There were several different objectives for this lab. It introduced the thermomechanical properties of thermoplastics, and provide familiarity with dynamic mechanical analysis (DMA) of thermoplastics. These DMA results were interpreted using time temperature superposition (TTS) and the master curve as a design tool, this could be used to determine the linear viscoelastic range and observe the creep behaviour of high density polyethylene (HDPE). Gaining familiarity with dynamic properties of HDPE was also intended for this lab.
The material used for testing was HDPE. Two sample types were used, one quenched in water and another cooled slowly at a rate of 1°C per minute.
All testing was carried out using DMA with a cantilever setup. Two different tests were carried out. For the first test, the HDPE was held at a constant temperature of 31°C and varying stresses were applied for two seconds at a time, during which the strain in the sample was recorded.
For the second test, a constant stress of 5MPa was applied while the temperature was increased inside the furnace of the DMA setup. This was achieved by heating the sample to one temperature for 10 minutes and holding at that temperature while the constant stress was applied, then heating again and holding, and so on. Strain was again recorded at constant time intervals for each temperature.
Figure 1 below is an isochronal graph showing the results of creep testing the sample of HDPE