Advanced Course on Fiber-based Materials and Products

Karl Schulte

Karl Schulte

Advanced Composite Materials

Technische Universität Hamburg-Harburg (Germany)
schulte@tuhh.de

Biography

Prof. Dr.-Ing. Karl Schulte has been head of the Institute of Polymers and Composites of the Technische Universität Hamburg-Harburg (TUHH), Hamburg, Germany, until September 2013. After working as an apprentice in electrician he studied General Mechanical Engineering at the Ruhr-Universität in Bochum (Germany). He received his Ph.D. from Ruhr-Universität Bochum in 1979, on “Fracture Mechanics and Fatigue Crack Propagation of High Strength Aluminium Alloys”. He worked until 1991 with DLR (German Aerospace Research Center, Institute of Materials Science) in Cologne, Germany. Within the field of lightweight materials he changed the focus of his research from metals to fibre reinforced composites. In 1992 he became Professor at TUHH and was teaching since than Polymers and Polymer Matrix Composite Materials. He had sabbatical leaves at Virginia Polytechnic Institute and State University (Virginia Tech) in Blacksburg, Virginia, U.S.A. and the University of Cambridge, Department of Materials Science and Metallurgy, Cambridge, U.K. His research focused on degradation of fibre reinforced composite materials, nanocomposites and the synthesis of carbon nanotubes (CNTs) and Aerographite, a three dimensional graphitic aerogel.

Prof. Schulte is member of the Editorial Boards of several national and international journals in the area of composite materials. He is the European Editor of the international journal “Composites Science and Technology”. Together with his collaborators he has published more than 400 peer-reviewed publications. ISIHighlyCited.com listed Prof. Schulte as “Highly Cited Researcher in Material Science”. He is an elected By-Fellow of the Churchill College in Cambridge, UK. In 2013 the “International Committee for Composite Materials” (ICCM) named him “Composites World Fellow” and in September 2014 he received the “Medal of Excellence in Composite Materials” from the University of Delaware, DA, USA. In 2013 he was nominated for the prestigious “Diesel Medal”.

Prof. Schulte continues to work scientifically in the composites field as a consultant and assessor and guides research projects on the synthesis of graphene based nanostructures and polymer nanocomposites.

Abstract

Fibre reinforced polymers (FRP) gain more and more in importance in times of growing demands of light, efficient and energy saving structures. FRP offer high mechanical properties at low density, resulting in excellent specific stiffness and strength having superior mechanical properties compared to conventional structural materials. They have been under intensive investigation for more than 40 years and already gained a very high standard, resulting in increasing use in technical structures, mainly aircraft, rotor blades for windmills, and in general engineering applications.    However, the design guides and the presently existing failure criteria lead to an insufficient use of their strength potential. This is due to a lack of understanding of the three dimensional stress state inside composite materials. It is therefore evident to investigate composite materials also under multiaxial loading conditions.

Damage development in tension and compression loading as well as fatigue, is a combination of different damage mechanisms like matrix cracks, fibre–matrix deboning, delamination and fibre fracture. All the observed types of damage cause stiffness degradation of the composite before ultimate failure. At tensile loading different damage mechanisms can be classified in three phases of damage accumulation. Phase I is characterised by inter fibre crack initiation and crack growth which leads to strong increase of the matrix crack density in the transverses layers resulting in a decrease in stiffness. Delamination growth and stress redistribution accelerate the degradation process and the finally causing fibre fracture yields to abrupt rupture of the composite. Damage caused by an impact has a negative effect on the performance of FRP. The failure mode of impact damage results in matrix cracks, delamination and fibre fracture.

Damage growth is difficult to evaluate in situ with state of the art NDE methods. In order to improve safety considerations, minimize down time, avoid sudden breakdowns and optimize maintenance, structural health monitoring (SHM) of FRP structures has gained increasing importance. Examples for NDE methods for FRP-structures are acoustic emission, thermography, X-ray, ultrasonic and optical techniques. Some of the techniques allow detailed insights in the health of FRP-structures, but most of them have serious drawbacks and are not suitable for the in situ health monitoring (sensing) of large or complex structures. A promising approach of SHM in FRP structures is the monitoring of the electrical material properties.

In the area of materials, there had been strong improvements in the development of nanocomposites (polymers filled with nanoparticles, as carbon nanotubes, graphene, etc.). Nanocomposites used as matrix for fibre reinforced composites have the potential to improve overall mechanical properties, as fracture toughness, first ply failure, impact and compression after impact etc. Other important properties can also positively be influenced, as electrical and thermal conductivity.

We will give an overview on the development of nanocomposites, its integration into fibre reinforced polymeric structures and the gain achieved in overall properties, so that the composite materials can even better compete with conventional materials, respectively are an even more attractive alternative.