Wood Polymer Composites
The basic procedure: two lab periods, one report compiling both lab periods
In this lab, you will examine two types of composites, one natural and the other a version of the natural material designed to optimize flexural strength. The natural composite is balsa wood in its native state. Your “design” will use balsa wood.
In the first lab, you will test the “natural” composite wood for flexural or bending strength using a simple hanging weight method. Be detailed in your observations and data collection that you are required to record in your lab notebook. Be sure to record the units you are using to measure.
· First examine the balsa wood blanks (starting material).
o What is the orientation of the “grain” of the wood?
o How does bending strength vary in three dimensions for balsa, based just on your finger evaluations?
· Now prepare your basic units of wood by slicing the sheets you have.
o Lay one sheet flat and measure a width of 5 mm.
o Your group can decide on the length, BUT IT CANNOT be longer than 180 mm.
o Using a metal ruler and blade, score the wood at this width.
o Repeat the scoring cut till you free the stick from the sheet.
o Repeat this process, each student in your group making 20 sticks.
· Evaluate the bending strength of balsa wood.
o Devise a physical test using fishing weights and buckets, as demonstrated.
o Weigh your bucket and string to get a base weight.
o Now test a single stick, then several sticks together
o Is the weight to break several sticks simply a multiple of one stick (Additive Property)?
§ Record your data, in table form, in your lab notebook
· In your lab book, record your observations.
o What did you observe by evaluating with your fingers?
o Design a structure that your group feels will hold the most weight
§ Base your design off of the results you have recorded thus far
§ If you choose to use glue or any other material, make sure you have tested how the material will effect the strength of the wood without the added material
§ See “Brainstorm” section, below, for additional things to consider when creating your structure
o Describe your test set-up with a drawing.
o Record your data in table form- you must have this!
o In your final report you will use your tables to discuss/reason your chosen design for optimal strength.
· Brainstorm, in your group, to come up with a designed structure to test.
o Think about the grain and how it affects bending strength.
o Think about the results from the previous lab.
o Your design should use 3 or more sticks glued/attached together but do not just stack them up in a layered structure. Be creative! You can also cut pieces from the sheets of material available.
o Think through how you will “build” your design: glue? Weights?
o Check your design with Coach B or Mr. Frazee before beginning construction.
o Make four copies of your designed structure and set them up to dry.
o Calculate cross sectional area for each of your samples.
§ For the sticks by themselves, calculate a force per stick area.
§ For your design, what is the working area, not air in between?
o Next lab you will test your designs, then write your final report. Each lab group member will write his/her OWN lab report. ONLY data can be shared between group members. The rest of the lab report should be an independent assignment.
o Try to find references that discuss flexural strength of materials that are currently being produced.
· Make conclusions regarding the properties of the design that you created.
o Try to find references to include in your paper that support any conclusions you have made based on your results
o See me or Coach B for any questions
The competition will take place during the second lab and your lab report will be due 1 week after the competition.