plastics

Overview

Cylindrical HDPE specimens are tested in compression at three different temperatures - one at room temperature, one at 130 degrees F and one at 10 degrees F. Analysis and results illustrate the effects of temperature on stress and strain.

prelab assignment

Typical 3-in. long specimens, one in insulation blanket

Objectives:

Demonstration of the effects of temperature on material strength. Plastics are highly sensitive to temperature.
Practice calculating and plotting stress - strain data with Microsoft Excel.

Safety Info	Safety! Safety glasses are required at all times while equipment is turned on. Not only are safety glasses a good precaution, they prepare students for industry where they are also required. Use caution when handling hot and cold specimens - use tongs and/or mitts to protect your hands if you need to.
	Equipment Used Dial calipers Instron 4400R testing machine or Instron 4485 testing machine Dial gage Procedure [excel data sheets] right-click, save target as At your table: Measure and record the diameter, length (Dial Calipers) and temperature of all three specimens in Table 2-1, 2-2 and 2-3. Dimensions should be measured at three locations and then averaged. Mark all three, and return the hot and cold specimens to the oven and freezer. Based on dimensions, calculate the following: Load application speed = 2% strain / minute Record load readings approximately every 0.5% strain Maximum strain = 10% Determine on the dial gage the increment loads are to be recorded. Establish on the data sheet the load increment column in preparation for reading loads. At the testing machine: Verify load application speed. Get three people organized: dial gage reader - to say "read" at the calculated increment load reader - read load aloud recorder - to write it down. Place the specimen in either the Instron 4485 or Instron 4400R Put a small holding load (less than 50 lb.) on the specimen and zero the dial gage. Start the test, read loads at calculated increments to 10 % strain. Unload for final reading. Repeat the procedure for the specimens at approximately 130°F and 10°F. Use the insulation blankets to reduce heat loss. Typical stresses at 10% strain are 1,000 psi for the hot specimen and 3,000 psi for the cold specimen.
	Data Development of Results Example of plots in adobe pdf format How-to-do-it in MS Excel 2007 videos in flash format calculations and one stress-strain (XY SCATTER) plot instead of using pencil and straightedge, add the construction lines for E and 0.2% yield but still label the numbers on the plot! How-to-do-it in MS Excel 2003 videos in RealMedia format. (free player, but click carefully - they have ones you have to pay for too.) plotting stress-strain on XY SCATTER plotting stress-strain results for all three specimens on one page instead of using pencil and straightedge, add the construction lines for E and 0.2% yield but still label the numbers on the plot!
	Published Data for Plastic Specimens High Density Polyethylene: Novapol Polyethylene HD-2007-H Nova Chemicals Calgary, Alberta, Canada Strength at Yield = 3300 psi