Thermophysics of a crack propagating in poly(methyl methacrylate)

Autor: L. I. Manevich, L. S. Zarkhin
Rok vydání: 2010
Předmět:
Zdroj: Polymer Science Series A. 52:942-948
ISSN: 1555-6107
0965-545X
DOI: 10.1134/s0965545x10090105
Popis: Temperature kinetics along the crack propagation path in the bulk of PMMA at 20°C and under impact loading is explained. The initial experimental data are taken from [1, 2]. The kinetic temperature-time curve includes six different regions. In this study, the sequence of regions in the temperature kinetics is interpreted as a sequence of stages corresponding to the extension and breakdown of polymer chains in a microregion with dimensions of ≈130 μm located on the trajectory of crack propagation. At the first stage with a duration of ≈8 μs, the temperature increases by ≈10°C. This temperature rise that is related to the arrival of a loading wave front. At the second stage with a duration of ≈5 μs, temperature decreases by ≈8°C. This process is controlled by the thermal elasticity of polymer chains. At the third stage, temperature increases up to ≈90°C owing to the plastic flow of the material. At this stage, ahead of a crack, a craze is formed. Rearrangement of the isotropic polymer structure into an anisotropic polymer structure proceeds within ≈7 μs. At the fourth stage, temperature strongly decreases (nearly down to −150°C). This temperature reduction is provided by thermoelastic deformation of valence angles and chemical C-C bonds of the polymer backbone. At the fifth stage, the material heats up owing to the dissipation of the stored elastic energy due to the breakdown of extended polymer chains. This stage of the temperature rise on polymer chains spans over ≈18 μs. This phenomenon indicates the marked spatial continuity (diffuse character) of a crack tip and is related to a broad length distribution of ruptured chains. During the sixth stage, temperature remains at a constant level of ≈100°C for more than 100 μs. This stage reflects the emergence of exothermic processes on the newly formed fractured surface.
Databáze: OpenAIRE
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