Faculty of Technology, Design and Environment
The light duty vehicle fleet in the UK is being electrified aggressively, with an ambitious target to ban the sale of all new internal combustion engine cars by 2030. At the same time, the electricity grid is also undergoing rapid decarbonization, potentially paving the way for a much greener use phase for electric vehicles. The paper presents a holistic prospective life cycle assessment of the environmental implications of these two interrelated transitions, while also considering an alternative scenario characterised by a gradual shift from traditional private vehicle ownership to shared mobility schemes. The results for both scenarios point to clear benefits in terms of reduced demand for non-renewable energy, carbon emissions and local air quality. However, a decisive behavioural shift towards shared mobility is shown to be crucial in order to offset the increased demand for Li, Co, Ni, Mn and Cu for electric vehicle power trains, and to avoid an otherwise potential increase in abiotic resource depletion and human toxicity impacts.
Limiting human-induced climate change represents a critical challenge for the future, and due to their disproportionate contribution to the problem, the energy and transport sectors are attracting the most attention in terms of emission reduction roadmaps and targets. Energy storage, particularly electrochemical storage, is poised to be a cornerstone in allowing those sectors to become more sustainable. This study presents the results of an integrated dynamic material flow analysis of the cumulative demand for lithium-ion battery metals (Li, Co, Ni and Mn) by the light duty vehicle and electricity generation sectors in the UK over the next three decades. Results have shown that recycling of end-of-life electric vehicle battery packs is very effective in “closing the loop”, and would enable driving the demand for all four metals back down to present levels by 2050, despite having achieved by then a complete shift to 100% electric vehicles. Additionally, repurposing end-of-life vehicle batteries for grid storage (with over 50 GWh of grid storage capacity expected to be in place by 2050) has been found to enable reducing purpose-built grid storage batteries to zero. Finally, an additional scenario analysis has indicated that a widespread behavioural shift from conventional vehicle ownership to shared mobility could even drive the demand for virgin battery metals into negative territory by 2040.
National Grid, the UK’s largest utility company, has produced a number of energy transition scenarios, among which “2 degrees” is the most aggressive in terms of decarbonization. This paper presents the results of a combined prospective net energy and environmental life cycle assessment of the UK electricity grid, based on such a scenario. The main findings are that the strategy is effective at drastically reducing greenhouse gas emissions (albeit to a reduced degree with respect to the projected share of “zero carbon” generation taken at face value), but it entails a trade-off in terms of depletion of metal resources. The grid’s potential toxicity impacts are also expected to remain substantially undiminished with respect to the present. Overall, the analysis indicates that the “2 degrees” scenario is environmentally sound and that it even leads to a modest increase in the net energy delivered to society by the grid (after accounting for the energy investments required to deploy all technologies).
The specification and use of recycled carbon fibre composites require the generation of reliable data that gives a comprehensive description of the material. Our research dealt with an experimental study of recycled, discontinuous, needle-punched, non-woven carbon fibre/epoxy composites. The property-constituent relationships of these composites require the adaptation of testing practices, coupled with an understanding of their failure mechanisms. The objective was to define a test protocol to determine their shear load limits. Four interlaminar shear test methods were investigated, namely, Short Beam Shear, Double Notch Shear, Double Beam Shear and Iosipescu Shear. A modified Iosipescu shear specimen provided a stress state in the composite that was much closer to pure interlaminar shear than that observed with other test methods. Identification of the weakest shear plane and re-fabrication of the test geometry enabled consistent interlaminar shear failures using the Iosipescu test method. We found that the shear behaviour was dependent on the internal fibre architecture of our particular material, thus enabling potential optimisation of such composites.
Electric vehicles (EVs) are increasingly regarded as the way forward to deliver a much-needed improvement in the transport sector's sustainability profile, and the UK is embarking on a major transition towards them. While previous studies focused mainly on greenhouse gas (GHG) emissions, this article assesses the extent to which EVs may contribute to reducing the UK's dependence on (mostly imported) non-renewable primary energy. The study combines a life-cycle model of a compact battery electric vehicle (BEV) with a prospective energy analysis of a range of electricity supply alternatives for the vehicle's use phase. The key metric analysed is the non-renewable cumulative energy demand (nr-CED). Results show that, already under current conditions, the nr-CED of a compact BEV in the UK is lower by approximately 34% with respect to that of an otherwise similar internal combustion engine vehicle (ICEV). Such reduction is then expected to improve further under all future scenarios, indicating that a transition to EVs is indeed a recommendable option to reduce the UK's demand for non-renewable energy, especially if this is accompanied by a shift to a more renewable electric grid.
A complete and fully consistent LCA-based comparison of a range of lightweighting options for compact passenger vehicles is presented and discussed, using advanced lightweight materials (Al, Mg and carbon fibre composites), and including all life cycle stages and a number of alternative end-of-life scenarios. Results underline the importance of expanding the analysis beyond the use phase, and point to maximum achievable reductions of environmental impact of approximately 7% in most impact categories. In particular, lightweighting strategies based on the use of aluminium were found to be the most robust and consistent in terms of reducing the environmental impacts (with the notable exception of a relatively high potential toxicity). The benefits of using magnesium instead appear to be less clear-cut, and strongly depend on achieving the complete phase-out of SF6 in the metal production process, as well as the establishment of a separate close-loop recycling scheme. Finally, the use of carbon fibre composites leads to similar environmental benefits to those achieved by using Al, albeit generally at a higher economic cost.
The study presented in this paper was carried out to assess the use of an embedded process zone based model in a commercial finite element code for predicting the behaviour of adhesively bonded structures. The relevant adhesive properties were measured using a variety of test methods and the results applied to the analysis of a single lap joint. Having demonstrated satisfactory accuracy in simulating the behaviour of the single lap joint the same methodology was then applied to a more complex structure. The structure used was a T shaped structure formed from two adhesively bonded aluminium rails. Despite some variability in the test results acceptable correlation with the analysis results was again achieved. The effects of variability in the adhesive material data on the output from the Finite Element analysis were investigated using a statistical study. This showed only a limited sensitivity to the interface toughness parameter
Internal combustion (IC) engines waste a majority of the energy they consume, with only 20% actually going into moving the vehicle. The drivetrains of electric vehicles (EVs) can operate at over 80% efficiency which shows that they have great potential in reducing the transportation energy demand. This paper initially quantifies the energy needed to run an EV, having similar dimensions and performance to modern IC vehicles. Simple range and cost calculations were used to establish the advancements needed in battery technology to match the ranges of IC vehicles. Factors affecting EV energy consumption are then addressed, with the aid of MATLAB® simulations, to ascertain what variations can be expected in real-world situations and the benefits of optimising vehicle parameters. The results are then compared with conventional and hybrid IC vehicles. It is shown that an optimised EV can achieve a 63%"tank-to-wheels" energy reduction over the best conventional IC vehicles available, and 60% over hybrids. The effects of either a badly optimised EV, hard acceleration during the driving cycle, or constant large accessory power draws, such as heaters and demisters, are each shown to increase the EVs energy consumption by 70%/km. To achieve the performance and practicalities comparable with modern IC vehicles, new battery technologies with specific energies of >300 Wh/kg are required.
This communication defines the key existing technologies for reversible adhesion and bonded joint disassembly, and introduces the reader to early experimental findings on the use of thermally labile functional additives in an adhesive matrix. These additives have been found to induce localized, out of plane stresses in a joint's bondline, allowing for an adhesive disbond. It has been found that the additive and adhesive matrix combination is key to the relationship between joint disassembly and joint strength.
Adhesively bonded lap shear joints have been investigated widely and several ideas have been proposed for improving joint strength by reducing bondline stress concentrations. These include application of adhesive fillets at the overlap ends and use of adhesive with graded properties in the overlap area. Another, less common, approach is to deform the substrates in the overlap area in order to obtain a more desirable bondline stress distribution. Previous work carried out by the authors on a number of different substrate materials indicated that a reverse-bent joint geometry is useful for increasing joint strength. Results from static stress analysis and experimental testing demonstrated that significant improvements could be achieved. This paper presents results of further work carried out to assess the fatigue performance of reverse-bent joints. Substrates with different yield and plastic deformation characteristics were used and the effects of different overlap lengths on strength were examined. The results of this research show that the improvements obtained under static tests conditions translate to even higher benefits in fatigue. The paper also explains the failure mechanism of the joints under fatigue loading.