Laboratory Scale - Fundamental Research

Manufacturing and mechanical properties of fibre hybrid composites with controlled microstructure: Assessment of synergetic effects by micromechanical modelling


Lightweight design is becoming an important criteria for various industries, particularly in wind energy, aerospace and automotive applications. The need of lightweight engineering materials is not only important to enhance the performance characteristics of the system, but to also reduce the greenhouse gas emissions associated with it. Fibre composites have been attracting great interest due to its high strength to weight ratio. Their stiffness and strength properties with respect to weight are superior to a range of other engineering materials including polymers, metals/metal alloys and foams. One commonly seen drawback of composites, however, is their limited toughness that comes at the expense of their high stiffness and strength.

A composite system comprising more than one type of reinforcing fibres in a common matrix is denoted as hybrid fibre composites. Such systems make it possible to allow more optimal design of the properties of composites to meet the required specifications. Furthermore, they exhibit a potential synergistic effect of having two (or more) types of fibres with different properties. Research on hybrid fibre composites started several decades ago, but the focus shifted towards production technologies and understanding the mechanical behaviour of the conventional single fibre composites. Over the years, improvement in failure strain and toughness of single fibre composites have been a highly active research area. These concerns have led the recent revival of researchers’ interest in “hybridization” of composites. 

PhD Objectives:

This PhD project aims to explore the correlation between the microstructure of hybrid composites and its performance characteristics. The project is divided into two parts – a modelling part, and an experimental part. The modelling part will focus on the development of micromechanical models and finite element models to predict optimal microstructures for wanted composite performance characteristics, e.g. static and fatigue mechanical properties. The project will explore the required microstructure that might lead to synergetic effects in hybrid composites. The experimental part involves the manufacturing of hybrid composites with desired microstructure and volumetric composition. Different materials systems and manufacturing techniques will be used. Image based microstructural analysis and materials characterization will be performed to study the synergies in hybrid composites. The obtained experimental data will be used as input parameters to validate the developed models. Industrial scale recommendations for the selection of fibre types, microstructure and manufacturing techniques will be identified for tailor-made mechanical performance of hybrid composites.

Research activities:

An overview of the tasks in the project, together with brief descriptions of the planned work.  

  1. Analytical modelling:
    Development of geometrical models that capture the local and global fibre volume fractions of the fibre types in hybrid composites. This will be integrated into micromechanical models to describe the interactions between the components of hybrid composites aiming at predicting the relationship between volumetric composition, microstructure and mechanical stress-strain behavior in tension, compression and fatigue. This will allow for evaluating synergetic effects due to these interactions.
  2. Finite element modelling:
    Computed tomography scanning will be used to capture the exact microstructure of the developed hybrid composites, and the microstructure will be implemented in FE modelling using the commercial FE software ABAQUS.
  3. Materials selection: 
    Focus on the conventional carbon and glass fibres, but alternative type of fibres such as natural and biopolymer fibres will also be investigated. Focus on thermoset matrices, but thermoplastic matrices will also be considered.
  4. Manufacturing:
    Different manufacturing techniques like pultrusion, vacuum infusion, and filament winding will be used. The Danish company Fiberline is part of the project and is going to manufacture the hybrid composites through pultrusion technique.
  5. Microstructural analysis:
    The microstructure of the hybrid composites e.g. spatial arrangement of fibres, will be quantified using techniques like optical microscopy, electron microscopy, X-ray tomography, and image analysis. The volumetric composition of hybrid composites will be measured by a gravimetric method, with focus on local and global fibre volume fractions.
  6. Mechanical characterization:
    The mechanical properties of hybrid composites will be measured with focus on static tension, compression and shear. In addition, dynamic testing, i.e. fatigue tests will also be performed to understand the behavior of hybrid composites under cyclic loading conditions.
    This work is a part of the HyFiSyn project that has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 765881.


Rajnish Kumar
PhD student
DTU Wind Energy
+45 22 40 03 56