About the Project
Background:
In a range of industrial sectors, multi-material constructions are used to optimise the performance of structures. In the transport sector, metal-to-carbon fibre reinforced polymers (CFRP) and steel-to-aluminium joints are seeing a dramatic growth in both R&D activity and commercial applications. As these materials are not weldable, directly, industrial joining solutions involve the use of mechanical fastening and adhesives. These dissimilar material combinations are highly susceptible to corrosion, as a result of galvanic coupling between parent materials with greatly differing electrode potentials.
Despite the widespread use fasteners to create these dissimilar joints, very little development of fastener coatings to mitigate corrosion has been performed. In the automotive sector, only 2 strategies are used for dissimilar metal and metal-to-composite joints, namely:
Carbon steel fastener + zinc coating (either; zinc flake, zinc nickel or zinc-tin).
Austenitic stainless steel fastener without coating.
For automotive applications very little long term corrosion data for mechanically fastened dissimilar joints are available in the literature and studies to optimise fastener materials and coatings have not been performed for metal-to-composite joints. Nevertheless, there are widespread concerns regarding the long term durability of dissimilar joints. In production cars, dissimilar joints are used almost entirely in ‘dry’ areas of vehicles, where exposure to water, salt and stone chipping from road surfaces does not occur, theoretically. In order to further reduce the risk of corrosion-induced failure, dissimilar mechanical joints in cars are coated with sealants, zinc-phosphate crystals and multiple layers of paint and lacquer. These measures are taken because present data show that, if paint layers are penetrated and dissimilar joints are exposed to electrolytes, rapid deterioration of the fastener and joint occurs.
An additional challenge seen by the fastener industry is the need to have a hard cutting surface with low friction to allow easier punching of high strength materials, in particular press hardened steels. It is known that piercing elements with hard surfaces and low coefficients of friction require lower setting forces, but developments on suitable coatings have been very limited. Industry standard coatings are based around relatively soft zinc, tin and nickel mixtures. A need for hardened coating developments has been highlighted by the automotive sector, but little work on this area has been performed.
Project Outline
The project objectives are as follows:
To experimentally determine the mechanical and corrosion performance of suitable commercially available coatings in fastener applications.
To generate data indicating optimum combinations of coated fasteners with dissimilar materials to minimise corrosion.
To produce a predictive model of corrosion performance based upon analytical electrode potential measurements.
Key words
Galvanic corrosion, CFRP, Metal, coatings, Fasteners
About NSIRC
NSIRC is a state-of-the-art postgraduate engineering facility established and managed by structural integrity specialist TWI, working closely with lead academic partner Brunel University, the universities of Cambridge, Manchester, Loughborough, Birmingham, Leicester and a number of leading industrial partners. NSIRC aims to deliver cutting edge research and highly qualified personnel to its key industrial partners.
Candidate Requirements
Candidates should have a relevant degree at 2.1 minimum, or an equivalent overseas degree, in an Engineering, Materials or Chemistry field. Overseas applicants should also submit IELTS results (minimum 6.5) if applicable.
Funding Notes
This project is funded by TWI and University. The studentship will provide successful Home/EU students with a minimum stipend of £16k/year and will cover the cost of tuition fees. Overseas applicants are welcome to apply, with total funding capped at £24k per year.
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