Tow-Based Discontinuous Composites (TBDCs) consist of a network of randomly positioned
and oriented carbon fibre tows, embedded in a polymeric matrix. These materials
provide a solution for combining the manufacturability and mechanical performance
for high volume production of structural components, e.g. in automotive/sporting
industry. The growing application of TBDCs in structures, in the meanwhile, urge
the need for an efficient design tool to account for their discontinuous nature and the
heterogeneous microstructure. This work therefore aims to deepen the understanding
on the mechanical response of TBDCs and develop design tools for TBDC structures.
An experimental study was conducted to compare the mechanical properties and
failure mechanisms of randomly-oriented TBDCs to their equivalent ply-by-ply laminate
counterparts. The results validated the equivalent laminate analogy used in literature
for modelling TBDCs, while measuring the 30% strength knock-down in TBDC due
to the intrinsic variability in the microstructure of TBDCs and hence highlighted the
need to account for this variability in modelling TBDCs.
To account for the intrinsic variability in TBDCs, an analytical strength model
based on stochastic equivalent laminate assumption was developed. This model predicts
the strength of TBDCs with good agreement to the experimental data, and is able to
capture the change in the strength of TBDCs with changing tow dimensions, and
therefore, can be used to aid material design and microstructural optimisation.
The analytical strength model developed is then integrated with a finite element
design framework to account for variability in TBDCs in structural components. By
conducting a case study on the engine bonnet lid of Lamborghini Huracan PERFORMANTE,
this design framework is shown suitable for large structures. The results from
this case study show that the variability in TBDC has signi ficant effect on the critical
load and failure initiation location of a TBDC structure.
Overall, this work develops an efficient design tool to account for the intrinsic variability
in the TBDC on the mechanical response of TBDC structures, which allows for
more efficient structural design with these materials.