Team Roles:

CET 3135-(002)Mechanics of Materials with Laboratory

Spring 2014Laboratory Report

Lab (2) (Poisson Ratio)

Submitted by: Haroon Rashidi

Laboratory Date: 02/06/14

Date of Submission: 02/13/14

Submitted to: Dr. Runing Zhang

Team Members: Haroon Rashidi, Anson Turner, Ceana Prado Nickel, Von Watren, Samuel DouglasTABLE OF CONTENTSABSTRACT........................................................................................................................3

THEORECTICAL BACKGROUND.................................................................................4

LIST OF EQUIPMENT......................................................................................................5

LIST OF MATERIALS......................................................................................................5

PROCEDURES..................................................................................................................6

DATA & RESULTS........................................................................................................7CONCLUSIONS................................................................................................................9

REFERENCES..........................................................................................................10

APPENDIX A Test Data & Computed Material Properties............................................11SIGNATURE PAGE..12

Abstract

The purpose of the following experiment is to determine Poisson's ratio for an aluminum bar. Poisson's ratio refers to a characteristic dimensionless number which accurately predicts the amount of strain experienced in non-parallel directions to an applied load. To find this value, the Instron 5569 was used to apply force to an aluminum bar with dual strain gages to record changes in lateral and longitudinal strain. Poisson's ratio for the aluminum specimen was found to be 0.347, which is less than 3.75% from the scientifically accepted 0.334.

Introduction & Background

When a material experiences deformation, it not only changes on the axis of the applied load, but also in the perpendicular direction as well. This is known as Poisson's effect and can be predicted by Poisson's ratio. For a specimen experiencing a simple uniaxial load, this ratio is expressed as:

An axial, concentric load will be applied to the aluminum tension specimen by the Instron Load Frame. This load application will cause deformation of the specimen. The axial elongation is measured directly using the BLH Strain Gage Recorder which will be attached to the specimen. From the axial load, the axial engineering stress can be determined using the following equation:

= /

Where is the axial engineering stress; P is the axial tensile load applied to the specimen; and A is the original cross-sectional area of the specimen. To determine true stress, rather than engineering stress, the same equation above is used. However, the actual cross-sectional area of the specimen, at the time the load measurement is taken, is used in the above equation to determine the true stress. In our case, the cross-sectional area of the specimen will always be decreasing as axial tensile load is applied.

When the specimen is subjected to load, the shape of the specimen is altered. The change in any linear dimension is called deformation. This deformation is typically reported as engineering strain which is deformation divided by the original specimen length and can be determined by the following equation:

= /

Where is the axial engineering strain; L is the total deformation or change in length due to the axial load application; and L is the original length of the specimen. To determine true strain, rather than engineering strain, the same equation above is used. However, the actual length of the specimen, at the time the load measurement is taken, is used in the above equation to determine the true strain. In our case, the length of the specimen will always be increasing as axial tensile load is applied. LIST OF EQUIPMENTSeveral pieces of equipment will be necessary to perform the Steel Tension Test. A 30 minute setup up time is recommended in advance of the start of the test. The list of equipment for this test is as follows:

1. Instron 5569 Load Frame (50 kiloNewton 11,250 lb. force capacity)

2. BlueHill Software

3. Tension grippers for Instron 5569 Load Frame

4. BLH Strain Gage Recorder (Wheatstone Bridge)5. All of the equipment was essential for the success and safety of the experiment. The Instron Load Frame was the equipment applying and taking away the load to the bar. The BlueHill Software was what controlled the Instron, and thereby the compressive load applied to the bar. BlueHill also collected all the data in the experiment, such as the amount of load applied and the deflection of the bar. The tension grippers for Instron 5569 Load Frame held the material in place. And the BLH Strain Gage Recorder recorded the strain.LIST OF MATERIALSThe specimen in the experiment was an aluminum bar.PROCEDURES

1. Start the computer with the BlueHill software.

2. Turn on Instron 5569 Load Frame. (this is where specimen will be placed)

3. Install BLH Strain Gage Recorder4. Initiate BlueHill software on microcomputer.

5. Open the pre-programmed spring compression test from BlueHill software menu.6. Ensure proper connections of the BLH Strain Gage Recorder to the specimen.

7. Begin loading and unloading.DataLoad [lb]Stress [psi] []Strain (longitudinal) [l]Strain (Transverse) [t]Young's Modulus [psi] Poisson's Ratio

000000

200519.485.10E-05-1.70E-051.02E+070.333

4001038.961.00E-04-3.40E-051.04E+070.34

6001558.441.49E-04-5.20E-051.05E+070.34899

8002077.921.98E-04-6.90E-051.05E+070.3484

10002597.42.50E-04-8.60E-051.04E+070.344

8002077.922.00E-04-6.90E-051.04E+070.345

6001558.441.49E-04-5.30E-051.04E+070.3557

4001038.961.00E-04-3.50E-051.04E+070.35

200519.485.00E-05-1.80E-051.04E+070.36

000000

Young's Modulus [sample] [psi]=E=/1.02E+07

Poisson's Ratio [sample]==-(t/l)0.333333333

Modulus of rigidity [for all values] =G=E/(2(1+))3822205.551

3876865.672

3876974.625

3893503.411

3880208.333

3862453.532

3831968.725

3848148.148

3819852.941

ConclusionThe results obtained in this experiment were acceptable. The percentage errors of this lab werent as high as they could be considering human error. The tools used in this experiment can also contribute to the high percentage error. Collecting more data could have brought the percentage error down slightly, but ultimately, a 3.75% error is not too unacceptable.References"Poisson's Ratio." Engineering Tool Box. N.p.. Web. 13 Feb 2014. .

Appendix

SIGNATURE PAGEMechanics of Materials Testing Laboratory CET 3135 Section 002

Laboratory No. 2 Poissons Ratio

Group No. 3: Haroon Rashidi, Anson Turner, Ceana Prado Nickel, Von Watren, Samuel Douglas

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