Lab Report 1a.docx

Mechanics of Materials Laboratory

ME 2140

Fall 2013

Lab Report No. 1A

Uniaxial Tension Tests

Student Name

Student ID

Individual grade %20

Group grade %80

Final grade

Kenneth Knowles

41107018 /100

Lab Instructor: Lin Wang

September 10, 2013


ME 2140

Fall 2013

Table of Contents

Abstract……………………………………………………………….……………1

Introduction………………………………….…………………………..…………1

Procedure………………………………….……………………………..…………2

Results and Discussions……. ……………………………………………...………4

Conclusion……………………………………….………………………..………11


ME 2140

Fall 2013

Abstract

In this experiment, the basic mechanical testing procedure was employed, to determine the tensile stress-strain relationship of several common engineering materials such as steel, aluminum, and brass, and to obtain their mechanical property parameters, such as the modulus of elasticity (Young’s modulus), the yield stress, the ultimate stress, the ductility ratio, the modulus of resilience, and the modulus of toughness based on the uniaxial tensile stress –strain data.

Introduction

The Model 5582 Instron Universal Materials Testing System made by Instron is capable of tensile and compression testing modes within a single frame.

Features of Model 5582 Materials Testing System:

Load capacity of 100kN (22,500 lbf) with load measurement accuracy: ±0.4% of reading down to 1/100 of load cell capacity, ±0.5% of reading down to 1/250 of load cell capacity

Speed range of 0.001-500 mm/min (0.00004 – 20 in/min) with an accuracy of ±0.1% of set speed

1309 mm x 575 mm (51.5 in x 22.6 in) test area Strain measurement accuracy: ±0.5% of reading down to 1/50 of full range Total crosshead travel of 1235 mm (48.6 in) with position control resolution

of 0.060 mm (2.4 min) Position measurement accuracy: ±0.02 mm or 0.05% of displacement

(whichever is greater) Up to 500 Hz synchronous data acquisition rate for all channels Hardware control panel for operator convenience Automatic transducer recognition for load cells and extensometers Bluehill® 2 Software compatibility Second test space option Library of ASTM and ISO test methods


ME 2140

Fall 2013

Experimental Procedure

1. Turn on the testing machine, wait until the indicator on the left hand side of the machine counts down from “8” to “2”, then run the Bluehill 2 Testing software. It will display data transfer window on the computer screen. After a loud clicking sound, the machine is prepared.

2. Click “Method” button in the software interface if you want to build up a new test method, otherwise click “Test” button and choose an existing method from the list. You can always configure and modify testing parameters later by switching to “Method” tab.

3. Measure and record the dimensions (in mm) of the tensile test specimen: Measure the width, thickness of five different positions along the straight gage section and get average value, measure the length of the straight gage section, measure width and length of the grip sections, as well as the total length of the tension test coupon. Keep up to 2 decimal points in the measurements if applicable.

4. Change to the proper grips or fixtures if need (depending on the overall dimensions of the test coupon and test type). Adjust the position of the crosshead so the grippers are at the distance of the tensile specimen grip section. Balance the load cell and then mount the tensile specimen by gripping its both ends with a slight pressure. Adjust the longitudinal axis of the tensile specimen to align as best as one can with the vertical (loading) direction of the Instron machine. Tighten the grips, and then mount the extensometer on the specimen. Draw two lines along the clip of the extensometer.

5. Balance the extension and the strain values inside Bluehill. Do not balance the load cell though (some small pre-load may exist and it is acceptable if it is well below the load level for causing plastic yield. Otherwise, use the specimen protect feature of the Instron/Bluehill when one mounts the tensile specimen).

6. Stay away from the Instron machine and wear safety glasses if needed. Run the uniaxial tension test via Bluehill software and monitor the progress of the test at the desktop computer.

7. When the tensile specimen is completely fractured and the Instron machine stops, wait for 10-30 seconds then stop the data acquisition in Bluehill (so there


ME 2140

Fall 2013

will have some data recording on zero load state upon either fracture or removal of the tensile specimen). Remove the specimen first, and then click “Return” button to make the crosshead revert to the original position. Measure the width and thickness dimensions of the gage section of the tension specimen.

8. If more than one specimen will be tested, mount the next specimen and repeat from step 3. Representative steel, brass and aluminum sheet metal tension coupons before and after tensile testing are shown below. If needed, one may also measure the dimensions of the fracture surfaces and study their surface roughness features by the Keyence digital microscope.


ME 2140

Fall 2013

Results and Discussions

1. Plots of the Stress-Strain diagrams

Each CSV data file has 4 columns: Time, Load, Extension , and Strain . The Load values (in N) are from the channel of the load cell, the Extension values (in mm) are from the channel of the moving crosshead, and the Strain values (engineering strain) are from the channel of the extensometer.

We can calculate axial normal stress (engineering stress). We can then plot the first engineering stress-strain diagram as well as the second engineering stress-strain diagram. If the mechanical extensometer works properly, the slight difference between these two diagrams reflects the approximate nature of the 2nd engineering stress-strain diagram (overestimated specimen displacement and underestimated specimen gage length); on the other hand, a large difference can be used to identify any potential problems in measurements of the engineering strain when the mechanical extensometer has a malfunction.

1 25 49 73 97 121 145 169 193 217 241 265 289 313 337 361 385 409 433 457 481 505 529

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Chart 1 Aluminum Stress-Strain

Strain [mm/mm]

Stre

ss [N

/mm

^2]


ME 2140

Fall 2013

2 90 178 266 354 442 530 618 706 794 882 970 10581146123413221410149815860

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Chart 1 Brass Stress-Strain

Strain [mm/mm]

Stre

ss[N

/mm

^2]

2 106 210 314 418 522 626 730 834 938 1042114612501354145815621666177018740

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Chart 1 Steel Stress-Strain

Strain [mm/mm]

Stra

in [N

/mm

^2]


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Fall 2013

2. Calculating the modulus of elasticity

The Young’s modulus of the material is the slope of elastic (and linear) deformation part on the stress-strain curve according to the Hooke’s law of isotropic linear elasticity. In principle, we can choose any data point on this linear elastic portion to calculate the slope. In practice, we first determine the proportional limit (linear portion) of the initial part of the stress-strain curve and carry out a linear curve fitting of all data points from the starting point up to the proportional limit.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24-20

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f(x) = 6.18169278835628 x + 16.5783994510369

Chart 2 Aluminum Modulus of Elasticity

The slope of the linear trendline is 73.47 GPa = modulus of elasticity


ME 2140

Fall 2013

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58 610

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400f(x) = 6.65336798773002 x

Chart 2 Modulus of Elasticity Brass

Strain [mm/mm]

Stre

ss [N

/mm

^2]


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f(x) = 11.6641370496098 x + 34.5891118753783

Chart 2 Steel Modulus of Elasticity


ME 2140

Fall 2013


3. Finding the yield stress point

To find out the plastic yield point, we can make a 0.2% offset line parallel to the elastic deformation portion. This straight line has an intersection point with the stress-strain curve. This intersection point is the 0.2% offset yield point. Yield strain and yield stress are coordinates of this point on the stress-strain diagram.

1 2 3 4 5 6 7 8 9 1011121314151617181920212223242526272829303132333435360

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200f(x) = 6.01654608477997 x

Chart 2 Aluminum Yielding Point

The 0.2% offset line intersects the stress-strain curve at (169.89, 0.00214)


ME 2140

Fall 2013

The 0.2% offset line for the brass specimen intersects the stress-strain curve at (390.85, 0.00523)


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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 210

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250f(x) = 12.5649615763454 x

Chart 3 Steel Yield Point

The 0.2% offset line intersects the stress-strain curve at (191.70, 0.00083).


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Fall 2013

Conclusions

From the raw data analysis, the tensile test specimen behave similarly to a ductile material, with a linear elastic region, a definite yielding point, and characteristic necking of the specimen beyond the ultimate stress point. The yield point for Aluminum was slightly more difficult to identify than the yield points for steel and brass. Using the observed characteristics from the experiment and obvious physical characteristics of the test specimen, the specimen are easily recognizable.

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Lab Report 1a.docx