Electronic Thesis and Dissertation Repository

Thesis Format



Master of Engineering Science


Mechanical and Materials Engineering


Henning, Frank


Karlsruhe Institute of Technology

2nd Supervisor

Hrymak, Andrew


A composite had been widely used for the lightweighting purpose amid increasing environmental concerns. Among composite manufacturing processes, compression molding is widely used for automotive parts. During compression molding, the mold geometry and molding process conditions significantly influence the fiber configuration and the mechanical performance.

Hence, this thesis aims to characterize the microstructural and mechanical properties of the complex shaped composite automotive components: outer seatback and inner seatback. Both parts were compression molded using commercial glass mat thermoplastic sheet with long glass fibers (30mm-50mm) embedded in the polyamide resin. The microstructural characterization results showed that the microstructural properties are influenced by geometries of the automotive components. Especially the geometries significantly influenced the fiber orientation of the nearby region. For the mechanical properties, both tensile and flexural properties were measured. The better mechanical properties were shown in the samples with higher fiber alignment in a loading direction.

Summary for Lay Audience

The automobile industry recently had been focusing on enhancing the fuel efficiency of automobiles due to increasing regulatory demands around the globe. As a result, the automobile industry turned its attention towards lightweighting. Lightweighting is a design concept that aims to reduce the vehicle weight by replacing the vehicle parts with materials of high strength and low density such as composite material. A composite material is a material made of two or more constituent materials. In this thesis, a composite of interest is a fiber reinforced composite, which contains fiber reinforcement and matrix. Fiber reinforcement adds strength to the composite material. Matrix holds fibers and transfers the load to fibers.

A composite material can be molded with a variety of molding methods, but this thesis is only concerned with compression molding. Compression molding is a composite molding method that uses a hydraulic press to compress the charge material into the desired form. During the compression molding, mold geometry can cause significant changes in the microstructural properties of a composite (i.e. fiber orientation), which are closely related to its mechanical performance. Therefore, the understanding of the impact of the mold geometry on the microstructural properties of the molded material is important.

Hence, this thesis first aims to evaluate the influence of mold geometry on the microstructural properties of the compression-molded automotive components. The experimental techniques are utilized to characterize fiber orientation, fiber concentration, and fiber length in various areas of different geometries. Also, this thesis aims to investigate the influence of the microstructural properties of composite automotive components on their mechanical properties.