Name__________________



MSE 2160/2170

Laboratory #4

A. Tensile Testing Lab

Our tensile testing machine was built by the Instron Corporation. Instron corporation has built so many of these machines, that they are often called “instrons”, even though the company produces many other types of testing equipment. For example, our Rockwell hardness tester was built by Instron. This particular machine uses a testing sample called a “dogbone”, because of its shape.

The specimen is placed in the machine and a load (force) is applied, resulting in a constant strain rate. As the specimen stretches, the machine records and displays the elongation versus the force applied. Your job is to perform a tensile test on the samples available to you in the laboratory, and gather the data from the data collection system.

Procedure

I. Measurements – as received

Measure and record the thickness and width of the narrow section of the sample. Measure the length between the points where it just begins to widen. This distance is the gage length. Mark the locations with a scribe scratch or a permanent marker and record the gage length.

| |

|[pic] |

|Figure 2 |

|Mark the location of the gage length ends. Exact location is not critical, but the same marks must be used before and after the test. |

II. Instron™

(Instructor's discretion to let student perform specific steps)

2. Turn on the main switch.

3. Turn on the computer (requires login).

4. Start the Bluehill software (control program of the Instron)

5. Click on Test.

Select a preset procedure for the test.

Click on NEXT.

6. Name the new sample – use today's date like "22Feb2012-A"

Click on NEXT.

7. Enter specimen label. Enter Length, Width, and Thickness

8. Mount the test specimen on the Instron™. The specimen must be perfectly vertical. The Instron™ jaws should grip at least ¾" of the specimen end tabs.

On the small console, press "Reset GL"

9. On the top line of computer screen, click on "Balance All"

10. Click on "Start" to initiate the test. Observe the computer screen to follow up on the test's progress.

11. At the end of the test, release the sample from the Instron™.

12 . Measure the width and thickness of the sample as close as you can to the fracture zone without the micrometer touching the broken area. Enter the measurements in computer.

13. Reassemble the pieces into as good a fit as you can. Measure and record the new gage length. Enter the gage length into the computer

| |

|[pic] |

|Figure 3 |

|Measure the width and thickness near the break. Measure the new gage length. |

14 .After entering the sample dimensions, click "NEXT".

Click on "Finish the sample"

15. If asked to continue another sample using same parameters, click YES.

16. This returns to step 6 for a fresh start for next lab group.

Data Sheet

Materials Testing Lab

Date __Feb 24, 2012______________ Time _____10 am_______

| | | | | |

|Sample material |Acrylic |Polycarbonate | | |

|Before.| |3.00 in |3.00 in | | |

|in. |Length | | | | |

| | |0.502 in |0.500 in | | |

| |Width | | | | |

| | |0.106 in |0.130 in | | |

| |Thickness | | | | |

|After, | |3.046 in |5.311 in | | |

|in. |Length | | | | |

| | |0.504 in |0.389 in | | |

| |Width (tip) | | | | |

| | |0.108 in |0.098 in | | |

| |Thickness (tip) | | | | |

Other

1. What materials did you test in the tensile testing machine?

|Materials Tested |Check |

|Acrylic plastic | |

|Polycarbonate | |

| | |

| | |

| | |

2. Does the tensile test output reflect engineering stress/strain data, or true stress strain data? Explain.

It reflects the engineering stress/strain data. It doesn’t measure the change in the material is the loads are applied.

3. How are the results different?

The polycarbonate stretches better and is less likely to break under lower loads.

4. Analyze the data collected for the following properties.

| |Acrylic |Polycarbonate |

|a. 0.2% offset yield strength |675 |675 |

|b. tensile strength |629.8 |580.0 |

|c. modulus of elasticity |8249 |3344 |

| | | |

|d. % elongation |36.67% |77.0% |

|e. % reduction in area |-3.9% |-3.8% |

|f. engineering stress at fracture |3945.2 |2974.35 |

|g. true stress at fracture |803.8 |2865.22 |

|h. modulus of resilience |62.59 |5.8 |

5. Based on measurements after fracture you can calculate the following

a. % elongation

b. % reduction in area

c. % engineering stress at fracture

d. % true stress at fracture

C. Three Point Bend Test

The bend test is used for brittle materials such as ceramics. Results from a tensile test on these materials show significant scatter. Often a sample breaks just putting it into the device. Instead, a compressive load is applied at three points on the sample. Perform a compressive bend test on the glass and ceramic samples available to you in the lab.

[pic]

6. Flexural strength is defined as:

[pic]

Calculate the flexural strength of the sample(s) you tested, based on the parameters shown in the picture above

| |Glass specimen |Ceramic specimen |

|Length between rollers, L |3.15 |3.15 |

|Width of the speciman, W |1.35 |3.03 |

|Thickness of the specimen, h |0.226 |0.315 |

|Force required to break the specimen, F | |132 |

|Specimen deflection | |0.015 |

|Flexural Strength | |2074.5 |

7. Flexural Modulus is defined as:

[pic]

Calculate the flexural modulus for the sample(s) you tested.

FM=726072.6

D. Charpy Impact Test

The ability of a material to absorb a sudden load is measured with impact testing. There are two common tests, the Charpy test and the Izod test. Our machine is a Charpy tester. The two tests differ only in the sample configuration and orientation, as shown in the diagram. In both a weight attached to a pendulum is allowed to strike the sample. Energy is absorbed by the specimen as it breaks, so the weight does not travel as far in the second part of its swing (back up). The energy absorbed is the difference in potential energy of the weight.

[pic]

E=gΔh

where E is absorbed energy

g is acceleration due to gravity

h is vertical distance between a reference point and the weight

Many impact testers, including ours, have scales measured directly in energy, so that the calculations are not necessary.

The energy absorbed in an impact test is related to the toughness measured with the tensile test. However, in the tensile test the load is applied comparatively slowly, allowing dislocations time to move and absorb the applied energy. Since the energy absorbed when a material fails is dependent upon how fast the load is applied, impact testing results are useful in comparisons between materials. They are not generally used as design parameters, since the design conditions rarely correspond to the testing conditions.

Impact testing measures how brittle a material is. Brittle materials do not deform when the weight impacts, and therefore do not absorb a large amount of energy. Ductile materials deform, and energy is absorbed. Think of hitting a ceramic bowl with a hammer, versus striking a bowl made out of Play-Doh. The ceramic bowl shatters, even though it is stronger than the Play-Doh bowl, which just deforms and absorbs the energy.

The ability of a material to absorb impact energy is affected by its crystal structure. Body-centered cubic materials in general absorb less energy than face-centered cubic materials, because the dislocations in FCC materials move more readily than the dislocations in BCC materials.

Temperature is also an important factor in the ability of a material to absorb impact energy. Consider a highly elastic material such as the polymer in a racquet ball. The ball bounces because it absorbs the impact energy when it hits the floor. The energy is then released as it pushes back against the floor. Now if we chill the racquet ball in liquid nitrogen and drop it on the floor what happens? The ball shatters, because it can no longer absorb the energy.

The same thing happens with metals – although the energy absorbtion mechanism is different. At low temperatures it is harder for slip to occur. In body-centered cubic materials in particular, below a temperature called the ductile-brittle transition temperature(DBTT), it is very difficult for dislocations to respond quickly to rapid impact (application of stress). In effect the slip systems become inactive, making it harder to absorb energy.

1. Determine the approximate ductile-brittle transition temperature for a racquet ball.

a. Drop a racquet ball from a convenient but measured height (the drop distance), and measure how high it bounces (the rebound distance).

b. Cool the racquet ball in ice water for 10 minutes, then repeat part a.

c. Cool the racquet ball with dry ice for 10 minutes, then repeat part a.

d. Cool the racquet ball with liquid nitrogen , then repeat part a.

| |Temperature |Drop distance |Rebound distance |Fractional Rebound |

| | | | |(rebound/drop distance) |

|Room temperature |75 °F |36 in |30 in |0.833 |

|Ice Water | | | | |

|Dry Ice | | | | |

|Liquid Nitrogen |-320°F |36 in |0 in |0 |

e. Plot your results, using the computer program of your choice. I suggest either MATLAB or EXCEL. Plot temperature on the x-axis and fractional rebound distance on the y-axis

f. Can you estimate a ductile/brittle transition temperature based on this limited data?

2. Milt or Joven will demonstrate the use of the Charpy impact tester, but we will not be doing the actual experiment, since you will have that experience in Strengths of Materials. However, the Strengths of Materials students have gathered data for you to analyze. Use this data, or attach a copy of data which may have been gathered more recently if it is provided.

| |Absorbed Energy |

| |Sample #1 |Sample #2 |Sample #3 |Sample #4 |

|Sample Identity → |C1045 CF |C1045 HR |SSteel 304 |C 1018 CF |

|Temperature ↓ |(cold worked) |(hot worked) | |(cold worked) |

|800 0F |19 ft lbf |29 ft lbf |126 ft lbf |45 ft lbf |

|75 0F |9 ft lbf |26 ft lbf |164 ft lbf |59 ft lbf |

|-108 0F |3 ft lbf |8 ft lbf |240 ft lbf |8 ft lbf |

|-320 0F |2 ft lbf |2 ft lbf |116 ft lbf |3 ft lbf |

3. Plot the temperature on the x-axis versus the absorbed energy on the y-axis for each of the samples. Based on this data do you think each sample is FCC or BCC? (Attach your graphs when you turn in this lab).

| |Identity/Description |BCC or FCC? |

|Sample #1 |C1045 CW |BCC |

|Sample #2 |C1045 HR |FCC |

|Sample #3 |Steel 304 |BCC |

|Sample #4 |C1018 CW |FCC |

4. Based on your graphs, what is the effect of coldworking the samples?

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