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Fiber-matrix interaction

The adhesion between fiber and matrix is crucial for the mechanical properties and the chemical and thermal stability of the fiber reinforced composite. It is governed by the interfacial region between fiber and matrix – the so called interphase. Focus of the group is the development of a fundamental understanding of the interphase structure, the interaction between carbon fibers and matrix systems and the resulting properties of the composite. To achieve this, the results from microscopic investigations are correlated to mechanical properties and failure mechanisms of the macroscopic composite. Our focuses are thermosetting and thermoplastic polymers as well as ceramic matrices.

 

Microscopic investigation of the interphase

Scanning probe microscopic investigation of the interphase between carbon fiber and polymer matrixThe interphase comprises the interface between fiber and matrix as well as the neighboring regions of fiber and matrix, which exhibit material properties that are different to that of the bulk materials. The extent of the interphase is strongly dependent of the materials used and ranges from some nanometers to some micrometers. One focus of the group is the characterization of materials properties of the interphase of carbon fiber reinforced polymers. Their extent, their structural, mechanical, chemical and thermal properties are characteristic for the system of fiber, sizing and matrix used as well as for the process parameters of composite production. In the case of thermoplastic matrices the development of transcrystalline layers in the vicinity of the fibers is of particular interest. The investigation of nano-scale variations of structural, mechanical and thermal properties is performed by scanning probe microscopy. Determination of the chemical composition and the binding structure of the interphase are done by scanning auger microscopy.

Micromechanical characterization

Single-fiber-push-out experiments on carbon fiber reinforced polymerOne particular focus of the group is the micromechanical testing of singe-fiber polymer composites and micro-composites. The bonding of single fibers to the surrounding polymer matrix is investigated, which has direct influence on the macroscopic mechanical properties of the composite material. The results of micromechanical testing are characteristic for the respective system of materials as well as the process parameters of composite production. Different micromechanical methods are used, e.g. the single-fiber pull-out test and the micro-bond test on single-fiber polymer composites and single-fiber push-out tests on composite materials. All of those methods are developed further to improve their interpretability. Ultimately, the aim is the development of a correlation between the micromechanical properties and the macroscopic properties of a composite.

Macromechanical characterization

The influence of fiber-matrix interaction on macroscopic mechanical properties of a composite is investigated mainly by interlaminar material parameters. Measurements of the interlaminar shear strength and the interlaminar fracture toughness (mode I, mode II, mode I/II) are performed. As alternative, fiber fragmentation tests under tension and compression loading can be used. To establish a correlation between microscopic fracture processes and macroscopic material properties acoustic emission measurements are performed during the mechanical tests.

Contact person:

Judith Moosburger-Will

Group members:

Thomas Guglhör

Eva Laukmanis

Michael Schulz