Thermoviscoelastic modeling of thermoplastic polymers/ Johannes Keursten.

Format:

Book

Author/Creator:

Keursten, Johannes, author.

Series:

SchriftenreiheKontinuumsmechanik im Maschinenbau Band 30.

Language:

English

Subjects (All):

Thermoplastics--Mechanical properties.

Thermoplastics.

Viscoelasticity--Mathematical models.

Viscoelasticity.

Polymers--Thermal properties.

Polymers.

Glass transition temperature--Industrial applications.

Glass transition temperature.

Thermodynamics--Irreversible processes.

Thermodynamics.

Physical Description:

1 online resource

Place of Publication:

Karlsruhe : KIT Scientific Publishing, 2025.

Summary:

Thermoplastic polymers are used in a variety of industrial applications, e.g., as a matrix material in fiber-reinforced materials. A central physical phenomenon in thermoplastics is the glass transition. In the glass transition regime, a significant change in thermomechanical material properties and a pronounced process-dependent material behaviour is observed, which must be taken into account in material modeling. In this work, first, the theory of linear thermoviscoelasticity is described in detail. The general thermoviscoelastic material models are derived within the framework of linear irreversible thermodynamics. Generalized Maxwell and Kelvin models are used to model viscoelastic behaviour and are extended by thermal expansion elements. It is shown that the models differ in their natural state variables. Depending on the load case, one of the two models is more suitable. A conversion method between the parameters of the two models, including thermal expansion elements, is presented as an extension of known numerical conversion methods of the purely viscoelastic models. To formulate the process-dependent caloric model, an analogy between stress relaxation and entropy relaxation is used. Next, the viscoelastic part of the model is applied to temperature–frequency tests of polyamide 6. Different load sizes and conditioning states are considered. The construction of master curves using extended time–temperature superposition is discussed in detail. Using a moisture-dependent reference temperature, the influence of different water contents due to different conditioning states is taken into account. The master curves give implications on the limits of linear viscoelasticity.

Contents:

Publications Zusammenfassung Summary Acknowledgments Notation, symbols and abbreviations Introduction Fundamentals Constitutive theory of thermoviscoelasticity Viscoelasticity in polyamide 6 Entropy relaxation in polystyrene Summary and conclusions Appendix A: Generalized thermorheological models Appendix B: Thermoviscoelasticity of PA6 Bibliography.

Notes:

Includes bibliographical references (pages) and index.

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