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Unformatted text preview: 4 Stress vs. Strain Lab
Introduction ........................................................................................................................................................................................................................................................2 Data ....................................................................................................................................................................................................................................................................3 Calculations & Analysis .......................................................................................................................................................................................................................................4 Conclusion ..........................................................................................................................................................................................................................................................5 5 Introduction
Objectives...  The objective of this lab is to demonstrate the relationship between stress and strain with the use of three different materials. Other objectives include graphing stress and then interpreting the graph results and discussing the differences in mechanical properties of materials. Next, procedures should be developed for testing tensile strength in common materials. Finally, the modulus or different materials should be calculated. Deﬁnitons...  Stress: External force applied per unit area.  Stain: Fractional change in dimension due to stress. Useful Equations...  Strain=ΔL/L  Stress=F/A  Young's Modulus=F/A=Y(ΔL/L) Procedure... 1. Set up two ring stands by connecting the rods to clamps attached to the lab table. 2. Then connect another rod between the two ring stands using smaller connector clamps (this will create a stable base to hang materials from). 3. Attach test material to center rod and measure initial length, width, and the thickness of the material. 4. At the hanging end of the material, attach a small mass rack in order to place more masses on later is the experiment. 5. Begin to apply masses to the rack. 6. After mass is applied, measure the length, width, and thickness of the object, keeping an organized record of all data points. 7. As more mass is applied, repeat step 4. 8. Keep adding masses and recording measurements until you have a minimum of 7 data points. 9. Repeat steps 26 for a minimum of two additional materials. 10. Calculate the stress and strain for every data point recorded for each material. 11. After recording stress and strain values for all data points. Create graphs expressing the relationship between stress for each individual material. 12. Calculate the value of Young's Modulus for each material using the equation given (F/A=Y(ΔL/L)). 13. Compare the slope of each graph to Young's Modulus. 6 Data 7 Calculations & Analysis Sample Calculations...  Stress=F/A=31.507/0.00000139=22944756.1  Strain=ΔL/L=(0.3010.266)/0.266=0.132 8 Conclusion
In the lab, we discovered that the ACE bandage had the greatest elongation, the plastic bag was second, and the Duct tape had the least amount of elongation. The Duct tape held the most weight at 187.327 N. However, this does not mean that the Duct tape had the had the greatest ultimate strength. Because you do not know how the object returns to its shape, you cannot determine its strength. The graphs demonstrate that the relationship of Hooke's Law holds true because the slope is positive showing that the stress is directly proportional to the strain. The slope of each line can also be identiﬁed as Young's Modulus. For the ACE bandage, Y = 7E + 06x  847,500. For the plastic bag, Y = 1E + 08x + 3E + 06. And for the Duct tape, Y = 2E + 08x + 2E + 06. Young's modulus or the slope is found by taking stress/strain. This means that the relationship between stress and strain is directly proportional. The results for this lab could be found in any object. As stress increases, strain will increase. The results will always be directly proportional. The possible sources of error would be the effect that our contraptions had on the objects. For example, we stuck the mass hanger through the ACE bandage, which could have caused the object to stretch more, or to not be able to hold as much weight. It was also very difﬁcult to get exactly accurate measurements using a meter stick. However, we did our best to avoid errors by using the most effective ways to hang each object and by carefully taking measurements. ...
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This note was uploaded on 04/20/2011 for the course ECON 101 taught by Professor Mankiw during the Spring '11 term at Abant İzzet Baysal University.
 Spring '11
 mankiw

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