Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article


Master of Engineering Science


Chemical and Biochemical Engineering


Hrymak, Andrew N.

2nd Supervisor

Henning, Frank


Karlsruhe Institute of Technology



The compression molding of glass mat thermoplastics (GMT) allows high volume manufacture of composite parts with a short production cycle. Computer simulation is often used to assist process development and optimization. Reliable simulation depends on input of material property parameters and accurate prediction of heat transfer. This thesis developed experimental methods to characterize material property and heat transfer process parameters. Results were obtained by applying the methods to a selected commercial GMT sheet. Heat transfer coefficients including convection coefficients during pre-heating and transfer, as well as contact conductance at sheet-mold interface were estimated by a parameter-fitting approach. Viscoelastic parameters of the composite were characterized by oscillatory torsion bar, which can be used to model the draping behavior. The elastic modulus and viscosity were fitted by a Williams-Landel-Ferry (WLF) and Cross-WLF model, respectively. Flow behavior of a stacked charge was also characterized by a 1-D squeeze flow model, where the apparent viscosity was fitted by a temperature dependent power-law model.

Summary for Lay Audience

In the automotive industry, light-weighting has become one of the top priorities as it provides better fuel efficiency and handling. Polymer composites are widely used in car manufacturing for this purpose. In general, it refers to a material that is composed of a polymer matrix (e.g. PP, PA) and fiber reinforcement (e.g. glass or carbon fiber). Automobile parts made of polymer composites not only enables light-weighting, but also possesses good mechanical strength. The process of forming raw composite material into desired part geometry is called molding. Various molding techniques have been developed, such as the compression molding, the resin transfer molding or the thermoforming.

To build a molding process for part production, it is often required to also establish a continuous and functional virtual process chain by means of computer simulation. Simulation results may accelerate and optimize the development of real process chain. One of the keys to reliable simulation output is the accurate input parameters. In terms of molding simulations, these parameters include material properties and heat transfer coefficients. Therefore, the characterization of these parameters is increasingly gaining interest by the industry.