Density Polyethylene Experiment
The tests where ran by Dr. Bob Bonenberger in the Modern Engineering Materials Instructional Laboratory. The aluminum and cast iron samples used were in the shape of cylinders so they had a circular cross sectional area whereas the HDPE was in a rectangular shape so it had a rectangular cross sectional area. The Tinius Olsen H25K-T benchtop universal testing machine applied an outward pulling force on each side of the sample. The machine has grips that can latch onto the top and the bottom of the sample and pull the sample from the top, causing each sample to begin to deform and eventually break. The first material that was tested was the aluminum cylinder. Dr. Bob Bonenberger put the sample into the machine and explained what was occurring through an enlarged webcam and live-action graph that was plotting the strain and the force applied. There was a loud sound when the material broke and then Dr. Bob Bonenberger removed the two pieces of aluminum, passed it around the class, and went over some key aspects that resulted during the test such as the ultimate stress etc. The same process was repeated for the cast iron and the HDPE. The HDPE however took a long time to fracture compared to the other two materials. It almost made the Tinius Olsen H25K-T benchtop universal testing machine go up to its max height. Overall, when the HDPE eventually did fracture it didn’t make a loud noise like the other two …show more content…
The yield tensile strength was 255 MPa, in where the aluminum we used had a yield stress of 350 MPa. However, unlike the tensile strength for both the yield and ultimate being drastically different, the young’s modules our aluminum had was around 71 GPa and the average for aluminum alloy 6061-T6, T651 was 68.9 GPa which isn’t a drastic difference like the other two quantities. For HDPE the yield stress that we ended up with was around .305 MPa but the average is around 13-200 MPa according to matweb. The ultimate strength that we got was 7.47 but the average is around 15.2 -45 MPa. The Young’s modules was also well below the average in where the young’s modules for our HDPE was around .175 GPa and the average was .62-1.3 GPa (2). The average yield stress for a cast iron is around 98-280 MPa and ours had a yield stress around 1.71 MPa. Our young’s modules was around 102 which fits in the average of cast iron which is around 82-140 GPA. The ultimate strength that our cast iron had was around 320 MPa which fits the average at around 150-450 MPa. The only item that doesn’t fit any aspect of the online averages that I searched was the HDPE that we used (3).
HDPE was very versatile in where an HDPE milk jug that weighs 2 ounces can carry a gallon of milk. The HDPE can easily be molded nearly into