Correlation between master curves obtained from rheology and mechanical testing

Thesis Type: Postgraduate

Institution Of The Thesis: Orta Doğu Teknik Üniversitesi, Faculty of Arts and Sciences, Department of Chemistry, Turkey

Approval Date: 2015




Characterization of viscoelastic materials has attracted attention since 1850s due to temperature dependent properties they perform. Time – temperature superposition principle is an important concept to estimate the behavior of viscoelastic materials. This principle is used to generate master curves for viscoelastic polymers by using time – temperature equivalence principle. There were mainly two techniques used in the recent studies. The most common characterization is mechanical testing and second technique is dynamic mechanical analysis (DMA). In this study, a HTPB (10-15%) based rocket propellant containing ammonium perchlorate (65-70%), aluminum powder (15-20%) was chosen and its master curves were estimated both with mechanical tests and rheometer. The aim was to compare the shift factors and master curves. At first, under certain frequency and temperature range the master curve was generated by rheometer. After that, shift factors and complex modulus were calculated. On the other hand, stress relaxation tests were performed to determine relaxation modulus and shift factor at different temperatures. According to test results, master curve of the given propellant was generated by time – temperature superposition principle. Finally, the results obtained from both rheometer and stress relaxation results were compared. For comparison, the complex modulus obtained from the rheometer was converted to relaxation modulus by taking the Poisson’s ratio as 0.5. The shift factors and obtained master curves were compared for each technique. As a result, for the propellant, no correlation was obtained between the techniques and it was concluded that, mechanical tests cannot be replaced with rheometer tests.