Aligned discontinuous fibre-reinforced composites are becoming more popular because they have the potential to offer stiffness and strength comparable to their continuous counterparts along with better manufacturability. However, the modelling of highly aligned discontinuous fibre composites is still in its infancy. This paper aims to provide a comprehensive review of the available literature to understand how modelling techniques have developed and consider whether all aspects which could affect the performance of aligned discontinuous fibre composites have been addressed. Here, for the first time, a broad view of the advantages, perspectives, and limitations of current approaches to modelling the performance and behaviour of aligned discontinuous fibre composites during alignment, forming, and mechanical loading is provided in one place as a route to design optimisation.

The aim of this research is to investigate basalt as a natural mineral-based fibre together with a vitrimeric resin as a sustainable alternative to standard composite materials. Vitrimers combine the properties of thermoset and thermoplastic polymers, enabling the repair of specimens and hence prolonging the lifetime of the composite material. The micro-mechanical characteristics between the basalt fibres and the vitrimer resin are reported and shown to match those of a standard Skyflex K51 epoxy resin. Discontinuous (4 mm) basalt fibres were employed to produce aligned discontinuous fibre-reinforced composites (ADFRCs) using the high-performance discontinuous fibre (HiPerDiF) technology. The mechanical characteristics of the laminates were investigated through tensile testing and the fracture zones were analysed under a scanning electron microscope. By normalising the results by their respective fibre volume fraction, it was discovered that the vitrimer–basalt ADFRCs exhibited, on average, a 4% higher strength and a 25% higher stiffness compared to their basalt epoxy counterparts. The repair potential of the vitrimer ADFRC specimens was explored during low-temperature compression repair. Two approaches were tested using double-sided local- and full-patch repair. Both successfully recovered a significant amount of their prime strength. In conclusion, the potential of the sustainable vitrimer–basalt composite is shown by its competitive mechanical performance. Combining this with the manufacturing flexibility, repair potential, and recyclability of the material, the vitrimer–basalt composite seems to be a competitive alternative to standard glass epoxies.

Aligned discontinuous fibre reinforced composites (ADFRC) have demonstrated an improved formability for small to medium sized parts with complex geometries compared to the continuous fibre based prepreg due to their stretchability along the fibre direction. The process simulation tool developed for this class of materials so far mostly concerns their tensile behaviour along the fibre direction. However, neglecting other deformation modes like the in-plane shear in a forming simulation may pose risks for the correct prediction of formed shape. This study verified a strategy which adopts previously developed analytical micromechanical models for tensile and in-plane shear deformation of ADFRCs, in a finite element framework. The implementation is validated by comparing results from virtual shear tests against experiments at different temperatures. This was then followed by virtual forming experiments on a doubly curved geometry, in which the tensile and shear properties of the material were varied separately to study the effects of each deformation mechanism on the simulated forming behaviour of the material.

Inherent limitations restrict the application of automated fibre placement (AFP) for manufacturing small components with complex geometries. As an alternative, flat, tailored preforms composed of fibre tows are first created and then formed into desired 3D geometries. However, the fibre orientation deviations between the as-manufactured and as-designed parts are inevitably introduced during forming. To address this issue, this study presents an iterative numerical forming/un-forming framework for the manufacture of highly aligned discontinuous preforms. At first, the as-designed preforms are “un-formed,” i.e., a reverse forming simulation, to achieve the corresponding flat preforms using the finite element modelling (FEM) method. To mitigate the deviations during forming, a pre-compensation strategy is then introduced by adjusting the initial fibre orientations derived from the un-forming analysis based on the calculated deviations through iterative re-forming simulations. A hypo-viscoelastic constitutive model implemented through a user-defined material subroutine captures the rate-dependent and orthotropic behaviour of the preforms during un-forming and re-forming. The FEM simulation results demonstrate significant reductions in fibre orientation deviation of formed 3D preforms through the iterative forming/un-forming framework, validating its applicability to a discontinuous fibre material on complex geometries.