Activity YM2 Pupil Sheet

Young’s Modulus GUIDE QUESTIONS:

(Answers)

Using the Information Sheet provided, and the results obtained from experimental work, answer the questions below:

1. What is Hooke’s law? = It states that in the elastic range of the material, strain is proportional to stress. The elongation of the material is directly proportional to the tensile force and the length of the material and inversely proportional to the cross-sectional area of the material and the modulus of elasticity.

2. Explain what happens when the elastic limit is exceeded:=If you exceed the elastic limit of a material there may be permanent deformation for ductile material and rupture if the material is brittle.

3. Explain what is meant by Young’s Modulus: =It is a property of a material and it determines the stiffness of an elastic material. It is a quantity used to characterize materials.

4. How is knowledge of Young’s Modulus helpful to an engineer when selecting materials for use in a given project? Give examples:= To be able to determine the stiffness of an elastic material.= To be able to characterize materials through its elasticity.

5. Explain what is meant by Poisson’s ratio:= It states that when a material is compressed in one direction, it usually tends to expand in the other two directions perpendicular to the direction of compression.

6. Young’s modulus can be measured by loading a wire and measuring the strain. Which method is likely to be more accurate? Explain your answer:

= Measuring the strain. This is becausein finding the Young’s Modulus, you just need to compute Load over Strain.

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Activity YM2 Pupil Sheet

Young’s Modulus – Part IIGUIDE QUESTIONS:

(Answers)

1. Use Excel file “Young Modulus Calculation-Extended.xlsx”.

2. Open the data file for ‘Sample A results’ by clicking on the tab at the bottom of the worksheet. This contains force and extension data for an unknown material. This data has been collected using a Tensometer, which basically stretches a sample of the material with increasing force.

3. Using the following equations, convert this data into stress and strain. Information on the sample dimensions is available in the spreadsheet.

stress = force/area strain = extension/original length

4. Plot a graph of strain vs stress.

= Graph already plotted. (See figure above)

5. What shape would you expect the graph to be? Can you suggest a reason for the shape of the graph at low strains?

= As we plotted the computed values of stress and strain, it formed a line that is diagonally upward to the right. As the stress goes higher, the strain also increases because its stress and strain is directly proportional.

6. What is the gradient of the graph? What should you do before using Excel to calculate the gradient?

= Before using excel to calculate the gradient, we must compute first for the stress and strain values. The slope of the line is diagonally upward from left to right therefore the stress and strain is directly proportional to each other.

7. What is the Young’s Modulus of this material? Can you suggest what the unknown material may be using the table of material data provided? How could you confirm this?

= The Young’s Modulus of the material can be found using the equation: (E = 6l/gradient x wh2).This equation determines the stiffness of the material. The unknown material A is Aluminium since its graph is similar to that aluminium should be like.

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Activity YM2 Pupil Sheet

8 ‘Sample B results’ contains similar data for a different unknown material. Convert the data into stress and strain and plot a graph as before. Comment on the shape of the graph. Identify the plastic and elastic regions of the graph.

= The stress and strain is already computed and placed on the file. The plastic region starts at the point where the line begins to curve and the rest of the point before that is that elastic region as shown in the graph on copper.

9 Calculate Young’s Modulus for this material. Can you find this value in the table of material data? If not, what do you think this material could be?

= The Young’s Modulus of the material can be found using the equation: (E = 6l/gradient x wh2). This equation determines the stiffness of the material. This material is called Copper since its graph is similar to that of aluminium.

Source:

www.wikipedia.comwww.google.com

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