The main objective of this workpackage was to define and characterise the nanocomposite joint interface (or interphase) and the technologies for the application of nanoparticles to create strong transition joints for both metal/metal and metal/composite joints.
The research and testing in Work Package 1 is now complete. One of the issues investigated in SAFEJOINT-WP1 was a methodology for optimising the orientation of MWCNTs at the joint interface as well as a simplified approach to the introduction of CNTs at the joint interface. A process that was thought to be suitable is the application of MWCNTs in a “fibre container” form through the incorporation of those in thin veils to be easily inserted at the metal/composite joint interface. In this way the nanotubes would be somewhat oriented in the joint to optimise the performance of the adhesively bonded area. The major challenge was to find a thermoplastic polymer into which the MWCNTs could be introduced that could subsequently be spun into thin fibres and then produced as a fine cloth. The polymer should also be able to dissolve into the epoxy adhesive either at room temperature or at an elevated curing temperature thus leaving an oriented MWCNT structure and also (being a thermoplastic fibre) offer some toughening benefit to the resin. PES and PVDF where the polymers studied but it was found that it was extremely to achieve that and the fibres that were produced would not dissolve into the epoxy adhesives investigated in SAFEJOINT.
The introduction of the MWCNTs in the polymer resin appears to have raised the melting point of the thermoplastic and the benefits expected did not materialise.
The Tasks in WP1 were:
Task 1.1- Dissimilar material joint benchmarking
This task undertook a review of dissimilar materials joining techniques, defined the geometries and service loads applicable to structural applications and ranked them in terms of fabrication cost, ease of maintenance, inspection regime and industrial impact.
Task 1.2 – Development of nanoparticle filled bar/wire/powder for dissimilar metal joints.
Nanoscale reinforcements with carbon nanotubes (CNTs) were used to develop reinforced composite materials through FSW (NTUA). NTUA investigated the influence of tool rotation speed and tool shoulder penetration depth on the efficiency of the multi-walled CNTs and on the final mechanical properties.
Task 1.3 – Plasma Enhanced Vapour Deposition of CNTs for dissimilar metal joints.
SAFEJOINT partner, NTUA investigated the opportunity to grow CNTs on the metal surface during the frictional stir processing. The growth of CNTs in situ, were carried out by plasma enhanced chemical vapor deposition (PE-CVD).
Task 1.4 – Electrophoretic Deposition (EPD) of CNTs for metal composite joints.
A detailed analysis of the CNT deposition was carried out in terms of the process parameters. The study included considerations regarding influence of homogeneity of dispersion of CNTs in solvents prior to EPD, type of commercial CNT solution, CNT concentration, applied electrical field substrate complexity etc. Properties/characteristics evaluated were deposit thickness, homogeneity and stability.
Task 1.5 – Application of thin veils of CNTs for metal composite joints.
Mechanical and fracture mechanics characterisation of bulk properties of adhesive-and-veil blends, information was used in a down selection procedure where the most appropriate material combinations were used in later work-packages.