Laboratory

 

Mechanical Properties of Nanoparticle Composite Materials

The Mechanical Engineering Module will teach you to prepare nanocomposites and to operate the Instron testing machine. You will obtain the engineering stress-engineering strain curves for a nanocomposite and a plain polymer material under tensile loading. From the obtained curves, the important mechanical properties of these materials can be determined, such as modulus of elasticity (Young’s Modulus), Yield Stress, Tensile Strength, ductility (percent elongation or percent area reduction) and so on. In addition, the experiment will reveal the effects of nanomaterials on the mechanical properties of polymers. (ADD PDF LINK)

 

Pre-lab Exercises
Be prepared to answer these problems before coming to lab.  We will discuss the answers during the first laboratory session.

1.   Review lecture notes from ChE 59808 Nanomaterials Course (available on blackboard): Nanomaterials&composites_mech_properties.pdf.
2.   What divides the engineering stress-strain curve into two regions, namely, the elastic and plastic regions?
3.   What is the difference between the behavior of the material in the elastic and plastic regions of the engineering stress-strain curve?
4.   What measurement should you take in order to be able to plot the true stress-true strain curve?
5.   Does the failure mode of polymers differ from that of metals? Why?
6.   Discuss how the microstructures of polymers and polymer-based nanocomposites make their behavior under mechanical loading different.

 

Lab Exercises

Experiment 1) Preparation of epoxy polymer and montmorillonite (MMT)/epoxy polymer specimenEpoxy Preparation:
Epoxy polymer is prepared by the mixing of an agent and a base in a 1:4 ratio. The mixture has to be stirred vigorously. When the agent comes into contact with the base bubble formation occurs indicating the onset of a polymerization reaction which leads to the formation of a polymer network and water. Bubbles are removed from the mixture using a defoaming set up on the mixer.

MMT/epoxy polymer  preparation:
A montmorillonite (MMT)/epoxy nanocomposite is prepared in analogous fashion as described in the previous procedure with one additional step. After the thorough mixing of the polymer mixture, a certain amount of MMT powder is added to the polymer mixture and stirred thoroughly to enable uniform distribution of the MMT clay particles in the polymer mixture.

Experiment 2) Tensile Stress Testing of Epoxy Specimen

1. Measure and record the length, width and thickness of you specimens (Table 1).
2. Input the data (material name, displacement rate, gage length, diameter, and geometry of the specimen) of the test into Blue Hill software.
3. Install the test specimen in the Instron machine (Figure 7).
4. Conduct tests on two of the plain epoxy specimens you have prepared or are given by the instructor.
5. Remove the test specimen from the Instron machine grips at the end of the test. Measure the specimen. Make sure to mark which side was up and which was down.
6. Repeat the measurement with two more epoxy specimens at a higher and lower rate.
7. You should have data for four specimens at this point.

Figure 7. A) Instron testing machine. B) Specimen mounted into Instorn machine.

 

Experiment 3) Tensile Stress Testing of Nanocomposite Specimens

8. Measure and record the length, width and thickness of you specimens (Table 1).
9. Input the data (material name, displacement rate, diameter, and geometry of the specimen) of the test into Blue Hill software.
10. Install the test specimen in the Instron machine (Figure 7).
11. Conduct tests on the six nanocomposite specimens (two different weight percents of clay) you have prepared or are given by the instructor.
12. Remove the test specimen from the Instron machine grips at the end of the test. Measure the specimen. Make sure to mark which side was up and which was down.
13. At this point you should have at total of 10 stress-strain curves.
14. Perform the Post-Lab exercises and turn them in with your lab report for the Mechanical Engineering Module 4.

 

Post-Lab Exercises

Use your tensile data and any necessary Excel spreadsheet to perform these exercises.

1. Calculate the elastic modulus for all specimens tested. Determine the yield point, the ultimate tensile strength, the percentage elongation, and the reduction in area for each of specimens if possible.
2. Did necking occur for any of the specimens tested?
3. Where did fracture occur for the specimens?
4. Did you observe any effect of strain rate on the failure mode and on the mechanical properties of the plain epoxy specimens?
5. Did you observe a difference in the nanocomposite specimens with the two different weight% MMT? What did you observe?
6. Did the epoxy and MMT/epoxy specimens behave identically?
7. Were the modes of failure of the epoxy and MMT/epoxy specimens similar? Why?
8. Discuss differences and similarities in the stress-strain data of your samples.