Abstract
This paper aims to explore the mechanisms of the complex thermo-mechanical behavior of polymer glass across a wide range of temperature variations. To this end, the free vibration frequency spectrum of simply supported poly(methyl methacrylate) (PMMA) beams was thoroughly investigated with the aid of the impulse excitation technique. It was found that the amplitude ratio of the multiple peaks in the frequency spectrum is a strongly dependent on temperature, and that the peaks correspond to the multiple vibrational modes of the molecular network of PMMA. At a low temperature, the vibration is dominated by the overall microstructure of PMMA. With increasing the temperature, however, the contribution of the sub-microstructures is retarded by β relaxation. Above 80 °C, the vibration is fully dominated by the microstructure after relaxation. The relaxation time at the transition temperature is of the same order of the vibration period, confirming the contribution of β relaxation. These findings provide a precise method for establishing reliable physical-based constitutive models of polymer glass.
Highlights
The mechanical properties of polymer glasses are dependent strongly on temperature and strain rate [1,2,3,4,5]
The relaxation time at the transition temperature is of the same order of the vibration period, confirming the contribution of β relaxation
This is due to the polymer glass’s amorphous microstructure which consists of the backbone molecular microstructure formed by the primary covalent bond and the sub-microstructures linked by the secondary bonds such as hydrogen bond and van der Waals’ force [6,7]
Summary
The mechanical properties of polymer glasses are dependent strongly on temperature and strain rate [1,2,3,4,5]. This is due to the polymer glass’s amorphous microstructure which consists of the backbone molecular microstructure formed by the primary covalent bond and the sub-microstructures linked by the secondary bonds such as hydrogen bond and van der Waals’ force [6,7]. Under thermal and mechanical loadings, the secondary bond can be broken and the structure can be rearranged cooperatively [8,9], making the mechanical properties of polymer glasses strongly temperature and rate dependent. The mechanical properties of the PMMA may be altered
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