Mechanics of Materials Laboratory

ME 2140

Fall 2013

Lab Report No. 1B

Uniaxial Compression Tests

Student Name

Student ID

Individual grade %20

Group grade %80

Final grade

Kenneth Knowles

41107018 /100

Lab Instructor: Lin Wang

September 24, 2013

Mechanics of Materials Laboratory

ME 2140

Fall 2013

Table of Contents

Objective……………………………..……………………………….……….……1

Procedure………………………………….……………………………..…………1

Analysis of the Raw Test Data………………………………………….………….3

Conclusion……………………………………….………………..………..………6

Mechanics of Materials Laboratory

ME 2140

Fall 2013

Objective

To determine the compressive stress – strain relationship for materials such as steel, aluminum, and brass, and obtain the mechanical properties such as the modulus of elasticity (Young’s modulus), the yield stress,and the equivalent tensile ultimate stress, uniform elongation strain, and ductility ratio, etc.

Materials, Tools and Equipment

Cylindrical compression test coupons, micrometer/caliper, tape measure, and the Model 5582 Instron Universal Materials Testing System with a non-contact video extensometer

Experimental Procedure

Set-Up and Prepare the Instron machine

1. Turn on the Instron machine and computer. Then open Bluehill software, wait until the connection sound.

2. Select the test method ‘compression test for ME2140’, and create a new data folder name. The loading ramp consists of a holding period, initial loading, unloading, reloading, and final holding (at a preset maximum displacement or loading level), and final unloading steps.

3. Measure the specimen dimensions (height and diameter of cylinder) five times, get the average value and fill in the ‘Method/Dimensions’ section of the Bluehill test method.

4. Manually move the platens for ±5 mm to make sure the light and tracking dots is stable.

5. Lubricate the top and bottom surface with extreme pressure premium red grease, or put Teflon tape both faces. Put the specimen in the center of the platens. Balance the load so the reading on the load is nearly zero. Do both coarse and fine adjustment using the control panel until the compressive load has large change.

6. Reset the compression extension so the starting extension is zero.

Mechanics of Materials Laboratory

ME 2140

Fall 2013

Set-Up and Prepare the video extensometer measurements

1. Camcorder set up of tripod and dots preparation and attachment

2. Turn on the light and adjust camera position

3. Turn on the camcorder to the record mode, manually zoom and switch to auto focus. Make sure the focus point is the dot.

Execute the compression test and video extensometer measurements

1. Start the Bluehill test session for the Instron machine and start recording with the camcorder simultaneously.

2. When the Instron machine stops, manually stop the recording in camcorder.

Assembly Test Data Files

1. Capture the recorded video in the save it in the computer.

2. Open the Labview file ‘open video and tracking dots.vi’ for video extensometer in the ‘Programming’ folder on the desktop. Press start arrow and load the saved video, then choose the file path to save video extensometer file.

3. Save the video extensometer file to ‘xls’ format, replace ‘: ‘ with ‘,’, delete ‘PM’ Go to Data/text to columns/delimiters (choose tab and comma). Then the time ( hour/min/sec/ were separated to three columns.

4. Save as ‘csv’ file. And close.

5. Open ‘cidapro.ini’ in ‘newVideoExt_Program’ file folder. Copy 'Convert a video extensometer data file into a new format' part to the top and change the corresponding file names. Then save.

Mechanics of Materials Laboratory

ME 2140

Fall 2013

Analysis of the Raw Test Data

After the test, the Instron machine will generate a raw test data file automatically. The Bluehill software will output the raw test data as a CSV file, which can be read and edited by Microsoft Excel. Here a typical raw data file of a uniaxial compression test is used as an example to explain how to process the data.

Plots of the Stress-Strain diagrams

Each CSV data file has 4 columns: Time (t), Load (P), Extension of the crosshead, and Extension measured by the non-contact video extensometer. The Load values are in Newtons and the Extension values are in mm. It should be noted that what we get from the non-contact extensometer measurement represents the extensions between the two loading platens that sandwiches the cylindrical compression sample. The average compressive strain of the sample is given as engineering strain. We can calculate axial normal stress (engineering stress) by using the compressive axial load and A0 the area of cross-section of the cylindrical sample. We then plot the engineering stress-strain diagram.

4 283 562 841 1120139916781957223625152794307333523631391041890

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Chart 1: Aluminum Stress-Strain Diagram

Strain

Stress [MPa]

Mechanics of Materials Laboratory

ME 2140

Fall 2013

2 147 292 437 582 727 872 10171162130714521597174218872032217723220

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Chart 2: Brass Stress-Strain Diagram

Strain

Stress [Mpa]

2 94 186 278 370 462 554 646 738 830 922 1014110611981290138214740

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Chart 3: Steel Stress-Strain Diagram

Strain

Stress [Mpa]

It is often observed that the initial slope of the compressive engineering stress-strain curve is rather small and nonlinear. It is mainly caused by the initial poor matching quality between the platen surfaces and the test sample surfaces. One

Mechanics of Materials Laboratory

ME 2140

Fall 2013

should thus use the linear portion of the stress-strain with a largest slope to compute the Young’s modulus and the correct the origin of the stress-strain curve. The elastic moduli, given by the slope of the line in Charts 4,5, and 6, is 8.70, 10.15, and 12.46 GPa for the aluminum, brass, and steel specimen respectively.

1 5 9 13 17 21 25 29 33 37 41 45 49 53 57 61 65 69 73 77 81 850

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f(x) = 1.4082823532867 x + 27.7638732068399

Chart 4: Young's Modulus Aluminum

Strain

Strain [MPa]

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 1061131201271341410

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f(x) = 1.6173037375983 x + 30.9508256390537

Chart 5: Young's Modulus Brass

Strain

Stress [MPa]

Mechanics of Materials Laboratory

ME 2140

Fall 2013

1 13 25 37 49 61 73 85 97 1091211331451571691811932052172292410

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f(x) = 1.94550715032563 x + 14.8462323322952

Chart 6: Young's Modulus Steel

Strain

Stress [Mpa]

The yielding stresses from the .002 offset yield points are 43.23, 52.33, and 43.18 [MPa] for the aluminum, brass, and steel specimens respectively. These values were found by interpolating the data for stress and strain just below and just above the .002 strain data values.

The reloading slope is found by finding the slope of the line approximated by Young’s Modulus during reloading of the specimen. The slope for aluminum using data points 936 and 1047 is 12.50 GPa; brass using data points 1049 and 1280 is 12.51 GPa, and steel using1173 and 1525 is 13.62 GPa.

Conclusions

From the raw data analysis, the compression test specimens behave as expected for a ductile material, with a linear elastic region. The stress-strain diagram for Aluminum was not as linear after reloading as steel and brass. The steel specimen reached maximum load the quickest, and the aluminum specimen the slowest. The steel and brass specimens were less compressible than aluminum specimen for the given load. Using the observed characteristics from the experiment and obvious physical characteristics of the test specimen, the specimen are easily recognizable.