are gaining increasing interest from society and industry due to their combination of good technological performance and low environmental impact. Bio-based composites are currently used for secondary structural components in transportation and building applications
, but their potentially high mechanical properties and low weight point to a future use also for primary structural components.
Below follows a list of research issues on bio-based composites that are addressed by the “Composites Materials and Mechanics” section at DTU Wind Energy, and that can form the topic of a student project:
The variability in mechanical properties. Compared to conventional fibres, natural fibres show typically relative larger variability in properties due to uncontrolled conditions during their growth and processing. It is believed that the variability in properties is primarily caused by the distribution of defects along the fibres.
The influence of humidity. In contrast to most conventional fibres, natural fibres absorb large amount of moisture from the surrounding atmosphere leading to changes in dimensions and mechanical properties.
The packing ability of fibres. In composites, the packing ability of the fibres determines the maximum obtainable fibre content. Natural fibres show typically lower packing ability than conventional fibres.
The fibre preforms. Natural fibres are widely available in the form of woven fabrics aimed for textile applications. Development is however needed to tailor-make natural fibre preforms for composite applications; optimization parameters are fibre twisting angle, yarn linear density, and yarn non-crimp configuration.
The use of biomass-based polymer matrices. To have fully biocomposite materials, both the fibre and the matrix phases should be derived from biomass-based resources. A range of commercially available thermoplastic and thermosetting biopolymers are currently being developed, and their technical performance must be evaluated with respect to their use in composites.
The processing of composites. Due to the many special characteristics of natural fibres and biopolymers, the conventional manufacturing techniques used for composites need to be modified.
The fibre/matrix interface in composites. Methods must be developed to characterize the interface bonding properties between natural fibres and biopolymers.
The porosity in composites. Bio-based composites contain typically a relative larger amount of porosity than conventional composites, and this must be included in the analysis of properties.
The mechanical performance of composites. Since bio-based composites are new types of materials, their complete mechanical performance (e.g. tension, compression, shear, fracture toughness, fatigue, creep) must be determined.
The modelling of composite properties. The irregular form and size of natural fibres lead to composites with a complicated microstructure, and this entails changes to the typically used micromechanical models.
Development of design models
Composites, materials science