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Transcript of Prany Formal
LAB REPORT 1:
TENSILE TEST OF ALUMINUM 6061-T6511
Date of Lab Experiment: January 19, 2010, January 26, 2010
Date of Submission: February 2, 2010
By
_______________
Prannoy A Agarwala
Submitted to Dr. David Lanning
Department of Aeronautical Engineering
College of Engineering
In Partial Fulfillment
Of the Requirements
Of
ES321
Engineering Materials Science Lab
Spring 2010
Embry Riddle Aeronautical University
Prescott, Arizona
Al 6061 Tensile Test i
Abstract
Aluminum alloys play a critical role in structural components of aircrafts and yachts. A specimen of Aluminum 6061-T6511 has been subjected to a standardized tensile test (ASTM standards). Data such as the Young’s Modulus, Ultimate Tensile strength and a Stress-Strain curve of the tensile test is reported. The published value of the Young’s Modulus for Aluminum 6061 is 10,000ksi. Alloys can exhibit ductile and brittle failure. Ductile failure is accompanied by plastic deformation whereas brittle failure is not. Necking exhibits plastic deformation and hence occurs in materials which are ductile when subjected to stress. The first phase of the experiment involves measuring dimensions, hardness, and roughness of the specimen before and after the tensile test. The second phase of the experiment involves, investigating the fracture surface macroscopically and microscopically with the use of a stereomicroscope and a scanning electron microscope.
The values obtained from the experiment are in accordance with the published values. Phenomena such as necking, strain hardening and a change in the texture of the surface after failure are observed. The specimen exhibits a transitional ductile to brittle fracture.
This paper introduces the theoretical principles behind ductile and brittle fracture and publishes data and results related to the tensile test of the specimen of Aluminum 6061-T6511.
Al 6061 Tensile Test ii
TABLE OF CONTENTS
Abstract ………………………………………….……………………………. … i
List of Tables …..……………………………………………………………….. iii
List of Figures …..………………………………………………………………. iv
List of Graphics ….……………………………………………………………. v
List of Symbols ………………………………………………………………… vi
List of Abbreviations/Acronyms ...…………………………………………… vii
1.0 Introduction ...……………………………………………………………… 1
2.0 Theory ………………………………………………………………………. 2
3.0 Apparatus and Procedures ...……………………………………………….. 9
3.1 Apparatus .…………………………………………………………… 9
3.2 Procedures …………………………………………………………… 13
3.1.1 Phase 1……………………………………………………….. 13
3.1.2 Phase 2 ………………………………………………………. 14
4.0 Results and Discussion ……………………………………………………. 15
5.0 Conclusions and Recommendations ……………………………………….. 22
6.0 References ………………………………………………………………… 23
7.0 Appendix I: Sample Calculations ………………………………………….. 25
8.0 Appendix II: Raw Data …………………………………………………….. 26
Al 6061 Tensile Test iii
LIST OF TABLES
Table 2.1: Aluminum 6061-T651 Data Sheet ………………………………… 4
Table 4.1: Dimensional Data of Al 6061-T6511 Specimen ………………….. 16
Table 4.2: Specimen Hardness Data ………………………………………... 17
Table 4.3: Specimen Roughness Data ………………………………………. 17
Al 6061 Tensile Test iv
LIST OF FIGURES
Figure 2.1: Stress Vs. Strain Curve for a ductile material ….………………………………….. 3
Figure 2.2: Ductile Overload ………………………….……………………………………….. 6
Figure 2.3: Transition from Ductile to Brittle Fracture ….…………………………………….. 7
Figure 2.4: Ductile and Brittle Fracture ………………….…………………………………….. 7
Figure 3.1: Tensile test bar ……………………………….…………………………………….. 9
Figure 3.2: Tensile Testing Machine …………………...……………………………………... 10
Figure 3.3: Surface Roughness Tester ………………...………………………………………. 10
Figure 3.4: Rockwell Hardness Tester ………………...……………………………………… 11
Figure 3.5: Vernier Calliper …………………………...……………………………………… 11
Figure 3.6: Micrometer Screw Gage ………………...………………………………………... 12
Figure 3.7: Ultrasonic Cleaner ……………………...………………………………………… 12
Figure 3.8: Stereomicroscope ……………………...…………………………………………. 12
Figure 3.9: Scanning Electron Microscope …...……………………………………………… 13
Figure 4.1: Stress vs Strain Plot ……………..………………………………………………. 15
Figure 4.2: Plot to find Young’s Modulus ……...……………………………………………. 16
Figure 4.3: Stereomicroscope Image 1, Necking …..………………………………………… 18
Figure 4.4: Fracture surface under stereomicroscope …..……………………………………. 19
Figure 4.5: Fracture surface under Scanning Electron Microscope -Al 6061-T651…...……... 19
Figure 4.6: Fracture surface under SEM (2500x) ………………………………..………….. 20
Figure 4.7: Backscatter image of fracture surface using SEM ………………..……………... 21
Al 6061 Tensile Test v
LIST OF GRAPHICS
Figure 2.1: Stress Vs. Strain Curve for a ductile material ………………..…………………… 3
Table 2.1: Aluminum 6061-T651 Data Sheet ……………………………..………………….. 4
Figure 2.2: Ductile Overload ……………………………………………….…………………. 6
Figure 2.3: Transition from Ductile to Brittle Fracture …………………….…………………. 7
Figure 2.4: Ductile and Brittle Fracture …………………………………….…………………. 7
Figure 3.1: Tensile test bar ………………………………………………….…………………. 9
Figure 3.2: Tensile Testing Machine ………………………………………...………………. 10
Figure 3.3: Surface Roughness Tester ………………………………………...…………….. 10
Figure 3.4: Rockwell Hardness Tester ……………………………...……………………….. 11
Figure 3.5: Vernier Calliper ………………………………………...……………………….. 11
Figure 3.6: Micrometer Screw Gage ………………………………...………………………. 12
Figure 3.7: Ultrasonic Cleaner ……………………………………...……………………….. 12
Figure 3.8: Stereomicroscope ………………………………………..……………………… 12
Figure 3.9: Scanning Electron Microscope ………………………….……………………… 13
Figure 4.1: Stress vs Strain Plot ……………………………………………………………. 15
Figure 4.2: Plot to find Young’s Modulus …………………………………………………. 16
Table 4.1: Dimensional Data of Al 6061-T6511 Specimen ………….………………….. … 16
Table 4.2: Specimen Hardness Data ………………………………….….……………......... 17
Table 4.3: Specimen Roughness Data ………………………………….…………………… 17
Figure 4.3: Stereomicroscope Image 1, Necking ………………………..………………….. 18
Figure 4.4: Fracture surface under stereomicroscope …………………….………………… 19
Figure 4.5: Fracture surface under Scanning Electron Microscope -Al 6061-T651………….. 19
Figure 4.6: Fracture surface under SEM (2500x) ……………………………….. ………... 20
Figure 4.7: Backscatter image of fracture surface using SEM …………………… ………. 21
Al 6061 Tensile Test vi
LIST OF SYMBOLS
σ……………………………...Stress...............................................Lb/in2
ε………………………………Strain………………………………..—
ν………………………Poisson’s Ratio……………………………..—
Al 6061 Tensile Test vii
LIST OF ABBREVIATIONS/ACRONYMS
ASTM………American Society for Testing and Materials……………………--
SEM……………….Scanning Electron Microscope…………………………...--
Al 6061 Tensile Test 1
1.0 Introduction
Ever since its discovery, Aluminum has been critical to human beings. Scientists and engineers have spent decades on studying and understanding the behavior and chemistry of metals under different conditions. With time, human beings have also learnt how to create alloys, which are matrices of different metals and elements.
Alloys such as bronze and brass have been known to man since prehistoric times. Alloys have an advantage over simple elements because their composition can be adjusted based on how they are being used. Qualities such as better resistance to corrosion, improved strength, better ductility and other benefits allow alloys to be used in the production and manufacture in a number of applications today.
Alloys of aluminum are extensively used in the production of yachts, aircrafts and also for welding. Many structural components in aircraft such as the fuselage and wings use these aluminum alloys. Hence, it is critical for us to understand how these alloys behave under extreme loads and conditions.
Aluminum alloy 6061 is one such alloy that has been employed over the years for the aforementioned applications.
The purpose of this lab, then, is to subject a test specimen of Aluminum 6061-T6511 to a tensile test and record data related to the test. After fracture, the fracture surface and the region around the fracture surface is viewed under and electron microscope and a light microscope.
The results of the tensile test of Aluminum 6061-T6511 are summarized. Details such as the Modulus of Elasticity, Proportional Limit and the Ultimate Tensile Strength are reported. Also, a discussion of the fracture of the specimen is carried out.
Al 6061 Tensile Test 2
2.0 Theory
Stress(σ ¿: Stress is defined as the force experienced by an element over the cross sectional area subjected to that force. Its units are expressed as force/area, for example – pounds per square inch(psi) or Newtons per square metre(N/m2).
Strain(ε): Strain represents the elongation experienced by a material due to application of a stress. It is dimensionless or unit less.
Young’s Modulus(E): Also known as the modulus of elasticity, is defined as the ratio of the axial stress over the axial strain. The three are related by the Hooke’s Law.
Shear Modulus(G): Also known as the modulus of rigidity, is defined as the ratio of the shear stress over the shear strain.
Poisson’s ratio(ν): Defined as the ratio of the transverse strain to the axial strain experienced by a material.
Stress-Strain curve: The stress strain curve is a graphical plot, representing the stress experienced by a material on the y-axis, and the strain experienced by the material due to the stress on the x-axis.
Elastic Deformation: When the stress applied to a material is removed, the material(solid) regains its original shape.
Plastic Deformation: Is the deformation experienced by a material when it no longer behaves as an elastic material. In other words, once the stress is removed from the material, it does not regain its original shape.
Fracture: Is the point at which a material breaks into two or more pieces due to an application of stress.
Ultimate Tensile Strength: Is the maximum stress a material can experience before fracture or failure. It is the maximum stress on the stress-strain curve.
Offset Yield Strength: Is found using the stress-strain curve, and is the stress required to produce a 0.2% plastic strain.
Proportional Limit: Defined as the maximum stress at which stress is directly proportional to the strain.
Hardness: Is the property of a material to resist indentation by a hard object.
Roughness: It can be defined as the measure of the texture of a surface.
Ductility: Is the ability of a material to deform before failure.
Al 6061 Tensile Test 3
Theoretical principles:Stress exists in two forms – normal or axial stress, represented by sigma (σ), and shear stress, represented by tau (τ). Shear stresses are caused due to forces acting in the plane of the cross section while normal stresses are caused due to forces acting perpendicular to the plane of the cross section.
The Stress-Strain curve illustrated in figure 2.1 is a means of expressing stress versus strain for materials. The stress vs strain curve is distinct for each kind of material and thus, is of significant importance as it is used to express the different material properties of materials.
Figure 2.1: Stress Vs. Strain Curve for a ductile material. (Source: Interactive Nano-Visualization in Science and Engineering Education,
2010)
The Young’s Modulus is usually found by measuring the slope of the linear portion of the stress-strain curve(i.e. the elastic region). In Table 2.1 below, we see that the typical value for the Young’s Modulus for Al 6061-T651 is around 10,000ksi. The Young’s Modulus is related to stress and strain by the Hooke’s Law.
Al 6061 Tensile Test 4
Physical Properties Metric English Comments
Density 2.7 g/cc 0.0975 lb/in³
AA; Typical
Mechanical Properties
Hardness, Brinell 95 95 AA; Typical; 500 g load; 10 mm ball
Hardness, Knoop 120 120 Converted from Brinell Hardness Value
Hardness, Rockwell A 40 40 Converted from Brinell Hardness Value
Hardness, Rockwell B 60 60 Converted from Brinell Hardness Value
Hardness, Vickers 107 107 Converted from Brinell Hardness Value
Ultimate Tensile Strength
310 MPa 45000 psi AA; Typical
Tensile Yield Strength 276 MPa 40000 psi AA; Typical
Elongation at Break 12 % 12 % AA; Typical; 1/16 in. (1.6 mm) Thickness
Elongation at Break 17 % 17 % AA; Typical; 1/2 in. (12.7 mm) Diameter
Modulus of Elasticity 68.9 GPa 10000 ksi AA; Typical; Average of tension and compression. Compression modulus
is about 2% greater than tensile modulus.
Notched Tensile Strength
324 MPa 47000 psi 2.5 cm width x 0.16 cm thick side-
Al 6061 Tensile Test 5
notched specimen, Kt = 17.
Ultimate Bearing Strength
607 MPa 88000 psi Edge distance/pin diameter = 2.0
Bearing Yield Strength 386 MPa 56000 psi Edge distance/pin diameter = 2.0
Poisson's Ratio 0.33 0.33 Estimated from trends in similar Al alloys.
Fatigue Strength 96.5 MPa 14000 psi AA; 500,000,000 cycles completely reversed stress; RR Moore
machine/specimen
Fracture Toughness 29 MPa- m½
26.4 ksi-in½
KIC; TL orientation.
Machinability 50 % 50 % 0-100 Scale of Aluminum Alloys
Shear Modulus 26 GPa 3770 ksi Estimated from similar Al alloys.
Shear Strength 207 MPa 30000 psi AA; Typical
Table 2.1: Aluminum 6061-T651 Data Sheet. (Source: Aerospace Specification Metals, Inc, 2010)
Figure 2.1 illustrates the elastic region of a material. This region is the region where elastic deformation takes place. As defined earlier, it is the region where the stress and strain are directly proportional to each other. Also, on removal of the load the material regains its original shape. The elastic limit or the proportionality limit is the point where the linear relationship between stress and strain ends. It is not well defined for every material and hence is not published on data sheets, compared to say the ultimate tensile strength. The reason for elastic deformation can be attributed to chemical bonding. As a tensile load is applied to a material, the bonds stretch and when the load is removed the bonds regain their equilibrium lengths. This is true for elastic deformation only (Fischer 2009).
Plastic deformation occurs when the metal or material no longer behaves as an elastic material. Qualities such as ductility and malleability are due to the plastic deformation of metals. All materials behave very differently in the plastic region. A phenomenon known
Al 6061 Tensile Test 6
as strain hardening is experienced by metals when a tensile stress is applied. This strain hardening actually strengthens metals. This phenomenon happens because as the crystals within the metal matrix are dislocated, a resistance to further dislocations is developed resulting in the observed strengthening of the metal. Another phenomenon observed under the application of tensile stress, is necking. Necking is the reduction of cross sectional area, where a large amount of strain is localized. It occurs around the region where fracture would eventually take place. In Engineering Materials, there are two kinds of fracture which take place, ductile and brittle. The main difference between the two is the amount of plastic deformation that can be withstood. Ductile materials can withstand plastic deformation whereas brittle materials fracture rather rapidly after the elastic region. In ductile materials, crack propagation is slow and the amount of plastic deformation is large. Only when a larger stress is applied will the crack propagate. In brittle materials, crack propagation is rapid and is not accompanied by a large amount of plastic deformation. The cracks continue to grow until fracture.
Figure 2.2: Ductile Overload. (Source: Argo-Tech Materials Laboratory, 2010)
Figure 2.2 is a scanning electron microscope image captured by ATC Labs based out of Cleveland, Ohio of a ductile material after fracture. At the microscopic level, ductile surfaces appear to have a large number of voids and dimples in a very irregular manner. The presence of ductile dimples indicates a ductile overload as seen in Fig 2.2. Also, as the smaller microvoids grow, they start linking up to form voids leading to cracks which lead to fracture. In comparison, brittle fracture seems to occur due to granular fracture. There are two kinds of granular fracture, transgranular or intergranular fracture. The former is when the crack travels through the grain of the material while the latter is when the crack travels through the grain boundaries. Fig 2.3 shows a ductile to brittle fracture
Al 6061 Tensile Test 7
transition. On the right hand side of the image we notice ridges, which is nothing but granular fracture. The transition occurs due to a change in density or temperature.
Figure 2.3: Transition from Ductile to Brittle Fracture. (Source: The Hendrix Group, 2010)
When observed at a macroscopic level, ductile fracture surfaces are rough and a noticeable shear tip is seen. Usually, ductile failure occurs due to shear stress resulting in a large necking region. As seen in Fig 2.4, the fracture on the left is ductile fracture, the shear tip can be seen, as well as the rough and irregular surface. Brittle fracture on the other hand seems to be a cleaner kind of fracture where the amount of necking occurring is smaller. This is due to the fact that a large amount of plastic deformation does not occur. The surface of fracture is also smoother.
Figure 2.4: Ductile and Brittle Fracture. (Source: Charles Sturt University, 2010)
Al 6061 Tensile Test 8
The tensile test is used to determine the properties of a material. The specimen used in the test is prepared in accordance with the American Society for Testing and Materials (ASTM) standards.
The fracture surfaces are usually observed under stereomicroscopes at the macroscopic level and scanning electron microscopes at the microscopic level. The magnification produced by stereomicroscopes is in the range of 10-2000x and visible light is used to produce the image. Scanning electron microscopes (SEM) have the ability to magnify up to 300,000x. They use high-speed electron to produce an image. The lens of an SEM is electromagnetic, while that of a stereomicroscope is glass.
Expected Results:
The values published for Aluminum 6061-T651 in Table 2.1, give an idea on what value the Modulus of Elasticity, Ultimate Tensile Strength, the Proportional Limit and the yield at 0.2% strain should be for our specimen. Also, as Aluminum is a ductile metal, its alloy should exhibit ductile fracture. However, there is a possibility for the alloy to exhibit a ductile to brittle transition fracture as shown in Fig 2.3. This is because of the presence of elements such as Silicon, and Nickel in the alloy.
Equations used:
Stress is measured using the equation:
σ=ForceArea Equation 2.1
Strain is measured using the equation:
ε = change∈lengthoriginal length Equation 2.2
Young’s Modulus of Elasticity is calculated using the equation:
σ = Eε Equation 2.3
% Elongation of gage section:
% elongation= Final length−Original lengthOriginal length
× 100 % Equation
2.4
% Reduction in Area:
Al 6061 Tensile Test 9
%reduction=Original area−Final areaOriginal area
× 100 % Equation
2.5
Justification:
Aluminum alloys are of great value, due to their relatively low weight, high yield strength and their ability to withstand a relatively large amount of plastic deformation. This makes them ideal for use in structural components in the aircraft and yachts. Aluminum alloy T6061 is widely used in the fuselage and wings of aircraft.
3.0 Apparatus and Procedures:
3.1 Apparatus:
The following equipment was used during the lab: One (1) Aluminum 6061-T6511 tensile test bar, One (1) Tensile testing machine, One (1) Extensometer, One (1) sheet of 600 grit sandpaper, One (1) TR200 Surface Roughness Tester, One (1) Rockwell Hardness Tester, One (1) Vernier Calliper, One (1) Micrometer Screw Gauge, One (1) Band saw, One (1) Ultrasonic cleaner, One (1) Stereomicroscope, One (1) Scanning Electron Microscope.
The Aluminum 6061-T6511 tensile test bar is prepared according to American Society for Materials and Testing (ASTM) standards. Figure 3.1 illustrates the bar.
Al 6061 Tensile Test 10
Figure 3.1: Tensile test bar.
The tensile testing machine used is illustrated in Figure 3.2. The machine measures force in pounds. The extensometer measures extension in inches.
Figure 3.2: Tensile Testing Machine. (Source: Direct Industry, Instron, 2010)
Gage sectionGrip section
Specimen length
Gage section width
length
Al 6061 Tensile Test 11
The surface roughness tester used is illustrated in Figure 3.3. It reads measurements in micrometers.
Figure 3.3: Surface Roughness Tester. (Source: M & I Instruments, Inc, 2010)
The hardness tester used is illustrated in Figure 3.4. It gives readings in the Hardness Rockwell B scale.
Figure 3.4: Rockwell Hardness Tester. (Source: FAR Asia Co., Ltd, 2003)
The Vernier Calliper used is illustrated in Figure 3.5. The readings are taken in inches.
Al 6061 Tensile Test 12
Figure 3.5: Vernier Calliper. (Source: Painter Guitars, 2010)
The screw gage used is illustrated in Figure 3.6 on the next page. It gives readings to a thousandth of an inch.
Figure 3.6: Micrometer Screw Gage. (Source: eHow, 2010)The ultrasonic cleaner used is illustrated in Figure 3.7.
Al 6061 Tensile Test 13
Figure 3.7: Ultrasonic Cleaner. (Source: MIT, 2010)The stereomicroscope used is illustrated in Figure 3.8. The images are captured on computer.
Figure 3.8: Stereomicroscope. (Source: Nikonians, 2010)The scanning electron microscope used is illustrated in Figure 3.9. The images are captured on computer. The units is expressed in micrometers.
Al 6061 Tensile Test 14
Figure 3.9: Scanning Electron Microscope. (Source: Carleton College, 2010)
3.2 Procedures3.2.1 Phase One
The following procedures were used for Phase One of the experiment that was conducted on January 19, 2010:1.0 The surface of the tensile test bar was smoothened with sandpaper. All
large scratches were removed.2.0 The dimensions of the tensile test bar was measured and recorded
using a set of vernier callipers and a micrometer screw gage. The gage section width, thickness, length and the specimen’s length were noted.
3.0 Three roughness measurements were made across the gage section using the roughness tester. The direction in which the measurement was made was perpendicular to the loading direction. The measurements were recorded.
4.0 Three Rockwell Hardness tests were made. The load used was set to a 100 kilograms. The readings were recorded.
5.0 Two pencil marks were made on the gage section approximately 2.5 inches apart. The actual distance between the marks was then recorded.
6.0 The bar was then tensile tested, by placing the grip sections in the appropriate slots and attaching an extensometer on the gage section to measure the elongation.
Al 6061 Tensile Test 15
7.0 The data was recorded computationally. The excel spreadsheet with the tensile test data was then obtained.
8.0 Repeat step 2. Dimensions after failure were recorded.9.0 Repeat step 3. Roughness tests around the region of failure were
undertaken and the readings were recorded.10.0 Repeat step 4. The hardness tests are carried out near the region of
failure to check for the phenomenon of strain hardening.3.2.2 Phase Two
The following procedures were used for Phase Two of the experiment which was conducted on January 26, 2010:1.0 The tensile test bar is cut using a band saw. The bar is cut at
approximately 1.5 inches from the failure surface.2.0 The 1.5 inch specimen was then washed in an ultrasonic cleaner for
about 5 minutes.3.0 The failure surface was then viewed under a stereomicroscope to
observe the failure surface macroscopically to look for details such as dimples, and necking. Digital photographs were taken.
4.0 The failure surface was then viewed under a scanning electron microscope. The objective was to observe whether the specimen underwent a ductile or brittle fracture. Digital photographs of the specimen under the SEM were taken.
4.0 Results and Discussion:
Al 6061 Tensile Test 16
0.002 0.004 0.006 0.008 0.01 0.012 0.014 0.016 0.018 0.02 0.022
-10000
0
10000
20000
30000
40000
50000
60000
Stress vs Strain
Yield @ 0.2% offset
Ultimate Tensile Strength
Stre
ss
σ(ps
i)
Strain (ε)
Proportional Limit
Figure 4.1: Stress vs Strain Plot.
Figure 4.1 is the plot for the Stress vs Strain for the tensile test of Aluminum 6061-T6511. From the plot we see that there is an elastic region, a plastic region and finally fracture. The plastic region shows that the alloy does show ductility as discussed in section 2.0 of this report. Comparing the values from Figure 4.1 to the published values in Table 2.1, we observe that the Ultimate Tensile Strength calculated experimentally is close to the published value. In fact, the published value for Al 6061-T651 is 45000psi, and that obtained from the experiment is approximately 49000psi, an error of about 8.89%. The Tensile Yield Strength published in Table 2.1 is 40000psi, the offset yield strength from the experiment was about 46000psi (from Figure 4.1). Also using a straight edge, and solving for the slope of the linear portion of the curve. We find the Young’s Modulus equal to about 10000ksi, which is in agreement with published values. We notice that the strain experienced at rupture was around the 0.02, very close to published values.
Overall, the stress strain plot obtained experimentally is agreeable to published stress strain plots of Aluminum 6061.
Al 6061 Tensile Test 17
-0.0005 0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.0040
5000
10000
15000
20000
25000
30000
35000
40000
f(x) = 10350661.5459156 x + 637.71933228307Stress vs Strain
Stre
ss σ
(psi)
Strain (ε)
Figure 4.2: Plot to find Young’s Modulus.
Figure 4.2 plots the linear portion of the stress vs strain curve for the tensile test of Aluminum 6061-T6511. The equation y = 10,350,661.55x + 637.72 is the equation for the trend line of the Elastic Region of the stress strain curve. It follows that the Young’s Modulus is approximately 10,350ksi. Again, this value is in accordance with published data as shown in Table 2.1, where the Young’s Modulus is gives as 10,000ksi.
Dimensional DataDimension Type Before Failure After FailureGage Section Width 0.4963 in 0.48 inGage Section Length 2.045 in 2.155 inGage Section Thickness 0.1283 in 0.1197 inSpecimen Length 8.22 in 8.468 in
Table 4.1: Dimensional Data of Al 6061-T6511 Specimen
Table 4.1, gives the record of the measurements made of the specimen, before and after the tensile test. As expected from theory, we see that the gage section width decreased after the test; the gage section length increased after the test; the gage section thickness
Al 6061 Tensile Test 18
decreased after test and the overall specimen length increased after the test. This dimensional data shows that necking did occur in the specimen before fracture. Hence, the theoretical principles hold true for the experiment.
This dimensional data allows us to calculate the % elongation of the gage section and the %reduction in Area of the gage section. We use equation 2.4 to calculate %elongation of the gage section and find it equal to 5.38%. The data published in Table 2.1, is the percent elongation at break for a 1/16in specimen and is equal to 12%. Our specimen, is about 1/10th of an inch, and hence has a lower percent elongation at failure. We can also calculate the % reduction in area of the gage section using data from table 4.1 and making use of equation 2.5. The % reduction in area of the cross section is equal to 9.89%. This shows significant necking in the region around fracture. Again, theoretical principles is backed by experimental data.
Hardness DataSerial No. Before Failure After Failure
1 59.2 HRB 65 HRB2 61.1 HRB 65.5 HRB3 60.6 HRB 64.7 HRB
Table 4.2: Specimen Hardness Data
Table 4.2 gives the record of the hardness data calculated before and after the test. From published values of the specimen hardness in table 2.1, where hardness in the Rockwell B Scale was measured to be 60HRB, we see that our specimen for the test has similar hardness, around the 60HRB mark. After the tensile test, we see that there is significant hardening of about 4HRB around the fracture region. This, is in agreement with theory where we had discussed about the phenomenon of strain hardening. Strain hardening occurs in our test specimen.
Roughness DataSerial No. Before Failure After Failure
1 0.309 μm 1.146 μm2 0.316 μm 1.510 μm3 0.281 μm 1.509 μm
Table 4.3: Specimen Roughness Data
Table 4.3 shows the roughness data accumulated before and after failure. We notice that the surface of the specimen around the fracture region got significantly rougher after fracture. This can be explained due to dislocation of the metal matrices due to the applied
Al 6061 Tensile Test 19
stress. This dislocation of the structure caused irregularities in the material causing the surface to become significantly rougher.
Figure 4.3: Stereomicroscope Image 1, Necking.
Figure 4.3, captures the fracture surface perpendicular to the loading direction. The image is taken by a stereomicroscope. Firstly, we observe the cross sectional area of the specimen decrease near the fracture region. This decrease in area clearly indicates necking in the specimen. Secondly, we notice a shear tip on the edge. This shear tip indicates that the fracture could be ductile. However, as we observe the shear tip is not very distinct, suggesting a fracture which could be a ductile to brittle transition.
Figure 4.4, is another image of the fracture surface, in higher magnification. We notice development of ridges right next to the fracture surface, suggesting that the fracture was pretty violent. There seems to be a shear tip on the edge of the fracture surface. However, the rest of the fracture seems is not as rough as a pure ductile fracture. There seems to be an element of brittle fracture. There is also a presence of dimples on and around the fracture surface. Macroscopically the ridges can indicate a presence of granular fracture. To confirm this fracture we would have to take a look at the surface at a microscopic level using a scanning electron microscope. This is illustrated in Figure 4.5.
Al 6061 Tensile Test 20
Figure 4.4: Fracture surface under stereomicroscope.
Figure 4.5: Fracture surface under Scanning Electron Microscope -Al 6061-T651.
Al 6061 Tensile Test 21
As mentioned on the previous page, we now take a look at the fracture surface microscopically in Figure 4.5 under an SEM. The image is magnified by a 1000 times and the charge of electrons used is 13kV. At first look at the image, we notice a few distinct features, such as the presence of a ridge which resemble a rift valley at the center of the image, we also notice an irregular distribution of voids and dimples. The surface seems to be very irregular in terms of whether it is purely ductile fracture or brittle fracture. The surface seems to exhibit features of both kinds of fractures. As discussed in section 2.0, and illustrated in figures 2.2 and 2.3, the fracture seems to be a transitional ductile to brittle fracture. The size of the central rift valley is approximately 25 micrometers, using the scale of 10 micrometers as a reference. Also the voids seem to be more profound around the central rift valley. This could be due to the presence of different types of atoms. Let us take a closer look at the rift valley under a higher magnification in the next image.
Figure 4.6: Fracture surface under SEM (2500x)
In figure 4.6, we take a look at the rift valley which we spotted in figure 4.6 under higher magnification (2500x). The so called valley indicates brittle fracture in that particular region. The valley is formed due to the propagation of voids along the grain boundaries or along the grains of the material. As discussed in section 2.0, this could be intergranular or transgranular fracture. Also the presence of distinct voids around the valley, indicates the presence of ductile fracture. This transition from ductile to brittle fracture and vice versa can be attributed to the presence of different atoms in the alloy, as Al 6061 has the
Al 6061 Tensile Test 22
presence of elements like Nickel and Silicon. To confirm this theory we use the same image in Figure 4.6 and increase the charge of the electron to 20 kV, using the back scatter of electrons to produce images of particles.
Figure 4.7: Backscatter image of fracture surface using SEM.
Figure 4.7 illustrates the image captured using the backscatter of electrons to produce images of the particles present in the specimen. We also notice the presence of another rift valley indicating granular failure. The dark patches indicate the presence of dimples, which are seen in ductile fracture. As mentioned before, there is a presence of a large number of particles of different sizes and densities, leading to the transitional ductile to brittle fracture.
Overall, the achieved results were in accordance with the published values and theoretical principles. Although, the ultimate tensile strength was higher than that published. This could be attributed due to the preparation of the alloy. The slightest change in composition of the elements in the alloy can lead to significantly different results.
Al 6061 Tensile Test 23
5.0 Conclusions and Recommendations:
This lab was performed to tensile test a specimen of Aluminum 6061-T6511. The experiment was performed over two phases. The first phase involved taking dimensional, hardness and roughness data of the test specimen, and then subjecting it to a tensile test. After the tensile test, the dimensions, hardness and roughness were measured. The second phase of the lab was to inspect the fracture surface under a stereomicroscope and a scanning electron microscope to discuss the kind of fracture that took place.
The results obtained were in agreement with the published values, such as the Young’s Modulus was found to be equal to 10,350ksi, the Ultimate Tensile Strength was found to be equal to 49000psi, the Yield at 0.2% offset was found to be equal to 46000psi, and the material was found to exhibit a ductile to brittle transitional fracture. The most significant result of the tensile test was that Aluminum 6061-T6511 exhibited both ductile and brittle properties in fracture allowing it to undergo plastic deformation even though there is a presence of brittle failure.
One of the most significant limitations encountered in the lab was the pressure of time on individual groups when it came to taking images of the fracture surface under the stereo and scanning electron microscopes. This could have been overcome if groups more time was available to perform the experiment.
The presence of scratches on the surface of the specimen could have also led to a discrepancy between published and experimental values. This limitation can be overcome by ensuring the removal of scratches by the use of sandpaper.
Al 6061 Tensile Test 24
6.0 REFERENCES
Aerospace Specification Metals, Inc (2010). ASM Material Data Sheet. Retrieved January 28, 2010, from http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA6061T6
Argo-Tech Materials Laboratory. (2003). SEM Imaging. Retrieved January 28, 2010, from http://www.atclabs.com/Photos.htm
Boyer, H.E., Gall, T.L. (1985). Metals Handbook. American Society for Metals, Materials Park, OH.
Carleton College. (2010). Scanning Electron Microscopy(SEM). Retrieved January 30, 2010, from http://serc.carleton.edu/research_education/geochemsheets/techniques/SEM.html
Charles Sturt University. (n.d.). Retrieved January 28, 2010, from http://www.hsc.csu.edu.au/engineering_studies/lifting/3210/index.html
Direct Industry. (n.d.). Tensile/Compression testing machines – INSTRON. Retrieved January 29, 2010, from http://www.directindustry.com/prod/instron/tensile-compression-testing-machine-18463-41713.html
Far Asia Co., Ltd (China). (2003). Rockwell Hardness Tester. Retrieved January 29, 2010, from http://www.farasia.com.cn/products/prod0071.htm
Fischer, Traugott (2009). Materials Science for Engineering Students. Burlington, MA: Elsevier Inc.
Hendrix Group, Inc. (2004). The Hendrix Group – Ductile/Brittle Fracture. Retrieved January 29, 2010, from http://www.hghouston.com/x/50.html
Interactive Nano-Visualization in Science and Engineering Education. (n.d.). Retrieved January 27, 2010, from http://invsee.asu.edu/srinivas/stress-strain/ssgraph.jpg.
Holt, J.M. (1996). Structural Alloys Handbook. CINDAS/Purdue University, West Lafayette, IN.
Massachusetts Institute of Technology. (2010). CPRL. Retrieved January 29,2010, from http://web.mit.edu/cprl/www/other.shtml
M & I Instruments Inc. (2008). Surface Roughness Tester TR200. Retrieved January 29, 2010, from http://www.microinstruments.ca/Products/SurfaceRoughnessTesters/SurfaceRoughnessTestersTR200.htm
Al 6061 Tensile Test 25
(n.d.). Tools. Retrieved January 29, 2010, from http://www.painterguitars.com/Dave/tools.htm
Al 6061 Tensile Test 26
7.0 Appendix I: Sample Calculations
Dimensional DataDimension Type Before Failure After Failure
Gage Section Width 0.4963 in 0.48 inGage Section Length 2.045 in 2.155 inGage Section Thickness 0.1283 in 0.1197 inSpecimen Length 8.22 in 8.468 in
Cross sectional area used for computing stress = gage section width X gage section Thickness= (0.1283in)(0.4963in) = 0.0637in 2
Final Area = (0.48in)(0.1197in) = 0.0575in 2
% reduction in area = (0.0637 – 0.0575)/(0.0637) X 100 % = 9.89%
%elongation of gage section = (2.155 – 2.045)/(2.045) X 100 % = 5.38%
Al 6061 Tensile Test 27
8.0 Appendix II: Raw Data
TESTNUM
POINTNUM TIME POSIT FORCE EXT
Stress σ(psi) Strain(ε)
525 1 7.3930.0420
521.424
9
-0.00054
8 336.3406-5.4829E-
06-5.49387E-
06
525 212.57
70.0459
527.426
750.00132
5430.56125
71.32501E-
051.32766E-
05
525 314.15
70.0512
2533.342
040.00223
9523.42293
62.23882E-
05 2.2433E-05
525 417.49
7 0.062340.512
520.00300
6635.98938
23.00638E-
053.01239E-
05
525 518.73
70.0663
2547.264
610.00370
1741.98760
33.70085E-
053.70825E-
05
525 619.80
10.0700
2554.233
110.00427
7851.38317
94.27656E-
054.28511E-
05
525 721.19
70.0746
562.615
50.00515
4982.97490
45.15379E-
05 5.1641E-05
525 822.25
90.0780
2569.670
560.00603
1 1093.72946.03102E-
056.04308E-
05
525 922.79
80.0798
7575.758
980.00661
61189.3089
56.61589E-
056.62912E-
05
525 1023.13
80.0811
2582.280
220.00771
2 1291.68327.71247E-
057.72789E-
05
525 1123.67
70.0829
7589.277
570.00860
81401.5316
38.60795E-
058.62517E-
05
525 1224.37
80.0851
2599.117
130.00986
91555.9989
79.86896E-
05 9.8887E-05
525 1324.91
70.0869
75107.25
43 0.01113 1683.7403 0.00011130.0001115
23
525 1425.25
7 0.0882113.38
60.01182
51779.9993
10.0001182
450.0001184
82
525 1525.61
80.0894
5120.18
130.01286
61886.6768
10.0001286
630.0001289
2
525 1626.13
80.0909
75129.37
160.01402
72030.9520
10.0001402
680.0001405
48
525 1726.68
10.0928
25140.17
790.01553
52200.5942
90.0001553
450.0001556
56
525 1827.03
70.0940
75146.29
510.01664
92296.6266
90.0001664
940.0001668
27
525 1927.37
7 0.0953154.12
930.01742
62419.6115
70.0001742
610.0001746
09
525 2027.91
70.0968
25163.13
20.01870
52560.9422
10.0001870
540.0001874
28
525 2128.25
90.0980
75170.11
490.01958
32670.5640
40.0001958
270.0001962
18
525 2228.43
70.0986
75176.43
420.02070
72769.7672
50.0002070
660.0002074
81
525 2328.79
80.0999
25183.79
220.02192
22885.2779
60.0002192
20.0002196
58
525 2428.97
80.1005
25189.86
620.02274
42980.6307
80.0002274
440.0002278
99525 25 29.31 0.1017 198.58 0.02381 3117.4316 0.0002381 0.0002386
Al 6061 Tensile Test 28
7 75 04 4 9 35 12
525 2629.67
7 0.1027204.61
11 0.024813212.1049
30.0002480
960.0002485
92
525 2729.85
7 0.1033210.52
64 0.025653304.9662
80.0002565
030.0002570
16
525 2830.19
70.1045
5220.19
280.02711
23456.7155
30.0002711
240.0002716
66
525 2930.55
90.1057
75229.78
710.02860
23607.3324
80.0002860
180.0002865
9
525 3030.91
7 0.107238.38
580.02981
73742.3210
20.0002981
720.0002987
69
525 3131.07
70.1076
25245.23
890.03106
93849.9043
50.0003106
910.0003113
12
525 32 31.440.1085
5252.40
940.03205
63962.4706
10.0003205
60.0003212
01
525 3331.79
80.1097
75263.02
80.03362
84129.1682
10.0003362
770.0003369
5
525 3432.13
80.1110
25273.48
790.03521
84293.3743
40.0003521
770.0003528
81
525 3532.49
80.1122
5284.09
210.03671
6 4459.84510.0003671
640.0003678
98
525 3632.85
70.1134
75294.49
440.03827
94623.1452
80.0003827
890.0003835
55
525 3733.19
7 0.1144303.59
81 0.039544766.0609
7 0.00039540.0003961
91
525 3833.55
90.1156
25 315.140.04151
44947.2534
60.0004151
380.0004159
68
525 3933.91
70.1168
75327.04
280.04329
65134.1091
90.0004329
570.0004338
23
525 4034.25
9 0.1181338.51
260.04498
65314.1691
20.0004498
620.0004507
62
525 4134.61
70.1193
25350.92
020.04697
85508.9512
80.0004697
830.0004707
22
525 4234.97
80.1205
5362.85
170.04875
15696.2592
60.0004875
110.0004884
86
525 4335.31
70.1214
75371.24
850.04995
7 5828.0770.0004995
730.0005005
72
525 4435.49
7 0.1221380.75
620.05134
6 5977.33430.0005134
630.0005144
9
525 4535.85
70.1233
5392.87
530.05327
46167.5867
30.0005327
430.0005338
09
525 4636.19
70.1245
75406.01
87 0.055126373.9195
70.0005512
020.0005523
05
525 4736.55
7 0.1258418.44
070.05711
26568.9283
30.0005711
230.0005722
65
525 4836.91
70.1267
25426.82
310.05829
16700.5189
80.0005829
110.0005840
77
525 4937.07
70.1273
5436.76
360.05979
96856.5711
20.0005979
890.0005991
85
525 5037.43
70.1285
75449.32
990.06178
27053.8445
10.0006178
180.0006190
53
525 5137.79
90.1298
25463.07
930.06375
67269.6900
20.0006375
560.0006388
31
525 52 37.960.1304
25471.62
03 0.064877403.7723
80.0006487
040.0006500
02
Al 6061 Tensile Test 29
525 5338.31
90.1316
5486.45
170.06712
87636.6047
30.0006712
750.0006726
18
525 5438.67
70.1328
75501.45
620.06952
27872.1544
40.0006952
170.0006966
07
525 5539.01
70.1338
25509.33
360.07073
77995.8181
80.0007073
70.0007087
85
525 5639.19
70.1344
25519.80
790.07228
18160.2499
60.0007228
140.0007242
59
525 5739.55
70.1356
75534.27
86 0.074528387.4195
50.0007452
010.0007466
92
525 5839.91
7 0.1369547.26
330.07660
48591.2606
90.0007660
360.0007675
68
525 5940.07
80.1375
25555.81
880.07789
28725.5706
10.0007789
20.0007804
78
525 6040.43
70.1387
5572.59
780.08042
38988.9770
70.0008042
330.0008058
41
525 6140.80
20.1396
75581.18
220.08189
49123.7392
50.0008189
450.0008205
83
525 6240.95
9 0.1403592.29
130.08343
9 9298.13690.0008343
880.0008360
57
525 6341.31
70.1415
25605.39
140.08547
79503.7899
30.0008547
660.0008564
75
525 6441.49
70.1421
5613.36
980.08669
29629.0394
40.0008669
190.0008686
53
525 6541.67
70.1427
5620.95
860.08778
89748.1720
10.0008778
850.0008796
41
525 6641.85
70.1433
75629.29
760.08918
79879.0833
20.0008918
660.0008936
5
525 6742.01
80.1439
75637.70
880.09033
810011.127
20.0009033
80.0009051
87
525 6842.19
7 0.1446645.68
720.09175
410136.376
70.0009175
430.0009193
79
525 6942.55
70.1455
25658.41
210.09344
510336.139
90.0009344
490.0009363
18
525 7042.73
70.1461
5666.67
910.09481
610465.919
60.0009481
560.0009500
52
525 7142.89
70.1467
75674.44
1 0.0959310587.770
50.0009593
040.0009612
23
525 7243.07
70.1473
75683.03
970.09722
810722.758
80.0009722
80.0009742
24
525 7343.25
8 0.148691.75
38 0.09848 10859.5580.0009847
990.0009867
69
525 7443.43
7 0.1486699.87
650.09974
110987.071
70.0009974
10.0009994
04
525 7543.64
70.1492
25708.57
620.10115
711123.644
80.0010115
730.0010135
96
525 7643.77
70.1498
5716.98
740.10259
211255.688
60.0010259
20.0010279
72
525 7743.96
20.1504
75725.16
770.10355
111384.108
70.0010355
150.0010375
86
525 7844.13
80.1510
75733.50
670.10501
411515.019
10.0010501
350.0010522
36
525 7944.47
8 0.1517741.29
750.10611
911637.324
10.0010611
930.0010633
15525 80 44.65 0.1526 752.89 0.10790 11819.421 0.0010790 0.0010811
Al 6061 Tensile Test 30
7 25 72 1 6 11 69
525 8144.83
80.1532
25760.86
1 0.1090811944.443
1 0.00109080.0010929
81
525 8245.01
80.1538
5769.22
890.11046
912075.807
60.0011046
890.0011068
98
525 8345.19
70.1544
75777.10
63 0.1116212199.471
30.0011162
030.0011184
35
525 8445.37
7 0.1551784.86
820.11284
512321.322
20.0011284
480.0011307
05
525 8545.53
9 0.1557792.68
790.11406
912444.079
50.0011406
930.0011429
74
525 8645.71
70.1563
25799.80
050.11517
512555.738
40.0011517
50.0011540
53
525 8745.89
70.1569
25807.86
550.11633
512682.346
60.0011633
550.0011656
82
525 8846.25
70.1578
5818.39
75 0.1178812847.683
80.0011787
980.0011811
56
525 8946.43
70.1584
75825.66
880.11903
1 12961.8340.0011903
120.0011926
92
525 9046.59
70.1590
75833.11
330.12034
713078.702
40.0012034
710.0012058
78
525 9146.77
7 0.1597840.32
70.12137
1 13191.9470.0012137
050.0012161
33
525 92 46.960.1603
25847.80
040.12271
413309.268
70.0012271
380.0012295
92
525 9347.13
80.1609
25855.31
710.12369
213427.269
70.0012369
160.0012393
89
525 9447.31
90.1615
5862.37
210.12469
713538.023
10.0012469
670.0012494
61
525 9547.49
70.1621
75869.93
20.12588
513656.703
40.0012588
470.0012613
64
525 9647.65
7 0.1628876.81
380.12701
813764.737
50.0012701
780.0012727
18
525 9748.01
70.1637
25888.37
020.12876
313946.156
60.0012876
310.0012902
07
525 9848.19
70.1643
25895.75
7 0.1297514062.118
7 0.00129750.0013000
95
525 9948.37
70.1649
5903.57
660.13089
2 14184.8760.0013089
230.0013115
41
525 10048.53
70.1655
5910.93
450.13206
214300.384
80.0013206
190.0013232
61
525 10148.71
70.1661
5918.36
460.13330
514417.027
10.0013330
470.0013357
13
525 10248.89
90.1667
75926.25
640.13450
214540.916
90.0013450
180.0013477
08
525 103 49.08 0.1674934.06
160.13577
214663.447
20.0013577
20.0013604
35
525 10449.25
7 0.168942.08
320.13684
114789.375
10.0013684
110.0013711
48
525 10549.43
70.1686
25949.94
610.13795
614912.811
70.0013795
590.0013823
18
525 10649.61
70.1692
25958.31
40.13926
315044.175
30.0013926
270.0013954
12
525 10749.95
70.1701
25969.40
850.14084
415218.343
90.0014084
350.0014112
52
Al 6061 Tensile Test 31
Hardness Data
Serial No. Before FailureAfter Failure
1 59.2 HRB 65 HRB2 61.1 HRB 65.5 HRB3 60.6 HRB 64.7 HRB
Roughness Data
Serial No. Before FailureAfter Failure
1 0.309 μm 1.146 μm2 0.316 μm 1.510 μm3 0.281 μm 1.509 μm
Note : the raw data shown above is one part of the entire data collected in the lab. More raw data is contained in the CD attached with this lab report.