel with diameter of 10.06 mm, copper rod with diameter of 9.94 mm, and Aluminium Alloy with diameter of 10.07 mm were tested until it fractured. In this tensile test the relevant material properties can be obtain and from the results how different materials behave under similar load can be determined. Tensile Test Machine

Clip on extensometer

Objectives

To understand how different materials behave under uniaxial tension load.

To determine the basic stress-strain response for different materials.

Determine and compare the mechanical and material properties of various materials.

Plot Stress versus Strain for steel for linear region, part of yield region, and for whole range of extension.

Calculate tensile strength, % elongation and % reduction of area after fracture for mild steel, copper and aluminium alloy. And youngs modulus, yield stress and 0.1% proof stress for mild steel. Determine the measurement errors and uncertainties.

Theory:The maximum load is the greatest load that the specimen can withstand without breaking. (12) The breaking load is the load at which the specimen breaks.(12)

The Yield Point is the first point at which permanent deformation of stressed specimen begins to take place. This is a point on the stress-strain curve at which the increase in strain is no longer proportional to the increase in stress. (13) 0.1% or 0.2% proof stress: When yield point is not easily defined based on stress-strain curve an offset yield point is arbitrary defined. The value for this is commonly set at 0.1 or 0.2% of the strain. High strength steel an aluminium alloy do not exhibit a yield point so this off set yield point is used on these kind of materials. (14) The percentage Elongation is a measurement of the deformation at the point of final fracture. % elongation is extent the specimen stretches before it fractures (12)

Where LO = Original gauge length, LU = Final length after fracture

The percentage reduction in area after fracture is measured by fracture ductility. This range from zero for brittle materials to high values (100%) for ductile material.

Where SO= Original cross section area, SU= Final area after fracture

i o Engineering Strain: = l = l o o Where, is the engineering strain lo is initial gauge length, and li is the instantaneous gauge length. (15)

l l

l

Engineering Stress:

(15)

Yield Stress is defined as a stress at which a predetermined amount of permanent deformation occurs (16). Prior to the yield point the material will deform elastically and will return to its original shape when the applied stress is removed (14) Upper Yield Stress is value of stress at the moment when first decrease in force is observed. Lower Yield Stress is taken to be yield strength when yield point elongation is observed this is the lowest value of stress at yield point. Breaking Strength is a stress required to break the material. It is measured in Newton per square millimetres of area. Tensile (yield) strength is very important value for engineering structure design. The maximum tensile load sustained by aspecimen during a tension test, divided by the original cross-sectional area. The maximum engineering stress sustained. Results are expressed in Newton per square millimetres of area. (17)

Youngs Modulus is measures of stiffness of an elastic material and is a quantity used to characterize material. It is defined as the ratio of the uniaxial stress over the uniaxial strain. It is expressed in Pascal (Kilo, Mega, and Giga). (18)

Method & Approach:

Firstly, for all of the three materials the original gauge lengths (mean diameter) were measured by taking an average with help of micrometer and we worked out the cross section area for each of the material. Lindley extensometer was being fixed to steel specimen. Then this specimen then inserted into the upper jaw of the testing machine with extensometer. Its necessary to adjust the load scale to zero at every time you record load. Engage the lower jaws of the testing machine with steel specimen. Check the functionality of the extensometer by applying a small load (1 or 2 kN). When the necking begun the extensometer was removed and the elongation of the specimen was recorder using a ruler. The load applied methodically and unhurriedly until the steel specimen fractured. The same process was applied for Copper and Aluminium Alloy specimen.

Result:Tensile strength, Breaking strength, Percentage elongation and Percentage reduction of area after fracture were tabulated from the results for Mild steel, Copper and Aluminium alloy. For Mild Steel specimen full reading were taken until it fractured see Table (1) Stress - strain graph for steel were plotted for linear region only Figure (1)

The youngs modulus was calculated with help of Figure (2) which was calculated to 211 GPa for steel. Stress Strain graph for steel for linear region and yield region were plotted see figure (2). From the same graph Yield stress of 374 MPa and 0.1% proof stress of 308 MPa were located. Figure (3) show the Stress- Strain graph for steel for the whole range of the extension. Table: 2Mild Steel 5280 0.219 8360 24.30 13 37 55.18 5.56 10.06 50 79.49 Copper 3200 0.198 4880 19.86 16 34 57.74 5.03 9.94 50 77.60 Aluminium Alloy 11200 0.351 12080 62.43 5 45 17.22 8.92 10.07 50 79.64

Breaking Load (lbs) Minimum Diameter at Fracture (inch) Maximum Load (lbs) Fractured Area (mm^2) Elongation (mm) Final length (LU) (mm) Final Cross Sectional Area (SU) (mm^2) Fractured Diameter (mm) Diameter (mm) Gauge Length (LO)(mm) Original Area (SO) (mm^2)

1 Lb (g) g (N) 1 inch (mm)

453.6 9.81 25.4

Table: 3Tensile Strength (MPa) Yield Stress (MPa) 0.1% of Proof Stress (MPa) Young's Modulus (GPa) % Elongation (LO-LU)/LO *100 (mm) % reduction In Area (SOSU)/SO*100 (mm^2) Breaking strength (MPa) Mild Steel 468 374 308 211 26 31 296 Copper 280 n/a n/a n/a 32 26 183 Aluminium 675 n/a n/a n/a 10 78 626

Breaking strength =

Tensile Strength =

Youngs modulus =

% Elongation

mm

Where LO = Original Length, LU = Final length

% reduction of area =Where SO = Original cross sectional area, SU = Final cross sectional area

Uncertainties: Tensile strength

=

Uncertainties in Tensile Strength =

=

Mild Steel,

=

=1.196

Pascal

Copper,

=

=1.589

Pascal

Aluminium Alloy,

=

=6.5923

Pascal

Mild Steel,

=

= 0.31

Copper,

=

= 0.26

Aluminium Alloy,

=

= 0.78

Mild Steel:

=0.310 N/

= (1.196

Pascal) + (0.31

=

Copper:

=0.260 N/

= (1.589

Pascal) + (0.26

=

Aluminium Alloy:

=0.78 N/

= (6.59

Pascal) + (0.78

=

Graphs

Figure (1)

Figure (2)

Figure (3)

DiscussionIn figure (1) graph the linear region of steel is elastic and where elasticity ends plasticity begins at a yield point. After a yield point the slope is steep which means Youngs modulus is high for the steel. Steel starts to plastically deform after this point until it break. Just after the ultimate tensile strength point steel is being fractured.

Comparison of tensile strength states that Aluminium Alloy has the highest tensile strength which means its strong material and cannot be easily plastically deform and require large amount of force to deform. While Mild steel has 2nd highest tensile strength and copper has lowest which means copper is soft material compared to aluminium and steel, can easily deform. In contrast steel and copper both are ductile material therefore tensile strength is relatively unimportant as too much plastic deformation takes place. Breaking Strength states how strong is material to break. Aluminium has high breaking strength while steel and copper has relatively low breaking strength which means aluminium is hard material to break in comparison of steel and copper. Percentage reduction in area show the how much area of material became thin after fracture. In which Aluminium has lowest area where thinning has undergone while copper has relatively large area. The percentage elongation states the plastic deformation before material breaks. This is used to check the ductility of a material. Mile steel and Copper are ductile material as they have relatively large % of reduction area and elongation then Aluminium therefore, when these materials are in tension it result in large plastic deformation before they fracture. While Aluminium is the other way round it is not a ductile material so it is rare for plastic deformation to take place before the fracture. Copper is weak material as it has low tensile strength and therefore it can be easily deform before fracture and it is easy to shape this material also it has high thermal and electrical conductivity therefore, used in machinery industry Steel is stiff and ductile material which can withstand