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Über dieses Buch

David Degenhardt develops an elasto-viscoplastic material model in order to predict the temperature and strain rate-dependent deformation and fracture behavior of thermoplastic polymers. The model bases on three supporting ambient temperatures, where a thermoplastic polymer has been characterized profoundly at the stress states 1) uni-axial tension and compression, 2) bi-axial tension and 3) shear. The core of the material model builds a pressure-dependent yield function with a non-associated flow rule. Further, it contains an analytical hardening law and a strain rate-dependent fracture criterion. The model is validated with components subjected to impact loading at different ambient temperatures. The comparison of the simulation and the experiments shows that stiffness, hardening, fractures strain as well as thicknesses can be well captured.

About the Author:

David Degenhardt is a calculation engineer in the chassis development department of a German automobile manufacturer and earned his doctorate while working at the Technische Universität Carolo-Wilhelmina zu Braunschweig, Germany.

Inhaltsverzeichnis

Frontmatter

Chapter 1. Motivation

Abstract
The use of polymer materials has been strongly increasing in the automotive industry in the past years [9]. Main advantage is the low weight and the possibility to design complex structures. For the application in vehicles, many polymer components have to pass various crash load cases at room temperature (RT, 18–22°C) for the fulfillment of legal requirements [10].
David Degenhardt

Chapter 2. Objectives, Scope and Outline of Work

Abstract
Thermoplastic polymers are very sensitive to temperature and strain rate influence, which needs to be considered in the modeling of such materials. Many authors focused their studies on the reproduction of either the temperature influence of semi-crystalline thermoplastic polymers [22–24] or the rate-effects [25–27]. However, there is a need for material models capturing both features as well as several additional polymer-specific characteristics in order to achieve a good representation of the material behavior in the crash load case.
David Degenhardt

Chapter 3. State-of-the-Art

Abstract
The thesis presents a new material model for a thermoplastic polymer under different ambient temperatures which is validated by experimental results. This requires a full understanding of the manufacturing and complex characteristics of the thermoplastic material itself. Basis of the development build many different experiments on small specimens.
David Degenhardt

Chapter 4. Experimental Work

Abstract
Parts of the experimental work chapter have been published in [7] and [2].
David Degenhardt

Chapter 5. Temperature-dependent Material Model

Abstract
The modules of the temperature-dependent material model have been published in [7]. Large parts of the publication are used here for explaining the material model modules.
David Degenhardt

Chapter 6. Model Validation

Abstract
Large parts of the validation chapter have been published in the publication [2].
David Degenhardt

Chapter 7. Critical Assessment of the Material Model

Abstract
In general, the new temperature-dependent material model well predicts the deformation, damage and fracture behavior of the talcum-filled PP/PE co-polymer for varying load cases, as outlined by the validation tests. There are, however, limitations of the material model, which are discussed in the following.
David Degenhardt

Chapter 8. Conclusions and Recommendations

Abstract
A generalized temperature-dependent material model that is able to represent the material behavior in the crash-relevant temperature range from −35C to 90C has been introduced. The model uses a non-linear interpolation of the mechanical properties ranging from elasticity, over yielding and hardening up to fracture. The material model bases on a profound material characterization and data analysis and is parameterized with a parameter identification procedure partially based on minimizing the error of global and local quantities between simulation and experiment.
David Degenhardt

Backmatter

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