Authors: Mrinal C. Saha, Sriram Mohan, Anandh Balakrishnan
Addresses: School of Aerospace and Mechanical Engineering, University of Oklahoma, 208A Felgar Hall, 865 Asp Avenue, Norman, OK 73019, USA. ' School of Aerospace and Mechanical Engineering, University of Oklahoma, 318A Felgar Hall, 865 Asp Avenue, Norman, OK 73019, USA. ' School of Aerospace and Mechanical Engineering, University of Oklahoma, 306 Felgar Hall, 865 Asp Avenue, Norman, OK 73019, USA
Abstract: Dynamic mechanical analysis (DMA) experiments have been performed on rigid polyurethane (PU) foams using a torsional rheometer. Circular disk samples were tested at several frequencies between 1-2,000 cpm and at temperatures between 25°C-150°C. The dynamic torsion tests were carried out in two phases. In the first phase, logarithmic frequency sweeps were carried out at each temperature with 0.05° angle of strain. In the second phase, linear strain sweeps in the range of 0.05°-5° angle of strain were carried out at a frequency of 100 cpm. The frequency sweep results allowed to obtain a master curve based on the principle of frequency temperature superposition at a reference temperature of 115°C. The predictions obtained from the master curve have been validated at selected frequencies. The shift factors were found to follow an Arrhenius relationship and the activation energy was found to be 264.46 kJ/mol. Results from the dynamic strain sweep tests indicate that samples go through predominantly viscoelastic behaviour. The strain sweep samples showed significant fracture near the ridges on the top die whereas the frequency sweep samples showed significant striations near the reference temperature.
Keywords: polyurethane foams; dynamic shear properties; frequency sweep; strain sweep; dynamic mechanical analysis; DMA; frequency-temperature superposition; fTSp; shift factors; activation energy; rigid foam; dynamic torsion; viscoelasticity.
International Journal of Materials Engineering Innovation, 2009 Vol.1 No.2, pp.235 - 253
Published online: 23 Nov 2009 *Full-text access for editors Access for subscribers Purchase this article Comment on this article