Thermoplastic composite overmoulding is an integrated process to manufacture components with combined continuous and short fibre reinforcements. These components benefit from high intrinsic mechanical properties, geometric complexity, and low production cycle times. The continuous fibre substructure is commonly designed as the main load-carrying region, whereas the injection moulded substructure, typically serving as stiffening, impact absorbing or functional features, can be tailored to carry significant loads. Thus, ensuring a strong bond at the overmoulded interface between the two substructures becomes a key objective. Characterisation of the overmoulded interface has been a focal topic of research within the scientific community, where models developed initially for non-isothermal thermoplastic bonding have been used to describe the average strength development across the interface area. However, little to no work has been devoted to understanding the variation of bond strength as well as the preform insert consolidation, where process-induced deformations have been shown to affect the mechanical performance, overall structural integrity, and component processability. This means that the modelling capabilities for predicting the mechanical performance at the overmoulded interface lack the required levels of complexity to capture the response of the interface, in the absence of bonding- and consolidation-influencing factors.

The aim of this research is to provide a refined description of the bonding and consolidation phenomena at the overmoulded interface in CF/PPS (Carbon Fibre/Polyphenylene Sulphide) and CF/PEEK (Carbon Fibre/Polyetheretherketone) overmoulded ribbed plates, through manufacturing trials, process simulations and experimental testing, such that the mechanical performance can be more accurately predicted. The investigation of different part designs and process parameters will lead to the identification of key parameter-process-property relations and serve to develop a set of design and manufacturing guidelines specific to overmoulding technologies.

This, in parallel with the development of novel predictive modelling techniques, will serve to contribute to the existing set of design and manufacturing guidelines for overmoulding technologies, such that the mechanical performance at the overmoulded interface can be accurately predicted in a variety of rib geometries manufactured under different processing conditions. This is achieved by investigating the bonding and consolidation mechanisms.

To investigate the bonding, the degree of healing between the injected compound and continuous fibre preform is predicted from Autodesk MoldFlow© process simulations. From this, an evaluation of the bonding at the interface within different regions of the component as well as at different process parameters is presented.

To investigate the consolidation, a bespoke compaction rig was designed and constructed to carry out a series of high temperature ramp-dwell loading experiments on representative specimens. A phenomenological material model, initially developed for toughened thermoset matrices, was assessed for its suitability in predicting the compaction response across a range of temperatures and pressures. The modelling approach was used in FE simulations of the overmoulding cycle, to capture the process-induced deformations observed in the manufactured ribbed plates.

The mechanical performance of the overmoulded interface under tensile rib pull-off conditions was assessed using a custom-built test fixture, where different failure types and failure loads are observed. An FE model of the rib pull-off test was developed to more accurately predict the mechanical performance of tested specimens compared to state-of-the-art techniques. This was verified against experimental data performed on specimens cut out from the manufactured ribbed plates, and using the bonding and consolidation data from previous chapters.